The QQDDQ magnet spectrometer “big karl”

Nuclear Instruments and Methods 214 (1983) 281-303 281 North-Holland Publishing Company

T H E Q Q D D Q M A G N E T S P E C T R O M E T E R " B I G KARL"

Siegfried A. M A R T I N , Arno H A R D T , Jtirgen M E I S S B U R G E R , Georg P.A. BERG, Ulrich H A C K E R , Werner H O R L I M A N N , Josef G.M. ROMER, Thomas S A G E F K A , Adolf R E T Z and Otto W.B. S C H U L T lnstitut fi~r Kernphysik, Kernforschungsanlage Jalich, D- 5170 Jiilich, FRG

Karl L, B R O W N Stanford Linear Accelerator Center (SLA C), Stanford, Ca 94305, USA

Klaus H A L B A C H Lawrence Berkeley Laboratory (LBL), Berkeley, Ca 94720, USA

Received 17 January 1983

A magnet spectrometer consisting of two quadrupoles, two dipole magnets and another larger quadrupole in front of the detector was designed and installed at the nuclear research institute of the KFA Jiilich. It has been used for charged-particle spectroscopy at the isochronous cyclotron since early 1979. Special features of the spectrometer are variable and high dispersion, coils for higher order field corrections in the dipole magnets and a focal plane perpendicular to the optical axis. A large mass-energy product of m E / q 2 < 540 u. MeV, an angular acceptance of d$2 < 12.5 msr, a high resolving power of p / A p up to 3 × 10 4 and the possibility of kinematical corrections up to K = 0.8 make the instrument a very versatile tool for many experiments in the fields of nuclear and atomic physics.

1 . I n t r o d u c t i o n

Besides "t-ray spectroscopy! ~ the spectroscopy of charged particles from scattenng processes or from nuclear reactions constitutes one of the most powerful tools for nuclear structure studies. Construction of a magnetic spectrograph by Browne and Buechner [1] stimulated similar instrumental developments in other laboratories. For example at Florida State University, Sheline and his coworkers used their scaled-up version of a Browne-Buechner spectrograph for stripping and pick-up reaction studies to determine spectroscopic factors which were combined frequently with ~- and con- version-electron data from neutron capture in the frame of international collaborations [2]. Extensive use has also been made of the magnetic spectrograph designed by Elbek [3] and his coworkers at the Niels Bohr Institute for inelastic scattering and transfer reaction studies.

The desire for larger apertures led Spencer and Enge [4] to design the split-pole type magnetic spectrograph, copies of which have been built and successfully used in different research centres. An example is the split-pole spectrograph at the Argonne National Laboratory used by Erskine [5] for investigations of nuclear structure.

The demands for even higher resolution at large solid angles of acceptance led to Enge's development of a

0167-5087/83/0000-0000/$03.00 © 1983 North-Holland

Q3D spectrograph [6]. Instruments of this type are used at Munich [7], Heidelberg [8] and other laboratories [9].

With the availability of more energetic beams, especially at cyclotrons, the need for magnetic spectrographs emerged which have - a significantly larger mass-energy product range, - large solid angles of acceptance, - very high resolution (1 part in 104 or better), - high and variable dispersion, and which have dispersion matching similar to that demonstrated by Blosser and his coworkers [10]. An example of this type of spectrograph is the large magnetic spectrograph "RAIDEN" [11] at the Osaka cyclotron. Dispersion matching is essential at accelera- tors having poor beam quality. A suitable beam transport system is required if both the momentum spread of the beam and its emittance are to be matched so that they do not impair the resolution. In addition the spectrograph should provide means to apply the necessary higher order corrections.

For high resolution charged particle spectroscopy at the isochronous cyclotron JULIC [12] a spectrograph was designed with a mass-energy product of m E / q 2 = 540 u. MeV. This new design was necessary because scaling of the Q3D would have resulted in a device too large and too expensive. For this reason another solu- tion had to be found. The result is the Q Q D D Q " BIG

282 S.A. Martin et al. / "'BIG KARL"

K A R L " spectrometer with Ht-windings [13] in the two

dipole magnets to be described in this paper. a later stage should permit an increase of the resolving power of the whole system.

2. The Q Q D D Q magnet spectrometer

The desire for high resolution combined with the propert ies of the existing Jtilich cyclotron beam [14], given in table 1, led to a magnet spectrometer design whose resolution is limited by the cyclotron beam. However improvement of the cyclotron beam quality at

2.1. Ion-optics

The ion-optical design of the BIG K A R L magnet spectrometer is based on calculations carried out with the computer programs T R A N S P O R T [15-17], TUR- TLE [18] a n d ENGPIS. ENGPIS is a combinat ion of Enge's ray tracing code [19] and the optimization code PISA [201.

Table 1 Characteristic data of the cyclotron and beam line, and ion-optical specifications of the QQDDQ spectrometer BIG KARL

Cyclotron: Projectile Energy (MeV)

p 22.5- 45 d 45 - 90 3He 68 -135 a 90 -180

Emittance c~, - ~y - 20 mm-mrad Momentum resolution p/Ap (fwhm) - 600

Beam line: Double monochromator magnet Mode of operation

dispersive achromatic

32 cm/% a) 0 232 mrad/% ~ 100 mrad/%

Spatial momentum dispersion Angular dispersion Momentum resolution p/Ap (fwhm) ~< 2× 104 600 Transmission 2% 100%

Target: Spot size

1 film < 2x 0 < 50 mm in horizontal direction of dispersion 1 mill < 2y0 ¢ 4 mm perpendicular to direction of dispersion

Spectrometer:

Angular range Mean radius of central ray Maximum particle rigidity Mass-energy product Solid angle Acceptance angle

horizontal + 25 mrad vertical + 125 mrad

Length of ~Iseful focal plane - 1 m

Tilt angle of focal plane - 90 ° Horizontal magnification Mx= 0.63 0.77 Vertical magnification My= 25.4 22 Variable dispersion D (cm/%) 0 6.3 Ratio D/Mx (cm/%) 0 8.2 Momentum resolution 0 8200 p/Ap (fwhm) for 2x 0 = 1 mm

- 10 o . . . 140 ° Oo = 1.98 m

Bmax'P0 = 3400 kG.cm mE~q: __< 540 u.MeV d12 < 12.5 msr

1.03 1 .26

10.2 1.94 18 26 17.5 20.6

17500 20600

a) The momentum dispersion is given here as the width Ax in the focal plane of a line with a rectangular profile and A p / p = 1%.

S.A. Martin et aL / "'BIG KARL" 283

2.1.1. First order design The physical limitations of the experimental areas

combined with the experiments to be carried out provided the basis for the first order design. The limiting factors were the phase space and stability of the cyclotron beam, the geometrical restrictions of the existing building, load limits and the height of the beam line above the floor. The final design parameters are listed in the lower part of table 1. The magnification and momentum dispersion were determined by the spatial resolution of the particle detector. A focal plane tilt angle close to 90 ° between the optical axis and the detector was considered optimum if one wants to maintain the option of ray tracing by using two detectors, e.g. in connection with the time-of-flight technique.

To first order the resolving power is given, for point- to-point imaging, by the equation [21]

R = E / A E =p /2Z lp = ( Z - lo)/(2Xo8o)

= fo tSx( ' r )h( ' r )dr l / (2Xo) , (1)

where 1 - 1 o is the path length difference of the outermost trajectory and the central ray, 2x o and R o are the target spot size and the maximum divergence angle of the beam leaving the target. The product h(~-)d~- = da is the differential bending angle of the central ray, with 1/h( 'r) = p(~') being the bending radius in the magnetic field. The "sine-like function" s x will be defined below. The integration limits in eq. (1) are the target position (z = 0) and the focal plane (¢ = t). Costs are minimized if the sine-like function sx(¢), which is equal to Ri2 in matrix notation, is essentially constant throughout the bending magnet. Fig. 1 shows the characteristic first

QI Q2 D1 02 Q3

II.~z 0.2 -

(~--'~",,) 0.0

-02 ~/~

-0.~, I -06

-10 r ~,

5 10 "L" (m)

Fig. 1. Sine-line function sx(~')= RI2 for different dispersions D = 6, 12, 16 and 22 cm/% in the focal plane as a function of the distance • from the target. Ql, Q2, Dl, D2, Q3 indicate the quadrupole (Q) and dipole (D) field regions.

50-

t,0-

30-

IXl(Cm) •

20-

QI Q2

l I

i

D1 D2 0.3 ~/////////A Y////////~ "/.~

0 5 10

T (rn)

Fig. 2. Horizontal ([xl) and vertical (y) second order beam envelopes for the QQDDQ spectrometer BIG KARL. The lower curve shows the vertical waists in the bending magnets D~ and D 2. The hnes labeled 1% and 2% show the trajectories for particles with a momentum differing from that of the central ray by !% or 2%, respectively.

order function RI2 of BIG KARL. In addition, low costs for dipole magnets require a small gap height. This condition can be fulfilled if the vertical beam envelope has a waist in the centre of both dipole magnets as shown in fig. 2. For the QQDDQ system the minimum half-gap height is - 2 cm [22] for a vertical phase space of + 0.5 mm. 60 mrad.

As can be seen from fig. 1, the quadrupole Q2 creates an intermediate image R~2 = 0 in the horizontal (x) direction. For higher dispersion this image moves in the direction of Q2, increasing Ri2 in the dipoles and therefore the resolution of the system. The vertically focusing quadrupole QI, on the other hand, increases the useful angular acceptance of the spectrometer and, in combination with Q2 it helps to form a very narrow beam in the vertical (y) direction. In this way QI and Q2 ensure a high transmission through the pair of dipole magnets DI and D2. The edge angles of DI and D2 combined with Q1 and Q2 provide the phase space matching [23] for the second dipole D2. The quadrupole Q3 allows a variation of the dispersion at the detector. Fig. 3 shows the ion optical parameters as a function of the field in Q3. An example of spectra measured with different dispersions is depicted in fig. 4.

2.1.2. Higher order corrections Higher order aberrations have been minimized

according to ref. 21. In this notation the aberration coefficients in the x-direction * are represented by

* The equations for the vertical y-direction are developed in an analogous way.

284 S.A. Martin et aL / "BIG KARL"

1.t,

Hx

Hy

1.2

1.0

0.8

06

20

10

J J

J

J J

, , , , I , , , ,

\ i i i i

O (cm/%) 20

10

f f J

J / t

j l

0

20

H x 10

J / / 0 ¸

-0.50 0 0.50 100

B(0.3)lBmax(Q3)

Fig.3. Magnifications M= and My, dispersion D and D/M~: as a function of the relative field strength B/Bm. ~ of the quadrupole Q3.

( x Ix;YoXOo~eP~o8 ~ ), (2)

and denote the coefficients o f the Taylor expansion

x ( t ) = E (xlx;yoXO~*~o3~)x;yoXOo~o3~, (3) ~,A,,u,v,x

which expresses the focal plane coordinate xO" = t) in

terms of the "s tar t ing" coordinates x o, Y0, 0o, ~0, 30 at the target (~-= 0),

The contr ibution from a multipole component of n th order to aberrat ions of order n (n = x + h + v +/~ + X) of a system with midplane symmetry can be expressed

200-

100'

~.00.

200,

200-

100-

200-

lO0- Z

0

200 -

100-

2001

100 l

0 •

200-

100-

0-

O=260Em/% SSNi (P,P') 5°Ni

Ota b =20*

. . . . . . . . . . . . . . . . ~._ iL !

D

O=6.3cm/% m r ~ ~ m ~ o .<

D=3.0cml% -* *=~ *~

D=l.5cml% ~m . ~

n ~

D =0.25c /°/o

D=-2Ocml% ~ " W

' i ; ' , 1 , ' ,

500 ~000 1500

C H A N N E L N U M B E R

Fig. 4. Spectra of 58Ni(p, p') measured for different dispersions D = 26, 16, 6.3, 3, 1.5, - , 0.25 a n d - 2 cm/~ . The spectrograph was optimized for D=- 16 crnZ%, "

S.A. Martin et al. / "'BIG KARL" 285

in terms of the first order functions

R , , ( r ) =- (XlXo) -~ c~(~) ,

("cosine-like function" in x-direction),

(xlOo)=- (" sine-like function" in x-direction),

R33( ,)=- ( ylYo)=- cy( , ) ,

("cosine-like function" in y = direction),

=- (xl,o) --- ( , ) ,

(" sine-like func t ion" in y-direct ion),

R I 6 ( . ) e (xlSo) ~ dx(q'), ("dispersion function" in x-direction),

and the fixed coefficients K . , K. _ 1,' • ", Ko as follows

n! ( x[x;yoXO~eO~o8 x) = +

K!X!I~!v!X!

x fo'aX(,, , ) 4 ( , ) 4 ( , > : ( , )

X Sy( r)dX('r) K.('r )dr

+ lower order terms for

K, ,_ , , . • . , Ko. (4)

For the correct sign in this equation see ref. 16. The Greens function G~ is given by

Gx(t , r) = Sx(t)Cx(¢ ) - cx(t)Sx(¢) , (5)

and the K , ' s are the coefficients of the multipole expansion

By(x, O, r) = ( Bp) E K , ( , ) x " (6) n-O

of the vertical component of the magnetic field in the midplane (y = 0), where B e denotes the magnetic rigidity for the central ray. The sign in eq. (4) depends on the combinat ion of K, X,/~, v, X-

If K,(z) is assumed to be constant over the length % - r 1 = L of the multipole element and zero elsewhere, partial differentiation of eq. (4) with respect to K, yields

O( xlx;y2@g,~oag ) nt -t

aK. - xtX!t~!vtX!

×f[2Gx(t,'c)c~,('r)CXy('r)

× s : ( . ) s ~ ( ¢ ) d x X ( z ) d r , (7)

which describes the coupling between an n th order multipole and an n th order aberration.

If furthermore the first order functions c~, Cy, s x, Sy, d~ are constant in the region of integration (e.g. for a

short multipole element), eq. (7) reduces to

O( xlx yo O& o # ) OS,, = + r!X!t*!~!X!

X Gx(t , ,)c~(,)cXy(z)S~x(, )

x (8)

where S, = LK, is the multipole strength, which is gen- erally defined as

s.=f?2K.(r)dr. (9)

The "coupling coefficient" (8) is a function of the location r(¢~ < r < ¢ z ) of the multipole element and reflects the influence of the multipole strength S, on the n th order aberration.

A helpful tool to find the position where the multipole should be placed in the system for an efficient correction of higher order aberrations is the function

Ol( xlxgy°XO°~g'~°8~ ) P"12 (10) = OK. '

k+X+l~+~+X=n

with P, = x~yoXO$q~or#, the maximum phase space at the target position. As an example fig. 5 shows this function and its analogue in the y-direction for sextupole corrections of second order aberrations at BIG KARL. As can be seen from this figure, the best locations for sextupole corrections for x-errors are inside the two bending magnets D~, D z, and for y-errors between the two quadrupoles Q~, Q2. Strength functions for correcting third and fourth order aberrations were determined in a similar way. Estimates with the computer programs ENG- PIS and TURTLE suggested variable and independent

200-

F~(T} 100-

0

2- F~(T)

k-

6-

01 Q2 Ol

i

J

D2 03 z////~.

0 5 110 T(m)

Fig. 5. Sextupole strength function F 2 for horizontal (x, upper part of the figure) and vertical (y, lower part) corrections of aberrations in BIG KARL as function of the distance of ,r of the correction element from the target.

286 S.A. Martin et al. / "BIG KARL"

sex tupo l e s , o c t u p o l e s and d e c a p o l e s wi th ( K , / K o ) ( 1 / a " ) = B , / B o up to 5 × 10 -4 where a denotes the distance between the central and outermost rays. For these corrections an octupole has been installed between Qt and Q2 and D t and D 2 have been equipped with two sets of H t windings (to be discussed below).

2.1.3. Field correction concept In order to generate variable multipole fields in

dipole magnets, the concept of Ht-windings proposed by Halbach [13] has been applied. Several conductors are imbedded into the iron of the pole pieces running parallel to the particle trajectories. At the iron-air inter- face of the pole piece an "Ht-current" causes a change of the tangential field component H t. This led to the name Ht-windings for this type of correction coils. With suitable currents in these coils the desired multipole field can be superimposed on the main dipole field. Midplane symmetry requires identical currents of equal sign in conductors located opposite to each other with respect to the midplane.

In the following discussion such a pair of identical currents will be called one Hi-current. The field "re- sponse" of a single Ht-current is shown in fig. 6. De- pending on the sign of the current, the main field level is increased on one side and decreased on the other side of the Hi-winding. A simplified analysis for the generated field step A B yields a linear dependence on the H t

current It/'

,~s = (~o/h ) ~r,,,, ( l l) where h is half of the gap width.

A more detailed analysis [13,24] exhibits significant

nonlinearities and a dependence of A B on the dipole main field B itself.

With the same currents in all n t windings the super- position of all responses leads to a quadrupole component.

In fig. 7 examples are shown of sextupole fields which are generated by linear current distributions. In a similar way it is possible to generate field components of higher multipolarities via higher order current distributions.

The practical use of the Hi-windings for correcting higher order aberrations is discussed in sect. 3.2-3.4.

2. 2. Technical realization

The location of the spectrometer in the cyclotron laboratory is shown in fig. 8. The height of the beam line above the floor is 1.40 m which restricted the mechanical design of the magnets and the support. The dimensions of the building set an upper limit of 10 m on the outer radius of the instrument. Furthermore, the thin wall of the experimental room required additional shielding around the beam dump in the scattering chamber. This was achieved by an igloo-type concrete housing which at the same time protects the detectors at the focal plane from the beam dump background radia- tion and kept costs for the shielding at a minimum. The program MAGBER was used to minimize the cost of the magnetic elements. The lay-out of the spectrometer is shown in more detail in fig. 9. It consists of the scattering chamber followed by an aperture defining slit system SLX,Y the two quadrupoles Q1 and Q2, a second antiscattering slit SLD in front of the two dipoles DI and D2 and the last quadrupole Q3 in front of the detector system. The standard detector system con-

7540

B(Sauss )

7530

7 5 2 0

7510

7500

HT5

I I I I i I I I i

"~''~ IHT5-+5 Yo ....,.--'"

I H T 5 = - 5 0 / o

I I I I I I I I I

-20 -10 0 10 20 x (cm)

Fig. 6. Measured field strength in dipole magnet DI as function of the radial distance x. The field step A B is caused by a single Ht-current (+ 5% of/.1. ~ = 250 A). The arrow (HT 5) indicates the radial position of the Ht-winding in the dipole.

7700

B (Gauss)

7600

7500

7400

7300

HTI HT2 HT3 HTG HT5 HT6 HT7 HTB

i i I I i i I [ i

f AIHT =÷~%

AIHT =+2°/0

IHT : 0

I L

-20

AIHT :-2%

AIHT =-/*%

I I I I I I I

-10 0 10 20 x (cm)

Fig. 7. Measured sextupole fields in dipole magnet DI generated by linear current distributions in the Ht-windings. Aln, is the relative current change between two neighbouring HFwind- ings. The arrows indicate the radial positions.


cally the vacuum does not increase above 2 × 10 -6 mbar . The chamber has an internal d iameter of 34 cm. Its opening of 50 m m horizontal and 30 m m vertical width allows the different beam match ing modes, and the exit of 50 m m hor izonta l and 20 m m vertical exten- sion allows the use of the full angle of acceptance of the Q Q D D Q spectrometer. The wall of the scattering chamber remains fixed relative to the spectrometer. The s ta t ionary top lid of the chamber carries the movable Fa raday cup and is equipped with a target lock system for easy target change without breaking the vacuum. Also the target angle and 6 target posi t ions can be chosen arbitrarily. All these operat ions can be carried out by remote control. The s tandard target lock (maxi- m u m of 6 targets) can be replaced by a mult i- target system (up to 40 targets fixed on a chain). Fig. 10 shows a pho tograph of the target region within the ' ig loo ' of B I G KARL.

Fig. 8. View of part of the cyclotron building of the nuclear physics institute in the nuclear research centre KFA Jiilich. The beam needed for high resolution work at the magnetic spectrometer BIG KARL is admitted to the target through a slit in a heavy concrete igloo, which houses the scattering chamber, the quadrupoles QI and Q2 and also the last quadrupole doublet QB6 of the beam line. The resolution of the cyclotron beam can be improved with the use of the monochromator magnets AM1 and AM2.

sists of a mult iwire propor t ional chamber (MWPC) and two plastic scintillators.

2.2.1. Scattering chamber For the initial measurements with BIG K A R L a

scat ter ing chamber was designed and buil t tha t per- mi t ted reaction studies at any angle between - 10 ° and + 140 °. For the measurements of angular dis t r ibut ions the scattering chamber is equipped with a sliding seal. A double O-ring system with differential pumping keeps the leakage dur ing angular variat ions so low that typi-

2.2.2. Magnets The dipole specifications are listed in table 2. The

tolerances are given together with fur ther specifications elsewhere [25]. The quali ty of the spect rometer is mainly de termined by the homogenei ty of the low carbon iron and the nar row mechanical tolerances. All magnets were fabricated f rom properly treated iron with a ca rbon con ten t less than 0.06%. At a field s t rength of 16 k G the homogenei ty of the relative permeabi l i ty A # / # is 0.6% for the pole pieces of the dipole magnets and 6% for the yoke parts of D l and D2 and for the componen ts of the

quadrupole magnets [22]. In order to re ta in the opt ion of measuring with BIG

K A R L at large backward angles the first quadrupole magnet Q1 had to be designed as narrow as possible in the hor izontal plane. For this reason and for cost reduc-

Table 2 Technical design data of the dipole magnets DI and D2.

Dl D2

Magnet gap 6 cm 6 cm Pole width 60 cm 82 cm Pole length 253 cm 260 cm Pole thickness 10 cm 10 cm Geometrical radius O0 192 cm 192 cm Angle of deflection a 0 78.3 cm 78.3 ° Edge angle at entrance 0 ° 30 ° Edge angle at exit 30 ° 0 ° Radius of curvature at entrance 105 cm -250 cm Radius of curvature at exit 106 cm - 357 cm Flatness of pole face + 0.025 mm + 0.025 mm Regularitiy of magnet gap + 0.05 mm + 0.05 mm Identity of pole contours + 0.05 mm + 0.05 mm Number of H t coils 40 48 Practically usable field 1.6-20 kG 1.6-20 kG Total weight - 50 t - 70 t

288 S.A, Martin et al. / "BIG KARL"

Q3

PLASTI[

D2 --... -.~ .~. "'",,,

MWP[ -2.5 - _ 0.8 " " tO

p = 1.9m

= 7 8 ° i 13t2= 30 ° ®

z' 7 7 7 f ~ | / 1 ' r

0 I 2 m ~ ~-~ ~ 7 . . . . . -[////~ II ~ *

/ TARGET

Fig. 9. Arrangement of the magnetic elements of the QQDDQ spectrometer BIG KARL. The central ray (optical axis) is shown as dashed curve. The outermost rays with the extreme radial distances are drawn as full lines. Four channels in the inner yokes allow NMR probes to be moved into the gaps of the dipoles for radial field measurements. The multipole element between QI and Q2 allows the correlation of vertical aberration.

tion Q1 and Q2 were built identically as "Col l ins type" quadrupoles [26]. The surfaces of the pole tips were machined so that they form rectangular steps which allow easy mechanical corrections [27]. The weight-of each quadrupole is - 2.5 t.

In spite of the elliptic cross section of the beam, measuring 70 cm in the x direction and 8 cm in the y direction a symmetrical quadrupole magnet was chosen for Q3 because three dimensional calculations [28] showed that the fringe field of an asymmetric quadru-

pole cannot be properly corrected. The design of this magnet allows easy removal of the pole pieces for adjustments without disassembling the whole magnet whose weight is - 10 t.

Special care was taken during the design and fabri- cation of the parts of the dipole magnets D1 and D2 which also carry the H t windings. Fig. 11 gives a view on D1 which together with D2 is described in detail in ref. 25. For easy disassembling the upper and lower yokes of the dipoles were fabricated out of two pieces

t~

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xt~


t / / / / / / / /

/ / / /

, t / / /

/ / / /

/ / / /

/ / / /

I i - i e n i-~ I- i I"I I

q I A a a A a I A . "/'" "/ ~ / H f coit

~//~c ha m be r / / c0il /

'ql

Fig. 11. View of the dipole magnet D1. The lower part of the figure shows the second half of the bottom yoke with the Ht-coils embedded into the iron. In D1 there are 10 Hi-coils in each half of the bottom and of the top yokes. (The dipole D2 contains 12 Ht-coils in each half.) The upper part is a section through the side yokes and the top yoke with the Ht-coils. Into the poles homogenizing slots are machined. The poles are top and bottom of the vacuum chamber. The wall of the vacuum chamber carries double O-ring seals which are differentially pumped.

because of the 15 t load limit of the crane. The edges of the poles at the entrance and exit were made removable in order to maintain the possibility to change their contour if necessary. Technical details about the pole pieces, the homogenizing slots in connection with the H t windings, and the design of the vacuum chamber in which the joints are double-gasketed with differential pumping have been described elsewhere [25]. The narrow tolerance on the parallelism of the two pole surfaces (___ 0.05 mm) was achieved by adjustment of the inner and outer yoke legs. Also the tolerances for the horizontal positions of the pole pieces (+0 .1 ram) were met through dowels and accurate assembling with hydro- static oilbearings [25].

The H t coils are inserted in concentric slots machined into the yoke pieces. The coils were prefabri- cated and fitted into the grooves before assembling the yokes. Slots were cut also into the pole pieces with the same radius as those for the H t coils in the yokes. This homogenizes the field in the gap and shifts the magnetic flux lines generated by the H t current closer to the pole surface [13]. Each H t coil consists of 4 turns of copper conductors 8 mm x 8 mm with a 2.5 mm diameter hole for the coolant. At the maximum power of 1000 A - turns the current density amounts to 12.5 A / m m 2. Each of the main coils in the dipole magnets has 112 windings with a maximum power of 120000 A . turns. They are made of a copper conductor with a cross section of 11.4 × 11.4 mm 2 with an internal 5 mm dia channel for

the coolant. The maximum current density is 5 A/ram 2. The coils of the quadrupole magnets Q1 and Q2

consist of 1 l0 turns of a hollow copper conductor with the dimensions of 8 m m x 8 mm and a 4 mm diameter channel for the coolant. At the maximum load of 60 000 A . turns the current density amounts to l0 A / r a m 2. For Q3 with 100 turns and a maximum of 70000 A • turns the same conductor has been chosen as in D 1 and D2 with a maximum current density of l0 A / m m 2.

Each of the five main magnet elements of BIG K A R L is connected to its own power supply which has the advantage of independent operation. The long term stability ( - 8 h) for the quadrupole power supplies is - 10 -5 and for each dipole supply it is even better by a factor of 2. The currents of these power supplies can be adjusted in steps of 10 -5 .

An additional set of 44 power supplies (20 in D 1 and 24 in D2) are necessary for the independent activation of the H t coils providing the possibility to have different H t corrections in the first and second halfs of both dipole magnets. At present all pairs of H t windings located in the first and second half of each dipole magnet are connected in series so that l0 power supplies are needed for D1 and 12 for the H t windings in D2. The maximum current of each supply is 250 A with a long-term stability of 10 -3. In order to measure the resulting magnetic field two so-called " fumble probes" can be moved in the radial direction through 20 mm wide holes into the inner field region of each dipole.

s..4. Martin et aL / "BIG K A R L " 291

The position accuracy is - 0.1 mm. The field strength can be measured either by Nuclear Magnetic Resonance (NMR) or Hall probes to better than 0.1 G.

2. 2.3. Detector systems

The main purpose of the detector system in the detector plane of the spectrometer is to measure the position of the ejectiles in the horizontal (dispersive) plane and to provide energy loss signals for particle identification. In addition to these there are several other parameters needed to test the performance of the spectrometer and to improve the quality of the measured spectra. Such parameters are, e.g., the vertical direction and the angle and timing signals of the reaction products. Several detectors are available and can be combined in a modular way in accordance with the requirements of the particular experiment.

For the measurement of light particles (A < 7) a two-dimensional multiwire proportional chamber (MWPC) [29] with delay line readout is currently in use. The active area of this prototype detector is 300 mm (x) x40 mm (y) and the spatial resolution is better than 0.5 mm in both directions. For particle identification a single wire proportional chamber with a sensitive depth of 35 mm providing a A E-energy loss signal with a resolution of A E / E - 0.17 is mounted a few millime- ters behind the MWPC. This detector is followed by two plastic scintillation counters [30] both with an active area of 1100 m m x 100 mm. (The length of 1100 mm was chosen for later use with a larger focal plane detector.) The NE110 scintillation detectors have thick- nesses of 10 and 90 mm in order to stop even high energy protons. Photomultipliers (PM) (RCA 8800) are coupled together with plexiglass light guides to both ends of the scintillator blocks and yield fast timing signals and analog signals proportional to the light output.

The effective speed of the photons in the plastic is about 10 cm/ns and permits the determination of the horizontal position with a resolution of - 3 cm by measuring the time difference of the PM signals.

A system of 2 two-dimensional multiwire drift chambers (MWDC) [31] with delay line readout and an active area of 900 mm x 90 mm was built at the Los Alamos Scientific Laboratory and the University of Texas [32] and will be installed in the near future in the detector plane of BIG KARL. These detectors have an expected spatial resolution of Ax, Zly < 0.3 mm allowing the measurement of x, y and the flight direction of the particles and therefore the reconstruction of the focus and later the determination of the time of flight (TOF).

For the measurement of heavier reaction products a 1000 mm long ionization drift chamber [33] has been built very recently. It yields position and A E signals. A charged particle passes a resistive wire proportional chamber followed by two 50 mm wide AE ionization

chambers, a second resistive wire proportional chamber, a 300 mm wide ionization chamber and a third resistive wire proportional chamber.

To supply the detector with various gas mixtures an electronic gas control system was designed and built. It allows to vary the gas pressure from 50 and 2000 mbar with a stability of 1 mbar and an average gas flow of about 4 1/h.

2. 2. 4. Support The height of the beam line being only 140 cm above

the floor of the spectrometer room limited the total height of the support to 67 cm. This lack of space severely restricted the possibilities for the design [25] of a suitable support. In addition, the laboratory is located in an earthquake region. Therefore the design must allow for movements of portions of the building by amounts that rule out concepts like oil bearings, where high mechanical precision and stability is required. The BIG KARL spectrometer rests on a flat platform equipped with air bearings. During the measurements the whole apparatus rests on only three points: a large bearing with tapered rollers in the pivot point under- neath the scattering chamber and two iron legs at a radius of about 7 m below the two dipoles. During the measurements this tripod guarantees the required reproducibility of the alignment of the QQDDQ system. The support carries all magnetic elements of BIG KARL, the scattering chamber and the particle detector system as well as a great number of auxiliary components. For changing the scattering angle, the air bearing mem- branes are inflated and lift the steel construction of the support which is then rotated by a motor driven wheel. The scattering angle can be set at any value between

- 10 ° and + 140 ° with an accuracy of 0.02 °. The concrete igloo rests on air pads too. It is loosely

coupled to the support and follow angular movements while remaining centered.

2.2.5. Vacuum system In order to reduce scattering by the residual gas

inside the spectrometer a vacuum better than 1 x 10 -6 mbar is maintained. Presently this is achieved by double gaskets and differential pumping where necessary and by four cryopumps, two sets of a roughing and a roots pump, one turbo-molecular pump and two differential pumps.

The entire vacuum system of the spectrometer is divided into three sections which can be separated by gate valves to allow partial ventilation of the system without breaking the vacuum in the whole spectrometer. The three vacuum sections are the scattering chamber, the magnet system and the detector front chamber. A vacuum of 1 x 10 -5 mbar is achieved within 6 min of pumping from atmospheric pressure in the scattering chamber. For the same procedure 150 rain are needed


for the magnet system and 10 rain for the detector front chamber. The entrance window of the multiwire proportional chamber [29] consists of a 19 ~tm mylar foil supported by 1 mm thick nylon wires (every 15 mm) separating the counting gas (p < 1700 mbar) inside the detector and the vacuum chamber.

The final pressure of the system is 6 × 10 -7 mbar. The operating time may exceed 300 h without the need to regenerate the cryopumps. More details about the vacuum system are given elsewhere [25].

2.2.6. Control The large number of system parameters involved in

operating BIG KARL demands for computer control and operating support. This becomes even more important because of the distance between the spectrometer, the cyclotron control room, and the electronics area with the room for the spectrometer control. Manual control has been retained as an option.

2.2.6.1. Hardware. The spectrometer is controlled by a PDP 11/40 computer. Since for most purposes hardcopy is more important than speed all but one terminal provide hardcopy facilities. Two terminals are Tek- tronix-TCS [34] compatible graphic terminals used mainly for analyzing magnetic field shapes. System and user disks are separated as usual for maximum salty. The magnetic tape unit is essentially used for logging and system maintenance.

All control and spectrometer status readout functions are handled by a two-crate CAMAC system using Borer 1533A single crate controllers. To cope with noise and ground unbalance caused by power supplies and stray-rf all signals are connected to CAMAC through opto-couplers or decoupled by transformers.

Current setting in the dipole magnets is accomplished with 24 bit re-readable output registers. On CAMAC write the 5 digit BCD-coded data value is strobed to the external data registers contained in the remote power supplies. The 24 power supplies for the H t windings are controlled by a common 18 bit data bus and 24 single strobe lines. The latter are generated by a modified output register producing 2 ms pulses on the data lines set to logic 1.

Control of aperture slits and positioning of the four fumble probes is performed by standard 24 bit I / O registers. The radial fields in the dipoles D 1 and D2 are measured by NMR or optionally by Hall probes for strong field gradients. Four 5½ digits digital Volt meters (DVM) with 0.5 s integration time define the position stepwidth by generating data ready interrupts on 32/16 bit I / O registers.

Power supply currents, pole-tip field strengths, gas pressures and detector high voltages are monitored by a remote differential relay multiplexer connected to another DVM. In total 64 channels are available in a 0.2

to 2000 V range with 5½ digits of resolution. Status lines can be monitored by a 128 bit line surveyor which automatically scans all lines and reports any change iia bit pattern to the computer.

2.2.6.2. Software. The DEC RSX-11M operating system was chosen to support multitasking on several independent terminals. Programming language is Fortran except for a very few routines which handle the basic CAMAC functions and interrupts. BASIC is available for users during the experiment.

The system startup is fully automatic including date and time setting from a battery buffered CAMAC clock, a short test of most important CAMAC functions and a reset of system parameter files. This allows an easy system restart in case of serious troubles even for the inexperienced user.

Apart from hardware test routines spectrometer control is performed by five correlated programs: CYCLE as the main control task to handle magnets,

slits, fumble probes etc,; STATUS to report on the actual spectrometer status

(also included as command in CYCLE); CYSTOP to interrupt lengthy control procedures; FUMMEL to,measure the radial dipole field; FUPLOT .tQ, analyze and plot the acquired field data.

All main programs have a few design features in common:

The system is self-explaining by appropriate HELP commands both a t the system and program level. Terminal input to the programs is format free. This minimizes the number of characters and mistypings especially on slow terminals. Commands together with parameters may~be typed on a line with automatic defaulting of omitted parameter values. The same commands may be read from a disk file in batch mode.

Terminal I / O is written to log files in batch mode format and it is occasionally saved on magnetic tape. SpectrOmeter and program status is kept in a system- wide common block accessed by all programs and on a backup disk file for restauration after power failure. Default parameters and permanent data are loaded at run time from system parameter files. This avoids changing the program if just a number has to be modified.

Tasks requiring more than standard privileges or excessive memory are created as subtasks to maintain system protection for the normal user. In addition the breakup into several main and subtasks allows control, analysis and status supervision to proceed in parallel. These features have proven to constitute an easy to use and highly stable operating system.

2.2.6.3. Control procedures. The normal procedure to adjust the fields in the main dipoles D1 and D2 is by using the CYCLE command. The current rises at a rate

S.A. Martin et al. / "BIG KARL" 293

of 1% of the maximum current per sec to yield saturation. It stays at maximum for 2 min and then decreases at 0.3%/s to approach the final value through a 10% undershoot. This "cycling" guarantees good reproducibility of the field value and shape especially with switched on H t windings. For small field variations a MOVE command allows a current change with variable slope but without the lengthy saturation loop. Im- mediate current setting is possible with a hardware defined slope of 1%/s but only used for test purposes. The three quadrupoles Q1, Q2, Q3 are directly field- controlled by measuring pole tip field strengths with Hall-probes and adjusting the corresponding current in an iterative procedure. Using this method eliminates calibration and reproducibility problems characteristic for larger magnets. Dipole and quadrupole fields may be changed simultaneously by the same percentage of the actual value by a single command SCALE ALL which alters the Bp-values but not the ionoptical properties of the spectrometer.

Hi-currents are given as polynomial coefficients of the expansion of the currents as function of the radial position in the dipole magnets. Therefore in linear ap- proximation 10 directly defines a quadrupole, I l determines the sextupole strength and so on. Single H t control is possible with fitted values returned for the status coefficients.

To measure and analyze the resulting radial fields in D1 and D2 the four fumble probes are moved in at constant speed and measurements are taken in 0.5 s time intervals. The data is then visualized on a graphics terminal and analyzed in terms of multipole strength. The two dipole fields are adjusted to the same level if the zero-order coefficients differ by more than 1 G to avoid mismatching caused by the pole face curvatures.

Finally currents in the last four beam line quadrupoles QB51 . - . QB62 are set by the IMMediate command or by a simple up /down pushbutton control with software-defined ramp speed. It is frequently used in visual optimization of beam spots on the target or focal plane viewers.

Two slits behind the scattering chamber and in front of D1 determine the entrance window to the spectrometer. Slit position is defined in terms of true center position and opening given in mrad for both x- and y-directions. These four degrees of freedom are essential for the experimental ray tracing with pencil beams in spectrometer optimization as explaind later in section 3.3.

3. Spectrometer setting and beam matching

In the following we briefly describe how BIG KARL is set and optimized [35] and how the beam line is prepared before using [22,36] the spectrometer for

high-resolution reaction spectroscopy.

3.1. Magnet setting

Using the control program CYCLE, the fields of all magnets of BIG KARL are set in the following way: - The currents of D1 and D2 are set according to the

Bp-value of the particle to be analyzed. For reproducibility the magnets are thereby always driven through saturation (20 kG at maximum current), and the field levels at the optical axis inside D1 and D2 are adjusted within + 1 G to avoid an unknown quadrupole strength resulting from the pole edge angles at the exit of D1 and the entrance of D2 as described in sect. 2.2.6.3.

- The settings of the quadrupoles Q1, Q2, Q3 additionally depend on the desired dispersion (i.e. energy bite in spectrum) and are calculated by the computer program MAGSET based on TRANSPORT calculations and empirical parameters. After this coarse setting of the magnetic fields, a fine

tuning of Q1 and Q2 is necessary in order to minimize the width of the spectrum lines.

3.2. Magnet optimization procedure

In order to maintain the resolution of the spectrograph for large solid angles, it is necessary to ensure horizontal and vertical focussing by correcting the angular aberration terms

R,2 = (x le0) , r,22 = ( x l O g ) , - . . ,

R34=(Y[Cko), Ta4a=(YI~2), " ' ' ,

and their allowed mixings

(x],~20), (yl00cPo), (y[002~o), etc.

Additionally the dispersive aberrations describing focal plane tilt and curvature

T126 = (x[00{~), TI266 = (xI00 ~2)

have to be minimized in order to provide a constant resolution along the focal plane.

The first order terms Rl2 and R34 may be easily zeroed using the quadrupoles Q2 and QI, respectively, whereas the higher order terms require field corrections of higher multipolarity, i.e. sextupole fields for second order aberrations, octupole fields for third order aberrations, etc. While some of the second order corrections have been included in the ionoptical design by using curved pole faces of the bending magnets (sect. 2.2.2), the remaining multipole strengths have to be generated inside the magnets by an appropriate setting of the H t windings (sect. 2.1.3).

For illustration, the correction methods for the most


important second order aberrations T122 and Ti26 will be described below. These methods hold for the third and higher order corrections as well.

The relation between aberrations and multipole fields has been described in sect. 2.1.2. As can be seen by eq. (4) an aberration of order n only depends on multipole fields of orders lower or equal to n. This has the important consequence, that a multipole of order n + 1 only influences aberrations of order greater than n, which allows one to correct the next higher order terms without changing already corrected terms of order n.

In the example of the aberrations 7"122 = (xl002) and 7"126 = (xl00~o) in the detector plane (position t) the connection to the correcting sextupole field strength at an arbitrary position • in the system is represented by the coupling coefficients [21]:

0T122/0S2(1", t ) = - [Sx ( t )Cx( T ) - Cx( t )Sx( r )ls~( T ),

(12)

~TIz6 ~S 2 (~, t ) = -21Sx( t )Cx(T ) - c x ( t ) s ~ ( z ) l

× s x ( ~ ) d x ( r ) , (13)

where the first order terms are assumed to be constant in the region of the sextupole, which is located at position ~.

In the case of point-to-point imaging [Sx(t)=0], these expressions reduce to

3T,22/3S2('r, t ) = Cx( t )s3 ('r ), (14)

~T126//~S2 ('I ", t) = 2 C x ( t ) s 2 ( ' r ) d x ( ' r ) , (15)

where c x (t) becomes the horizontal magnification M~ at the focal plane.

Fig. 12 shows the coupling coefficients 7"12 z and TiE 6 of BIG KARL plotted as functions of z for different dispersions R ~6. The most efficient locations of correcting sextupole fields are inside both dipoles D1, D2 for TiE 2 and inside D2 for TIE 6. Because OTIz6/~S 2 is small inside DI, it is possible to correct both aberrations. The correction procedure is as follows: 1) Minimize T12 6 by using the Ht-windings of D2. 2) Minimize Tt2 z by using the Ht-windings of DI,

thereby leaving 7"12 6 almost unchanged.

3. 3. Experimental raytracing

In order to determine the real aberrations of the spectrometer, the experimental "raytracing method" is applied. For this purpose a coarse pencil beam is formed with the use of the entrance slits and Q1 is set so that focussing is sufficiently good in the y-direction. There- after the entrance slits are closed down to A0 < + 2 mrad around 0 and A~ < + 10 mrad (y direction) for a detailed determination of the focussing properties of BIG KARL in the direction of dispersion (x) through

0.1 Q2 01 D2 Q3 V/A~__. .___.~/ / / / / ' / / / / /A ~///////////A V//A

0 ~X~ = - - ~

-10"

,ff ~-20. ~ p,,-o

-50-

0

i -2- 12

\z~/

o ; ,'o T (m)

Fig. 12. The second order coupling coefficients ~T122//~$2 and 0Ti26/0S 2 of BIG KARL as a function of the distance z from the target.

the measurement of the positions x i of several spectrum lines i (with different 80) in the focal plane as a function of 00 .

x, = x , ( O o ) , X 2 = x 2 ( O o ) , . . . , x , = x , ( O o ) . (16)

These distributions contain all of the information needed to determine the unknown aberrations by simple polynomial fits. For this purpose the interactive computer program "MATRIX" was developed:

"MATRIX" takes over the distributions eq. (16) directly from the acquiring system and calculates the spectrometer aberrations in the following two steps:

First each of the distributions eq. (16) is fitted as a polynomial in 00

N

xi = Y'. a,kOo k, (lV) k=O

where normally N is chosen as N = 5 or 7. The coefficients aik represent distributions in

a,~ = a~(8 , ) ,

which in a second step are fitted as polynomials in 8, M

ak = E tkt 8l. (18) I ~ 0

S.A. Martin et aL / "'BIG KARL" 295

The tk/'s are the searched aberration terms of order up to N + M:

t k , = (x100%') ( k = l . . . N , l = 1 . . . M ) .

For example:

R16 = ( X 1 3 0 ) = tOl , R I 2 = ( X l O 0 ) = tlO ,

r 12 2 = ( x l ~ ] g ) = t20 , T126 --- (XlOo3o) = t,,.

Furthermore "MATRIX" estimates the line broadening along the focal plane due to different aberrations and calculates optimal multipole settings for the aberrations to be minimized.

3. 4. Example of optimization

In the following an example will be given illustrating how the spectrometer optimization, using the program MATRIX is accomplished. For the investigation of the 15~Eu(p, d)~5°Eu reaction at 25 MeV incident energy the l°9Ag(p, d)l°SAg reaction was used in the optimization procedure because the cross section was sufficiently large and several states (E x = 79-607 keV) could be used to cover the detector plane at a dispersion of D = 12 cm/%.

The beam line resolution was determined to be 6 keV using a thin (100 /xg/cm 2) target of l°9Ag and a very narrow spectrometer entrance slit of AlO = + 2 mrad in order to be independent of the spectrograph's aberrations. By opening the solid angle horizontally A 20 = + 15 mrad and vertically A2#,---- +60 mrad (dO= 3.6 msr) the resolution increased to about 12 keV. At first the positions of the peaks were measured as function of 0 with AO = + 2 mrad as explained in section 3.3. For this procedure 1 mg/cm 2 target was used. Fig. 13a shows the plot of the position of a particular peak at around channel number 1030 near the center of the detector. The fitted curve contains the information of the angular aberrations at this position. Fig. 13b, c display as examples the matrix elements R12 and 7"122 along the focal plane. The total peak broadening BROAD for AO = + 15 mrad along the focal plane and the analysis of the contributions of the aberrations R~2, T~22, T~222 is shown in fig. 13d. In order to minimize the main contribution T122 the linear component of the Hi-windings in D1 was increased from 3% to 4% of/max" The result of this measurement is shown in fig. 13e. The matrix element Ri2 is strongly dependent on the position in the focal plane corresponding to a large 7"126 term. In order to zero T~26 the program MATRIX calculated a change of the linear term of the Ht-windings in D2 from 0.3% to 0.6%. The result is shown in fig. 13f. The line broadening due to the spectrometer aberrations are smaller than 6 channels corresponding to 4 keV in the active detector range from channel 600 to 1700. Since this is small compared to the beam line

resolution of 6 keV the optimization is finished. The resulting high resolution spectrum is shown in fig. 14. Later it will be shown (see fig. 19) that under better beam conditions and a smaller solid angle d O - 1 msr in another measurement a higher spectral resolution of A E - 4 keV could be obtained.

3.5. Matching between beam line and spectrometer

A particle which leaves the entrance slit of the beam line system with the coordinates (x00080) is transformed down the beam line (matrix B). In front of the target in the scattering chamber we get the coordinates (x~0~80). 80 has not been transformed because the energy has not been changed. The target transformation T takes care of the reaction angle (a) and the target angle (~z).

The starting coordinates for a particle entering the spectrometer are (x 2, 02, 82) with

x 2 = Tx, , T = c o s ( ~ - ~ T ) / / C O S C]~T, (19)

82 - defined randomly within the angle acceptance of the spectrometer

3 2 = K ( O 2 - Oi) + C3 o.

K and C describe the kinematics of the reaction.

1 0Pout . ~Pout Pin IC=?ou__ - - a , , ' c : ae , n P o u , (20)

If we call S the matrix describing the transformation of the spectrometer from behind the target to the detector plane the total transformation to the detector plane is given by

0 = S 02 ~ T ~ 01 ~ B 00 .

8 [ 82 ] 80 80

behind target in front cyclotron the transfor- of the extraction target mation target (21 )

The transformation in the bending plane from the cyclotron extraction to the detector plane is given as

x = X o ( S n b u T - s16b21K)

+ 00 ( s n b 1 2 T - s16b22K)

+ 80 ($11bl6T- s16b26K + Sl6C ) + 02 (s ,2 + s , , / c ) . (22)

It is the aim of the proper matching to zero the coefficients of 0 2, 8 o and 0 o. The resolving power in the matched system is then given as

R = P 1 sl6 (23) 2Ap 2X 0 Mov"

This is the general formula for the resolution where the overall magnification is given by

Mov = ( s u b n T - s j r b 2 1 K ) .


T h e m a t c h i n g p r o c e d u r e is u s u a l l y d o n e by a 4 s tep

T R A N S P O R T [ 17] ca lcu la t ion :

Step 1: T u n e s p e c t r o m e t e r for

s12 = - s l 6 K . (24)

T h i s c o r r e s p o n d s to t he c lass ica l kinematic displacement, so ca l led b e c a u s e these c h a n g e s cou ld be a c c o m p l i s h e d

b y a m o v e m e n t o f the foca l p lane . T h e d i s p l a c e m e n t L

is t h e n d e t e r m i n e d b y

1050.00

POSITION (CHANNL)

1040.00

. . . . . . . . . . . . . . I . . . . . . . . . . . . . . I . . . . . . . . . . . . . . I . . . . . . . . . . . . . .

tt PEAK-NR 4 tt ~ tttt*~ FITTED WITH DEGREE 3 tor t

t t I t t

=8 t

tO t l

1030,00 t

t $

I 1020.00 0

t I

t

1010000 I---t . . . . . . . . . . I . . . . . . . . . . . . . .

ttttt tt I

tt of/= I t

It

ot

t t

tt, ol

*t i . . . . . . . . . . . . . . I . . . . . . . . . ; . i

-20.00

0.02

R12 CH/I~

0,01

-10.00 0.00 THET~OI~aD)..__ 20.00

b . . . . . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . .

I t ADERRATI~ R12 t t FITTED WITH DEGREE 1

-h20E-03

T122 CN/NR2

-1.40E-03

-1.60E-03

-1.80E-03

-2.00E-03 500.00

I ~* t t 0 $tltt$ I $$$$t

tltt* t t t l t

o.0o I" . . . . . . . . . . . . . . . . . . . . . r . . . . -frill tt*$ . . . . . . . . . . . . . . . . . . . . . . . .

i ~ , , , ,~"P'

-0,01 - 0 $**t$ I I I : t*t* I t l l l I l i

-0,02 I . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . 500.00 1000.00 1500.00 2000,00

POSITION (CHANNEL) c

. . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . .

$$ ABERRATION T122 *$ FITTED WITH DEGREE I I I

t ~ ~ 0 I o I I I I o I

$$$t15t$tt$$$$t$tt$ I I ttttttlttttttttttttttttttttt~ttttttttttttttt I I I

I I I I I 0 0 I I I I I I

................... I ................... I ...................

1000.00 1500.00 2000,00 POSITION (CHANNEL)

d ~ 0 ' 0 0 I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

O0 LINE DROADENINO FOR SEX = 0 +- 15,0 l-R12 BROAD 0000 2-T122 (CHANNL) 000 00000 3-T1222

O-TOTAL 30,00 - 0000 00000

2222222222222222222220~0~0000000000000000000000002~2~02~i 222

20,00333111 3333111

]333111 3333311

33331 10,00 333333333 1111111

3333 111 33333: 133333 11113333

o.oo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . . . . . ~ l i 3 ~ . . . . . . . . .

0.00 I000.00 POSITION (CHANEL~ 000'00.

40,00 I ----~- . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I

BROAD 1 LINE BROADENING FOR SLX = 0 ÷- 15,0 I-R12 (CHANNL) 000 2-T122

000 3-T1222 30,00 - 000 O-TOTAL -

000 : o0o 111 o00 o0o0 I 111 0000 000

20,00 3333 I11 0000 0000 : 3333 1111 00~00 000000022222222222 : 333 111 2222222222000000000002222 I 2222222222233]32222222

33331111 33 lO,O0 333 111 3333

3333111 33331 3333111 3331

333111 33331 333311 333311

0,00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . l . . . . . . 33311 . . . . . . . . . . . . . . . . . . 0,00 1000,00 2000,00

POGITION (CHANNEL) f

15,00 I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BROAD O0 LINE BROADENING FOR GLX : 0 4- 15,0 I-R12 (CHANNL) I O0 2-T122

: oo 3-T1222 11 oo O-TOTAL

11 O0 10.00 I I I O0

11 O0 OOI

11111% 0 O0 O0 ! 333 II O0 O0 1

3333 11 O0 O0 I I : I 333 11100 O0 11 I

5.00 - 3333 II00 O0 11122233 : 333 1100 00 222223333 : 1 3333 1100 O0 222221 333 : 22 333 1000 000222 113333 : : 222222 3333 1100000002 1333 I : 22222 3332221 333 : : 22222 22222 333311 3333 '

0,00 I ................. 222222 ...... I .... 3331 ..................... 0.00 1000.00 2000.00

POSITION (CHANNEL)

Fig. 13. Some of the functions provided by the computer code MATRIX for a fast minimization of the spectrometer aberrations. (a) shows the detector plane position as function of the horizontal entrance slits (THETA) for a particular peak at channel near 1030. (b) and (c) display the derived aberration R 12 and T122. In (d) the line broadening for an angle opening of + 15 mrad is shown as derived from the measurement displayed in (a, b, c). The aberration T122 is the dominant contribution. In (e) and (f) the aberrations are minimized as explained in the text until the expected line broadening from the spectrometer is comparable or smaller than the beam line resolution.


l°gAg(p,d ) 1°SAg, E p =25 MeV, Otab= 10 °

.J ,,, 60 Z Z -r k_J

1--

20

i I I , I

0 500 1000 1500 2000

CHANNEL NUMBER

Fig. 14. Spectrum of 1°gAg(p, d)l°SAg after optimization allowing the large solid angle of dO= 3.6 msr without loss of resolution which is 6 keV in this case. Excitation energies in keV are given for those peaks used in the optimization.

(L 01(0 6) 0 1 0 s21 822 s26 0 0 1 0 0 1

11 + /-'321 L322 S16 + /'326 / / S210 S220 8216 / ~ (25)

from the condition eq. (24) we get

L - s l 6 K (26) 822 + S26 K"

Since this method changes the dispersion and resolution it is therefore recommended to change the element st2 in eq. (24) with the quadrupoles Q1, Q2 and keep the

detector position at the same place in order to ensure a constant energy calibration.

Step 2: Tune the beam for

s n b a r T - s16b26K + sl6C = 0. (27)

This gives a restriction on the dispersion of the beam line.

K ) (28/ 616 = - - S16 ( C _ 626. ~ Sll \ 'T

For K = 0 (light particle on heavy targets) one gets the well known dispersion matching condition

Dbeam =- (--~'~)Spect .... ter'-~-~ " (29)

Because C and T are always close to 1 the rule is: the dispersion of the beam bl6 has to be equalized by the resolution of the spectrometer Slr/S n. If the target is used under reflection T = - 1 the sign of the beam dispersion has to be reversed.

Step 3: For a finite K value the beam line tune has to fulfill the condition

b,2/b22 = (s16/81,) K I T . (30)

This is the kinematic defocusing of the beam at the target. The defocusing distance can be estimated by multiplying a drift matrix with the undisturbed matrix.

In analogy to eq. (25) this defocusing distance L is given by:

L = ( s , 6 / s , ) K / T . (31)

Step 4: As a result of three previous steps the final resolution for the completely matched systems is given by eq. (23).

The resolution of the total system will usually be- come worse for high K-values. This is discussed by Ikegami [37]. Only for full telescopic conditions for beam line (b21 = 0) and spectrometer (s21 - 0) with no angle dispersion (b26 = s26 -- 0), the resolution would be independent of the kinematic value K. To get the correct beam line setting we used the plunger method

Object Plunger

;ram

I~Y 4mmg

a b c

First intermediate Second intermediate Target image image image

Fig. 15. Photographs of three images of an object plunger at intermediate locations in the beam line (a, b) and at the target (c). The plunger is located at the exit slit of the double monochromator in dispersive mode operation.

298 S.A. Martin et a L / "BIG KARL"

which was originally developed at MSU [38]. A "plunger" is inserted as object at the entrance of the beam line system [14]. The image of this plunger is observed in the beam line at two intermediate images and at the target. With this method the signs and the magnifications of the images can be set to the values as proposed by the TRANSPORT calculation. Fig. 15 shows examples of these images taken as photographs from the television screen.

Using this tuning procedure an energy resolution of E / A E - 5000 can usually be achieved for kinematic values up to K = 0.10 when using the beam line system in a high dispersive mode operation. The acceptance of the beam line for this mode is about 2-4% of the total cyclotron beam.

4. Data handling

Data acquisition and analysis are performed on a VAX-I1/780 computer with two RK07 disk drives for system and program development, a RM05 user disk and TEl6 magtape. All programs necessary for the preparation of experiments (beam transport, kinematics, energy loss calculations), the on-line data taking, experiment supervision, and the off-line data analysis are run in parallel on this machine with the on-line process having the highest real-time priority.

4.1. Hardware

A special hardware system MEMPHIS has been developed which easily interfaces to 16 or 32 bit com- puters via standard CAMAC direct memory access (DMA). The system has been described elsewhere [39]. The main features are illustrated in fig. 16.

The system is modular for quick adaption to changing experimental requirements. The desired mode of operation is accomplished by downloading a soft-switch data file to the MEMPHIS microprocessor controller. This allows transparent configuration logging in the host computer and minimizes mistakes.

MEMPHIS is designed to accept 16 parameters with 128 bit /event at data rates up to 2 × 104 events/s. Parameters from external ADCs, TDCs or bit pattern untis are interfaced to the MEMPHIS bus through 32 word FIFO buffers which compress the input addresses and map them to any position of the 128 bit output word. The events are then written to a 2K by 16 bit double-buffering RAM module and transferred into two corresponding list mode buffers in VAX memory by CAMAC DMA. Derandomizing and transfer functions are continuously monitored by the MEMPHIS microprocessor controller which also keeps an error file.

Several special function modules allow event pre- processing in hardware to diminish the CPU load of the host and list mode data rates:

NIH ADC's

COMPEX

HULTI- PARAHETE

SYSTEH

VAX 11/780 with

1 Parameter Dispt

2 Parameter DispL

CAHAC

RS 232 P0rt

Fig. 16. Block diagram of the MEMPHIS data acquisition system.


- One-parameter (8K) and two-parameter (8K by 8K) window units may be included in hardware coincidence or as a marker bit in the event word.

- Linearization units can map every A D C address to a new software loaded pseudo-address.

- More complex functions of two parameters may be defined in a bit slice processor unit used for example to calculate x- and y-positions in a multiwire proportional chamber. An independent monitor and display system is con-

nected in parallel to the M E M P H I S input lines. It contains 8K one-parameter and 8K by 8K two-parameter R A M modules that can be incremented directly by the ADCs. The generated one- or two-dimensional spectra are displayed on a hardware scope. Display cycles run in COMPEX mode on the C A M A C bus concur- rently to normal C A M A C cycles for reading the spectra into the VAX. This monitor system is particularly useful when running M E M P H I S in a mixed singles/coincidence model: Coincidence events are defined by external or internal ADC coincidence and written to the VAX meanwhile singles spectra are collected simultaneously in the COMPEX RAMs.

4.2. Software

The software to support the physicist in preparing, running and analyzing an experiment follows the same guidelines as described in section 2.2.6. Even more extensive use is made of command procedures to increase flexibility and comfort. The main on- and off-line program used for data handling is an adaption of the Princeton University " A C Q U I R E " code [40] to our hardware setup. To monitor and analyze high resolution spectra within reasonable time the central on-line terminal is a fast D M A graphics display with 4K by 4K resolution and superposed storage and refresh modes (Tektronix G M A series). Hardcopies are available on the systems matrix line-printer. Graphics I / O on all terminals including the G M A is supported by a modified A G I I / P L O T I 0 [34] library and an interactive graphics monitor I G M [41]. The development of a suitable general-purpose analyzing system is in progress.

msr), typical experiments are carried out with E / A E = 3000-6000 and solid angles of dO = 2.5-3.5 msr. The dispersive beam line mode reduces typical beam currents of several /xA but poor resolution E / A E - 3 0 0 extracted from the cyclotron to about 100 nA with an energy resolution so that data with E / A E = 3000-6000 can be taken with BIG KARL. At present this beam resolution is the limiting factor in high resolution experiments.

The main research activities at BIG K A R L involve inelastic scattering for the investigation of 1 ÷ spin-flip states [42,43], giant resonances [44] at very forward angles ( 0 > 1.5 °) and transfer reactions [45,46] for nuclear spectroscopy. In addition, in the field of atomic physics, high energy studies ( E = 6 8 - 1 3 0 MeV) of atomic charge transfer have been completed [47].

In the following a few examples will be presented in order to give an idea about the results obtained with the spectrometer under typical experimental conditions.

5.1. Inelastic scattering

Fig. 17 shows typical spectra of inelastic proton scattering on 48Ca, 58Ni and 2°spb targets at 45 MeV incident energy measure for the search of 1 + states [42,43] in medium and heavy nuclei. The resolution of 7-12 keV was sufficient to resolve 30-40 new energy levels in 4SCa ( E x = 9-10.7 MeV) including the 1 ÷ state at E x = 10.212 MeV and a similar number of new levels in 5SNi ( E x = 7-8.5 MeV), In 2°spb the recently identi- fied isoscalar 1 ÷ spin flip state [48] at E x = 5.841 MeV is clearly resolved. From these examples it becomes obvious that these investigations of 1 ÷ states performed in order to obtain information on the spin dependent nucleon-nucleon force greatly benefit from high resolution.

For the investigation of the giant resonances it is essential to measure inelastic scattering at very forward angle 0 > 1.5 ° and possibly under 0 °. This is important because e.g. the giant octupole (L = 3) and the giant dipole (L = 1) cross section angular distributions do not differ in shape at angles 0 > 7 ° while there are drastic differences at more foreward angles which are not accessible to measurement with solid state detectors.

5 . M e a s u r e m e n t s 5.2. Transfer reactions

Since 1979 when BIG K A R L came into operation it has been used for a variety of nuclear and atomic physics experiments. Measurements have been performed in a wide range of momenta from Bp = 320-2000 k G . cm and momentum dispersions from D = 4-24 c m / % . Though it could be shown that energy resolu- tions of E / A E = 10 4 and better are possible under special conditions (small beam current in dispersive beam line mode, very thin targets, solid angle dO < 1

Highest resolution and large solid angles are required in transfer reactions if one wants to tackle unresolved problems of nuclear spectroscopy. One example shown in fig. 18 is a 2°9Bi(d, 3He)2°gPb spectrum measured at 45 MeV [49]. In the same (d, 3He) reaction on the closed shell 2°spb nucleus the shell model p ro ton-hole

states (3s~/2, 2d3/2, lh l t /2 and 2d5/2) can be seen undisturbed. This reaction on 2°9Bi with a lh9/2 proton in the ground state displays a splitting of the hole states

300 S.A. Martin et aL /"'BIG KARL"

700

350"

O-

200 -

z 1S0.-

8 100.

I,,- z

8 SO-

z0epb(p,p') Ep =/,,-5 HeY Ot~ b : 2/+ 0

o

j u~

SeNi(p,p') Ep =4.5 HeV ! Olab = 2 0 o

270- t'eCa(p'P') Ep : k/,,../,,. H eV Otab=32.3 °

180" 90 i ~" ~ I ~ o~,, . . . . . ~1

0 .... " ..... , ~ , , . ~ . . 0 400 800 1200 1600

CHANNEL NUMBER

Fig. 17. Sample spectra of inelastic proton scattemig on 48Ca, 5SNi and 2°spb at 45 MeV measured with the spectrometer BIG KARL. The resolution was 7-12 keV with solid angles of typically 2.5 msr and beam currents of 50 nA. Lines from t2C and 160 impurities in the target (see 4SCa spectrum) are very broad due to kinematical effects which are corrected for the target nucleus (R 12 = 0) using quadrupole Q2.

in multiplets due to the residual interaction of the par t ic le-hole coupling. The resolution of 12 keV is just sufficient to resolve, e.g., the doublets atE~ = 3.96 and 4.38 MeV which are essential to deduce the effective residual interaction.

The doubly odd nucleus 1°SAg is located between the vibrational nuclei of Pd and Cd and is therefore well suited to study the coupling of neutrons and protons and their coupling to the vibrational modes. The resulting multiplets are extremely complex even at low excitation energies as can be seen from fig. 19 showing the lower part of a l°gAg(p, d)l°SAg spectrum [45]. The

2O9Bi (d,3He) z°spb

E d =/+5 HeY "a 8tob=12"50

80 $

m e , i m

. . . . . . . . . , . . . . . . . . . , . . . . . , . . . . . . . . ,

4.00 600 800 Channel number

Fig. 18. Measured spectrum of the 2°9Bi(d, 3tte)2°spb reaction. The resolution was 10-12 keV for a solid angle of d~ = 1.92 msr and typical beam currents of 80 nA.

resolution of 4 keV allowed to identify nearly all states known up to about E x = 1.2 and to identify many new states up to 2.1 MeV.

5.3. Atomic charge transfer

Several theoretical models [50] with different results have been proposed for the electron capture (%) and electron stripping (%) cross sections at high incident energies. Because of the lack of data it is not known which model is the correct one. The spectrometer BIG K A R L is well suited for these measurements because of its large ME/q2< 540 u . MeV. We investigated 3He+ yields [47] at energies up to 130 MeV (ME/q 2= 390 MeV) by bombarding different solid targets with 3 He++ beams.

For these experiments the spectrometer was set to 8ta b = 0 °. The dipole and quadrupole fields were adjusted to focus the 3He ÷ ions into the focal plane. The 3He2+ beam with Bp(3He++)=½Bp(3He ÷) was

bent onto the inner wall of the first dipole D1 used as Faraday cup. With increasing target thickness the 3He+ fraction increases from 0 to the saturation, where stripping and capture processes are in equilibrium. From these curves (see fig. 20) described by N(%/Os)[1- e x p ( - % d ) ] with N = b e a m intensity and d = t a r g e t thickness both cross sections o c and % can be determined.

S.A. Martin et aL / "BIG K A R L " 301

aJ t - l -

t -

.41,.. c

o

1,00

200

~Ag (p.d)~Ag E~b=25MeV Olab=10 °

-4"

~01.~ co l . n LQur ~ ~ O o

u4

,4"

÷

. .~ ~ . c ~ o,~ " "

I I I I I

u!

,,o

N

u'~

I:o

I I J /

" 0

___A I

m

u-/

_A I I

...t LQ en,,o O

.~-.t u ' i~ o'i

)/¢ . . , .Jl

i ' ' 5 0 0

I I

0 500 1000

Channet number Fig. 19. High resolution spectrum of the (p, d) neutron pick up reaction on l°gAg at 25 MeV incident energy and a solid angle of 1.2 msr. The resolution was 4 keV.

~ x 1 0 -8

-~20- i i

*~u 10-

3He+++ C-..3He ++ C*

..-+

E ( 3 H e ) = 130 M e V

0 . . . . . # . . . . . ~.0 80 200 ~00 (IJglcm 2 ) Tnrgef Thickness

Fig. 20. Measured yields of the (3HEY+, 3He+) atomic charge transfer at 130 MeV on C targets as function of the target thickness. Charge state equilibrium is achieved for targets thicker than about 40 > # g / c m 2. For the fitted curve (solid line) and the deduction of the capture o c and the stripping o s cross section see text.

[- . °

.... :.. IOOMeV 3He" YieLd at ,.. x ..~. Mylar Foil I00 :.-', \ . .. . : ' . . ",, ~ . , 3He +gos-3He ÷gas

--~ ",~. " ~ . target forget

A r\}\ N 2k',,,~{. Ne~ 0.1 ' I \ , ~ @Gas pressure

O. 0.05 0.1 0.15 0,2 0.25 0.3 ( to rr)

Fig. 21. Experimental results of the (3He2+, 3He+) atomic charge transfer on gas targets are displayed as function of the gas pressure in the spectrometer. For details see text and ref. 47.

302 S.A, Martin et a L / "'BIG KARL"

To investigate scat ter ing on gas targets [51] a modified technique has b e e n used. The whole spectrometer, separated from the beam line by a thin mylar foil was filled with the gas (e.g. N 2, Ne, Ar) at a pressure of p < 0.25 mbar . The 3He2+ ions were separated in D1 f rom the 3He + particles which passed to a thin mylar foil between D1 and D2 to be s tr ipped again completely to avoid fur ther uncontro l led stripping. In this arrange- men t the field of D2 was set to one half of the field in DI . Fig. 21 shows the measured 3He + yields as funct ion of the gas pressure for several gases.

The authors wish to thank R.F. Holsinger (Field Effects Inc.) who kindly offered us the POISSON group programs and gave us useful suppor t for the magnet design. We are also grateful to H.J. Scheerer (TU Mianchen) and Ch.A. Wiedner (Max Planck Inst i tut , Heidelberg) for their cooperat ion. It is our pleasure to express cordial thanks to Prof. Mayer-BOricke for his engaged suppor t and interest in the early stage of the design. We are deeply indebted to H.A. Enge (MIT) and S. Kowalski (MIT) who kindly permit ted us to use the p rogram R A Y TRACE. We are very grateful for the con t r ibu t ions f rom other divisions in the K F A (AP, JULIC, ZAM, ZAT, ZEL, TD-EV).

References

[1] C.P. Browne and W.W. Buechner, Rev. Sci. Instr. 27 (1956) 899.

[2] R.K. Sheline, C.E. Watson, B.P. Maier, U. Gruber, H.R. Koch, O.W.B. Schult, H.T. Motz, E.T. Jurney, G.L. Stru- ble, T. v. Egidy, Th. Elze and E. Bieber, Phys. Rev. 143 (1966) 857.

[3] J. Borggreen, B. Elbek and L. Perch Nielsen, Nucl. Instr. and Meth. 24 (1963) 1.

[4] J.E. Spencer and H.A. Enge, Nucl. Instr. and Meth. 49 (1967) 181.

[5] T. v. Egidy, O.W.B. Schult, D. Rabenstein, J.R. Erskine, O.A. Wasson, R.E. Chrien, D. Breitig, R.P. Sharma, H.A. Baader and H.R. Koch, Phys. Rev. C6 (1972) 266.

[6] H.A. Enge and S.B. Kowalski, Proc. 3rd Int. Conf. on Magnet technology, Hamburg (1970) p. 366.

[7] M. L0ffler, H.-J. Scheerer and H.K. Vonach, Nucl. Instr. and Meth. 111 (1973) 1.

[8] C.A. Wiedner, M. Goldschmidt, D. Rieck, H.A. Enge and S.B. Kowalski, Nucl. Instr. and Meth. 105 (1972) 205.

[9] H.A. Enge, Nucl. Instr. and Meth. 187 (1981) 1. [10] H.C. Blosser, G.M. Crawley, R. de Forest, E. Kashy and

B.H. Wildenthal, Nucl. Instr. and Meth. 91 (1971) 61. [11] H. Ikegami, S. Morinobu, I. Katayama, M. Fujiwara and

S. Yamabe, Nucl. Instr. and Meth. 175 (1980) 335. [12] L. Aldea, W. Br~utigam, R. Brings,C. Mayer-B0ricke, J.

Reich and P. Wucherer, Proc. 9th Int. Conf. on Cyclotrons and their applications, Caen (France) (1981) p. 103.

[13] K. Halbach, Nucl. Instr. and Meth. 107 (1973) 515. [14] J. Reich, C. Mayer-BOricke, K.L. Brown and F.E. John-

son, AIP Conf. Proc. no. 9 (1972) p. 716.

[15] K.L. Brown, D.C. Carey, Ch. Iselin and F. Rothacker, TRANSPORT, a computer program for designing charged particle beam transport systems, CERN-80-04 (Geneva 1980).

[16] K.L. Brown, Stanford Linear Accelerator Center, SLAC- 75 (1967).

[17] K.L. Brown and S.K. Howry, Stanford Linear Accelerator Center, SLAC-9I (1970), NAL-91 (1973).

[18] D.C. Carey, NAL-64 (1971). [19] H.A. Enge and S.B. Kowalski, private communication. [20] K. Halbach, Proc. 2nd Int. Conf. on Magnet technology,

Oxford (1967), p. 40. [21] K.L. Brown, Proc. 3rd Int. Conf. on Magnet technology,

Hamburg (1970) p. 348, reprinted in Appendix of CERN80-04.

[22] A. Abdel-Gawad, A. Hardt, S. Martin, J. Reich, K.L. Brown and K. Halbach, Proc. 5th Int. Conf. on Magnet technology, Rome (1975) p. 45.

[23] K.L. Brown, Nucl. Instr. and Meth. 187 (1981) 51. [24] A. AbdeI-Gawad, Dissertation, Jii1-1329 (1976) (unpub-

lished). [25] H. Haas, J. Wimmer, H. Fey, A. Retz and M. KOhler,

Proc. 5th Int. Conf. on Magnet technology, Rome (1975) p. 52.

[26] R.A. Kilpatrick, Proc. 1st Int. Symposium on Magnet technology, Stanford (1965), p. 262.

[27] K. Halbach, Nucl. Instr. and Meth. 74 (1969) 147. [28] E. Horlitz and P. Weidner, Jiil-782-MA (1971) (unpub-

lished). [29] H. KOhler, K.D. Mtiller, H. Stoff, M. Teske, G.P.A. Berg,

A. Hardt, S.A. Martin, C. Mayer-BOricke and J. MeiS- burger, NucL Instr. and Meth. 175 (1980) 357.

[30] G. MCiller, G.P.A. Berg, A. Hardt, H.J. Kelleter, S.A. Martin, J. Meissburger and A. Retz, Jiil-Spez-84 (1980) (unpublished).

[31] L.G. Atencio, J.F. Amann, R.L. Boudrie and C.L. Morris, Nucl. Instr. and Meth. 187 (1981) 381.

[32] Part of the detector has been built at the University of Texas with the kind cooperation of Prof. C.F. Moore.

[33] This detector was designed similar to those described in the following references: D. Shapira, R.M. DeVries, H.W. Fulbright, J. Toke and M.R. Clover, Nucl. Instr. and Meth. 129 (1975) 123.

[34] Tektronix PLOT l0 Terminal Control System and Advanced Graphing II Systems Manual, Tektronix part number 070-4112-00.

[35] W. H0rlimann, Dissertation, Jiil-Spez-104, Report of the Kernforschungsanlage Jiilich ( 1981).

[36] J. Reich, S.A. Martin, D. Protic an G. Riepe, 7th Int. Conf. on Cyclotrons and their application, ZiJrich (1975).

[37] H. Ikegami, Nucl. Instr. and Meth. 187 (1981) 13. [38] E. Kashy, private communication (May 1979). [39] H. Stoff, G. Brandenburg, M. KOhler, K. Krafft, K.D.

Miiller, W. Stevens and M. Teske, Proc. Nuclear science Symp. Orlando, Florida (1980).

[40] R. Kouzes, NucL Instr. and Meth. 155 (1978) 261. [41] U. Hacker, Ing. Arbeit, KFA Jiilich. [42] G.P.A. Berg, W. Htirlimann, I. Katayama, S.A. Martin, J.

Meissburger, J. ROmer, B. Styczen, F. Osterfeld, G. Gaul, R, Santo and G. Sondermann, Phys. Rev. C25 (1982) 2100.


[43] G.P.A. Berg, W. H~irlimann, 1. Katayama, S.A. Martin, J. Meissburger, F. Osterfled, J.G.M. ROmer, B. Styczen, J. Tain, G. Gaul, R. Santo and G. Sondermann, Proc. Int. Conf. on Spin Excitations in Nuclei, Telluride 1982.

[3,4] H.P. Morsch, M. Rogge, P. Turek, P. Decowski, L. Zemlo, C. Mayer-B6ricke, S.A. Martin, G.P.A. Berg, I. Katayama, J. Meissburger, J.G.M. ROmer, J. Reich, P. Wucherer and W. Br~iutigam, Phys. Lett. 119B (1982) 311.

[45] G.P.A. Berg, W. H0rlimann, I. Katayama, S.A. Martin, J. Meissburger, J. R6mer, H. Seyfarth and B. Styczen, Neu- tron capture gamma-ray spectroscopy and related topics (The Institute of Physics, Bristol and London, 1981) p. 183.

[46] G.P.A. Berg, M. Demarteau, A. Hardt, W. Hiirlimann, S.A. Martin, J. Meissburger, W. Oelert, H. Seyfarth, B. Styczen, M. K6hler, I. Oelrich and J. Scheerer, Nucl. Phys. A379 (1982) 93.

[47] I. Katayama, G.P.A. Berg, W. Hiidimann, S.A. Martin, J. Meissburger, W. Oelert, M. Rogge, J.G.M. ROmer, J. Tain, B. Styczen and G. Gaul, Phys. Lett. 92A (1982) 385.

[48] K. Wienhard, K. Ackermann, K. Bangert, U.E.P. Berg, C. Bliising, W. Naatz, A. Ruckelshausen, D. RiJck, R.K.M. Schneider and R. Stock, Phys. Rev. Lett. 49 (1982) 18.

[49] G. Mairle, K. Schindler, P. Grabmeyer, G.J. Wagner, U. Schmidt-Rohr, G.P.A. Berg, W. HOrlimann, S.A. Martin, J. Meissburger, J.G.M. R/Smer, B. Styczen and J.L. Tain, Phys. Lett. 121B (1983) 307.

[50] B. Belkic, R. Gayet and A. Salin, Phys. Rep. 56 (1979) 279.

[51] I. Katayama, G.P.A. Berg, W. Hiirlimann, S.A. Martin, J. Meissburger, W. Oelert, M. Rogge, J.G.M. ROmer, J.L. Tain, L. Zemlo and G. Gaul, to be published in Phys. Rev. Lett.

Documents

The QQDDQ magnet spectrometer “big karl”