INJECTOR CYCLOTRON CONCEPTS
M. Inoue, T. Itahashi and I. Miura
Research Center for Nuclear Physics, Osaka University
Suita Osaka, Japan
Abstract
Concepts of an injector cyclotron for the ring cyclotron have beenstudied. A solid pole cyclotron, a connected sector magnet cyclotron and aseparated sector cyclotron with a Cockcroft-Walton preinjector have been
compared.
1.

Introduction

An accelerator complex composed)of two ring cyclotrons has been proposed
as a new project of the RCNP, Osaka 1 . A general progress of the project will
be reported in this symposium. It will be able to accelerate both light andheavy ions up to medium energy. An injector cyclotron and eventually a heavy
ion linear accelarator will be added in this system. The injector is important to decide beam intensity and qualities. In the first phase a compact
cyclotron has been proposed as a light ion injector. To improve beam qualities, however, external ion sources are useful. In this study, a connected
sector magnet cyclotron with an axial injection and a separated sector cyclotron with a Cockcroft-Walton preinjector have been examined.
2.

Condition for the injector

The proposed injector should be able to accelerate. protons up tc 25 MeV
and heavy ions up to 70 q 2 /A MeV, where q is charge of an ion and A is particle
mass number. As an injection radius of the next stage cyclotron is 135 em,
the extraction radius of the injector has to be 67.5 em, 135 em or 270 em.
3.

Solid pole cyclotron

A small cyclotron is commercially available. For example, the SUMITOMO~CGR-MeV Model 680 cyclotron is suitable for our injector. But the maximum
magnetic field should be increased for heavy ions and the central region
should be modified for heavy ion sources. The two resonators with 72° dee
electrodes are good for matching with a ring cyclotron in which particles areaccelerated in harmonic mode of 4,6,8 and 12.
4.

Connected sector cyclotron

The external ion source is useful for heavy ions and essential forpolarized ions. An ordinary solid pole cyclotron is acceptable for an axial
injection system. But the injection energy should be as low as 10 keV for
beam centering in the cyclotron. It is desirable to increase the injectionenergy to SO keV or more especially for heavy ions as a space charge effect islarge at a low energy. To accept such a high energy beam it is necessary to
decrease magnetic fields. An inflecter electrode in the magnetic field may
be useful for axial injection system. It becomes larger as the injectionenergy becomes higher. In case of a moderate gap magnet a large inflecter
could not be situated in the magnetic field. The proton injection energy of
50 keV has been chosen in our case. On the other hand the extraction systemshould be located in a field free region to improve extraction efficiency andbeam qualities. Therefore a connected sector cyclotron has been designed torealize a rather flat low field at a central region and a four symmetry-127-

sector field at a larger radius. A plan view of this injector cyclotron isshown in fig. 1. Except for the coynecting part of the central region it
resembles to the VICKS! cyclotron. 3 •5.

Separated sector cyclotron

A Cockcroft-Walton preinjector for the separated sector cyclotron isdesirable to get high intensity light ion beams and heavy ion beams. Forproton)beam the SIN injector II is very powerful to accelerate more than 1 rnAbeams 2 . However, our accelerator does not accelerate such high intensity
beams and it is a variable energy machine. Low sector fields are useful tomake a variable energy injection system. A low field separated sector cyclotron has been designed as a second alternative of our injector. A 300 keV
Cockcroft-Walton is used as a preinjector and a electrostatic injection
system is adopted. The vertical betatron frequency is below vz=l.O. Two 18°
delta electrode of the RF system is used for matching with the.next cyclotron.
It is similar to the SIN injector II, but has a variable plate to change aresonance frequency. The extraction efficiency is expected to be almost 100%.
6.

Discussion and Conclusion

Main characteristics of the above mentioned three cyclotron as an injector
are listed in table 1. As an injector of a large accelerator the separated
sector cyclotron with a preinjector is most preferable but it needs large
amount of steel. Choice of an injector depends on a size of total accelerator
system as well as costs.
References
1)
2)
3)

I. Miura et al., in these proceedings.
S. Adam et al., Proc. 7th Int. Conf. on cyclotrons and theirapplications (1975), 123.
K.H. Maier, ibid., 68.

Table 1

Injector cyc.locrons

K.,70 for Heavy ion, 25 M11!.V for proton----:
Solid Pole

COnnected sector

Separated sectorso•so•

o. of Sector
Sector anqle

Connected at the centor

Extraction radius
Maqnet qap

67.5 em

135 Cia

270 emhill 20 em•=•=valley 35 em
Max.

t~~aqneticfield

18 leG

16 kG

Bl<GMa.qnet weight

120 ton

150 ton450 tonMain coil. power

100 kW

100 kW

100 kW

Trim coil power

SO kW

30 kW

No. of cavity

2 {72°)

2 (36°)

RF frequency

2D"u32 MHz

20'\132 MHZMaximum voltaqe

Fig. 1.

/30 kW2us•)

2Q'\o12 MHz

sa kV

50 kV

50 kV

RF power

30kWx250kWx2100kWx2Ion source

internal

external SO kV

external
300 kV CockCroft-waltonA connected sector magnet cyclotron-128-