PERGAMON

INTERNATIONAL JOURNAL OF

IMPACT ENGINEERING

International Journal of Impact Engineering 26 (2001) 299-308 www.elsevier.com/locate/ijirnpeng

MICROPARTICLE ACCELERATION FOR HYPERVELOCITY EXPERIMENTS

BY A 3.75MV VAN DE GRAAFF ACCELERATOR AND A 100KV ELECTROSTATIC ACCELERATOR IN JAPAN

SUNAO H A S E G A W A * , Y O S H I M I HAMABE**, A K I R A F U J I W A R A * , H A J I M E Y A N O *, SHO S A S A K I **, H I D E O OHASHI **~,

T O H R U K A W A M U R A * ~ * , K E N - I C H I N O G A M I ****, K O I C H I KOBAYASHI*****, #, TAKEO 1WAI **'~**, and H I R O M I S H I B A T A ~t**~

*Research Division for Planetary Science, Institute of Space and Astronautical Science, Sagamihara-shi, Kanagawa 229-8510, Japan; **Division of Science, University of Tokyo, Bunkyo-kn, Tokyo 113-0033, Japan; ***Division

of Fisheries Science, Tokyo University of Fisheries, Mitato-ku, Tokyo 1084)075, Japan; ** **Facility of medicine, Dokkyo University of Medicine, Shimotuga-gun, Tochigi 321-0293, Japan; *****Research Center for Nuclear Science and Technology, University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan; #Institute of Accelerator

Analysis Limited, Kawasaki-shi, Kanagawa 214-0013, Japan

Abstract--ln-situ dust detectors have been calibrated by dust electrostatic accelerators that can accelerate projectiles to expected mass and velocity ranges of space debris and micro- meteoroids. Unfortunately, In Japan, there was no such a facility dedicated to space science research until our research group was established a few years ago. Therefore, we have developed two high voltage accelerators. One is a modified 3.75MV Van de Graaffaccelerator operated by High Fhience Irradiation Facility, Research Center for Nuclear Science and Technology, the University of Tokyo 0-l/T), and the other is a 100kV accelerator dedicated to dust experiment at the Institute of Space and Astronautical Science (ISAS). The particle velocity using the HIT Van de Graaffaccelerator is higher than those reported in other accelerator facilities under the same particle mass conditions and encompasses the desired velocity range of micro-meteoroid. Time-Of-Flight dust mass spectrometer and Hybrid dust detector which are under development in Japan have been investigated using HIT dust accelerators. We have also constructed a 100kV electrostatic accelerator designed for easier handling and lower cost operation which is dedicated to dust acceleration, because the HIT Van de Graaff accelerator is being used for ion beam experiments mainly. © 2001 Elsevier Science Ltd. All rights reserved.

Keywords: High velocity impact, Dust electrostatic accelerator

I N T R O D U C ~ O N

Hypervelocity impact phenomena have been paid much attention for the last few decades, because extreme transient pressure with relatively low temperature and production o f shock wave in target materials are not caused by a common situation o f collisional phenomena on the ground [1, 2]. For almost materials, the hypervelocity regime has been reached under the condition that impact velocity exceeds 1 km/s. Relative orbital velocities o f minor bodies in solar system are also above several km/s as they collide. Those phenomena, therefore, have been engaged by not only material science but also space science and engineering.

Collisions o f two large objects like asteroids are rare events, but impacts o f small particles whose typical sizes are less than 1 micron are far more frequent. Accordingly, an early objective o f meteoroid impact in space is not o f scientific interest as a safety problem for satellites and astronauts. Safety problems have been getting worse since the 1980's due to the increase o f space

0734-743X/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 7 3 4 - 7 4 3 X ( 0 1 ) 0 0 0 9 8 - 7

300 S. Hasegawa et al. / International Journal of Impact Engineering 26 (2001) 299-308

debris. On the other hand, there is strong scientific motivation beyond these hazard problems. As meteoroids bring us precious information of the solar system origin and evolution, m-situ

dust detectors for space debris and meteoroids in space have been employed for the benefits of both solar system science and for the advancement of human space activities.

Various active in-situ dust detectors have been developed over the last 50 years. Orbital debris around the earth and meteoroids in interplanetary space involve hypervelocity impacts on satellites and spacecraft at a velocity range between a few and several hundred km/s. Almost all of recent in-situ dust detectors onboard spacecraft adopt an impact plasma detection method as impact plasma detectors could deduce its element, composition, mass, and velocity from impacted meteoroids.

In-situ dust detectors have been calibrated by dust accelerators that can accelerate projectiles to expected mass and velocity ranges of debris and micro-meteoroids. There are many concepts for micro- and larger particle acceleration up to velocities above 1 km/s. The two stage light gas guns were developed to permit laboratory studies of millimeter and centimeter sized projectiles accelerated to velocities to 8 km/s [3]. The gun may accelerate well-defined particles to particular velocities, and micrometer sized projectiles can be accelerated using a split sabot [e.g,, 4], but existence of gun debris following the projectiles is the defect of micro-particle acceleration by the guns. The plasma drag accelerator is useful and virtually the way to launch about 50 ttm to sub-mm sized projectiles at speed above ten km/s [e.g., 5]. For large particles (more than about fifty micron), the plasma gun produces fast projectiles, but it is difficult to determine the mass and shape of projectiles less than about fifty micron.

A typical impact ionization type dust detector is capable of measuring the mass range from 10 -13 to 10 -21 kg (a few micron to several tens nanometer in diameter). Because accelerating below a few micron particles is difficult using the two stage light gas guns and the plasma drag accelerator, they are unsuitable for the calibration of the impact ionization type dust detector.

The electrostatic accelerator is the conventional instrument for accelerating less than micron sized conductive particles up to velocities more than several km/s. We developed a pilot model ofa 25kV accelerator about one decade earlier, and have performed fundamental research for an advanced facility. The dust particle velocity using our 25kV accelerator was not sufficient to calibrate in-situ dust detectors. Hence, we have developed two high voltage accelerators. One is a modified 3.75MV Van de Graaff accelerator [6, 7], and the other is a new 100kV accelerator dedicated to dust experiments currently at the Institute of Space and Astronautical Science (ISAS).

In the following sections we will explain the general features of a dust acceleration system, and some results of dust acceleration and hypervelocity impact phenomena.

THE DUST ELECTROSTATIC ACCELERATOR SYSTEM

The dust electrostatic acceleration method was developed by Shelton etal. (1960)[8]. Their techniques were enhanced by Friichtenicht (1962)[9] and Lewis and Walter (1970)[10]. A dust source was connected to the top terminal of a Van de Graaff accelerator. Their techniques were used and modified for the Van de Graaff accelerator at Max-Planck-Institut flit Kernphysik in Heidelberg [11], Unit for Space Sciences and Astrophysics of University of Kent at Canterbury [4, 12], the Ion Beam facility of the Los Alamos National Laboratory [13], and the Faculty of Engineering of Kyoto University [14].

The dust electrostatic accelerator system consists of four sections: a dust source section, an accelerator section, a measurement section of particle charges and velocities, and an experimental section including a target chamber. Figure 1 shows a schematic view of these

S. Hasegawa et al. / International Journal of lmpact Engineering 26 (2001) 299-308 301

Van de Graaff or 100kV accelerator

Target High Potential Chamber Terminal

[Target [Deplete r " ~ - ] Deflector ~ ' ~ , ~_ ~_. ~ ~ , , , , , , , , , , , , , , , , , , - , ,

I / ,H. h IV ,lta ,Oe~ztorl Oe?tor Dus t , , ,~ ~ , / I~l. gn v°ltag.el I I Souce

v" 7 IPulse Circuit I ~ C h a r g e \ ' I \ / \ /Cha rge Sensitive . I . l l Sensitive Amplifier I_ PC./ _ . I I ]Amplifiers

I Processing Unit I

Fig. 1. Schematic view of the dust electrostatic accelerator system.

sections. The dust source, which puts positive charge onto dust particles, is located inside the terminal of the accelerator. The top view of the dust source is illustrated in figure 2. The dust powder is reserved below the tongue electrode. The two kinds of high voltages are supplied to the two electrodes. One is continuous DC high voltage around a few tens kV which is added to the surrounded electrode and the other is pulsed DC high voltage from zero to a few tens kV (maximum voltage equals to the continuous DC high voltage) applied to the tongue electrode to

Tongue Insulator

. . . . . . . . . l -

Fig. 2. Top view of the dust source (GrOn Type).

302 S. Hasegawa et al. / International Journal of lmpact Engineering 26 (2001) 299-308

excite dust particles vibrating between the walls inside the dust reservoir. The pulse width is about 10ms and the duration is about 50ms. The dust reaching the needle tip accidentally gets the charge from the tip whose shape is spherical.

Charged-up particles are accelerated toward ground potential. As each particle arrives at ground potential, its kinetic energy E is E = mv 2 / 2, where m is the particle mass and v is its velocity. The final velocity v of a particle accelerated through a potential of Vis given by

v = (2 Q V / m ) la , (1)

where Q is the particle charge. The accelerated particles pass between two sets of deflection plates called steerers in figure

l, which align the dust beam to the center of the beam line. On the beam line three cylindrical detectors ("Detector 1, 2, and 3" in figure 1) are set to measure projectile dust charges which are induced as a dust particle passes through the detector. The cylindrical detector is connected to a charge sensitive amplifier. Output voltage of the charge sensitive amplifier is proportional to the particle charge. The particle velocity is calculated by the time of flight between two cylindrical detectors. Thus, one can calculate the particle mass, momentum and energy by substituting the known value for the charge Q, the velocity v and the acceleration voltage V into eq. (1). If the density of the particle is known, one can calculate particle diameter by assuming it is spherical.

The particle selector is indispensable to select a specific particle condition, because a beam of accelerated particles has a broad distribution of mass and velocity range. It is composed of a deflector, a high voltage switching circuit and processing unit. As a particle passes parallel plates ("Deflector" in figure 1) in the beam line, only a desirable dust particle can pass that deflector by switching deflection voltage between them.

A target chamber consists of a vacuum vessel with a turbo-molecular pump, movable target stage and several view ports for impact flash (UV, visible, IR, X-ray) measurements.

THE MODIFICATION OF 3.75MV VAN DE GRAAFF ACCELERATOR FOR DUST PARTICLE ACCELERATION

The HIT (High Fluence Irradiation Facility, University of Tokyo) at the Research Center for Nuclear Science and Technology, University of Tokyo has a 3.75MV single-ended Van de Graaff accelerator, usually installed with Penning-Ionization-Gauge type or Radio-Frequency type ion source and four beam lines for studies of the ion beam simulation of neutron for nuclear fusion materials, ion beam irradiation effects and advanced techniques of trace element analysis. The modification from an ion accelerator to a dust one is usually achieved by replacing an ion source by a dust source at the high voltage terminal of a Van de Graaff accelerator. A new beam line consisting of charge and velocity measurement sensors, a deflector, and a target chamber for dust experiments is installed at the zero degree port-of the accelerator.

Results of the dust acceleration using the Van de Gl"aaff accelerator are shown in figures 3. Accelerated particles were sphere-shaped carbon and silver micro-particles whose size distributed over 0.3-1.5 and 0.5-2.0 ttm in diameter, respectively. Figure 3a shows accelerated particle velocity as a function of particle diameter and 3b shows particle velocity versus particle mass. The particle velocity distribution achieved by using the HIT Van de Gl"aaff accelerator almost equaled previous data reported at other acceleration facilities (Kent Univ. and MPI-K) under 2MV condition. Besides, range of dust velocities using the HIT Van de Graaff accelerator with 3 MV was higher than those using HIT, Kent Univ., and MPI-K with 2MV.

S. Hasegawa et al. / International Journal of lmpact Engineering 26 (2001) 299-308 303

E

>., o~ O O

>

fJ

10

1 0.1

. . . . . . . . ! . . . . . . . . ! . . . . . . . . . . . . . . . . ~x [ o 2MV Silver (HIT) ! o 2MV Silver (HI'r) |

x . / o 2MV Carbon (HIT) i i o 2MV Carbon (HIT) I × ~ x × / × 2MV Iron (MPI-K) =:"~ ×× i il x 2MV Iron MPI-K *+ ×~ . [ + 2MV Iron (Kent Univ.) ~ : ~ t * : : * 2Mvron~ent~.iv.)l

~_~t ~ ~ % | • 3MV Silver (HIT) .~d , ~ X t ~ o % :: :: * 3MV Silver (HIT) [ ++ . ~ x + o ~ [ ,, 3MV Carbon (HIT) +K .x=~l~. ! i[ * 3MV Carbon (HIT) I

+* +÷ × ~., i ÷ * * + + ~ , ~ o F ' ~ J , , n :: i . . . . . . . . . . . . . . . . . ~ × ~ t ~ " * " ~Y " ~ . ~ " . . . . . . . . . . . . . . . . . . . . . . . . ~-- 10 .................. ,~r::~:~;~,~''~ .................... ~ . . . . . . . . . . . . . . .

+ +~ ×+~. : •

o. . - - o ~ r - ~ o

a ) ! ~ ( b ) ::~ 1 0 "17 1 0 -16 1 0 -15 1 0 -14 10 "13

part ic le d iameter [micron] part icle mass [kg]

Fig. 3. Experimental performance for various particles by dust accelerators. (a): particle velocity versus particle diameter. (b): particle velocity versus particle mass. Open circles, open diamonds, times crosses, plus crosses, filled circles, and filled diamonds indicate silver and carbon particles

accelerated by the HIT Van de Graaffunder 2MV, iron particles by the 2MV Van de Graaff accelerator at Max-Planck-Institut fiJr Kernphysik (MPI-K) and University of Kent at

Canterbury, silver and carbon those by the HIT with 3MV, respectively. Data of MPI-K and Kent Univ. in this figure are obtained from Martin (1998, Personal Comm.) and Burchell at al.

(1999)[4], respectively.

Under the same mass condition, the particle velocity is dominated by the particle charge Q and the acceleration voltage V(see eq. (1)). However, maximum charge received from the tip is limited by the effect of the field emission from the dust particle [11, 13]. Therefore, the performance of the electrostatic acceleration of dust particles is generally governed by only accelerating voltage.

IMPACT EXPERIMENTS WITH THE HIT DUST ACCELERATOR

Measurements of chemical elements of dust particles in space will reveal origin and evolution of the dust particles. Dust particles are ionized by their hypervelocity impacts onto a target, and the produced ions are distinguished by measuring their flight times from target and detector, which depend on the masses of ions. A new dust analyzer with time of flight mass spectrometry (TOF-MS) was designed. The device will be loaded in spacecraft in the future, as it is compact, light in weight as well as high in mass resolution. To calibrate the performance of the new device, impact experiments of micro-particles were carried out using the HIT Van de Graaffdust accelerator [6]. In these experiments, silver and carbon particles ranging from 0.1 to 2.0 Ixm in diameter were used as impacting projectiles.

As the first step of development of the dust analyzer, a linear type TOF-MS (Figure 4) was used in order to clarify the process of ion production by hypervelocity impact. A linear TOF-MS consists of three parts; an ion source made up of a metal target and a front mesh, a field free drift region and a detector (MSP: Micro-Sphere Plate). Silver particles around 1 micrometer in diameter were accelerated up to 2-6 km/s, and three metal sheets of aluminum, molybdenum and gold were employed as a target material for TOF-MS. The start of TOF measurement was determined from the target signal, which was divided into two types: The first

304 S. Hasegawa et al. / International Journal of Impact Engineering 26 (2001) 299-308

High Voltage

Accelerating Region

El

Field-Free Drift Space

Dust Particle ~f Ag : HIT t. Fe : MPI-K

Accelerating ~* Region

....... ~N- "~., Detector Fast ' ~ ' i (MSP) Amp.

_.~_-_.

"\ ~ Grid "f Target Electrode

CSA

Digital High Voltage

Fig. 4. Conf igura t ion o f l inear T O F - M S .

L , = 8 m m , Lf = 141mm, L 0 = 9 m m , V~ = 1000V, Vd = 2700V

High Voltage Power Supply

CSA

Accelerating Region

Target | ~._L , ,f

• Dust Particle

/ / ~, ~ o,,~ , Rel]ectlng RegIon

]1111111 .e,,e t,on • i Plate

Fast Detector I [ ~ _ ~ . I -~.-~" ".~"~ " i

rap. ~ L~ .................. ~ 1

ee Dr,,, Space /

High Voltage I I Accelerating " ~ ] High Vo]lagc ] Power Supply I -- Rc g l ~ ' ~ - la,,-ion

[ Power Supply [

Fig. 5. Conf igura t ion o f ref lectron type T O F - M S .

This is the ref lectron T O F - M S whose ref lect ing region is parallel . L~ = 8ram, Lr = 120ram,

Lr ' = 119ram, L, . = 109mm, L a = 9 m m , Vt=4OO-1800V, V, -= 1800-2400V, V d = 2 7 0 0 V

S. Hasegawa et al. / International Journal of lmpact Engineering 26 (2001) 299-308 305

type when one particle directly impacted on the target with charges. The second type was when several fragments, produced by the collision of a projectile with the front mesh of the ion source, impacted onto the target at the same time. The former gives an effective TOF spectrum, but the latter is not useful for TOF analysis because the projectile is not ionized [15].

In the impacts experiments, ions from both silver projectiles and/or targets were detected when molybdenum and gold targets were used, but neither was detected for the aluminum target[16]. To determine the reason and to select the best material that ionizes the impacting dust particles, impact craters formed on these targets were observed by a typical scanning electron microscope (SEM) with emitted characteristic X-ray spectrograph. It is a principal theme to know the mechanism of crater formation as a function of projectile and target materials as well as impact velocities not only for space science but also material sciences. Crater observations suggested that the sizes and shapes produced by crater impacting depend on the differences of target material and impact velocity. On the molybdenum target, two types of craters were observed: One was a crater with projectile residues inside the crater or on the rim, which means that the impact velocity of projectile was not enough to vaporize the projectile. The other was a crater without residues, which is called ripple-shaped crater in this paper. Ripple-shaped crater suggests that the projectile impacted with higher velocity and vaporized completely.

Secondary, a reflectron type mass spectrometer was produced (Figure 5) and the performance experiments were carried out. In addition to the three parts of linear TOF-MS, this device has a reflecting region constructed by parallel electric field. Carbon particles of 0.1-2.0 lxm in diameter were impacted on the three targets with velocities ranging between 5 and 20 km/s. The TOF spectra for three targets were obtained more repeatedly than the spectra of linear TOF-MS. The peaks were similar each other for three target materials, nevertheless the impact velocity of projectile was different for every impact. The common peaks to three targets are regarded as cluster and multi-charged ions of carbon such as C2 +, C3 +, C4 +, and C52+ or ions from impurities of projectile or target materials such as Na + and K +. However, no peaks were detected before Na +, for example, C + and O + which were expected to be main components, were not observed.

Mass resolution (M/AM) is one of the most important factors for mass spectrometry. The

mass resolution (M/AM) of reflectron TOF-MS was more than 70, which was larger than that of

linear TOF-MS (M/AM - 20). However, these two mass resolutions cannot be simply compared, because the material of the impacting projectile was different. The impact velocities of silver and carbon projectile are different because their velocities depend on their masses when the projectiles are accelerated by the HIT Van de Graaff accelerator (see eq.(1)). The projectile material difference causes the difference in ionization of projectile and target materials. We need more studies on the effect of impact velocity and difference of projectile and target materials.

Post flight analysis on retrievable surfaces and simple passive dust collectors on satellite are low-cost and a well-established technology. In-site dust detectors onboard spacecraft can produce time resolved information and orbital parameters, which provide compositional data for origin determination. This information is relayed to ground stating for analysis. We are developing a Hybrid dust collector and detector (HD-CAD) which overcomes these issues while this still capturing particles intact. As fundamental processes of impact flash production, however, are not well understood quantitatively, we also made impact experiments using silver projectiles of 0.5-2.0 ~tm in diameter accelerated to 2.5-4.0 km/s by the HIT dust accelerator onto various kinds of high purity metal plates with distinctive physical properties.

306 S. Hasegawa et al. / International Journal of lmpact Engineering 26 (2001) 299-308

THE DUST DEDICATED 100KV ACCELERATOR AT ISAS

The HIT Van de Graaff can not be dedicated full-time to dust acceleration. Due to this situation, developments of various dust detectors and studies o f hypervelocity impact phenomena progress slowly. Therefore, we are constructing an accelerator that can always be used for dust particle acceleration. We designed the accelerator from views of easier handling and lower-cost operation. Thus, maximum voltage of the accelerator is set at 100kV. The dust source of the 100kV accelerator at ISAS is compatible with the HIT dust accelerator. The 100kV accelerator uses the same detectors for measurements of particle charges and velocities as before. The view of the dust dedicated 100kV accelerator is shown in figure 6.

Fig. 6. A rear-side view of The dust dedicated 100kV accelerator. The right side on the picture is the high voltage terminal. When the picture was taken, the accelerator is test phase. Therefore,

the beam line of it had only one particle detector.

Typical plots of velocity versus diameter and specific charge Q/m vs. diameter of accelerated particles are shown in figure 7. Particle velocities increase with the diminution of particle mass and surface charge. This is a common feature of the dust electrostatic accelerator. Charges on less than 0.1 lxm particles produce a very small output voltage comparable to a noise level from a charge sensitive amplifier. For this reason, it is quite difficult to measure charges of less than 0.1 p,m particles. In particular, noise level at the HIT is larger than that at ISAS.

Consequently, it is hard to detect particle charge with below 0.3 ~tm particles using the HIT dust accelerator system. Thus we are planning to develop a new charge detecting system.

S. Hasegawa et al. / International Journal of lmpact Engineering 26 (2001) 299-308 307

E

0

>

m o , m

t~ ¢x

100

10

0.1

. . . . l -~-~'~-'Carbon 90kV (,OOkV)[I

. . . . . . . . .

0.1

particle diameter micron]

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-~- 103

0 g 102

0 101

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. . . . i . . . . . . . . i • , .

- - m - - C a r b o n 90kV (lOOkV I ; [ * Carbon3MV (HIT) I

0.1 1

particle diameter [micron]

Fig. 7. Plots for carbon particles from the 3MV HIT dust accelerator and the 100kV accelerator at ISAS. (a): particle velocity as a function of diameter. (b): specific charge as function of

diameter. Cross squares and filled diamonds indicate carbon particles by HIT dust accelerator under 3MV and by the dust dedicated accelerator under 90kV, respectively.

In figure 7 (a), Fitting to carbon dJata on the condition that accelerating voltage is 90KV and 3MV yields

v = 1.3 D -°.85, r = 0.99, (2)

and

v = 7.3 D -°.92, r =0.96, (3)

where D is the particle diameter in micrometer, v in krn/s, and r is the regression coefficient of the fitting. According to Eq (1), particle velocity is proportional to the square root of accelerating velocity. The square root of 3MV (HIT dust accelerator) divided by 90kV (the dust dedicated accelerator) is 5.8, and ratio ofeq. (2) Divided by eq. (3) is 5.6. Taking into account the unsteady charging efficiency of each particle, and measurement error, these values are consistent.

CONCLUSION

We developed the two dust accelerators for space science and engineering. One is the modified 3.75MV Van de Graaff Accelerator at HIT. The dust accelerator can be achieveded 1 p,m carbon particle to 10km/s, and the particle velocity using the HIT accelerator is higher than those reported in other acceleration facilities under same particle mass conditions and encompasses the desired range for an analogue of micro-meteoroid velocity. Dust detectors such as TOF and HD-CAD which are under development was investigated using HIT dust accelerators.

A 100kV accelerator dedicated to dust experiment at ISAS have been developed due to the HIT Van de Graaff can not be dedicated full-time to dust acceleration. The particle velocity using the 100kV dust accelerator is about six factor of magnitude smaller than one using the HIT accelerator, but is easier handling and lower cost operation than the HIT accelerator.

308 S. Hasegawa et al. / International Journal of Impact Engineering 26 (2001) 299-308

Acknowledgments---We wish to thank Mr. G. Schafer, Dr. R. Srama and Prof. E. GrOn, MPI-K for discussions and their advice about detail of the dust accelerators and for providing their dust source. We are also grateful to Mr. M. Cole, Dr. M. J. Burchell and Prof. J. A. M. McDonnell of Kent Univ. for giving us useful advice of accelerator design. We also thank to Mr. M. Narui and Mr. T. Omata for their help with HIT dust experiments. We are greatly indebted to Prof. T. Nakajima, Kyusyu Univ. for providing their accelerating tube and insulators. This study was carried out as a part of"Ground Research Announcement for Space Utilization" promoted by Japan Space Forum.

R E F E R E N C E S

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[2] Kissel J. and KrUger F. R. Ion formation by impact of fast dust particles and comparison with related techniques. Appl. Phys. A 1987; 42: 69-85.

[3] Crozier W. D. and Hume W. High velocity light gas gun. J. Appl. Phys. 1957; 28: 892-894. [4] Burchell M. J., Cole M. J., McDonnell J. A. M., and Zarnecki J. C. Hypervelocity impact studies using the

2 MV Van de Graaff accelerator and two-stage light gas gun of the University of Kent at Canterbth-y. Meas. Sci. Techol. 1999; 10: 41-50.

[5] Rose M. F., Best S., Chaloupka T., Stephens B., and Crawford G. Hypervelocity impact facility for simulating material exposure to impact by space debris. In: LDEF-69 Months in SpaceSecond Postretrieval Symposim, NASA Conf. Publ. CP3194, Part. 2, 1992: p. 479-492.

[6] Hasegawa S., Fujiwara A., Yano H., Nishimura T., Sasaki S., Ohashi H., Iwai T., Kobayashi K., and Shibata H. Desin of electroctatic accelerators for the development of microparticle detectors in Japan. Aa$,.SpaceRes. 1999; 23: 119-122.

[7] Hasegawa S., Fujiwara A., Morishige K., Yano H., Nishimura T., Sasaki S., Hamabe Y., Ohashi H., Nogami K., Kawamura T., Iwai T., Kobayashi K., and Shibata H. Acceleration of micro-particles to hyper velocities by using a 3.75 MV Van de Graaff accelerator. Lunar and Planet. Sci. Conf. XXX, Huston, FL. 1999: #1546.

[8] Shelton, H., Hendricks C. D., and Wuerker R. F. Electrostatics acceleration of microparticles to Hypervelocities. J. Appl. Phys. 1960; 31: 1243-1246.

[9] Friichtenicht, J. F. Two-million-volt electrostatic accelerator for hypervelocity research. Rev. Sci. Instr. 1962; 33,:209-212.

[10] Lewis A. R. and Walter R. A. Electrostatic acceleration system for hypervelocity microparticles with s elected kinematic properties. NASA Techical Note TN D-5780 1970.

[11] Fechtig, H., Griin E., and J. Kissel. Laboratory simulation. In: McDonnell J. A. M., editor, Cosmic Dust, Wiley-Interscience Publications, Chichester, UK, 1978. p. 607-669.

[ 12] Green S. F., Clarke C. D., and Stevenson T. J. A 2MV Van de Graaff accelerator for cosmic dust impact simulation. J. Brit. Interplanet. Soc. 1988; 31: 393-396.

[13] Keaton, P. W., Idzorek G. C., Rowton L. J., Seagrave J. D.,. Stradling G. L, Bergeson S. D., Collopy M. T., Curling H. L., McColl D. B., and Smith J. D. A hypervelocity-microparticle-impacts laboratory with 100-km/s projectiles. Int. J. ImpactEng. 1990; 10: 295-308.

[14] Fukuzawa, F. Mirco particle ionbeam (macron beam). Oyo-Butsuri 1991; 60:720-721 (in Japanese). [15] Hamabe, Y., Kawamura T., Nogami K., Ohashi H., Shibata H., Sasaki S., and Hasegawa S. Development

of dust analyzer with TOF mass spectrometry. Lunar and Planet. Sci. Conf. XXX, Hnston, FL. 1999: #1760.

[16] Hamabe, Y., Sasaki S., Ohashi H., Kawamura T., Nogami K., Yano H., Hasegawa S., and Shibata H. Crater on metal target formed by hypervelocity impact of micron-size particles. Proc. 32th ISAS Lunar and Planet. Syrup., Kanagawa, Japan, 1999: p. 93-96.