The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Secondary-Electron-Emission 'fYpe of Beam Profile Monitor for the IDMAC-Injector (6 MeVIo)
Akio HIGASID, ):Ukio SJXID*, Daisuke OHSAWA*, FuminoriSOGA*,Suguru MUfO**, Yshinori HASHIMOTO*** and Yi.Jzo FUJITA***
Health and Welfare Dep., Hyogo Pref. Gov.
1-2-1, Kooto, Shingu-cho, lbo-gun, Hyogo 679-5162, Japan*National Institute of Radiological Sciences (NlRS)
4-9-1, Anagawa, Inage-ku, Qriba 263-8555, Japan**High Fnergy Accelerator Research Organizatim (KEK)1-1, Oho, ThukuOO, Ibaraki 305-0801, Japan***High Fnergy Accelerator Research Organizatim (KEK)
3-2-1, Midori-cho, Tanashi, Tokyo 188-8501, JapanAbstract
A beam profile monitor with the secondary-elecllmemission Jbenomenm has been developed for radiation-biology
experiments at the HIMAC (Heavy Ion Medical Accelerator inOriba}-injector (RFQ + 100MHz Alvarez). It is basicallycomposed of three thin electrodes whose effective area and gap
distances are 32 x 32 mm2 and 2 mm, respectively. 1 mm-thick
AI foil is used as a central electrooe. Electrodes on both sides are
2 mm thick alminized polypropylene films having a pattern of 16
strip-lines (1.5 mm wide and 0.05 mm spaced). These are,respectively, used for sensing vertical and horizontal profiles ofsecondary electrons emitted from the stripped electrcxle. It may be
noted that the thickness of our beam profile monitor is very thin,i.e., the total amoont of matter is less than 750 mg'cm2• The
charges induced in each strip-line is integrated with a respective
pre-amplifier and the online beam profile isprocessed with a micro-computer. Thesensitivity of the amplifier is determined by thebeam intensity of the injector, i.e., 0.1 nA order.
The overall characteristics of the beam profile
monitor under the bombardment with 6 MeV!ua and C>'- ions from the HIMAC-injector are
discussed

emission yields and vacuwn-surface conditions was studied [2].
The relatioo between the SE emissioo yields and Atomic number(z) ofvarioos injected ions was also discussed [3].
The importance for beam profile mmitors is now increasingin the radiation-biology experiments and accelerator physics. In
the former case it is used to obtain the information on a precise
irradiation intensity and its distribution. On the other hand, in thelatter case the knowledge about the spatial distributim ofaccelerating particles is extremely necessary to study the beamtuning. In this case it is particularly desired the amount of matterfor the monitor is as possible as little.
In the present work, we describe the outline of the developed
two-dimensional SE emissim type of beam profile monitor foc
the HIMAC-injector. Experimental results and characteristics arealso presented.

1 Introductim
In the previous wotks, we reported a verythin secondary electrm emission mmitor(SEEM). It was designed as an intensity
monitoc for radiatioo-biology experiments,
instead of the Faraday-Cup, and for studying thetime structure of bunched heavy-ion beams
from the HIMAC-injector in NIRS [1 ]. The
relation between the secondary electron (SE)Fig. 1. Schematic view of the SE emission profile mmitoc. 1\vo collimators madeof copper and three foils whose thickness is 1 J..Ull are shown.

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Fig. 1 shows a schematic view of the present beam profile
monitor. It consists of three electrodes \\hich has 32 x 32 mm2active area, and two collimators. The arrangement of electrodes is
the same as that in the previous SEEM [1]. The central electrodeis 1 mm thick AI foil, attached 1 mm thick copper frame whose
interior area is 32 x 32 mm2• Other two electrodes having thepattern of 16 strip lines mounted in 2 mm thick ceramic frame
placed at the both sides of the central electrode. The forming ofpattern (1.5 mm wide and 0.05 mm spaced) is made with the laser
cutting. These are used for the measurement of horizontal- (X)and vertical-profile (Y), respectively. Gap distance between thecentral and other electrodes is kept 2 mm with teflon spacers. Twocollimators, made of copper and 2 mm thick, are placed outside
inlet- and outlet-electrode. These are not only for limiting thebeam size but also for adjusting the outside electric field of inletand outlet-electrode, i.e., they provide an adequate ground level tothe outside electrodes of SEEMs with three electrodes.
The profile monitor was located in the vacuum chamber on
the beam line, and operated under the vacuum of 10-6 - 10-8 Torr. It
is connected to the integrated circuit through a "doubly-shielded
coaxial cable" with a length of 5 m \\hich would be effective toreduce the noise. Digitized signals from the data acquisition
system are fed into the measurement room 40 m far from theaccelerator room. The plus voltage was applied to the central
electrode via Keithley electrometer. The inlet- and outletelectrode were set in a ground level. Signals from total 32 striplines are individually fed into the pre-amplifier of the dataacquisition system. Beam profiles in the X and Y directions per
pulse are displayed as an online data. Fig. 2 shows a timing chartof the data acquisition system. A control signal of switchingmagnet located downstream the linac was used as a trigger signalof the acquisition system. In this system, minimum trigger
repetition is 0.5 sec and sufficiently fast to the linac beams (1.67Hz). While the gate signal of the acquisition system starts 250
nsec later than the trigger signal, this delay does not influence tothe measurement error, e.g., less than 0.1 %. Any gate width of100, 500 )lSec and 1 msec can be selected by a rotary switch.
Usually the beam is started about 700 J..LSec later than the trigger
signal.
In the arrangement of applied voltage of our profile monitor,
only SE electrons are emitted from surfaces of the inlet and outlet
electrode facing the central electrode contributes to the signals,
that is, SE from outside surfaces of them and both surfaces of thecentral electrode do not contribute to the signals.
3 Experimental ResultsFig. 3 shows the measured two beam profiles for c:?- heavy

1.4

yfocused beam.tE

1.2E~T-.!

1.032

X

0.4
0.2
0.004812162024

position [mm]de-focused beam

L•

X
y28

32

0

1.2~ nsec

28It)

0.6

1.4

trigge~X
y5mm0.8a) beamb)

•0

1.0

0.8

L_c) gate

0.6
0.4

msec max0.2d) integr~-------------------

0.0

Fig. 2. Tuning chart of data acquisition system. a) an input beam
whose width are changeable in 5-300 )lSec. b) a control signalof switching magnet downstream of the linac used as a trigger
pulse. c) a gate signal generated in the data acquisition system. d)an output of integral charge connected to a computer. 250 nsec
delay of the gate from the trigger is negligible.

-04

8

12

162024position [mm]Fig. 3. Comparison of line shape with beam size. c:?- beam fromlinac was used. Beam was tuned for upper: focused circle shapeand lower. defocused ellipse one.

91-The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

.....
E 1.0
E.....
~ 6.5

rr-- -f----- +---- -1
it-- -i---- -l---- -1caCl)

a. 6.0

0:::E 5.5:I:

a: 5.0Xo• y4.5 .___.......__ _.__ __,__ ___._ _.___.......__ _,
0

50

100

150

200

250

300

350

applied voltage [V]Fig. 4. Voltage dependence on line shape. Full width at halfmaximuri:J. (FWHM) of profile are shown at 30 - 300 V onelectrode. Shapes of profile measured at X and Y foils can beregarded as gaussian for example in Fig. 3.
ions from the lllMAC-injector. While beams are tuned like afocused circle shape or like a defocused ellipse one, the precise
information about the beam profile can be obtained as indicated inthe figure. These beam profiles are also confirmed by the dosesensitive paper. The full width at ninth maximum are given in theupper left corner in each figure. As shown in the figure, the bothprofiles agree with each other very well.
While, in the previous experiment, it is found that the kinetic
energy of SE is alm<N less than 20 eV [1], the characteristics ofemission yield versus q>eration voltage should be in detailinvestigated. The operation voltage was applied up to 300 V. Fig.
4 shows the relation between the full width at half maximum(FWHM) and operation voltage. There is no change due to the:I4Swnmery
We have developed a very thin SE-emission type of beamprofile monitor with an effective area of 32 x 32 mm2 foc heavy
ion at the lllMAC injectoc. Two-dimensional profile information
is obtained with electrodes having 16 strip-lines, \\hich are 1.5mm wide and 0.05 mm spaced Basic characteristics of the profile
monitor are tested in the vacuum of 1cr to 1~ Torr tmder thebombardment with a. and C* ions with an energy of 6 MeV!u. It
was foond that the dependence of q>eration voltages is foond tobe negligible small, i.e., in the operation voltage of30 V to 300 V
the yield is constant By changing the beam intensity, weconfirmed the monitor is usable for the beam intensity of a 0.1 nA
level. Since the amoont of matter of the monitor is very little, it
may be applied to the therapy with the lllMAC beam.

Acknowledgement
The authors are very gratefull to Dr. T. Honma, lllMAC
operators, Mr. T. Owada of Antex Ltd, Mr. M. Mitani ofMinotos
Ltd, Mr. T. Kadowak:i and Mr. J. Yoshizawa of Kaizu Works Ltd.
This experiment was performed under 11p-009 of Research
Project with Heavy Ions at NIRS-lllMAC, \\hich has been
supported by the Science and Technology Agency of Japan.

.....1oo9 ....,..,.,-n---,.-,--r-T""T""1rTT,.....-""T""--r:-T-,'2

operation voltage in the range of 30 - 300, 30 V on electrodevolt·age is enough to collect the emitted SE.
The yield characteristics of SE emission from metalized
films have a good linearity foc the beam intensity [1 ]. To study thebeam intensity dependence on the yield an attenuator was inserted
into the beam line. Befoce inserting the attenuator the beam
intensity at the peak was 8 JlA (the pulse width of 50 J.!SeC). By
inserting varioos attenuators the beam with the intensity of 1/3,
1/10, 1/30 and 11100 of the ociginal beam can be obtained As
shown in Fig. 5, the present beam profile monitor can be used in
the range of beam intensity of 100 times. In addition theattenuation factocs measured were consistent with the above
designed ones.

·s
76~-.
t!

:s.!.
ca

References!

ca 109ca
8Cl)
7~

a.

[1] Y Fujita, Y Hashimoto, S. Muto, A Higashi, Y Sato, D.

X-a--+-Y

65~~U--~-~~~~._-~~~~

5 6 7 80.01

234 5 6 7 8 0.1

234 5

attenuator
Fig. 5. Attenuator dependence on peak area. Attenuation factocs
indicated at its control panel are shown. Beam intensity was about
8 JlA at peak and 50 J.1SeC width of beam pulse in thismeasurement

Ohsawa and F. Soga, Proc. of EPAC98 at Stockholm,1503(1998).
[2] D. Ohsawa, Y Sato, A Higashi, Y Fujita, Y Hashimoto and
S. Muto, Proc. ofBEAMS98 at Kyoto (1998).
[3] Y Sato, A Higashi, D. Ohsawa, Y Fujita, Y Hashimoto andS. Muto, submitted to Phys. Rev. A foc publication.

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