DESIGN STUDY OF MAGNETIC DEFLECTION CHANNELS FOR THE RIKEN SSC
Norio Kishida and Yasushige Yano
The Institute of Physical and Chemical Research
RIKEN SSC was previously
theforsystem
extraction
beamThereportedl)-3 ). This system consists of an electrostat ic deflection channel, twomagnetic deflection channels( MDC1 and MDC2) and two uniform-fie ld bending
magnets. Required characteris tics of each element were tabulated in Ref. 1.
The present report describes the calculated results of the magnetic field
distributio n by the designed MDC systems.
A pure shim channel is more attractive than a current septum channel fromthe economical and mechanical points of view. But the shim channel cannot beadopted in our energy variable SSC, because it cannot adjust the fieldstrength and causes inevitably an undershoot field problem. The maximum fields
reduced by MDC1 and MDC2 are 0.05 T and 0.17 T, respectivel y. Finally weadopted current septum without iron shims for MDC1, but with iron shims for
MDC2. The iron shims were used for MDC2 to avoid enormous increase of current
density of the septum coils.
Design study of the MDC systems was performed using the least-squar es
method similar to Ref. 4 which minimized field disturbance outside thechannels and uniformed the field distributio n inside. In designing the MDC
systems we assumed that these field distributio ns were produced by superposing
the magnetic field of current cells upon the magnetic field by the sector
magnet(the base field). The base field was calculated by the magnetosta tic
calculation program TRI~). The magnetic field generated by each current cell
was obtained by subtracting the base field from the magnetic field which wascalculated with a current cell inserted in an air gap of the sector magnet.
The field strength produced is completely proportiona l to current values of
the cell up to 2500 A at the base field of 1.675 T.
The overshoot field inherent to the use of a current septum channel iscompensated within a distance of 6 em from the extraction orbit( E.O. ) not toaffect the last acceleratin g orbit( L.A.O. ) and not to make a harmonic field.
The configurati on of MDC1 is shown in Fig. 1. The current septums wereplaced apart from the median plane in order to increase a field uniformity
inside MDCl. But a required current became large. The field distributio n near
MDCl is shown in Fig. 2. Field expansion coefficient s of quadrupole andbeam width (l. em) are -1. 02x 10-3 cm- 1 anda
withinterms
sextupole-8. 13 x 1 o- 5 cm- 2 , respectivel y. The deformation of the beam shape, therefore,
is negligibly small in the beam passing through MDC1. The undershoot field wasfound to be almost zero(O.Ol mT).
A cross section of MDC2 is shown in Fig. 3. The iron shims decreased thebase field by about 0.06 T inside the channel and produced an undershoot fieldof about 0.003 T outside the channel. This undershoot canceled out the12 6overshoot field by the current septums in the case of extracting c + ions at
But tworequired.
not
werecoilsncompensatio
thethatsoMeV/u,
135
compensatio n coils were adopted to elminate an undershoot field in the case of
extracting other ions. Figure 4 shows the field distributio n near MDC2. Thefield inhomogene ity was a little larger than that of MDCl, but the deformationof beam shape was rather small in passing through MDC2.

-309-References
1) Y. Yano ~~at.: Proc. 9th Int. Conf. on Cyclotrons and Applications,p. 473(Caen, France, 1981).
2) A.Goto ~~at.: ibid., p. 439.
3) N. Kishida ~~ ~.: RIKEN Accelerator Progress Report, 15, 183(1981).
4) H. Braun: Proc. Int. Conf. on Magnet Technology, p. 1620(Hanburg,Germany , 19 70 ) .
5) J. S. Colonias and J. H. Porst: Magnet Design Applications of theMagnetostatic Problem called, TRIM, UCRL-16382(1965).

~~~----+----1?/Y~'~'~'W.!.«.

365

370

373 375-380

385

r(cm)

r(cm)

Fig. 1. Schematic drawing of MDCl.
r denotes the radial distancefrom the center of the SSC. Iand r 4 indicate the currents ihat
flow through the respective
compensation coils.

Fig. 3, Schematic drawing of MDC2.
The width of iron shim is 0.25
em,.I!Bmt.B(ntr)

50

370

J1=I:f 658 A

40t

lz=I 4= 918 A
30

L.A.O.

t

E.O.

R<CM>

20-0.05
10-10-0.10

R<01lI1= 2169 A-20

12= 684 A!3= !4= 0 A-0.15(\-0.20

Fig. 4. Magnetic field distribution produced by MDC2 at

Fig. 2. Magnetic field distribution produced by MDCl at
BbaseBb= 1.675 T.

-310-ase = 1.675 T.