JAERI-Conf

95-021

PA43
Horizontal COD measurement and correction
system in HIMAC synchrotron
M.Kanazawa, M.Sudou, A.Itano·, M.Kumada, E.Takada, K.Noda, K.Sato**,M.Katane···,J.Sagawa···, T.Miyaoka····, E.Toyoda····, and T.Yagr···National Institute of Radiological Sciences.
4-9-1 Anagawa, Inage-ku, Chiba-shi 263, JAPAN* Public Health & Environment Department, Hyogo Prefectural Government, Kobe 650** Research Center for Nuclear Physics, Osaka University, Osaka 567*** Hitachi Works, Hitachi LTD, 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki 317* * * * Toshiba Corporation, 1-1-6 Uchisaiwai-cho, Chiyoda-ku, Tokyo 100
Abstract
A horizontal COD measurement system has
been made which has twelve electrostatic pick-up
monitors beside focusing quadrupole magnets. The
measured horizontal COD has maximum value of
14mm, and is corrected down to 2mm with simple
way by use of twelve steering magnets which havebeen set at same places of the monitors.

To measure the horizontal COD, electrostatic
pick-up monitors with triangular right and left
electrodes have been made. The electrodes that are
260mm long are made of stainless steel SUS316L.
The aperture is 238 mm wide and 32mm height,
which is defined with window frames to prevent thenoise due to lost beam hitting. The capacitance isllOpF and its balances between the right and left
electrodes in each monitors are adjusted within 2 pF
with a movable ground plate (see Fig.l).
steering magnet.

I. Introduction
300

HIMAC synchrotron[!] has been designed toaccelerate heavy ions from He to Ar. Injectionenergy is 6MeV/u and maximum energy is
800MeV/u for ions of e/m=0.5. The maximum
required beam intensities for each ion species aredetermined to have dose rate of 5Gy/min. In thecarbon case which is being used for cancer
treatments now, required beam intensity is 4xl09ppp.
To obtain this value in the synchrotron, the multitum
beam injection scheme is adopted. Hence, horizontal
and vertical acceptances of the ring are 260;t and26;t mm mrad, respectively. Slow beam extraction
with third order resonance is used, and this process
requires extra horizontal space for last three tum. To
determine the sizes of vacuum chambers and goodfield regions of magnets, additional spaces forresidual COD after the correction are added. Hencethe maximum apertures are ± 122 and ± 28mm inhorizontal and vertical directions, respectively. Non
uniform contraction and deformation of base concrete
after final alignment deteriorate its accuracy, andincrease the COD. To correct these horizontal CODs
and maintain the machine acceptance large, thehorizontal beam position monitor and the steering
magnet systems have been constructed.
II. Electrostatic pick-up monitors

2r0-I

4S

To check the output, test signal with a rod in
the monitor chamber bas been used. Amplitudes of- 147-JAERI-Conf 95-021

output signals from right and left electrodes (VR andVJ have been measured as a function of the rodposition. With simple assumption the position (x) isgiven as follows;
X = (W/2)(VR-VJ/(VR+VJ,(1)where W is electrode width.. In Fig2 the measured
values of (VR-VJ / (VR+VJ are plotted versus thehorizontal rod position, and show linear dependence
on X in the full aperture· with 24% larger value ofthe coefficient W (294mm) than the geometricalelectrode width (238mm). If there are unbalanced
capacitances or setting errors of right and left
electrodes, measured beam position has offset error.
If this error was larger than 0.5mm, we adjusted thecapacitance valance to reduce the measured positionat the center.
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00-90 -75-60000-45 -30 -150000o0I0153045607590The rod position (mni)II[ Monitor electronics

Monitor electronics is similar to the one[2],[3]in an acceleration system except for following points.
1) Between pick-up electrode and first FET
amplifier, there is semi-rigid cable of 40cm which
has resister of lOOQ in the middle. As shown inFig.3 this attached resister permit to amplify thebeam signal without distortion by the signalreflection. And this cable permit to attach the first
amplifier away from the vacuum chamber and to
decrease radiation damage of the FET amplifier.
2) There is only one beam signal processor for
position detection, and the beam signals from twelve
monitors are selected with diode switches. Isolation
between input channels are better than 62dB, which
value is good enough for our purpose. Switching
speed is 200ns and this fast speed make it possible
to measure twelve horizontal beam positions in ashort time as flat base period.
At the end of signal processor a low pass filterof 1kHz is used to reduce . the white noise. The
measured output values are shown in Fig.4. In thismonitor system, frequency range of input signal isfrom 1 to 8MHz, and gain range from 0 to 60 dB(range used in daily operation). With difficulty of thefine adjustment in the wide range of frequency andgain, monitor electronics have offset errors of± 2mm. Owing to the wide horizontal aperture of± 122mm, this error is acceptable.

Fig.2 Output values of (VR-VJf(VR+VJ versus rodpositions.

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-0.2

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0.6

1.0

Fig.4 Output of the monitor processor versus input
value of (Vr-Vl)I(Vr+Vl) with the monitor gain of
20dB and the frequency of 8MHz.
N. Steering magnets

Fig.3 The upper is the input signal from signal~generator and the lower signal is the measured outputof the monitor electrode.

Twelve steering· magnets have been installed at
the same place as monitors to correct the horizontal
COD. The magnets have been made with laminatedcore to make possible the pattern operation for COD-148-JAERI-Conf 95-021

correction at flat top. Maximum field strength isdetermined to correct the expected CODs at the flat
top field which are 16rnrn. The value is 800 Gauss
with the magnet length of 10crn. The magnet power
supplies are controlled with pattern data of 12 bits.
V. COD measurement and correction
To check the monitor, beam positions weremeasured for different RF capture frequencies (seeFig.5). Changing RF frequency (of), the beam
position (ox) varies as follows;(2)
ox = TJ r 2 r ,/( r ,,2- r 2 1 o f!f,theisrmonitor,
where TJ is dispersion at theenergy in units of the particle rest energy, and r tr is
the value at the transition energy. In the HIMAC
synchrotron r tr =3.67, T/ =2.5m, and r =1.0 at
injection. By use of these parameters,(3)
X = 2.7 X 0 f/f (m),imd this coefficient is consistent with the measured
value of 2.8m.

Measuring the displacement of beam position at
the monitor with excitation of one steering magnet,
determined
this matrix elements of A can beexperimentally.
At the flat base the COD could be reduced
to the value smaller than 2mm (see Fig.6) withsteering magnets, whose field strengths werecalculated with a equation-(5).

10 I-rOJ .I .•

II.L- IE

E-1o~~~~~~~~~~~..._...

0010()

o~--•-- •• - · - - - -•5EE•c:Fig.6 Measured COD before correction (fop), aftercorrection (Bottom).

0:e(IJ
0c.

0-E•

C'CIQ)

VI. Acknowledgements

IllThe authors would like to appreciate engineersof Iwatsu electric co., LTD and Sukegawa electricco., LTD for their effort to produce the nicecomponents in this system. they are also grateful tothe operating crews of AEC for their skillful
assistance.

•-5

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1.048
1.046
RF frequency (MHz)VII. References

Fig.5 Measured beam positions with different RF
capture frequencies.
Assuming linear lattice for COD correction,
displacements of beam positions can be expressed asfollows,
(4)
X= AO
where Xi is displacement of beam at the i-thposition monitor, and i is deflection angle with ith steering magnet. The deflection angles (to correct the COD (Xco0 ) is given with the inverse
matrix of A as follows;

ee= K Xcon·1e)(5)[1] Y.Hirao et al., "Heavy Ion Synchrotron for
Medical Use," Nucl.Phys.A538,541c(1992)
Y.Hirao et al.,"Heavy Ion Medical Accelerator
in Chiba, "NIRS-M -89,HIMAC-001,1(1992)[2] M.Kanazawa et al., "Beam Monitors for RF
Feedback Control in HIMAC Synchrotron" Proc.
of the Workshop on Advanced BeamInstrumentation, 504(1991 ).
[3] M.Sudou et al., "Beam Monitor of HIMAC
Heavy-ion Synchrotron" Proc. of 8th Symp. on
Accel. Sci. & Technol., RIKEN, Saitama,Japan,
320(1991).

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