(1_Particle and Field Measurements of the Starfish Diamagnetic Cavity

Particle and field measurements of the Starfish diamagnetic cavity

Palmer Dyal1

Received 2 May 2006; revised 10 July 2006; accepted 25 September 2006; published 16 December 2006.

[1] Recently analyzed beta particle and magnetic field measurements obtained fromfive instrumented rocket payloads located around the 1962 Starfish nuclear burst are usedto describe the diamagnetic cavity produced in the geomagnetic field. Three of thepayloads were located in the cavity during its expansion and collapse, one payload wasbelow, and the fifth was above the fully expanded cavity. This multipoint data setshows that the cavity expanded into an elongated shape 1840 km along the magnetic fieldlines and 680 km vertically across in 1.2 s and required an unexpectedly long time ofabout 16 s to collapse. The beta flux contained inside the cavity was measured to berelatively uniform throughout and remained at 3 � 1011 beta/cm2 s for at least 7 s. Theplasma continued to expand upward beyond the fully expanded cavity boundary andinjected a flux measuring 2.5 � 1010 beta/cm2 s at H + 34 s into the most intense region ofthe artificial belt. Measured 10 hours later by the Injun I spacecraft, this flux wasdetermined to be 1 � 109 beta/cm2 s.

Citation: Dyal, P. (2006), Particle and field measurements of the Starfish diamagnetic cavity, J. Geophys. Res., 111, A12211,

doi:10.1029/2006JA011827.

1. Introduction

[2] A diamagnetic cavity was formed by the Starfish1.4 MT nuclear explosion on 9 July 1962, 09 hours 00 min09.029 s UT in the ion-loaded geomagnetic field 400.1 kmabove Johnston Island. This paper presents new, heretoforeunpublished particle and field measurements obtainedduring the first critical minutes after production of plasmawith known energy and mass (�1.5 � 1022 ergs and�1500 kg) in the magnetosphere. These measurementsfill a gap in the understanding of the formation andevolution of the Starfish diamagnetic cavity and betaparticle injection into the inner radiation belt noted earlierby several authors [Van Allen, 1966; Hess, 1968; Walt,1980]. Initial quick-look results were published in asymposium on trapped radiation at the Goddard SpaceFlight Center [Dyal, 1963]. Availability of new opticalscanning and digital data reduction techniques hasresulted in this more complete analysis of the first insitu �1 MeV beta flux and magnetic field measurementsof plasma expanding into the geomagnetic field. The 0.1 mstime response and the 30-s recorded time and 16-min realtime measurements in this experiment allowed threeprocesses to be studied: (1) in the first second, plasmaexpansion produced a diamagnetic cavity in the geomag-netic field; (2) collapse of the cavity in approximately 16 s;and (3) injection of beta particles into the Van Allenradiation belts, which occurred during the first fewminutes. The earliest particles and fields measurementspreviously published on the Starfish event [Van Allen,

1966] were obtained 42 min after the detonation usingGeiger tube detectors on the Injun I spacecraft. Analysisof Van Allen’s measurements produced the first constantflux contours of the intense Starfish radiation belt. Thislate time phenomenon associated with the trapped elec-trons has been studied by many investigators who pub-lished a collected set of papers in a volume of theJournal of Geophysical Research dedicated to this event[Brown et al., 1963]. Subsequently, many papers havebeen published in the Journal of Geophysical Researchand other journals on the geophysical effects of theStarfish cavity. Similar studies to better understand dia-magnetic cavities produced in the Earth’s magnetospherehave been conducted by the AMPTE missions [Bernhardtet al., 1987] and the CRRES missions [Huba et al., 1992], inthe Jovian magnetosphere by the Shoemaker-Levy cometimpact [de Pater et al., 1997], in the solar atmosphere duringcoronal mass ejections [Wagner, 1984], and in the labo-ratory [Gekelman et al., 2003]. These cavities share manymagnetohydrodynamic features in common but vary con-siderably in size and energy. Energies vary as follows:laboratory �108 ergs, CRRES/AMPTE �1013 ergs, Starfish�1022 ergs, Jupiter/comet impact �1027 ergs, and solarCME �1032 ergs.[3] The sections in this paper follow the sequence of

particle and field events measured by the five rocket pay-loads surrounding the burst, as shown in Figure 1. Thediamagnetic cavity expanded past payloads P-6, P-7, and P-4but stopped before reaching P-2 above and P-3 below theburst point. As the cavity decelerated and stopped, plasmainstabilities developed that allowed beta particles and possi-bly the radioactive debris to propagate upward across the fieldlines into the inner radiation belt.[4] This paper focuses on the analysis of plasma measure-

ments obtained in a high dose rate radiation environment.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A12211, doi:10.1029/2006JA011827, 2006

1Los Altos Hills, California, USA.

Copyright 2006 by the American Geophysical Union.0148-0227/06/2006JA011827

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Therefore a brief description of the experiment design andpayload properties is given in Appendix A and B.

2. Fission Prompt Gamma and Fusion NeutronMeasurements

[5] The arrival of the fission prompt gamma radiation(average energy 8 MeV, traveling at the speed of light) wasthe first event detected by the gamma-neutron and betadetectors at all five payload locations. These measurementsprovided a time mark of the detonation event for all thescientific instrument data. The later arrival time of the14.5 MeV neutrons traveling at 52,070 km/s from the fusionreactions was used to calculate the distance to the burst pointfor each payload since the time between emission of thegammas and neutrons at the burst location was much shorterthan the travel time of the neutrons to the payload.Measurements from the gamma-neutron detectors for pay-loads P-3, P-4, P-6, and P-7 are shown in Figure 2. Thetime difference averages of the gamma-neutron and thebeta detector measurements for each of the payloads wereas follows: P-3 = 3.32 ms, P-4 = 16.20 ms, P-6 = 1.85 ms,and P-7 = 6.20 ms. Distances were then calculated usingequation (1)

d ¼ VnVc

Vc � Vn

� �Dt ð1Þ

where d is the distance from the payload to the burst point,Vn is the neutron velocity, Vc is the velocity of light, anddelta t is the time difference between the neutron andgamma peaks. The distances measured by this method arelisted in the sixth row of Table 1 and the values are within1% of those calculated from the trajectory data. Theneutron time-of-flight measurements were considered to bemore accurate and were used for plasma velocitycalculations. The P-2 distance to the burst point wasobtained only from trajectory data calculations, since thetape recorded gamma-neutron data was not transmitted tothe ground receivers due to a preflight discriminatoradjustment error.

3. Plasma Diamagnetic Cavity Expansion

[6] The second event detected by the five payloads wasthe expansion of the ionized fission fragments, debris, andbeta particles into the ion loaded geomagnetic field. Six betadetectors, three ion detectors, and a magnetometer on eachpayload were used to measure the properties of this expan-sion as it produced a diamagnetic cavity. During theexpansion, most of the momentum is carried by the debrisions and the coupling through the magnetic field to theelectrons transfer this momentum to the air ions. This typeof coupling between the moving and stationary ions wasproposed by Longmire [1963, 1969] as ‘‘Larmor radius’’

Figure 1. Payload trajectories were located in the plane of the magnetic meridian through JohnstonIsland. At the Starfish burst time the payloads were positioned near the beginning of the short thick 5 mmenhanced portion of the trajectory which depicts the 30 s time period that high-frequency data wererecorded for 3 s before, through 27 s after detonation. The expanding plasma boundary is shown at threetime steps as it was measured by P-6 beta detectors at H + 0.66 s, then P-7 at H + 0.63 s, and P-4 field atH + 0.993 s. P-2 and P-3 were outside the bubble boundary during the rapid expansion and collapsephase. The contour at H + 1.20 s was determined from P-2 and P-4 magnetic field measurements and P-3and P-7 beta particle measurements as the spacecraft traveled through remnants of the stopped debris.

A12211 DYAL: STARFISH DIAMAGNETIC CAVITY

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coupling and would be applicable at early times in theexpansion. The Larmor radius is

r ¼ mVc

eBcm ð2Þ

where m is the mass, V is the electron or ion velocity, c is thespeed of light, e is the charge on the ion, and B is themagnetic field. For fission fragments of mass 100 moving at1670 km/s in a 0.22 gauss field, the radius is 80 km, forionosphere mass 16 O+ is 13 km, for 1 MeV betas is0.07 km, and for ionosphere electrons is 43 cm. Longmireshowed that the air ions begin to be picked up in 1/2pLarmor periods of the air ions in the compressed field of theexpanding cavity boundary. At early times across themagnetic field lines the energetic beta particles should be

coupled within a few beta Larmor radii to the debris ions.During cavity expansion therefore the beta particlemeasurements from the P-6 and P-7 instruments that areacross the field lines should track most of the debris ionswithin approximately two O+ Larmor radii.[7] In addition the following rationale indicates that the

high flux of beta particles may have been coupled withintens of kilometers to the debris ions: (1) Photographicmeasurements of the expanding debris velocity are similarto those calculated from peak beta flux arrival times [Zinn etal., 1966]. (2) Rule of thumb estimates place 25% of thenuclear explosion energy into the kinetic energy of thedebris, which results in an average velocity of 1.5 �108 cm/s. This is reasonably close to the 1.67 � 108 cm/sfrom the arrival of the peak beta flux as measured at the P-6position. (3) Rocket payload P-4 located 1021 km from theburst in the magnetic meridian toward the southern conju-gate region measured a sharp decrease in the magnetic fieldat the cavity boundary, which was nearly coincidence withthe peak of the first large pulse of beta flux. (4) The initialhigh flux of betas do not show a trapped angular distributionand are either omnidirectional as measured at P-6 and P-7locations or are unidirectional as measured at P-4. Thiswould indicate that the betas are either in the cavityboundary or inside the cavity. (5) The P-6 measurementsof the betas contained within the cavity are within 15% ofthat calculated by J. B. Cladis (personal communication,2000), who developed equations to compute the flux offission decay betas on missiles after a nuclear burst ataltitudes greater than 140 km. He assumed that all the betaswere trapped within a spherical cavity and that the rate ofproduction from radioactive decay was �(1 + t)�1.2. Boththe debris driving the cavity expansion and the betas wouldbe at higher densities at the reflecting boundary. (6) Finally,the high flux of betas did not arrive from the burst point toany of the payload locations with an average velocity ofa 1 MeV beta guided by the geomagnetic field over thatdistance.[8] The beta particles and debris ions expanding along the

magnetic field lines to the P-4 instruments may be separatedby much larger distances. Betas originating in the shellsurrounding the cavity can escape immediately along thefield lines and will not be retarded by the charge separationelectric field, since air ion and electron density are muchgreater than the beta particle density. However, none ofthese beta particles was detected. The early beta streamerthat traveled to the southern conjugate region, comparableto the one detected at H + 0.030 s in the northern conjugateregion described by Longmire [1969], may have traveled

Figure 2. Prompt fission gammas and 14.5 MeV fusionneutrons as measured by P-3 and P-6 in the bottom graphand P-7 and P-4 in the top graph. The first peak produced bythe gamma radiation provides a time mark for all the particleand field measurements and the second peak produced bythe neutrons permits the distance to the burst to becalculated from the time-of-flight technique.

Table 1. Payload Parameters for Starfish Located at (16.468N, 169.630W, 400.1 km) and Burst Time (H-0 = 9 July 1962, 09 hours

00 min 09.029 s UT)

Parameter P-2 P-3 P-4 P-6 P-7

Latitude, deg 20.096 15.645 9.458 15.594 18.387Longitude, deg 191.187 190.319 188.986 190.271 190.968Altitude, km 1057.2 216.6 932.6 348.18 696.98Trajectory measurements to burst point, km 802 207 1025 116 383Gamma-neutron time of flight, km no data 209 1021 117 391IGRF 1962 magnetic field, gauss 0.22515 0.30960 0.22234 0.29205 0.25661Measured magnetic field, gauss 0.23000 0.31306 0.22279 0.29302 no data


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undetected under P-4 if the streamer radius was less than170 km.[9] The plasma cavity expanded outward to payload P-6

which was located 117 km from the burst point and at anangle of 57 degrees to the field line through the burst.Measurements from one of the three beta detectors orthog-onal to the payload spin axis are shown in Figure 3. Thefirst detection of beta particles from the debris occurred atH + 0.010 s and the maximum beta flux arrived in 0.066 s,which indicated a velocity of 1773 km/s for the peak flux ofbeta particles. The Larmor radius of curvature would be64 km if the average fission fragment ion had mass 100and traveled with this velocity in the 0.287 gauss field.

Longmire [1963] described this mixture of ionosphere,debris ions, and magnetic field as a shell of material thatis pushed ahead of the bulk of debris forming thediamagnetic cavity. The betas born inside the closedmagnetic field cavity are contained and a portion of thoseborn in the shell will escape along open field lines. Thisshell most likely produced the step in the rise time of thebeta flux measurement as seen in Figure 3 and was detectedfromH + 0.01 s to H + 0.05 s. The shell traveled at 1773 km/sand was therefore �70 km thick. This was relatively close tothe Larmor radius of the fission fragment ions.[10] During the initial expansion phase the outer case

material emitted �1 keV X rays which increased the

Figure 3. The P-6 beta flux and magnetic field at 117 km from the burst point. The maximum fluxoccurred at H + 0.066 s which indicated a velocity of 1773 km/s. The bubble reached maximum size at H +1.2 s and the flux remained relatively constant as the bubble started to collapse. The magnetic field abruptlyincreased at H + 10.5 s due to the lower boundary collapsing upward and at H + 12.8 s due to the upperboundary collapsing downward. At H + 16.4 s the collapse was complete and betas changed from anomnidirectional to a trapped distribution.


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ambient ionosphere [O+] density to �3 � 105 cm�3 (R. W.Kilb, unpublished data, 1997). Therefore the local Alfvenspeed was

VA ¼ B

4pnmð Þ1=2¼ 292 km=s ð3Þ

Since the debris traveled at a velocity of 1773 km/s asshown in Figure 3 and listed in Table 3, it was considered tobe super-Alfvenic [Huba et al., 1990] and should haveproduced a magnetohydrodynamic (MHD) shock. However,the magnetometer on P-6 did not function during the timeinterval H-0 to H + 2.6 s due to saturation of the photodetector from the prompt gammas and bremsstrahlung.Therefore the magnetic field properties of the shock werenot measured. (This shock was measured at P-2 which waslocated 802 km above the burst and will be discussed later).The average magnetic field measured after H + 2.6 s was0.06 gausswhich indicated that P-6was still inside the plasmacavity. The time dependence of the beta flux for the first 6 s asshown in Figure 3 was a function of the expansion velocityand the beta emission rate of the fission fragments. J. B. Cladis(personal communication, 2000) developed the followingequations for the beta flux in an expanding magneticcavity:

J tð Þ ¼ 5:73� 1021YF

V 30 t

31� 1þ tð Þ�0:2h i

beta=cm2s for t � tm

ð4Þ

and

J tð Þ ¼ 5:73� 1021YF

V0tmaxð Þ31� 1þ tð Þ�0:2h i

beta=cm2s

for tmax � t � 5tmax ð5Þ

where J(t) is the flux of betas in the cavity, YF is thefission yield of the nuclear device in MT, V0 is the initialexpansion velocity of the debris in km/s, t is the time inseconds, and tmax is the time when the cavity is fullyexpanded. These equations fit the measured values shownin the top part of Figure 3 to within 15% for the timeperiod H + 0.2 s to H + 6 s.[11] The diamagnetic plasma cavity expanded upward

and was detected by instruments on P-7 at 391 km abovethe burst point and 82 degrees across field lines. The peakbeta flux was measured at H + 0.63 s as shown in the lowerpart of Figure 4. Therefore the average velocity of the peakbeta flux was 620 km/s for the expanding beta flux in thevertical direction across the magnetic field lines. The Alfvenvelocity at this location was 2900 km/s, showing that theplasma expansion had transitioned from super-Alfvenic tosub-Alfvenic. The beta flux rise time was 0.2 s and waslonger than 0.064 s as measured at the P-6 position,signifying a more diffuse plasma boundary as the expansionslows. The step in the measured rise-time produced by theshell of early mixed debris with air ions was 0.05 s �620 km/s = 31 km thick. Again, assuming the averagefission fragment ion has mass 100 and travels with this

velocity in the 0.257 gauss field, the Larmor radiuswould be 25 km, close to the shell thickness. The timedependence of the beta flux inside the cavity from H +1.2 s to H + 4.13 s was also reasonably approximated byequations (4) and (5). The magnetometer on P-7 did notmeasure the magnetic field from 3 s before H-0 until 2.96 safter H-0, as shown in Figure 4. The tape recorder timer wasinadvertently set for 3 s longer than the tape loop rather than3 s shorter. This resulted in the loss of 3 s of magnetometerdata and the addition of 3 s of beta detector data.[12] Optical images in the declassified films and reports

of the Starfish Prime Test [Bechtel Nevada, 2000] alsoshowed that the cavity expansion was not sphericallysymmetric but rather expanded upward and downward ata slower rate than horizontal.[13] The plasma cavity expanded along the magnetic field

line toward the southern magnetic conjugate region to P-4 at1021 km from the burst point. P-4 was located on themagnetic meridian through the burst point but was 170 kmabove the field line that went through that point. A signif-icant difference existed between the characteristics of theStarfish plasma flow in the direction of the field and theflow across the field. P-4 first detected the plasma cavity asa small decrease in the magnetic field, as shown in the lowerpart of Figure 5. This field decrease was caused by theexpanding diamagnetic sphere in the collisionless plasmaand produced a tension in the direction along the lines offorce [Jackson, 1962]. The decrease began at H + 0.378 sand reached a minimum of 0.2057 gauss at H + 0.479 s. Thevelocity of 2132 km/s calculated from the time of this dip inthe field was close to the post X-ray flash Alfven speed of2000 to 2800 km/s between P-4 and the burst point. Themagnetic field then started to decrease down to the insidecavity value of 0.06 G at H + 0.993 s. This drop indicatedthat the boundary of the cavity expanded south at a velocityof 1098 km/s and was most likely driven by the ionizeddebris. Hybrid particle simulations of a Starfish type burstshow that the debris ions separate by mass, with the highermass near the outer boundary [Brecht, 2001]. As shown inFigure 5, the first beta particles arrived at H + 0.544 s andattained a broad maximum flux centering at H + 1.085 s andresulting in an average velocity of 941 km/s for this fluxtube of beta particles. This velocity also indicated that theplasma flow was sub-Alfvenic in the southern direction. Thesharp decreases in beta flux at H + 0.962 s and H + 1.330 swere produced by the angular response of the detector andthe payload spin with a 2.583 Hz frequency, as shown inTable 2. With knowledge of the spacecraft orientation at H-0and measurements from all six beta detectors, the flow ofdebris and beta particles was determined to be nearly unidi-rectional and toward the south. During this time period,spacecraft P-6 and P-7 inside the cavity detected beta particlesthat arrived equally from all directions. This unidirectionalflow of beta particles and debris ions toward the southernconjugate region is one of the ‘‘beta tube’’ propertiesdescribed byDavidson and Hendrick [1980]. After the initiallarge pulse of betas ended at H + 1.514 s and before the cavityboundary collapsed past P-4 at H + 2.162 s the beta flux wasomnidirectional.[14] Another possible source of this large pulse of beta

flux could be betas that originated in the shell around thecavity as it expanded 170 km upward, at the velocity


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measured by P-7, to intersect the field line that passedthrough P-4. This mechanism was not very likely, however,since the arrival time would have been less than H + 0.3 srather than the measured H + 0.544 s.[15] The plasma cavity continued upward and stopped

before it reached P-2 at 802 km above the burst point. P-2first detected the cavity by a step increase in the magneticfield at H + 0.297 s, as shown in the lower part of Figure 6.The local Alfven speed at P-7 after the X-ray flash was�2900 km/s and at P-2 it was �11,000 km/s. Assuming thatthe step increase in field traveled at the Alfven speed fromP-6 and using post X-ray flash ion densities provided by R.W. Kilb (unpublished data, 1997), this time was calculatedto be H + 0.342 s. This calculated time was in reasonableagreement with the measured time. Subsequently, the sharp

decrease in magnetic field at H + 0.692 s indicated thepassage of the shock front that was initiated earlier when theplasma was super-Alfvenic. The beta particles did not arriveuntil many seconds after the cavity started to collapse;therefore the plasma expansion stopped at some pointbetween P-7 and P-2. A rough estimate was obtained byassuming that the plasma cavity could be modeled as anexpanding superconducting sphere in a uniform magneticfield B0. The intensity of the field B at a distance r outside asphere of radius R is

B ¼ B0 1þ R

r

� �3

1� 3 cos2 q� �"

þ 1

4

R

r

� �6

1þ 3 cos2 q� �#1

2

: ð6Þ

Figure 4. The P-7 beta detector at 391 km above the burst point measured the prompt gammas at H-0and then the maximum flux of the expanding bubble boundary at H + 0.63 s. This indicated that theaverage velocity was 620 km/s for the debris in the upward direction. The average magnetic field insidethe diamagnetic bubble was 0.06 gauss and it increased to near ambient as the bubble collapsed past P-7at H + 4.13 s. The beta flux then changed from an omnidirectional to a trapped distribution. Note theraised 0.00 gauss level for clarity.


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where q is the angle of r with respect to the uniformmagnetic field lines. The measured ambient field before H-0was 0.230 gauss, the field at H + 1.20 s was 0.268 gauss atmaximum cavity size, the distance to the estimated center of

the sphere was 620 km, and the angle to the field line was72 degrees. Substituting these values into equation (6) andallowing the choice of the sphere center to determine theerror amount, the cavity boundary in the direction of P-2

Table 2. Payload Parameters for Starfish at H + 30 s

Parameter P-2 P-3 P-4 P-6 P-7

Latitude, deg 20.321 15.109 8.996 15.259 18.623Longitude, deg 191.220 190.221 188.974 190.777 191.022Altitude, km 1090.78 309.48 947.98 439.88 776.57Trajectory measured distance to burst, km 846 184 1083 150 465Spin rate, Hz 2.710 2.449 2.583 2.921 2.632Spin axis angle to IGRF 1962 field lines, deg 72.7 86.0 72.8 83.4 75.4

Figure 5. The P-4 beta flux at 1021 km south of the burst point was unidirectional toward the south andattained a broad maximum at H + 1.085 s which corresponded to a velocity of 941 km/s. The magneticfield started to decrease at H + 0.993 s as the cavity boundary reached the payload and this indicated avelocity of 1098 km/s. The field was restored in the beta tube at H + 2.25 s and the betas changed to atrapped distribution.


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was calculated to be 450 km from the sphere center andbetween 500 and 550 km from the burst point. This value isabout the same (500 km) as that reported by Zinn et al.[1966] for the stopped distance of the vertical moving debrisfrom their photographic data and calculations.[16] If the plasma cavity had been spherically symmetric,

it would have reached payload P-3, which was at 209 kmbelow and across the field lines in less than 1 s. P-3 did notdetect the high velocity expanding plasma, as the beta fluxmeasurements show in the lower part of Figure 7. The betaflux starting at H + 2.15 s exhibited trapped characteristicssince the intensity varied at twice the frequency of thepayload spin rate (listed in Table 2). These betas were

probably due to the azimuthal drift around the cavity ofthe betas that were trapped in the curved and compressedmagnetic field at the front of the cavity. Another possiblesource could have been the betas mirrored back from thesouthern conjugate region since the first trapped betasdetected by the P-4 instruments occurred at H + 2.25 swhen the cavity boundary collapsed past the payload. TheP-3 magnetometer photo detector was saturated by brems-strahlung radiation and did not measure the field from H-0to H + 3.25 s. However, the magnetometer on the sparepayload operated on Johnston Island measured a pulseincrease at H + 3.7 s in magnetic field intensity caused bythe cavity expanding down into the ionosphere and com-

Figure 6. The P-2 beta detector at 802 km above the burst measured prompt gammas at H-0 and a broadbeta peak at H + 25 s that varied with an 8 s period. This indicated that the bubble stopped expandingbefore it reached P-2 and instabilities were initiated that sent flutes or jets of debris upward. Acompression wave traveled at the Alfven speed from the expanding bubble caused the sharp rise in themagnetic field at H + 0.297 s. Subsequently, the bubble collapsed and the field started to decrease at H +1.76 s.


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pressing the ion-loaded field as shown in Figure 8. The fieldgeometry could have changed in a way that guided the betaparticles into the P-3 position. The Johnston Island meas-urements were 400.9 km below the burst point and the fieldchanges were attenuated by the intervening ionosphere. Thelarge pulse from H-0 to H + 0.013 s in Figure 8 could beeither the electromagnetic pulse from the burst or themagnetic part of the electromagnetic signal launched bythe expansion [Gisler and Lemons, 1989]. The character-istics of the magnetic field measured on Johnston Islandwere very similar to those of a geomagnetic storm. The firstfield increase of 138 gammas at H + 3.9 s was caused by thecavity expanding downward and producing a compressionwave. This wave was delayed by the ionosphere and was

similar to the ‘‘sudden commencement’’ part of a storm. Thesecond field increase of 260 gamma at H + 27 s, caused bythe general compression of the geomagnetic field, was likethe ‘‘initial phase’’ of a geomagnetic storm. The last largefield decrease of 730 gamma at H + 71 s was similar to the‘‘main or inflation phase’’ of a storm. However, the largeamplitude indicated that this inflation phase was probablyasymmetric and would have decayed much more rapidlythan an equivalent geomagnetic storm. These same time-dependent magnetic field characteristics at lower amplitudeswere measured by other magnetic observatories on theEarth’s surface. The 60 Hz sine wave was produced byground currents from the local island utility power source.These payload and ground measurements indicate that the

Figure 7. The P-3 data at 209 km below the burst showed that the bubble stopped above the spacecraft.The beta flux at H + 3 s occurred simultaneously with the compressed field on Johnston Is. P-3 traveledinto the debris at H + 14.5 s and 187.5 km below the burst.


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high velocity cavity expansion was stopped above P-3 butnear enough for some beta particles to be guided to thepayload by the magnetic field. Subsequently, as shown inthe top part of Figure 7, the beta flux increased sharply atH + 14.5 s and 187.5 km below the burst as P-3 traveledinto the debris deposited in the ionosphere. This distanceagrees with the photographic data by Zinn et al. [1966]that set a limit of slightly more than 180 km for thedownward debris expansion.[17] The above measurements, incremented at 1/4 s

intervals during the plasma cavity expansion, are summa-rized in Table 3. The last three columns show that the fluxof beta particles was almost uniform for the last third of theexpansion period, indicating that the internal cavity pressureextended into the beta tube. Cavity boundaries as shown inFigure 1 were drawn from data obtained by all five payloadsat three times during expansion. The shape of the two-dimensional boundaries beyond the spacecraft point meas-urements was determined by (1) assuming a simple shapethat would be consistent with the P-2 magnetic fieldmeasurements; (2) examining the boundary calculated bya collisionless magnetohydrodynamics (CMHD) code forthe Starfish expansion at 0.8 and 1.0 s [Fajen and Kilb,1982]; (3) examining the particle plot of the debris locationat 0.24 s from the hybrid particle code SHYPS [Brecht,2001]; and (4) examining the computed shape of the debrissurface at 0.5 s from a MHD code in the work of Zinn et al.[1966]. The first boundary was determined by the P-6detection of betas at 0.066 s in the horizontal directionand by the calculated velocity of the first peak beta fluxmeasured by P-7 in the vertical direction. The secondboundary was determined by the P-7 peak beta flux detec-

tion at 0.63 s in the vertical direction, by the P-4 magneticfield sharp decrease at 0.96 s in the southern direction, andby the boundary shape in the computer codes. The boundaryat 1.20 s was determined by the magnetic field measurementat P-2 and P-4, and the shape of the boundary calculated bythe computer codes. The lower boundary was determined byP-3 at H + 8 s where it was 188 km from the burst point andmeasured an increase in beta flux as it approached the debrisdeposited in the ionosphere. This boundary probably rep-resents the maximum extent of the plasma cavity in thedownward direction. The particle and field measurementsall indicate that the cavity expansion stopped for approxi-mately 0.5 s, the magnetic field pressure then dominated,and the cavity started to collapse.[18] The volume of the diamagnetic cavity allowed the

total number of beta particles to be calculated for timeswhen at least one payload was inside the cavity. At H + 1.0 sthis volumewas calculated from two different sources: (1) theP-2 measurements of an estimated sphere and (2) the CMHDcode calculation for the volume of this irregular-shapedexpansion boundary. At H + 1.0 s the volume was �3 ±2 � 1023 cm3. Payloads P6, P-7, and P-4 all measured 3.8 �1011 beta/cm2 s at H + 1.00 s inside the cavity, as shown inTable 3. At 1 s after 238U fission occurred, the average beta

energy was 2.5 Mev and had a velocity of 2.95 � 1010 cm/s.The volume was �3 � 1023 cm3 indicating the cavitycontained (3.8 � 1011) � (3 � 1023)/(2.95 � 1010) = 3.9 �1024 betas. The beta decay rate for fission fragments wasapproximately constant for the first second and then decayedas n = n0 t

�1.2. Estimates based upon the calculations byWest[1966] indicated that 5% of the 238U fission fragments betadecay had occurred by 1 s. Therefore the total number of

Figure 8. The expanding diamagnetic bubble compressed the magnetic field in the downward directionand this was measured on the surface of Johnston Island with the spare payload at H + 3.75 s. The firstlarge pulse at H + 0.01 s was caused by the electromagnetic pulse from gamma ray interaction with theionosphere and the large excursions starting at H + 20 s resulted from ring currents that were measuredworldwide. The 60 Hz oscillations were caused by the power stations on the Island. The measurementsbefore the burst were within a few gamma of the International Geomagnetic Reference Field (IGRF) forthe year 1962.


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fission betas was estimated to be 7.8 � 1025. This estimaterepresented 10% of the 8 � 1026 total betas expected fromStarfish.VanAllen [1966]usedmeasurements fromhis Injun1spacecraft to estimate that 1.3 � 1025 electrons were trappedfrom radioactive fission fragments, representing 17% ofthe electrons in the cavity and a comparable trappingefficiency.

4. Plasma Diamagnetic Cavity Collapse

[19] The third event detected by the payloads was thecollapse of the fully expanded cavity. The first indicationwas a decrease in the magnetic field measured by the P-2magnetometer as shown in the lower part of Figure 6. Themagnetic field started to decrease at H + 1.76 s as thevolume of the cavity decreased and the geomagnetic fieldwas restored. The rate of decrease was slower than the rateof field increase during the expansion phase. Magnetic fieldand beta flux measurements obtained from the other fourpayloads also show that the collapse phase occurred at aslower rate than did the expansion phase.[20] The next event associated with the cavity collapse

was measured by P-4 instruments at H +2.25 s when themagnetic field abruptly increased from 0.047 to 0.192 gaussas it was restored to near ambient value. Also at this timethe beta flux changed from an omnidirectional flow to thetrapped distribution shown in the lower part of Figure 5.The P-4 magnetometer also measured an oscillating mag-netic field near the inner boundary of the beta tube with afrequency of 11.2 Hz and average peak-to-peak amplitudeof 0.025 gauss. The approximate 3 degrees latitude width ofthe beta tube as projected down to the northern conjugateregion is similar to the 3 degrees in latitude elongation ofthe peaks in the debris deposition contour map in thesouthern conjugate region measured by D’Arcy and Colgate[1965].[21] Subsequently, the plasma cavity boundary was mea-

sured as it collapsed downward past P-7 and the field wasrestored at H + 4.13 s as shown in the lower part of Figure 4.Themagnetic field increased from avalue of 0.06 gauss insidethe cavity to 0.226 gauss outside the cavity, which is near theambient preburst value of 0.256 gauss. Simultaneously, thebeta particles changed from an omnidirectional flux of 1.13�1011 beta/cm2 s inside the cavity to a trapped flux of 1.17 �1011 beta/cm2 s immediately outside the cavity boundary.

There was neither gradual nor sharp increase in beta flux asthe inside boundary approached the payload. The beta fluxcontainedwithin the cavitywas relatively uniform throughoutand only varied between 1 to 3 � 1011 beta/cm2 s during thefirst 7 s of its collapse. This relative constant flux indicatedthat the debris ions and beta particles remained near thelocation of the outer boundary of the fully expanded cavityand/or continued outward through instabilities, flutes, andbeta tubes, and were not significantly trapped inside thecollapsing cavity. The average velocity of the plasma bound-ary was 46 km/s as it traveled 135 km downward from theoutermost position at H + 1.20 s to P-7. The velocity wassimilar to the value of 40 km/s thatZinn et al. [1966]measuredfrom photographs taken from Maui at H + 3, 8, and 16 s.The P-7 magnetometer also measured an oscillating fieldat 11.5 Hz frequency and an average peak-to-peak am-plitude of 0.038 gauss near the inside of the cavityboundary.[22] The cavity did not continue to collapse in the same

way past spacecraft P-6 where conditions were more cha-otic. The average magnetic field inside the plasma cavitywas measured to be 0.06 gauss, which was similar to that atthe P-4 and P-7 sites as shown in Figures 4 and 5. Thesefigures also show the International Geomagnetic ReferenceField (IGRF) for the year 1962 at the spacecraft locations[King, 2004]. Magnetometers on all five spacecraft operatedcontinuously during the collapse phase since transientradiation effects were minimal. As the plasma cavity col-lapsed past the P-4 and P-7 sites, the magnetic fieldoscillated at 11 Hz for a fraction of a second, as previouslystated, and then increased from this low value to one nearambient (approximately 0.2 gauss) in a few tenths of asecond. Simultaneously, the beta particle flux changed inthis short time period from an omnidirectional flux at P-7and at P-4 in the beta tube to a trapped distribution.However, at the P-6 location (as measurements show inthe top part of Figure 3) the magnetic field started at thesame 0.06 gauss inside the cavity and then slowly increasedto a plateau of 0.09 gauss and remained there from H + 8to H +10 s as the beta flux decreased from �2 � 1011

to �2 � 1010 beta/cm2 s. Then at H + 10.5 s an abruptincrease in magnetic field occurred from 0.09 gauss to0.16 gauss, and at H + 12.8 s another step increaseoccurred from 0.12 gauss to 0.19 gauss. Both increaseswere preceded by the 11 Hz oscillations. One interpreta-

Table 3. Beta Flux and Magnetic Field Measurements During Plasma Cavity Expansion

ParameterP-2 Outside

CavityP-3 Outside

Cavity P-4 in Beta TubeP-6 InsideCavity

P-7 InsideCavity

Maximum betaFlux arrival time, s

24.3 2.5 0.96 (field drop 0.993 s) 0.07 0.63

Cavity boundaryvelocity, km/s

(11.3) after stop N/A 1098 from magneticfield drop

1670 620

Beta flux at H + 0.25 s,beta/cm2 s

below threshold<3.24 � 109


6.5 � 109 4.8 � 1012 below threshold<3.25 � 109




6.5 � 109 2.0 � 1012 1.87 � 1010




2.8 � 1011 4.0 � 1011 3.9 � 1011




3.8 � 1011 3.8 � 1011 3.8 � 1011




3.5 � 1011 3.5 � 1011 3.2 � 1011


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tion was that the first step increase was produced by thelower boundary at 100 kmdistance, collapsing upward to P-6,and the second step was produced by the upper boundarycollapsing downward past P-7 to P-6 at 540 km distance fromthe upper boundary. The average velocity for the downwardmoving boundarywas 46 km/swhich agreedwith the velocitymeasured at the P-7 site andwith photographicmeasurementsby Zinn et al. [1966], who described it as a downwardmovingshock. If it was a shock, then the 11 Hz oscillations measuredat the P-4, P-6, and P-7 positions as the magnetic field wasrestored may have been associated with the air ion gyrofre-quency [Kennel and Petschek, 1968]. An O+ ion had agyrofrequency of �11 Hz in the 0.11 G field at the P-6location. The average velocity for the upward moving plasmawas calculated to be 11 km/s. However, the characteristics ofthe beta flux at P-6 did not significantly change during eitherof the magnetic field step increases as it did during theboundary collapse past P-4 and P-7. These measurementsmay indicate that during the final stages of the collapse, whenthe cavity approached the size of the instabilities, the field andparticles measurements would require many closely spaced,instrumented sites with higher time resolution than the onesite at P-6 to describe its motion adequately.[23] The above measurements of the collapsing Starfish

plasma cavity are summarized in Table 4. The outerboundary averages at three selected times as it traversedthe payloads are shown in Figure 9. The end of the collapseperiod was chosen at a time when the Earth’s magnetic fieldapproached preburst values and all spacecraft detectedtrapped beta particles. This occurred at H + 16.4 s whenP-6 measured the angular distribution of trapped betas.[24] The magnetic field measurements obtained during

the expansion and collapse of the diamagnetic cavityrepresented larger-scale phenomena than the particle meas-urements and provides a useful guideline for comparisonwith theoretical modeling calculations. Comparison of themagnetic field and beta particle flux measurements withpublished model calculations for Starfish exhibited similartime amplitude characteristics. This comparison verifiedthat the most important physical processes in the modelswere appropriate. However, for time periods after theexpansion was completed, the amplitude and time compar-isons between the experiment and models differed by afactor of 10. Future studies of plasma instabilities occurringat the time of maximum cavity size may significantlyimprove these comparisons and our understanding of thecollapse phase.

5. Early Beta Particle Injection Into theMagnetosphere

[25] The fourth event detected by the spacecraft was thetransition of an omnidirectional beta flux in the cavity to atrapped flux in the geomagnetic field. Instabilities probablydeveloped at the cavity boundary permitting some of theions and beta particles to stream across the field lines intothe inner radiation belt. These electrons could be identifiedamong the natural electrons by their energy spectrum foralmost 10 years [Teague and Stassinopoulos, 1972]. Betaparticle and magnetic field measurements by this experi-ment provided information about the transport of betaparticles to B,L coordinates where the lifetimes of theT

able

4.BetaFluxandMagnetic

Field

MeasurementsDuringPlasm

aCavityCollapse

Param

eter

P-2

OutsideCavity

P-3

OutsideCavity

P-4

inBetaTube

P-6

InsideCavity

P-7

InsideCavity

Betafluxat

H+1.76s,

beta/cm

2s

below

threshold

<3.24�

109

below

threshold

<3.04�

109

2.0

�1011

3.5

�1011

3.0

�1011

Betafluxat

H+2.25s,

beta/cm

2s

below

threshold

<3.24�

109

5.2

�109trapped

2.54�

1011

betatubecollapse

2.9

�1011

2.4

�1011

Magnetic

fieldat

H+2.25s,gauss

0.254decreasingto

ambient

nodata

increase

0.054to

0.192,

distinct

11.2

Hzwave

nodata(rises

from

0.027to

0.11G

at2.6

s)nodata

Betafluxat

H+4.13s,

beta/cm

2s

below

threshold

<3.24�

109

below

threshold

<3.04�

109

5.06�

1011trapped

2.0

�1011

1.13�

1011cavityboundary

transitsP-7

Magnetic

fieldat

H+4.13s,gauss

0.232nearam

bient

0.277

0.146

fastrise

from

0.039

to0.081at

4.06s

fastrise

from

0.033to

0.226,

distinct

11.5

Hzwave

Betafluxat

H+17.5

s,beta/cm

2s

0.30�

1011trapped

1.02�

1011trapped

1.31�

1011trapped

1.05�

1011trapped

0.34�

1011trapped


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injected beta particles would be on the order of months toyears. This section is organized by discussing the betaparticle and magnetic field measurements in sequence, fromthe beta tube at P-4 to the lowest altitude spacecraft P-3 inthe ionosphere, up through P-6 and P-7, and finally to P-2.This section also covers the beta particle measurementsobtained in real time from H-0 to H + 16 min where P-7attained the highest altitude at coordinates B = 0.212 gaussand L = 1.307 which was near the most intense region of theartificial radiation belt.[26] One mechanism that could have produced this arti-

ficial belt was the restructuring of the diamagnetic cavity byRayleigh-Taylor instabilities into jets or flutes that propa-gate outward after the cavity stops expanding and starts tocollapse [Colgate, 1965; Huba et al., 1990; Ripin et al.,1993; Winske, 1988]. Another mechanism, proposed byCladis [1968], contends that betas were trapped at highL values because the debris tube becomes elongated anddistorted, mainly because an eastward electric field appearsacross the tube that causes the tube to E � B drift outward.Both Zinn et al. [1966] and Cladis [1968] ascribe the thickStarfish belt to such an eastward electric field, but they differon the source of this field. Zinn et al. [1966] ascribe it to themotional electric field (E = �V � B), produced by theoutward motion of the debris across the magnetic field atthe upper boundary of the cavity, and propagated along thedebris tube as an Alfven wave. Also, as described by Cladis[1968] and modeled by Cladis et al. [1979] and Cladis et al.[2006], this eastward electric field was produced by thedifferential azimuthal drift of the energetic ions (toward thewest) and electrons (toward the east) as these ions (debris,etc.) expanded along the tube from the cavity.

[27] Beta flux measurements for the entire flight time ofeach payload were obtained in real time from one of thethree detectors with entrance aperture directed along thespin axis. The data were smoothed by plotting an envelopeof the trapped beta flux spin oscillations as shown inFigure 10. These real-time measurements along with the30 s recorded measurements were used to develop a two-dimensional graph of the trapped beta flux in the magneticmeridian through Johnston Island as shown in Figure 11.All payloads measured trapped betas at H + 23 s and thedata is summarized in Table 5 and listed by each payload inFigure 11. At that time the measured magnetic field inten-sity was very close to the preburst ambient field as predictedby the IGRF 1962 model and the angular distributions werestable for periods from 5 to 20 s. The boundaries of thecolored bands in Figure 11 were determined from real-timebeta detector measurements obtained during the time H-0 toH + 15.8 min. There existed some substructure within thebands, and for descriptive purposes the bands are labeledfrom the lowest to the highest as P-3, P-6, P-7, and P-2.[28] The beta tube produced simultaneously with the

expanding plasma cavity channeled a large amount of debrisand beta particles directly to the southern conjugate region,where delayed fission gamma rays were measured byD’Arcy and Colgate [1965]. Measurements of these par-ticles in transit were obtained by P-4 located inside the betatube 1021 km south of the burst point. After restoration ofthe geomagnetic field in the beta tube, betas were thentrapped and the angular distribution at H + 3.67 s wascalculated by averaging the beta flux during three payloadspins. The results as shown in the bottom left graph ofFigure 12 indicated that many of the betas at smaller pitch

Figure 9. The outer boundary of the Starfish plasma bubble measured by payloads P-4, P-7, and P-6 atfour time steps as it collapses and disappears. Boundaries are averages of the instability driven structuresas the geomagnetic field was restored to its original configuration.


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angles would be lost by interaction with the atmosphere.During the time period H + 2.4 s to H + 5.5 s the beta fluxwas at the highest level measured at the P-4 location. Atapproximately H + 5.7 s the beta flux decreased by a factorof 4 and the angular distribution changed to one broadenedby losses to the atmosphere. This distribution persisted tothe end of the data recording period as shown in upper partof Figure 5. In addition, the real time P-4 beta fluxmeasurements detected the boundary between the P-3 andP-6 bands shown in Figure 11 as P-4 traveled downwardthrough the boundary at H + 359 s at an altitude of 701 km.P-4 also exited the lowest boundary of band P-3 at H + 470 sat 446 km altitude. During this later time the field intensity

and structure were near preburst ambient conditions, and thetrapped betas remained stable for many minutes. Most ofthese particles would be lost to interactions with theatmosphere over the South Atlantic Anomaly, since theL value was 1.17 at this measurement location. However,the debris remaining in the flux tube containing the burstregion maintained a trapped flux at >1 � 1010 beta/cm2 sfor 6 min based upon the P-4 real-time measurementsshown in Figure 10.[29] Payload P-3 located 202 km below and across the

magnetic field lines from the burst point detected a low-intensity pulse of trapped betas starting at H + 3 s as shownin the top part of Figure 7. These trapped betas were

Figure 10. Beta flux measured along the payload spin axis until reentry. These data show where thefission debris was located after the bubble collapsed and instabilities had diminished.


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coincident with the delayed magnetic pulse passing throughthe ionosphere from the expanding debris as shown inFigure 8. The low-intensity pulse of beta particles was thenfollowed by a steady increase of beta flux as P-3 traveled upinto the ionosphere. This very turbulent period was fol-lowed by a field decrease at H + 14.5 s at 187.5 km belowthe burst point where the cavity had stopped, depositeddebris and then receded during the collapse phase. At theP-3 location the betas again had the angular character-istics of being trapped. There followed by a 4.7 s periodof more intense beta flux which then decreased to asteady trapped flux at H + 22.7 s, as shown in the upperright of Figure 12 by the angular distribution (calculatedby averaging flux from three payload spins). P-3 detectedthe boundary between the P-3 and the P-6 band (shownin Figure 11) as it traveled up through it at H + 85 s at463 km. P-3 also detected the lowest boundary of bandP-3 as it traveled downward through it at H + 829 s andan altitude of 452 km.[30] Of the five payloads, P-6 was located nearest to the

burst point and measured the most intense beta flux and themost turbulent magnetic field changes for the longest time

period as shown in the top part of Figure 3. The rubidiummagnetometer measured the field from H � 5.13 s to H-0and from H + 2.56 to H + 25.44 s. During these time periodsthere were three major changes in the magnetic field duringthe collapse phase of the plasma cavity. The first twooccurred at H + 10.5 s and H + 12.8 s when the cavityboundaries collapsed from below and above the burst point.The third change occurred at H + 15.5 s when the magneticfield approached its ambient configuration and trapped betaparticles were observed. This payload was the last to detectthe transition of the beta flux from an omnidirectional to atrapped angular distribution. At H + 15.8 s the magneticfield rapidly decreased from 0.20 to 0.17 gauss, and the betaflux started to exhibit the characteristics of a trapped angulardistribution that persisted for the duration of the flight. Theangular distribution of the beta flux calculated by averagingflux from five payload spins at H + 23.5 s is shown in theupper left of Figure 12. The relatively narrow distributionindicates that these electrons were in the early stages ofoscillation between mirror points and had not been scatteredto a significant extent by the atmosphere. P-6 also measuredthe boundary between the P-6 and P-7 bands in Figure 11

Figure 11. Starfish omnidirectional beta flux at H + 23 s when all five payloads first measured trappedbeta angular distributions. The bands following the geomagnetic field lines were determined from bothrecorded data shown in the previous figures and the real time measurements shown in Figure 10.

Table 5. Beta Flux and Magnetic Field Measurements During Particle Injection Into the Earth’s Magnetic Field

Parameters P-2 P-3 P-4 P-6 P-7

Beta flux at H + 23 s, beta/cm2 s 4.66 � 1010 2.92 � 1010 1.24 � 1011 1.45 � 1011 2.26 � 1010

Magnetic field at H + 23 s, gauss 0.22601 0.24981 0.20205 0.19590 0.25450IGRF 1962 field at H + 23 s, gauss 0.22322 0.29927 0.22104 0.28278 0.25057L value at H + 23 s 1.266 1.081 1.136 1.102 1.191Walt/Newkirk decay time constant (1/e), days 275 <0.1 <0.1 <0.1 168


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when the real time beta flux decreased to a minimum as itleft the boundary at H + 475 s at an altitude of 1037 km.[31] The P-7 payload located 391 km above the burst

point and across the magnetic field lines measured magneticfields and beta particle fluxes from the Starfish burst thatbest fit the model of an ideal diamagnetic cavity expandinginto the geomagnetic field. Measurements shown in Figure 4indicated that the field was quickly restored from 0.06 to0.227 gauss at H + 4.13 s as the boundary of the plasmacavity collapsed past P-7. Simultaneously, the beta fluxchanged from 1.3 � 1011 beta/cm2 s omnidirectional to1.2 � 1011 beta/cm2 s trapped angular distribution asshown in Figure 4. The trapped angular distribution wascalculated by averaging four spacecraft spins, and theresults are shown in the middle left of Figure 12. The

timing, angular distribution, and intensity indicated thatthe betas originated from a region near the cavity boundaryand not from a broader region. The 1.64 s period of relativelyhigh beta flux just outside the boundary of the cavity is similarto that measured by the P-4 instrument when the magneticfield was restored in the beta tube. Since the boundarycollapse speed was �46 km/s, the 1.64 s period of relativelyhigh beta flux indicated that this region was�75 km thick. AtH + 5.5 s the beta flux sharply decreased from 1.02� 1011 to4.4� 1010 beta/cm2 s as these betas spread across field lines.The angular distribution widened as shown in Figure 12.At H + 10 s the magnetic field had returned to almost preburstambient conditions and the trapped beta flux remainedrelatively constant to the end of the recording period.At H+ 30.3 s when P-7was 464 km above the burst point, the

Figure 12. The angular distribution of trapped beta particles measured by all five payloads. P-6 at H +23.5 s in the upper left graph shows the early time characteristics before significant scattering andabsorption by the atmosphere. P-7 in the middle left graph shows that atmospheric effects produced adistribution that was wider and more uniform. P-4 in the lower left graph shows the characteristics thatimmediately followed the restoration of the field in the beta tube at H + 3.67 s and then at H + 23 s whenatmospheric effects had commenced. P-3 in the upper right graph shows the distribution at H + 22.7 s and183 km below the burst point where the debris was stopped by the ionosphere. P-2 in the middle rightgraph shows the distribution at H + 34 s and H + 69 s when the distance from the burst point was 851 kmand 895 km. Variations in the distribution indicated that the instability structures were maintained duringthe injection of betas into the most intense region of the Starfish artificial radiation belt. P-2 in the lowerright graph shows the angular distribution measured at H + 34 s transformed to an equatorial distribution.Studies by Walt [1966] indicated that beta particles at these coordinates (B = 0.220 gauss and L = 1.277)would have a lifetime greater than 275 days.


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angular distribution (calculated by averaging 10 payloadspins) broadened by atmospheric scattering and did notexhibit the high-frequency time variations that were mea-sured at earlier times. Spacecraft P-7 then traveled upwardthrough three regions of trapped betas. At H + 28 s thespacecraft entered the first region at 766 km altitude; the fluxstarted to increase and reached a maximum at H + 51 s at analtitude of 829 km, then decreased to aminimum atH+ 96 s atan altitude of 930 km. This maximum real-time flux mea-surement occurred at the location of the fully expandedplasma cavity boundary as shown in Figure 1,which probablyindicated that some of the debris remained after the cavitycollapsed downward. The minimum at 930 km was used todefine the boundary between the P-7 and P-2 bands. P-7reached a slightly lower maximum flux inside the secondregion of the P-2 band at H + 144 s and altitude 1022 km andthen ended at H + 200 s at an altitude of 1109 km. The thirdregion also had a slightly lower maximum flux of 3.7 �109 beta/cm2 s at H + 300 s and altitude 1210 km withcoordinates (B,L = 0.213 G, 1.292). Then P-7 reenteredthe upper boundary of band P-2 at H + 650 s at analtitude of 1015 km as shown in Figure 11.[32] As previously stated, the Starfish upper cavity

boundary stopped at H + 1.20 s approximately 260 kmbelow P-2. The most intense beta flux arrived at P-2 at H +�25 s, as shown in the upper graph of Figure 6. Thisindicated an upward velocity of �10.4 km/s. There was oneflute or flux tube that preceded the most intense one andthere were six more that followed in approximately 8 sintervals and all exhibited trapped beta characteristics. Thebeta flux measurements shown in Figure 6 are from one ofthe three detectors with aperture viewing along the spin axisof the payload. The rubidium vapor magnetometer wasmounted on a telescoping mount that shielded 23% of thesolid angle of this detector. This spinning shield produced

an oscillation in the measurements of a trapped beta fluxthat had a frequency equal to the payload spin rate. The P-2discriminator on the prompt gamma coincidence circuit wasset too high and as a result the tape recorder transmittedonly high-frequency magnetometer data for the 27-s periodafter H-0. The beta flux measurement in the top part ofFigure 6 is composed of 30 s of real-time data from H-4 s toH + 26 s and 46 s of recorded data from H + 26 s to H + 69 s.The three detectors with viewing directions orthogonal to thespin axis and also perpendicular to the magnetic field wereused to measure the angular distribution and the results fromone of these detectors are shown in Figure 13. It exhibits anoscillation in the beta flux at twice the spacecraft spin rate andwas used to calculate the angular distribution at H + 34 s bycalculating an average of 4 spins and atH+ 69 s by calculatingan average of 12 spins. The results are shown in the middleright P-2 panel of Figure 12. The payload then reachedthe upper edge of the shaded boundary at H + 185 s and1163 km, and the flux decreased below the instrumentthreshold.[33] The low-frequency particle flux oscillations occur-

ring at �H + 15, 25, 33, 42, 51, and 58 s in the top panel ofFigure 6 could have been caused by Rayleigh-Taylorinstabilities developed at the boundary of the stoppedbubble. These flute-like instabilities with rotational flowcharacteristics were similar to those described by Bernhardtet al. [1987] and Huba et al. [1992] in their study of sub-Alfvenic plasma expansions of the AMPTE and CRESSbarium releases. Many investigators have studied and mod-eled plasma instabilities with similar properties [Brecht andGladd, 1992; Colgate, 1965; Huba et al., 1990; Ripin et al.,1993; Winske, 1988].These beta flux oscillations could alsohave been related to the standing wave of the debris tubeexcited by the electric field in the tube [Cladis, 1968; Cladiset al., 1979].

Figure 13. The P-2 trapped betas measured by a detector orthogonal to the payload spin axis from 817to 895 km above the burst point. The 8 s periodicity in the beta flux is similar to that observed by P-2detectors oriented along the spin axis shown in Figure 6. Beta flux measured during 11 spins at H + 34 sand 7 spins at H + 69 s were averaged to calculate the two angular distributions shown for P-2 inFigure 12.


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[34] The data for P-2 in the middle right panel ofFigure 12 at H + 34 s were used to calculate the equatorialpitch angle distribution shown in the lower right panel.Since the L value is 1.269 at this location, a significantfraction of these beta particles would have a 1/e lifetime ofgreater than 275 days [Able and Thorne, 1998; Newkirk andWalt, 1968]. This flux of 2.5 � 1010 beta/cm2 s at the (B, L =0.153 G, 1.269) location was near the most intense region ofthe artificial belt mapped by Van Allen [1966], who measuredthe flux to be 1 � 109 beta/cm2 s at H + 10 hours with theInjun I spacecraft. As P-7 traversed this region at H + 5 min,the flux was 3.7 � 109 beta/cm2 s at coordinates (B, L =0.213 G, 1.292). The L values and angular distributions forthe beta flux in the middle of the P-7 band indicated a 1/elifetime of 168 days. The L values and angular distributionsfor the betas in the P-3, P-4, and P-6 bands indicated a 1/elifetime of less than a day, as listed in Table 5, since each driftthrough the South Atlantic Anomaly would have dumpedmost of the electrons into the atmosphere.

6. Summary

[35] In summary, this experiment measured the formationand evolution of the Starfish diamagnetic cavity produced inthe Earth’s magnetosphere.[36] Five instrumented rocket payloads located in the

magnetic meridian around the Starfish burst point firstdetected the prompt fission gammas and then the 14.5 Mevfusion neutrons. These measurements were used to calculatethe distance from the payloads to the burst point and alsoprovided a time mark for the detonation event.[37] The expansion velocity of the ionized fission frag-

ments and beta particles into the ion loaded geomagneticfield was measured to be super-Alfvenic at H + 0.066 s and117 km distance from the burst and then transitioned to sub-Alfvenic speed before H + 0.630 s and 391 km distant. Thediamagnetic cavity boundary expanded past P-6, P-7 acrossthe field lines at 117 and 391 km distant, respectively, andalso past P-4 which was 1021 km along the field linestoward the southern conjugate region. The expanding cavityboundary stopped at H + 1.2 s before it reached P-2 and P-3which were 802 km above and 209 km below the burstpoint, respectively. Both payloads were across the fieldlines. P-4, P-6, and P-7 measurements showed that thecontained beta flux was uniform and relatively constant at�2 � 1011 beta/cm2 s during the last phase of the expansionand for at least 6 s of the collapse. The magnetic shock andcompression wave were measured 802 km above the burst.When P-2 was at 804 km above the burst this compressedfield started to decrease at H + 1.76 s, which indicated thatthe diamagnetic cavity had started to collapse. Simulta-neously, ions and electrons escaped along field lines to thenorth and south conjugate regions as measured by P-4which also detected the magnetic field restored at H +2.25 s as the beta tube collapsed. The uppermost cavityboundary collapsed downward past P-7 at 46 km/s and themagnetic field was restored to near ambient values at H +4.13 s. P-6 located near the center of the cavity measuredthe upper boundary continuing to collapse downward withvelocity 46 km/s and the lower boundary collapsed upwardat 11 km/s. All instrumented payloads detected trapped betaparticles at H + 16.4 s, indicating that the geomagnetic field

was restored and the diamagnetic cavity collapse wascomplete.[38] The early time trapped beta fluxes were measured

from H + 3 s to H + 15 min at the B, L locations of therocket payloads. These beta particles were probably injectedinto an artificial radiation belt by plasma instabilities thatoccurred near the time of maximum cavity size. Theseinstabilities may have restructured the boundary into flutesthat permitted the fission fragments and beta particles totravel upward at 10.4 km/s across the field lines. An equallyprobable mechanism that could have injected the betas intothe higher L value locations was a standing wave in thedebris tube that was excited by the electric field in the tube.P-2 measured a maximum omnidirectional flux of 4 � 1010

beta/cm2 s during the passage of these structures at H + 25 s.P-7 later traveled upward through this location at H +10 min and measured a flux of �6 � 109 beta/cm2 s. Thelocation of P-2 was B = 0.153 G and L = 1.269, which wasnear the most intense region of the artificial belt mapped byInjun 1 at H + 10 hours with a peak flux of 1 � 109 beta/cm2 s.[39] The following main uncertainties may be inferred

from these measurements: (1) the distribution, shape, andsize of the flutes over the entire cavity at the time ofmaximum cavity size and (2) the fraction of betas injectedinto the radiation belts from the instabilities, beta tubes,debris patches, and other processes. Many more than fivepayloads would be required to measure adequately theseStarfish diamagnetic cavity properties.

Appendix A: Plasma Diamagnetic Cavity SizeEstimation and Spacecraft Site Selection

[40] An estimation of the radial extent of the Starfishplasma cavity was calculated in order to select locations forinstrumented payloads to measure the particles and fieldsassociated with the burst. Rule-of-thumb estimates of nuclearweapon energy partition indicated that approximately 60%would go into X rays, 25% into debris kinetic energy, and15% into neutrons, gamma rays, beta particles, etc. Thisenergy partition is strongly dependent upon weapon designand the surrounding hardware. For a rough estimate the yieldwas approximated as�1 MTwith a weight of�1 ton of ironthat expanded as a spherical shell from the burst point.Therefore the following kinetic energy of the debris wasdetermined: K.E. = (0.25 MT) � (4.2 � 1022 erg/MT) =1.05 � 1022 ergs = 1/2 mbvb

2, where mb = bomb mass =(2000 lbs) � (454 gm/lb) = 9.08 � 105 gm. and thedebris velocity is therefore vb = 1.52 � 108 cm/s.[41] The local Alfven speed after the X-ray flash was

�300 km/s, so the plasmawas categorized as super-Alfvenic.After a few microseconds the debris was assumed to becompletely ionized and the expanding plasma to be collision-less and highly conducting. It would therefore push thegeomagnetic field outward and the electrons would pick upall the ambient air ions. Considering conservation of momen-tum per steradian and ignoring charge exchange and momen-tum transfer to the field:

mbvb

4p¼ mair

4pþ mb

4p

h iv ðA1Þ


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and

v ¼ vbmb

mb þ mair

ðA2Þ

where mb is the bomb debris mass, vb is the debris velocity,and mair is the mass of air ions swept up by the expandingdebris plasma.[42] Considering conservation of energy per steradian:

1

4p1

2mair þ mbð Þv2

¼ 1

4p4

3pR3

� �B2

8p

� �ðA3Þ

where R is the plasma expansion radius and B is theintensity of the geomagnetic field. An expression for theradius of expansion is obtained by substituting v fromequation (A2) into equation (A3) and solving for R:

R3 ¼ 3v2bm2b

B2 mb þ mairð Þ ðA4Þ

with the initial condition that vb = 1.52 � 108 cm/s and inthe final state vb = 0 at the full expansion radius.[43] If one assumed a uniform magnetic field and no air

ions, then the plasma expansion radius would be R =[3(1.52 � 108)2 (9.08 � 105)/(0.287)2]1/3 = 914 km.[44] For the distances involved, both the mass of the air

ions mair and the geomagnetic field vary as a function of R.Estimates were calculated for the horizontal, vertical, anddownward direction by integrating the amount of air ionsand magnetic field in each direction.[45] In the horizontal direction it was assumed that the

X rays did not contribute additional ionization, that onlyair ions were picked up at the 400 km altitude, and thatthe magnetic field was a constant 0.287 gauss. The O+

and H+ density at this altitude was approximately 2.8 �10�17 gm/cm3 and therefore the maximum radius was calcu-lated to be R = 425 km.[46] In the vertical direction the ion density was approxi-

mated with the equation r = 2.3� 10�16 e�h/1.3�107 gm/cm3,where h= r + 400� 105 cmand r is the distance from the burst.Themagnetic field varied as 1/r3 and the upward distance wascalculated to be R = 950 km.[47] In the downward direction a significant number of air

ions were produced by the bomb X rays. An approximate fitto the ion profile was estimated to be

r ¼ 1:5� 106 þ 4:6� 1013e�400�r11:8km

� �ions=cm3 ðA5Þ

and the calculated distance in the downward direction wasR = 210 km.[48] On the basis of these calculations a decision was

made that a minimum of five instrumented payloads wouldbe placed in the magnetic meridian around the Starfish burstat the locations shown in Figure 1. These positions werechosen to bracket most of the early time phenomenology.The fission beta particle flux, ion density, and magneticfield were selected to be measured at each site for a periodof 30 s with a frequency response greater than 1 kHz. Low-frequency data at 55 Hz were transmitted continuously

during the entire flight period. The trajectories of thesepayloads are shown in Figure 1 and some of the locationparameters measured at burst time are listed in Table 1. Thedark-enhanced portion of the trajectories depicts the dis-tance traveled during the 30-s period that high-frequencydata were recorded and continually transmitted to receivingsites located on islands shown in Figure 1. Payload altitude,latitude, longitude, and distance to the burst point at H-0 areshown in Table 1 and the same parameters 30 s later areshown in Table 2. The differences in coordinates anddistance to the burst point between these two times weresmall compared to the plasma bubble sizes. Therefore thevariation of each parameter with time can be treated as alinear function.[49] A spare payload was also operated on Johnston

Island and measured the magnetic field from H-0 to H +360 s. H-0 s refers to the burst time of the Starfishdetonation.

Appendix B: Instruments and SpacecraftProperties

[50] The general approach was to define a set of instru-ments, payloads, and booster rockets that would producereliable measurements and be robust enough to survive andoperate in the Starfish radiation environment. All instrumentand payload systems were designed to be identical and eightpayloads were fabricated and tested. Lithium drifted siliconsolid state detectors were chosen for beta particle measure-ments, as well as silicon surface barrier detectors for thegamma and neutron measurements. A Faraday Cup waschosen for a low-energy ion detector, and a rubidium vapormagnetometer for magnetic field measurements. Significantamounts of shielding mass were required to minimize theradiation effects on the electronics and this in turn requiredthe use of the upper two stages of the flight-proven Scoutvehicle as the booster system to place the payloads into theselected positions around the burst.

B1. Instruments

B1.1. Beta Detectors

[51] Six beta detectors were located around the payload at120-degree increments as shown in the lower right side ofFigure B1. Three detectors had view angles orthogonal tothe spin axis and three along the spin axis. The flightattitude of this system was maintained after second stageburnout until reentry and splash. A schematic drawing of anoutward and upward looking beta detector is shown in thelower left side of Figure B1. Each detector consisted of a0.5 � 0.5 cm2 lithium-drifted solid state detector with a1mm thick depletion layer. A photograph of this detectormanufactured by Solid State Radiation, Inc. is also shown inFigure B1. The detectors were covered with a 0.002-cmthick aluminum foil and were recessed 1.83 cm into thecenter of a 2.24 cm diameter hole in the 3.81 cm. thicknylon cylinder. The geometrical view angle was calculatedto be 66 degrees. The angular response of both the outwardand upward looking detectors was measured with 1.047MeVinternal conversion electrons from 207Bi, and a typical resultis shown in Figure B2. Those data show that approximately85% of 1 MeV betas will be counted within the geometrical


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Figure B1. A scale drawing of the payload is shown in the lower right section of the figure. The longestdimension was 5.2 m and the maximum diameter was 0.79 m. It was constructed of fiberglass, aluminum,and nylon. The lower left side is a drawing of the beta detector in the nylon bremsstrahlung shield. Eachsensor was 0.5 � 0.5 cm square lithium-drifted solid state detector with a 1 mm thick depletion regionand covered with a 0.002 cm thick aluminum foil. A photo of the detector is shown in the middle leftside. The top photo shows the rubidium magnetometer which is a quantum electronic instrument thatmeasures the Larmor frequency of the Rb nucleus as it precessed in the Earth’s magnetic field.


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view angle of 66 degrees. The detector geometric factor was0.253 cm2 steradian for detectors with view anglesorthogonal to the spin axis. The fiberglass telescope usedto extend the magnetometer away from the electronicsreduced the upward viewing detectors’ geometric factorby 23%.[52] The energy response was limited at low energies by

the 0.002 cm thick aluminum foil, which stopped electronsbelow 55 KeV and was dependent upon the depletion layerthickness at the high-energy end. Low beta intensity cali-brations utilized 137Cs monoenergetic 0.662 MeV electrons,Bi207 monoenergetic 1.047 MeV electrons, and single-pulseoperation of the General Atomic linear accelerator from0.5 to 15 MeV. High intensity beta calibrations wereconducted at Oak Ridge with a 1200 Curie 90Sr betasource that emitted 4.44� 1013 beta/s at 2.18 and 0.61 MeV.The General Atomic linear accelerator was also used in thesingle and multiple pulse modes to calibrate the detectorswith electrons from 1 to 15 MeV and intensities up to1014 electrons/cm2 s. The best fit to all of this calibrationdata is shown in Figure B2.[53] The output of the beta detector instrument was

current in microamps as a function of time, and in orderto convert the measurements to omnidirectional beta/cm2 s,the beta energy spectrum must be known. The Oak RidgeIsotope Generation and Depletion Code (Version 2) wasused to determine the beta spectrum for 238U fast fission forthe first 30 s after fission [Croff, 1980]. The average betaenergy varied from 2.5 MeVat 1 s and 1.55 MeVat 30 s and

in order to calculate the flux an average value of 2.5 MeVwas chosen for the incident beta energy. From the energyresponse curve in Figure B2 a 2.5 MeV beta depositedapproximately 0.5 MeV in the detector. Therefore since allsilicon detectors required 3.6 eV loss by a beta particle toproduce one electron-hole pair, it followed that one micro-amp of the detector current was

1mA ¼ 1� 10�6C=s� �

3:6eVð Þ 4psrð Þ �.

1:602� 10�19C� �

0:5� 106eV=beta� �

0:253 cm2sr� ��

ðB1Þ

1mA ¼ 2:234� 109 beta=cm2s: ðB2Þ

This was the conversion factor used in the last stage of betadetector data reduction.[54] Preflight estimates of the beta flux levels at each of

the five payload positions required a detector system thathad a dynamic range of 5 decades. The high-frequency betaflux measurements recorded for the first 30 s in this paperwere selected from the detectors looking orthogonal to thespacecraft spin axis that had the highest telemetry frequencyresponse and the best overall characteristics of these threedetectors. The average error for these measurements wasapproximately ±4% for the variation between detectorswhen the spacecraft was inside the plasma cavity and theflux was omnidirectional. The total error depended upon thebeta particle angular distribution since the six detectorscovered only 6.072 steradians out of the total 4p steradians.

B1.2. Magnetometers[55] Each payload contained a magnetometer that mea-

sured the total magnetic field intensity as a function of time.The magnetometer sensor was located at the top end of afiberglass telescope which used a gas generating device tomove the sensor 1.5 m above the electronics housed in thenylon cylinder after second stage burnout and nose coneejection. This kept the spacecraft-generated magnetic fieldlevels below 5 � 10�5 gauss at the sensor position. Themagnetometer measured the Larmor frequency of the 85Rbspinning nucleus magnetic moment as it precessed in theEarth’s magnetic field. This frequency depended upon themagnitude of the ambient magnetic field, the magneticmoment of the nucleus, and known physical constants[Forbes, 1987]. The gyromagnetic ratio of 85Rb was4.667 Hertz/10�5 gauss. The ambient magnetic field at theStarfish burst point was 0.287 gauss which produced aLarmor frequency of 4.667 � 28,700 = 133,942.9 Hertz andthis signal was transmitted to the ground. The frequencyresponse of these magnetometers was measured to be lessthan one Larmor period [Dyal et al., 1969]. The magne-tometer responded to a step increase in field from 0 to0.19 gauss in less than 3 ms and the average error forthese measurements was ±0.5%. A photograph of therubidium vapor magnetometer sensor is shown in the topof Figure B1.

B1.3. Gamma-Neutron Detectors[56] The gamma-neutron detector consisted of a surface

barrier silicon solid state device with a polyethylene foil

Figure B2. The top graph is the energy response of thebeta detector using a collimated beam of electrons from 0.06to 15 MeV. The bottom graph is the angular response of thebeta detector using collimated 1.047 MeV betas from a207Bi source.


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covering the front that utilized a neutron-proton recoilreaction to detect energetic neutrons. This detector hada 1 cm2 sensitive area and a depletion region 180 micronsthick produced by a 60 volt bias. The output of the chargesensitive amplifier was a 0 to 5 volt signal for an input of1.11 � 1010 to 1.11 � 1015 gamma Mev/cm2 s. It wascalibrated over its complete dynamic range at four facilities:(1) the electron linear accelerator at General Atomic whichgenerated a pulse intensity from 1 to 1� 1017 electrons/pulseand operated from a single pulse to 800 pulses/s, (2) TheTRIGA MK II 6400 megawatt pulsed nuclear reactor atGeneral Atomic which operated in a single 10 ms longpulsed mode producing 4 � 1016 neutrons/cm2 s and 4 �107 gamma rads/cm2 s during the pulse, (3) The Godiva IIbare pulsed critical 235U assembly at the Sandia Corporationwhich operated in a 60 ms pulse width mode and an intensityof 1 � 1017 neutrons/cm2 s and 1 � 107 gamma rads/s, and(4) The Oak Ridge National Laboratory hot cell facilitywhich possessed a 4000 Curie 60Co source that emitted 1.17and 1.33 MeV gammas at 1.48 � 1014 gamma MeV/s.[57] The detector was shielded from high-energy beta

particles by being located at the center of the payload. Forthis paper, the early time data from this instrument was usedto measure the distance from the burst to the payload by atime-of-flight technique. Prompt gamma rays (�8 MeV)from the fission burning phase of the Starfish device and the14.5 MeV neutrons from the fusion reactions were producedin a time much shorter than the response time of ourtelemetry system. The gammas reached the detector at thespeed of light (2.998 � 1010 cm/s) and the 14.5 MeVneutrons traveling at a velocity of 5.207 � 109 cm/s arrivedat the detector at times late enough to be differentiated byour telemetry system, thereby allowing the distance to theburst point to be calculated. The prompt gamma pulsewas also used as a fiducial time mark for all the othermeasurements.

B2. Rocket Payloads

[58] Trajectories for the five payloads are shown inFigure 1. Magnetic field lines are shown in the geomag-netic meridian plane that intersects Johnston Island. Thepayload trajectories were chosen to be as close aspossible to this plane during the measurement period.Postflight data analysis determined that all the payloadswerewithin 11 kmof themagneticmeridian plane through theburst point during the 30 s period of high-frequency datarecording. During the remainder of the flight all payloadswere within 1 degree of the meridian except P-6 which endedflight 8.5 degreeswest of themeridian. The trajectory altitude,latitude, and longitude were calculated from telemetryreceiving antenna look angles. The distance from the burstpoint to the payload was determined from this trajectory dataand from the fusion neutron time-of-flight measurements.The results are shown in Table 1 and in addition the magneticfield measurements provided added information on the accu-racy of these results. The neutron time-of-flight measure-ments were more accurate and were used to calculate plasmaexpansion velocities at all payloads except P-2.[59] The payload in flight configuration shown in

Figure B1 weighted 321.5 kilograms and the cylindricalsection that housed the electronics was a nylon cylinder

38.1 cm long, 66 cm diameter, with 3.81 cm thick walls.This low Z nylon was also chosen to minimize thebremsstrahlung produced by the fission fragment betaparticles. The electronic subsystems were shielded fromthe electromagnetic pulse from the Starfish burst and the10 watts of VHF power radiated from the telemetry antennasby a thin laminated copper-clad fiberglass cylinder coveringthe entire inner surface of the nylon cylinder.[60] The rocket boosters used to position the five pay-

loads around the Starfish nuclear burst were the second andthird stages of the flight proven Scout Vehicle. Two addi-tional Thiokol Recruit X-19 boosters were added to initiallyassist at liftoff. The entire rocket assembly was aerodynam-ically stabilized during the first stage of flight through theatmosphere and inertial spin stabilized during the secondstage boost and for the remainder of the suborbital flighttime. The spin rates remained constant and the spin axisangle with respect to the local magnetic field direction at H-0is shown in the seventh row of Table 2.[61] The design of the telemetry system conformed to the

Department of Defense telemetry standards developed bythe Inter-Range Instrumentation Group (IRIG). This systemtransmitted information at a 100 KHz rate by frequencymodulating a very high frequency (VHF) carrier. Carrierfrequencies for the five spacecraft were as follows: P-2 =247.3 MHz, P-3 = 237.0 MHz, P-4 = 229.9 MHz, P-6 =221.5 MHz, and P-7 = 216.5 MHz. This minimized theblackout period following the burst.[62] Owing to the severe attenuation of the VHF carrier

signal at the time (H-0) of the Starfish burst, a 30 s closedloop tape recorder was used to store data from H-3 to H +27 s. This recorded data was then played back repeatedlythrough the transmitter to receiving sites at islands shown inFigure 1. The tape recorder had two tracks: one for therubidium magnetometer and another for the 17 channels ofbeta detector, gamma-neutron, and Faraday Cup data. Atimer was used to stop the record-erase function of the taperecorder after a time 3 s less than the 30 s tape loop time.This timer was started by the prompt gammas from thenuclear burst. The prompt gamma detector assembly con-sisted of three surface barrier silicon solid state detectorsconnected so that a coincidence from any two would triggerthe tape recorder timer. These detectors were located nearthe center of the nylon cylinder and had an area of 1 cm2, aresistivity of 4000 ohm/cm, and were biased at 60 volts. Thecoincidence circuit triggered on any gamma pulse with arise time less than 2 � 10�6 s, a flux rate greater than 2 �104 rad/s, and gamma ray energy approximately 1 MeV.

[63] Acknowledgments. This work was supported by the DefenseThreat Reduction Agency (DTRA) under contract DTRA01-99-C-0035.The author wishes to thank Kenneth Schwartz of DTRA and Bernard Rothof Mission Research Corporation for their support and encouragement inthis data analysis effort. A large amount of credit is due to the DASAScientific Organization and the Air Force Weapons Laboratory at KirtlandAFB, NM for their support of Project 6.7 during the Johnston Islandoperations. As principal investigator for the development of the rocketpayloads and conduct of their flight, the author is indebted to Robert Bland,Edward Breen, Robert Reynolds, Warren Simmons, and Thom Yium fortheir assistance in designing, building, and field operations of this exper-iment. I also thank two anonymous reviewers for very valuable commentson this paper.[64] Zuyin Pu thanks James Van Allen and John Cladis for their

assistance in evaluating this paper.


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ReferencesAble, B., and R. M. Thorne (1998), Electron scattering loss in Earth’s innermagnetosphere: 1. Dominant physical processes, J. Geophys. Res., 103,2385–2396.

Bechtel Nevada (2000), Historical Nuclear Weapons Test Film Number0800062-Starfish Prime Test Interim Report by Commander JTF-8; Fish-bowl Auroral Sequences, 1962.

Bernhardt, P. A., R. A. Roussel-Dupre, M. B. Pongratz, G. Haerendel,A. Valenzuela, D. A. Gurnett, and R. R. Anderson (1987), Observationsand theory of the AMPTE magnetotail barium releases, J. Geophys. Res.,92, 5777–5794.

Brecht, S. H., and N. T. Gladd (1992), Structuring of a plasma shellexpanding into a magnetized plasma at sub-Alfvenic speed, IEEE Trans.Plasma Sci., 20, 6.

Brecht, S. H. (2001), Hybrid particle simulations of high altitude nuclearexplosions in 3-D using HPC, paper presented at Users Group Confer-ence, Dept. of Def. High Performance Comput. Mod. Progr., Albuquer-que, N. M.

Brown, W. L., W. N. Hess, and J. A. Van Allen (1963), Collected papers onthe artificial radiation belt from the July 9, 1962 nuclear detonation,J. Geophys. Res., 68, 605–758.

Cladis, J. B. (1968), Dynamical motion of geomagnetic flux tube resultingfrom injection of high energy particles, in Earth’s Particles and Fields,edited by B. M. McCormac, p. 307, Reinhold, New York.

Cladis, J. B., G. T. Davidson, W. E. Francis, L. L. Newkirk, and M. Walt(1979), Improvement of Specter II code: Injection and evolution of anartificial radiation belt, Rep. AFWL-TR-78-236, Air Force Weapons Lab.,Kirtland Air Force Base, N. M.

Cladis, J. B., D. W. Datlowe, M. A. Rinaldi, and M. Schulz (2006), Trans-mission line model of nuclear debris motion, Rep. AFRL-VS-PS-TR-2006-1080, Air Force Res. Lab., Kirtland Air Force Base, N. M.

Colgate, S. A. (1965), The phenomenology of the mass motion of a highaltitude nuclear explosion, J. Geophys. Res., 70, 3161–3173.

Croff, A. G. (1980), ORIGEN2—A revised and updated version of the OakRidge isotope generation and depletion code, Rep. ORNL-5621, OakRidge Natl. Lab., Oak Ridge, Tenn.

D’Arcy, R. G., and S. A. Colgate (1965), Measurements at the southernmagnetic conjugate region of the fission debris from the Starfish nucleardetonation, J. Geophys. Res., 70, 3147–3159.

Davidson, G. T., and R. W. Hendrick Jr. (1980), Particle injection by nucleardetonations, in The Trapped Radiation Handbook,D.N.A. 2524H, 2nd ed.,edited by J. B. Cladis, G. T. Davidson, and L. L. Newkirk, pp. 7.1–7.30,Def. Nucl. Agency, Washington, D. C.

de Pater, I., F. van der Tak, R. G. Strom, and S. H. Brecht (1997), Theevolution of Jupiter’s radiation belts after the impact of Comet D/Shoe-maker-Levy 9, Icarus, 129, 21–47.

Dyal, P. (1963), Debris expansion experiment, in Symposium Proceedings:Trapped Radiation, Def. At. Support Agency 1394, DASA Data Cent.Spec. Rep. 16, pp. 173–181, NASA Goddard Space Flight Cent., Green-belt, Md.

Dyal, P., R. T. Johnson Jr., and J. C. Giles (1969), Response of self-oscillatingrubidium vapor magnetometers to rapid field changes, Rev. Sci. Instr., 40,601–602.

Fajen, F. E., and R. W. Kilb (1982), Early time Starfish calculations,Rep. DNA 5991F, Gov. Ascension AD–A131179, Def. Nucl. Agency,Washington, D. C.

Forbes, A. J. (1987), General instrumentation, in Geomagnetism, vol. 1,edited by J. A. Jacobs, pp. 90–96, Elsevier, New York.

Gekelman, W., M. Van Zeeland, S. Vincena, and P. Pribyl (2003), Labora-tory experiments on Alfven waves caused by rapidly expanding plasmas

and their relationship to space phenomena, J. Geophys. Res., 108(A7),1281, doi:10.1029/2002JA009741.

Gisler, G., and D. S. Lemons (1989), Dynamics of a plasma expanding intoa uniform magnetic field, J. Geophys. Res., 94, 10,145–10,149.

Hess, W. N. (1968), The Radiation Belt and Magnetosphere, pp. 155–209,Blaisdell, Waltham, Mass.

Huba, J. D., A. B. Hassam, and D. Winske (1990), Stability of sub-Alfvenicplasma expansions, Phys. Fluids, B2, 1676–1692.

Huba, J. D., P. A. Bernhardt, and J. G. Lyon (1992), Preliminary studyof the CRESS magnetospheric barium releases, J. Geophys. Res., 97,11–24.

Jackson, J. D. (1962), Classical Electrodynamics, p. 315, John Wiley, NewYork.

Kennel, C. F., and H. E. Petschek (1968), Magnetic turbulence in shocks, inPhysics of the Magnetosphere, edited by R. L. Carovillano, J. F. McClay,and H. R. Radoski, pp. 485–513, Springer, New York.

King, J. H. (2004), National Space Science Data Center, NASA GoddardSpace Flight Cent., Greenbelt, Md.

Longmire, C. L. (1963), Notes on debris-air-magnetic interaction, Rep.RM-3386-PR, 8 pp., Rand Corp., Santa Monica, Calif.

Longmire, C. L. (1969), Study of coupling in Starfish sanitized, Rep.LANC-R-5, DASA-2474, 73 pp., Los Alamos Nuclear Corp., Los Alamos,N. M.

Newkirk, L. L., and M. Walt (1968), Radial diffusion coefficient for elec-trons at low L-values, J. Geophys. Res., 70, 1013–1017.

Ripin, B. H., J. D. Huba, E. A. McLean, C. K. Manka, T. Peyser, H. R.Burris, and J. Gunn (1993), Sub-Alfvenic plasma expansion, Phys.Fluids, 5, 3491–3506.

Teague, M. J., and E. G. Stassinopoulos (1972), Model of Starfish electronsdetermined for epoch Sept. 1964, NASA-TM-X-66211, X-601-72-48;NSSDC-ID-64-054A-21-OM, NASA Goddard Space Flight Cent., Green-belt, Md.

Van Allen, J. A. (1966), Spatial distribution and time decay of the inten-sities of geomagnetically trapped electrons from the high altitude nuclearburst of July 1962, in Radiation Trapped in the Earth’s Magnetic Field,edited by B. M. McCormac, pp. 575–592, Gordon and Breach, NewYork.

Wagner, N. J. (1984), Coronal mass ejections, Annu. Rev. Astron. Astro-phys., 22, 267–289.

Walt, M. (1966), Loss rates of trapped electrons by atmospheric collisions,in Radiation Trapped in the Earth’s Magnetic Field, edited by B. M.McCormac, pp. 337–351, Gordon and Breach, New York.

Walt, M. (1980), History of artificial radiation belts, in The Trapped Radia-tion Handbook, D.N.A. 2524H, 2nd ed., edited by J. B. Cladis, G. T.Davidson, and L. L. Newkirk, pp. 6.1 –6.60, Def. Nucl. Agency,Washington, D. C.

West, H. I. (1966), Some observations of the trapped electrons produced bythe Russian high-altitude nuclear detonation of October 28, 1962, inRadiation Trapped in the Earth’s Magnetic Field, edited by B. M.McCormac, pp. 634–662, Gordon and Breach, New York.

Winske, D. (1988), Short-wavelength modes on expanding plasma clouds,J. Geophys. Res., 93, 2539–2552.

Zinn, J., H. Hoerlin, and A. G. Petschek (1966), The motion of bomb debrisfollowing the Starfish test, in Radiation Trapped in the Earth’s MagneticField, edited by B. M. McCormac, pp. 671–692, Gordon and Breach,New York.

��P. Dyal, 26405 Ascension Drive, Los Altos Hills, CA 94022, USA.

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Documents

(1_Particle and Field Measurements of the Starfish Diamagnetic Cavity