CENTRAL REGION OF THE INJECTOR CYCLOTRON
M. Inoue, T. Itahashi and I. Miura
Research Center for Nuclear Physics, Osaka University
Ibaraki, Osaka 567, JAPANAbstract
Central region of the injector cyclotron for the ring
cyclotron project of the RCNP has been studied to accelerate
axially injected beams. An electrostat ic inflector and asmall deflector are considered to accept proton beam withinjection energy of 60 keV.
1. Introduction

A ring cyclotron project has been proposed at the RCNP,Osakal) • As the injector is important to decide the beam
qualities we have compared several types of the injectors2) .
A compact cyclotron with an external ion source is a candidate in the first phase. The external ion source is useful
to improve beam qualities and essential to accelerate apolarized beam.
The existing AVF cyclotron of the RCNP has also thepolarized ion source and an axial injection system. Our
experiments for the beam development s have shown that thephase slit at the central region is important to get a goodtime structure but insufficien t to realize the single turn
extraction, and that only a small emittance beam is able togo through the mirror electrode system. Our existing
cyclotron and many other cyclotrons have the axial injection
system with injection energy of about 10 keV while the TRIUMF
cyclotron has a very large geometry and its injection energy
is 300 keV. As high energy injection is preferable to getgood quality beams, an injection proton energy of about 60
keV has been adopted for the injector cyclotron. For heavy
ions injection voltage is proportiona l to B 2 q/A, where B ismagnetic field strength, q is the ion charge and A is theparticle mass.
2. Central geometry
The RF electrode system of the injector cyclotron
consists of double 60° dees and works in 2nd and higher
harmonic acceleratio n mode to match the RF frequency of thering cyclotron which is 20~32 MHz. The peak value of thedee voltage is 50 kV. A system composed of a spiral inflector and a small deflector has been considered to accept
relatively high energy injected beams. The small deflector
is placed for correction of the beam centering. A verticaldeflector system is also situated at the first turn radius.
For the 60 keV proton, the field strength of the spiralinflector and the small horizontal deflector are 18 kV/cm
and 16 kV/cm respectively and the magnetic field is 10 kG.
Fig. 1. shows the central geometry and a beam orbit.
3. Model test-101-

The injector cyclotron is commercially available but it
is necessary to modify the central region. A small test
magnet was designed to examine the central region of theinjector. A field measuring system is now in preparation.
Main characteristics of the injector is listed in Table l.
References
1.
2.

I. Miura et al., Proc. 8th Int. Conf. on Cyclotrons &their Applications IEEE-NS-26 ~2, 2074 (1979}.
M. Inoue et al., Proc. 3rd Sym. on Accel. Sci. & Tech.
p. 128 (1980}.
Table lMain characteristics ofthe injector cyclotron
extraction radius

67.5 emmagnet gap hillvalley
main coil power

13 em
28 em

150 kW

trim coil power

25 kW

magnet weight

110 tons

RF cavity

2

RF frequency

20 32 MHz
50 kV

maximum voltage

Fig. 1.

60° dees

harmonic

2. 3. 4

RF power

250 kW

Ion source

external 60 keVCentral region of the injector cyclotron-102-