STATUS OF THE RCNP AVF CYCLOTRON
A. Shimizu, I. Miura, T. Yamazaki, K. Hosono, M. Inoue,T. Saito, T. Itahashi, N. Matsuoka, H. Sakai, K. Hatanaka,
K. Nisimura*, H. Shimizu*, S. Nagamachi and M. Kondo
Research Center for Nuclear Physics, Osaka University* Department of Physics, Kyoto University
Abstract
During the past five years, the AVF cyclotron at RCNP, opento outside users, has been operated well and used mainly fornuclear research experiments. The machine is able to deliver not
only ordinary light ions but also polarized protons and deuterons
and a variety of heavy ions with variable energies of wide range.
Several developments have been made to increase the variety ofion species, to improve beam qualities, reliabilities and reproducibilities.
1. Operation

The details of the RCNP cyclotron is described elsewhere 1 ) .
The resonance conditions for ion acceleration by the cyclotron
are shown in Fig. 1. The machine operation is scheduled of 5.5 x
24 hrs/week and regular maintenance is scheduled on every Monday.
The beam time has steadily increased especially as for the polarized protons and deuterons at request of users as shown in Fig.
2. Machine developments and improvements have been made using
about 5% of scheduled beam time and long period shut down time.
The setting parameters of the magnets, trim coils and RF
system are given from the control computer PDPll/40 by putting aparticle, charge state and energy. The internal beam can beeasily tuned using just these parameters and the extraction
requires a fine adjustment of Dee and deflector voltages, and acentering of the beam by valley coils. The extraction efficiency
is more than 90% for protons but around 50% for high energy 3 He,a. and heavy ions. This difficulty originates from a slightchange of beam path along deflectors due to a change of main
field shape at high field excitation.
2. Improvements of Beam Qualities
To get stable and excellent quality beams (energy resolution,emittances, time structures), beam diagnostics, control systemand stabilities of electric and magnetic fields are essential.
Phase probes and phase selection slits have been developed andimproved.
A movable slit is used to select the beam at the first half
turn in the central region. This accepts usually two different
phases. These two beams are accelerated up to maximum radius in
the isochronous field. Fig. 3 shows two peaks corresponding to
the two selected beams measured by a movable phase probe. One of
the two beams should be dropped out to improve the energy resolution. The magnetic field has been slightly modified from theisochronous field by changing one of the trim coils, then one of
the two beams has been slipped to the decelerating region andanother has remained at the acceleration region by different
phase excursion during the acceleration. The extracted beam withthis procedure has had small energy spread as well as small phasewidth.

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The new slit systems (3rd and 4th) have been installed at acyclotron radius of about 30 em. These are effective to reduce
the phase width and radial emittance. The single turn extraction
would require further magnetic field and Dee voltage stabilities
with these phase slits. So the stability improvement with theestablishment of refined tuning method is a key to the refinementof the beam qualities.
3. Polarized Ion Acceleration
The atomic beam type polarized ion source is located on thesecond floor outside the cyclotron vault. The polarized beam isaxially injected into cyclotron center and then inflected by goo
by an electric mirror system. The spin directions of the polarized beam is altered by RF spin transition units very quickly(0.5 to 500 Hz). No appreciable change of beam intensity isobserved when the polarization states are altered by ·the RFtransition. The beam intensities of polarized protons, vectorand tensor polarized deuterons are between 20 to 50 nA on thetarget in the achromatic mode of the beam transport. To accelerate
protons with spin in the horizontal plane, an Wien filter wasinstalled in the course of axial injection, and the spin direction
was rotated by goo. The maximum value of the horizontal componentof the proton beam polarization accelerated up to 65 MeV w~smeasured to be about 70% of the initial value at the ion sourc2i
Details are presented to this conference by K. Hatanaka et al.
4. Heavy Ion Acceleration
The "heat insulated" cathode PIG heavy ion source has beendeveloped and improved. Up to now, C, N, 0, Ne (including smallabu~dant 13 C, 15 N, 22 Ne) ions have been requested by users andAr 7 ions have been tested to accelerate in the 3rd harmonicmode. The life time of the source is usually limited by either
the cathode (Ta) life or the shorting out of the arc due tobridge between cathode and anode with flakes of sputtered tantalum.
This difficulty is reduced by adjusting gas flow rate minutely
and by keeping a larger space between anode and cathode holder.
By these improvements, N and Ne beams are stably accelerated formore than 20 hrs. with moderate intensity. To accelerate c, 0ions, so the arc is rather unstable compared with N2 gas, severalgas(CH 4 , CO, C0 2 and 0 2 ) and supporting gas (N 2 , Ne, etc.) havebeen tested to improve beam intensity and life time with stablecondition. These tests showed CH 4 and 0 2 gases are most likely
to accelerate C and 0 ions, respectly, in RCNP ion source.
Recently, BF 3 gas was tried to accelerate B or F ions. The
unstable arc behaviour revealed that some supporting gas islikely to be mixed.
To accelerate metal ions, sputtering electrode installed in
the anode is now under development. Pulsed power supply (0.3 ~10 kHz) to get higher charge states is also now under conditioning.
References1)
2)

M. Kondo et al., Proceedings of the 7th Int. Conf. on Cyclotrons and their Applications, p. gs
M. Kondo, RCNP Annual Report (lg76) p. l
K. Hatanaka et al., Contribution to this conference.

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FREQUE NCY

Fig. 1.

Resona nce condit ion of RCNP cyclot ron.

hrs
SCHEDULEDSHUT DOWNUNSCHEDULEDSHUT DOWN
SET -UP &MAINTENANCE

Fig. 3a. The phase probe s~gnal.
Two phases are separa ted.

TOTAL
BEAM TIME

'77

'78

'79

Fig. 2. Develo pment of time
distrib ution of RCNP cyclot ron.

Fig. 3b. One of the two beams was
droppe d by modifi ed field.
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