The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

High Stability Operation of the RCNP Ring Cyclotron
Takane SAITO, Kenji SATO, Takashi YAMAZAKI, Takahisa ITAHASHI, Akira SHIMIZU,Kichiji HATANAKA, Keisuke TAMURA, Shinji ANO, Mitsuru KIBAYASHI and Hitoshi TAMURA
Research Center for Nuclear Physics, Osaka University,
10-1 Mihogaoka, lbaraki Osaka 567, JAPANAbstract
In order to accelerate high quality beams, high stability of the magnetic field and the acceleration voltage
are needed. The correlation between magnetic field andthe temperature of the trim coils is found. to control
the temperature of the cooling system for the magneticsystem, the stability of the magnetic field is significantlyimproved. together with the highly stabilized RF system, high quality beam is accelerated stably for morethan 180 hours without any adjustment of accelerator
parameters.

the energy gain increases 4 X 10-5 and the peak position shifts about 5°. For effective operation of the flattopping system, the voltage and phase stability are very
important.
Phse....------~-~...
o.ooo5 f--+---!----f-"'"-<<r~~-P'-c--l.,bO~\0~ -0.0005 1---/'-t---7!''---1-·-t-\.,·b -0.001
0.!! -0.0015 1----t'+----+-+--+--+-+--+----'1~1 Introduction-0.002-0.0025

The RCNP ring cyclotron has been operated toserve various kind of high quality beams for the nuclear physics experiments. An emphasis is placed on
the design to accelerate high quality beams for precise
experiments. In order to realize high beam energy resolution and single turn extraction, a variable frequency
flat-topping system is used[1]. Various efforts for improving the beam quality and the beam extraction efficiency have been done. The voltage fluctuations of theacceleration cavities are less than 10-4 . The RF phasedrifts of the cavities are less than 0.1 o. The current stability of the main coils are better than 4 X 10-6 for theinjector cyclotron and the ring cyclotron. The stabilityof the trim coils are less than 1 X w- 5 • For stabilityof the magnetic field, it is not sufficient to stabilize currents of the magnet. With change in temperature of themagnet, the magnetic field is drifting. Recently the correlation between magnetic field and the temperature of
the trim coils is found. It is shown that the effect of theroom temperature and main coil temperature can be effectively compensated with controlling the temperatureof the cooling water for the trim coils. To control thetemperature of the magnet, the field drift is suppressed
below ±1 X 10- 6 jweek.

-0.003 L----'----'-'-----'---...I.L--L---'-510-1015
05-15

degreeFig. 1 Effective acceleration voltage vs. rf phase.
Deceleration voltage is 1/9Vacc·lO.OOnA

I:0.000111111

0.000111111

v;v

100.000.

Fig. 2 Typical turn pattern of 450MeV 3 He beamat the extraction region measured by a profile monitor.
Upper: with flat-topping. Lower: without flattopping.

2 Flat-topping system
The RF system consists of three single gap acceleration cavities and a single gap flat-topping cavity toaccelerate high quality beam. The frequency range ofthe acceleration cavities is 30,..,52MHz. The frequency
region of the flat-topping system is 90,.,.156MHz, whichcorresponds to the third harmonic of the acceleration
frequency. Fig. 1 shows an energy gain vs. rf phase withand without flat-topping. The width of the phase region where~< w- 4 is 1.62 ° without flat-topping.
The phase region is expanded to 15.1° with the flat~
topping system, where flat-topping voltage is -1/9Vacc·As in Fig. 1 if the phase shifts 0.1° from optimum value,lOO.OOOm!nlO.OOnAThe temperature of the cooling water for the cavities
are controlled within 0.1 o variation by a PI temperature
regulator. The control circuits for the RF· system areoven-controlled within 0.01° temperature drift. The filament power supplies, bias power supplies and screen
grid power supplies for the RF power amplifiers are stabilized. Typical phase excursion of the cavities is lessthan 0.1° /week. Voltage variations are le11s than 0.01
and 0.05% for the acceleration and the flat-topping, respectively. Fig. 2 shows a typical turn pattern at theextraction region with and without flat-topping.

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[%)

100.

Fig. 3 Tr_end data of the magnetic field.

3 Stabilization of the magnetic fteldStability of the magnetic field is affected by the current of the power supply and temperature of the iron coreof the magnet. The magnetic field of the sector magnetsof the ring cyclotron are monitored by NMR-probes.

Yoke
Yoke
Yoke
Yoke
MainCoil~PoleSPa c e r

TrimCoil[g)PoloVoko
Yokefield. Fig. 3 shows the trend data of the magnetic field.
Around thermal equilibrium, temperature change of 1°
causes change in field drift of -1.6 x 10- 5 /day. Effect oftemperature change of the main coil or room temperature was little. Fig. 4 shows schematic view of the sector
magnet for the ring cyclotron. The magnet has spacers,
and magnet gap is determined by the spacers. The trim
coils are made of ceramic coated copper plates. Eachtrim coil is mounted on the pole face through 0.125mm
thick capton film[3]. There may be a proper and uniform thermal contact between the pole tip and the trim
coils. Thermal contact between the iron core and themain coil or air is relatively small. With this structure,under small temperature variation, the thermal expansion of the magnetic gap is mainly determined by thetemperature of the trim coils. The variation of the magnetic gap causes drift of the magnetic field. Field driftof -1.6 X 10- 5 /day corresponds to temperature changeof 0.5° /day. So it is possible to stabilize the magnetic
field with controlling the temperature of the trim coils.
The temperature change other than that of that of trim
coils can be compensated by the temperature of the trim
coils. By adjusting the temperature of the cooling water for the trim coils, the stability of the magnetic field
better than 1 >< w- 6 /week is achieved.

VokoYokeFig. 4 The schematic view of the sector magnet for
the Ring Cyclotron.
After long shut down of the cyclotron, the magnetic field usually satarts to drop with a rate of about
w- 5 /day from start up of the ring cyclotron and after
a week the field stability become better than 10- 6 /day.
The weight of the iron core of the sector magnet is 370
tons. A simplified model calculation of heat conduction for the iron core shows that if there was an initial
temperature difference of 5 °, it needs more than 100hours to reach thermal equilibrium within 0.1 °[2]. Fromthese reason, the origin of the drift is considered to be achange in temperature of the magnet core. It was foundthat the temperature of the cooling water for the trim
coils strongly correlates to the stability of the magnetic-72-

The lith-Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997--ph2,_____::c___ ::__ ph3·······----------·-----i·-···--ph4---phS--------- ph6- - ph70-- --•--- phS-20-40050100150200250300Hours

350

Fig. 5 Trend data of the Proton beam phase monitored for a period of 2weeks.
Extracted energy is 300Me V.
Together with the highly stabilized RF system, highquality beams are accelerated stably for long times. The
high beam quality is kept more than 150 hours without any readjustment of the parameter of the accelerator. Fig. 5 shows trend data of the accelerated beamphase. The beam phase is monitored by the eight nonintercepting electrodes. Each electrodes is placed radially at equal intervals. The figure shows the phaserelative to the signal of the inner most phase monitor.
The beam current was few-thenths of a nA to lJLA. The
beam current was ajusted with a slit or the ion source
which are eqipped on the injector system. Typical energy spread was ""300KeV independent of beam current.

References[1] T. Saito, M. Uraki and I. Miura, "THE FLATTOPPING SYSTEM FOR THE RCNP RING CYCLOTRON", Proc. 14th Int. conf. on Cyclotrons andtheir Applications,(1995)169.
[2] Y. Kumata et al., SHI Co. Ltd., "Private communication".
[3) K. Hosono, M. Kibayashi, I. Miura and J. Abe,
"MAGNETIC SYSTEM FOR THE RCNP RINGCYCLOTRON", Proc. 12th Int. conf. on Cyclotrons
and their Applications,(1989)474.

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