INJECTION SYSTEM FOR THE 1ST RING CYCLOTRON
T. Itahashi, A. Shimizu and I . Miura
Research Center for Nuclear Physics, Osaka University,Suita, Osaka 565, JapanAbstract
An intermediate energy particle accelerat~f complex is being• This variable
designed as a new accelerator facility at RCNP
energy accelerator complex covers a wide energy range and accelerates ions from proton through uranium with high intensity andIt consists of a injector cyclotron and/or
good beam quality.
linac and two separated-sector cyclotrons. Beam injection into
the lst separated-sector cyclotron should be designed to meet thenecessities of variable energy and variable particles. Several
methods for beam injection to equilibrium orbit from the injector
have been considered.
1. Introduction
Injection into cyclotrons is, in many cases, the most difficult part because the magnetic field has to bend the injectedbeam more than the internal beam. Generally, there are three
injection methods; that is, axial injection, trochoidal injection
and direct injection along a valley. The last method is very
suitable for the separated-sector cyclotron where the weak fringe
field in the valley deflects the beam only a few degrees before
it reaches the central region, where magnetic and electrostatic
bending devices can guide the beam onto the lst equilibrium
orbit. The design for various magnet and electrostatic devices,
should be appropriate for the injection of the particle of themaximum rigidity.
2. The Proposed Injection Systema) Most simple injection system consists of one bending
magnet located in the central region and magnetic inflector
channel (MIC) in sector magnet. This design is very attractive
as it means lower power consumption. However, the magneticinflector channel may disturb the field around the 2nd equilibrium
orbit because the orbit separation between the 1st and 2ndequilibrium orbit is 30 mrn even at the maximum acceleration gain
(0.8 MeV/turn). And, the field of MIC required for the beam to
be on the equilibrium orbit has to be increased by about 0.3 to
0.4 T over the range of the MIC. Moreover, one bending magnet
which is positioned close to the MIC is not feasible both physically and magnetically. As a result, this method, even if it ismuch simple, can't be used practically.
b) The alternative system consists of two bending magnets inthe central region, a magnetic inflector channel (passive +active) in the pole-tip of a sector magnet and an electrostatic
inflector channel (EIC) in the next free valley. The beam fromthe injector cyclotron is guided by final steering magnet andfocussing elements near the chamber of ring l and transported
into the central region. The beam enters the lst bending magnet(BMl) which produces a maximum field strength of 0.5 T and bends
the beam through 23°. This directs the beam into the second
bending magnet (BM2) in which maximum field of 1.4 T bends thebeam through 105° and injects the beam into the MIC in the lst-39-

sector magnet, and if necessary final adjustments can be madewith an electrostatic inflector channel in the free valley of thesecond quadrant. By the orbit calculation, the MIC must increase
the field in the gap of the pole-tip by a maximum of 0.3 T toguide the beam onto its inner most centered orbit. It only thefield strength is needed, it will be obtained by the simplemagnetic shims in the 1st sector magnet. However, they havedisadvantage that the MIC field is always proportional to thesector magnet field and no finer field setting can be accomplished. These conditions for the MIC can be realized by active
magnetic device along with floating shims to reduce the current
density of the MIC. A preliminary layout of injection system isshown in fig. 1.
3. Status of Progress
In the design of the MIC, there are some problems; that is,
fringing field of the lst sector magnet around the injection
orbit, effects of shims and/or floating shims, field distribution
inside the MIC and positioning of the MIC on to guide for beam tothe equilibrium orbit. At the first step, magnetic field measurement of effect due to shim or floating shim has been done using al/3.5 scale model magnet of the lst ring. A calculation of
optical properties of this injection system, especially matchingcondition to the lst equilibrium orbit is under progress.
Referencel) I. Miura et al., RCNP Annual Report 1978, p.23l

FROM _INJECTOR··········••...
A. F.

A~·~,(}Np.TOR·..

SECTOR-MAGNETFig. l

Layout of injection system to the lst ring cyclotron-40-