The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

RF CAVITY FOR TABLE-TOP PROTON SYNCHROTRON
Z . F a n g ，K . E n d o , K . E g a w a , K E K , T s u k u b a ，J a p a n
T . H i r a s h i m a ，D e n k i K o g y o C o ” A i k o u - g u n ，J a p a n

Abstract
An r f cavity is being developed for a table-top proton
synchrotron with a ring o f circumference o f 11.9m. The r f

RF CAVITY STRUCTURE
The r f cavity has been designed and developed with 2cavity is required to be o f a wide bandwidth with thecells loaded with 4 high-permeability magnetic alloyfrequency sweeping from 1.64MHz to 14.26MHz, and acores in each cell as shown in Fig. 2 and Fig. 3. The corehigh gradient with the maximum acceleration voltage o fdimension is 397 mm and 170 mm in outer and inner

20kV. The acceleration section consisting o f 2 cells o f r f

diameters, and 25 mm in length. The length o f each cell iscavity loaded with 4 high-permeability magnetic alloy

200 mm, and the total length o f the acceleration section iscores in each cell has been designed. The calculation and500 mm. A push-pull power amplifier w ith two tetrodetubes 4CX35,000C will be used to drive the 2 cavities intest results o f the cavity will be presented.

parallel [7-8].

INTRODUCTION
The table-top proton synchrotron is being developed
for proton therapy [1-6] with a ring o f circumference o f
11.9m. F i g . 1 shows with protons accelerated from 2MeV
to 200MeV within 5ms, the fundamental r f frequency will
increase from 1.64MHz to 14.26MHz, and the required
fundamental voltage in the cavity has the maximal valueo f 13kV at the start o f acceleration. Since high orderharmonics will also be applied to the cavity to get a flat
region in the cavity voltage signal to increase the capture
efficiency, the r f cavity is designed to produce maximal
gap voltage o f about 20kV. Thus the r f cavity with a wide
bandwidth and a high gradient should be designed toobtain a high shunt impedance over the whole operation
frequency range.

-f(M H z)-A -V c a v (k V )Figure 2: Structure o f r f cavity.

-« -W (M e V )Y Z X 5> ou

50> 令s>

nbJ
9.I

o>

00 J多Figure 1 :fundamental r f frequency, cavity voltage, andproton energy, as functions o f acceleration time.

Figure 3: RF cavity.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

EQUIVALENT CIRCUIT AND CAVITY
CHARACTERISTICS

10000

Since the cavity wall is connected to the ground and the2 r f cavities are driven by a push-pull amplifier, theequivalent circuit o f the r f cavity can be illustrated by—u7，(KEi >28-1)—u"(KE 丨128-2)— *~-u"(KE 丨128-3)
U〃(KE 丨>28- 4)
卿 u"(KE 丨133-1)■u"(KE 丨>33-2)^ 1 — u7，(KEi >33-3)>33-4)—O*—■u"(KE 丨，一 ♦ = _ • u"(KE< >33-5)
33-6)u"(KEl 丨—O—U^CKEI >33-7)— O— u，#(KE< >33-8)— O— u#，(KEi I33-9)
u#，(KEi 133

using Fig. 4. Since the r f cavity consists o f 4 same units,
the cavity characteristics can be evaluated just with theimpedance o f one unit ，namely, one quarter o f the r fcavity.

— 0— U*(KE028-1)—O — UXKE028-2)~ ^ r -u ，(KE028-3)-~«Sr~-u，(KE028-4)
一
金
一u’(KE033-1)
u’(KE033-2)— ■ — u，(KE033-3)—♦ ~ u ，(KE033-4)
u’(KE033_5)— A— u'(KE033-6)
一•--u ，(KE033-7)—uf(KE033-8)—♦ ~ u ，(KE033-9)
一•■一u’(KE033-10)

100

Figure 4: Equivalent circuit o f r f cavity.

10

100

Frequency (MHz)The impedance o f one unit is calculated by:

Figure 5: Measurement results o f permeability o f 14cores.

帅，- j t / ) L 0 + J

where u = u ’ 一j u ” is the complex permeability o f cores,TEST RESULTS OF CAVITY IMPEDANCE
The impedances o f the 4 units have been measured asand i 0 = i ^ / 2in A = 2 x lO '7x / ?ln ~ , where a and b are2kaathe inner and outer diameters o f cores, and h is the core
length. C is the distributed capacitance for one unit.

shown in Fig. 6. It is shown that the impedances o f the 4units are very close，that is, a very good balance has beenobtained. The impedance amplitude o f each unit is about
215Q at 1.6MHz，and 268Q at 15MHz. The test results o f

CORE PERMEABILITY

the average value o f impedance o f the 4 units have beenFirstly 4 cores, and later 10 cores, totally 14 cores, aremanufactured and tested. The measurement results o fcompared with the calculation results, as shown in Fig. 7.
It is shown that the test results agree with the calculation

permeability o f the 14 cores are shown in Fig. 5. We canresults very well. The distributed capacitance for each unit

see there is a large discrepancy o f permeability between

is about 35pF. Also as shown from Fig ，7, the r f cavity isthese cores. For example, at 1.6MHz, \u\ can be from 2214

o f a very good performance o f frequency response, with ato 2842, namely, 士12% around 2528. At 15MHz, \u\ canhigh shunt impedance over the whole operating frequency

be from 388 to 469, namely, 士9.5% around 428.5. Fromrange.

these 14 cores, the best 8 cores with relatively higher

For the cores used in this cavity, the measured average

permeability are chosen out and used in our cavity.

value o f core permeability is:

Furthermore, considering the balance o f the impedance o f

u = 2 4 0 9 x (-^ -)* 08
0.5

each unit in the r f cavity, a core with a relative higher
permeability and another core with a relative lower
permeability are combined to form a pair. Thus 4 pairs are
obtained and filled in the r f cavity.

and u " ニ6 0 4 7 x ( - ^ - ) - ° 85
0.5

where / i s in MHz.
The high power test o f the r f cavity is planned in thecoming months.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

"4oo" laZ_2aSU M M A R Y*—Z_lbZ 2bThe r f cavity has been designed and developed to be o fa wide broadband and high gradient. The test results agreeoo

3nom(test o f the r f system will be performed soon.

2REFERENCESooll)o § p d q<Dwith the calculation results very well. And 狂high power[ 1 ] K.

(DEndoet al,Compact ProtonSynchrotron,1Proceedings o f the 4th Symposium on Accelerator andoo

Related Technology for Application (ARTA 2001),
Japan, 11-14, Oct. 2001.

510Frequency (MHz)15[2] K. Endo et al, Compact Proton and Heavy Ion
Synchrotron for Cancer Therapy and Bio-Science,
Proceedings o f the 13th Symposium on Accelerator

Figure 6: Test results o f impedance amplitude o f 4 units
in r f cavity.

Science and Technology (SAST 2001) ，Japan, 426-428,Oct. 2001.
[3] K. Endo et al, Compact Proton and Carbon Ion—か一Z_amp(c=35.pF)

o Z_av.(Test)

Synchrotrons for Radiation Therapy, Proceedings o fthe 8th European Particle Accelerator Conference(EPAC 2002), France, 2733-2735, Jun. 2002.
[4] K. Endo et al, Development o f High Field Dipole andHigh Current Pulse Power Supply for Compact Proton
Synchrotron,

Proceedingsofthe2003

Particle

Accelerator Conference (PAC 2003) ，USA, May 2003.
[5] K. Endo et al， Development o f Compact Proton
Synchrotron for Radiation Therapy, Proceedings o f the5thSymposiumon

AcceleratorandRelated

Technology for Application (ARTA 2003) ，Japan, Oct.
2003.
[6] K. Endo et al, Development o f High Field Pulsea) Impedance amplitude
一^—phase(c=35.pF)

Magnet and Power Supply for Proton Therapy, thisconference.

o Pha av.(Test)[7] Z. Fang et al，RF Cavities and Power Amplifier for theCompact Proton Synchrotron, Proceedings o f the 2003
Particle Accelerator Conference (PAC 2003) ，USA,May 2003.
[8] Z. Fang et al, Development o f the RF System for theCompact Proton Synchrotron, Proceedings o f the 5thSymposium on Accelerator and Related Technologyfor Application (ARTA 2003) ，Japan, Oct. 2003.

t.

-90 —1— 1— 1— i— i— i— i— i— i— i— — i— i— i—051015
Frequency (MHz)b) Impedance phase
Figure 7: Test and calculation results o f average value o f
impedance o f one quarter o f r f cavity.