The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Analysis of the Injection and Extraction Systemsfor the RIKEN Superconductin g Ring Cyclotron
Shiro FUJISHIMA, Hiroki OKUNO, Akira GOTO, and Yasushige YANORIKEN (The Institute of Physical and Chemical Research)
2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan
Abstract

Design of the Injection and Extraction Systems forthe RIKEN Superconducting Ring Cyclotron (SRC) is inprogress. Purpose of present analysis is to optimize thelayouts and specifications of the injection and extraction
elements in the SRC. Lot of care was taken especially tominimize not only the required fields of the elements but
also the differences of trajectories in the elements.
1 Introduction

The sector magnets of the SRC generate strong fieldof 4.3 T at the maximum in the magnets, and also generate stray field in the valley originated from saturationof the iron yokes. This stray field gets up to -0.6 T at
the maximum and depends non-linearly on the magnetic
rigidities of the beams. Thus, the trajectories of various
beams differ considerably from each other. The difference of trajectories requires wide bore of the element.
Besides, the injection and extraction elements should beinstalled in a small space limited with the sector magnets, RF-resonators, and vacuum chambers. Because of
the space limitation and high rigidity of the beam, theinjection and extraction elements should generate considerably high fields. These difficulties make the designof the injection and extraction systems quite challenging.
2 Property of the beams

Table 1 shows the energies and magnetic rigidities ofthree typical beams. The beam of 16 0 7+ (1) has thelowest magnetic rigidity. On the other hand, the beamof 238 U 58+ has the highest one. Between these twobeams, the difference of trajectories is most remarkable.
The beam of 16 0 7+ (2) has the highest electric rigidity.

trim coils of the sector magnets has not been optimized
perfectly, so the calculated fields of the sector magnets
include about 0.3% of error. Error of the field causes
position error to the injection and extraction trajectories. To correct relative position error of the trajectories, the energies of the injection or extraction beams
were slightly changed as the length of the first or lastequilibrium orbits become equal to the design value, respectively. And then, to trace the beam trajectories, anequation of motion was solved with Runge-Kutta-Gill
method. In the calculation, electric or magnetic field ofeach element was superimposed on the field of the sector
magnets.
4 Layouts

Figure 1 shows a schematic layout of the injectionand extraction elements, and shows the trajectories of
two typical beams of 16 0 7+ (1) and 238 U 58 +. Thislayout has not been optimized completely, so may be
modified partly. Because of the stray field in the valley,
two trajectories differ considerably from each other. Theinjection system consists of six bending magnets (BM1,. . _, BM6), two magnetic inflection channels (MIC1 andMIC2), and an electrostatic inflection channel (EIC).
The extraction system consists of two bending magnets(EBM1 and EBM2), three magnetic deflection channels(MDCI, MDC2 and MDC3), and an electrostatic deflection channel (EDC). All MICs and all MDCs are installed between upper and lower coils of the sector magnets. The beams from a pre-accelerator are introduced
crossing the EIC, so that the EIC should has a hole topass the injection beams. To minimize the hole diameter, each trajectory was adjusted to cross at the same
point on the electrode of the EIC.
5 Specifications

Table 1
Energies and magnetic rigities of typical beams.

Energy [MeV /u]

Bp [Tm]

Inj.

Ext.

lnj.

Ext.

16 07+(1)

74.2

200

2.89

4.90

16 07+(2)

126.7

400

3.83

7.25

238 u 58+

58.0

150

4.57

7.52

3 Method of analysis

At first, magnetic fields of the sector magnets were
calculated with a three-dimensional computer code,"TOSCA". But the design of the normal-conducting

Table 2 and Table 3 show specification of the injection and extraction elements, respectively. The MIC1and all MDCs consist of normal-conducting coils. On
the other hand, the MIC2, all BMs and all EBMs consist of superconducting coils. The BM1 and BM2 haveidentical structure and size to reduce fabrication cost.
For the same reason, the BM3, BM4, BM5 and BM6 areidentical. Each magnetic element consists of main dipolecoils and compensation coils to suppress fringe field on
the first or last equilibrium orbits. Gradient-field-coils
are built additionally in the MIC2, BM1 and BM2 toadjust the injection beam envelopes. Length of each element was determined in consideration of the balance
between the difference of trajectories in the element andthe required field of the element. Table 4 shows the differences of trajectories and bores in the elements.

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The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Fig.l Schematic layouts of the injection and extraction elements and trajectories of two typical beams.
Table 2Specifications of the injection elements.

Table 3Specifications of the extraction elements.

RadiusAngle

LengthMax. Field

RadiusAngle

LengthMax. Field[em][deg.][em][kV /em], [T][em][deg.][em][kV /em], [T]EIC

1000"'4280

variable

101.7

100

EDC

1690"'4410

variable

212.5-105

MICl

112.7

45.5

89.5

0.30

MDCI

185.0

37.0

119.5

-0.15

MIC2

95.6

69.3

115.5

1.12

MDC2

190.0

39.0

129.3

-0.27

BMl

117.0

49.0

100.1

4.70

MDC3

203.5

36.8

130.7

-0.48

BM2

117.0

49.0

100.1

4.40

EBMl

169.4

17.7

52.3

-4.00

BM3straight-

41.9

0.25

EBM2

152.4

39.1

104.0-4.50

BM4straight-

41.9

1.36

BM5

straight-

41.9

0.90

BM6straight-

41.9

-1.00

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The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

5.3 BMl and BM2

Table 4
Differences of trajectories and bores in the elements.

Difference

Bore [mm)[mm)Verti. x Horiz.

EIC (movable)61

12 (Horiz.)

MICl

530 X 35

MIC2 "'BM2

about 1330 X 40

BM3 "'BM6

less than 70

30 X 100

EDC (movable)75

12 (Horiz.)

MDCI "' EBM2

about 1330 X 40

Background stray field from the sector magnets isstrong especially around the BMl. To prevent undesirous opposite bend of the beams, the distance betwee:.
the cryostat of the sector magnet and the coils of theBMl is required as short as possible. For that purpose,
no-bend-up coil structure was adopted to minimize theedge size of the BMl.

5.4 BM3 "' BM6

5.1 MICl
Horizontal size of the MICl is limited with turn separation of 54 mm between the injection trajectories andthe first equilibrium orbits. And, on the first equilibrium
orbits, fringe fields of the MICl should be suppressed
less than 100 gauss. Vertical size of the MICl is limited with the gap of 60 mm in the beam chamber of thesector magnet. Because of small space for installation,
superconductin g coils are not available, but the MICl
should generate comparatively high field and suppress
its fringe field with a compensation coil.

5.2 MIC2
Figure 2 shows trajectories in the MIC2. The trajectories in the MIC2 go out at the BMl side, because
magnetic fields of the sector magnet decrease aroundthere. Because of small bending radius of 96 em, it may
be difficult to support inner coils of the MIC2 perfectly.
How to wind and support inner coils is the key of stability of superconductin g state in the MIC2. Prototype ofthe MIC2 will be fabricated in this fiscal year.[l)5.5 EDC
Figure 3 shows trajectories around the EDC. The
EDC moves in the radial direction by 75 mm to accept
the difference of trajectories. And, the EDC consists ofthree arcs conected with two hinges to adjust its curvature. Designed E*V value of 13230 (kV) 2 /em is considerably high. Therefore, R&D for the EDC is requierd toestablish its feasibility.

]

I400--200--01--200

1--4001-l:l:3'fil0ll.

J

238 u 58+ -1607+(1)

-97

:5I

"0~IIII~!

~

The injection beams should pass through the small
hole on the EIC, and go through a long valley filled with
non-linear stray fields, so that the differences oftrajectories increase in the BM3, BM4, BM5 an.:: BM6 (BM3-6).
To suppress the difference of trajectories as small as possible, the length of the BM3-6 was shortened comparedwith other magnetic elements. However, the differencesof trajectories are still large in the BM3-6. Thus, theBM3-6 have wide horizontal bore.

-5050.JI-5000l-4950_I-4900

Radial Position [mm]96

Fig.3 Trajectories around the EDC.
95

238 u 58+

References[1) H. Okuno et. al., "Design Study for the Injection and Extraction Systems for the RIKENSuperconducting Ring Cyclotron ", in thisproceedings.

94

200160160
140
Azimuth around the center of arc of the )I]C2 [deg.]

Fig.2 Trajectories in the MIC2.

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