The 9th Symposium on Accelerator &i.ence and Technology, Tsukuba, Japan 1993

Design of Profile Monitors for ATF
T. Naito, H. Hayano, M.Kikuchi, J. Urakawa, and M. Yoshioka
M. Oyamada*, S.Urasawa*, T.Nakazato*, T.Yamakawa*
KEK, National Laboratory for High Energy Physics,
1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305 Japan*Laboratory of Nuclear Science, Tohoku University,
1-2-1 Mikamine, Taihaku-ku, Sendai-shi, Miyagi-ken, 982 Japan

Abstract
A profile monitor using a fluorescent screen
is designed and tested. A random shutter cameraand a video analyzer system are used for themeasurement with shot by shot. In order to realize
high resolution, a thin fluorescent screen and ahigh magnification lens system are designed. An
another type of profile monitor using opticaltransition light is also described in this paper.
I. INTRODUCTION
The Accelerator Test Facility (ATF) consistsof 1.54 GeV Linac and Damping ring is underconstruction. for development of accelerator
components to realize the Japan Linear Collider(JLC). The beam parameters of the linac arefollowing, repetition rate: 25Hz, charge number:
2x10 10 electrons/bunch, bunch number: 20
bunches/shot, bunch space: 2.8 ns.
The main purpose of this facility is to makeRsnoom 9l.JtrEJ
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Screen monitor systema low emittance and multi-bunch beam. Precise
monitors and control systems are required. To
monitor the beam siz~ and the position in thelinac, fifteen screen monitors will be installedwith other monitors(wire scanners, strip lineBPMs, etc.). The screen monitor has an advantage
compared with the wire scanner. It can measure
the beam profile and position shot by shot.
An optical transition light(OTR) will beobserved when a metal screen is used instead offluorescent screen at the energy over several ten
MeV. A wave form of OTR is the same as bunchshape, we can measure profiles of each micro
bunch by using a fast shutter camera with image
intensifier and 3ns gate.
II. SCREEN MONITOR SYSTEM
The system configuration is shown in Fig. 1.
The screen monitor system consists of afluoresce.nt screen(alumina with chromiumoxide: AF995R), an actuator, a random shutter
camera, a freeze memory and a video analyzer.
The screen is inserted to the beam line by the air
actuator. The random shutter camera canmemorize the light from the fluorescent screen
when a beam hits the screen with shot by shot.
The camera is synchronized to a machine trigger.
The image which is frozen by the timing ofmachine trigger is converted to a video signal
with a video cycle(60 Hz). The video signal is sent
to the control room by the CATV system. The vidko
analyzer calculates the peak position(X,Y) andbeam size(lcr) by gaussian fitting in real time.
Twiss parameters and emittances are measured
by this system.[lJIII. EXPERIMENT AT TOHOKU UNIV.

Beam stze data

The prototype of the screen monitor, wirescanner, strip line BPM were tested at Tohoku
Univ. Linac.[2] The beam parameters and beam
shapes using a amorphous core CT is shown in-373-Energy
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Fig. 2 Beam shape ofTohoku Univ. Linac

Fig. 3a Beam profile..

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Fig. 5 Fluctuation ofbeam profile
Time domain fluctuation of the beam
intensity was observed from the wave form of theCT in Fig. 2. The transverse fluctuation wasmeasured by this monitor. Fig. 5 shows thefluctuation of peak value, center position, andbeam size. The fluctuation of each value of Y
direction was 40% for peak value, 3% for center
position, 8% for beam size. The fluctuation of X
direction was almost the same as Y direction. The
fluctuation of center position and the beam size
were small compared with the peak value. We
thought it was caused by the fluctuation of thegun grid pulser.

Fig. 3b 3D distribution·- f::·
f:=--·---Fig. 4a Beam profile(X) Fig. 4b Beam profile(Y)Fig. 2. The camera is set to 40 em distance fromthe beam line. The screen is viewed by
f=75mm(F1.8) and x2 magnifier lenses. The viewarea is 8.8 x 6.6 mm and a magnification is almost
1. The thickness of the screen is 130J.Lm in thistest. The total system error is estimated about
50J.Lm.
A. Beam size measurement
The beam profile and the three dimensional
intensity distribution of the linac beam are shownin Fig. 3a, 3b. The projection of X and Y direction
is shown in Fig. 4a, 4b. From these data, wecalculated the peak intensity, the center position
and the beam size(lcr) using a gaussian fitting.
The results were <1x = 300J.!.m in the case of focused
beam in X direction.

-374-B. Emittance measurement
Emittance is estimated by measuring eachbeam size at each current of the upstream Q
magnet. The spot size at the screen is given by amatrix as the function of strength of the Q
magnet(k) [3],cr;1 = A(k-B) 2 +C.
The measured size is fitted to a parabola function.
The square of spot size versus strength of Q
magnet for X and Y direction is plotted in Fig. 6a,6b. The optical matching was not adjusted, thus
the spot size is not well focused in Y direction.
From these fitting value, the emittace(Ex, Ey) and~~Ilj_,,.1

Fig. 6nFig. 6b

Square ofbenm size
versus strength of QlX)

Square of beam size
versus strenh>th of QlY)

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the normalize emittnce(Enx, Eny) are
Ex= 2.16 x 10·7 m rad (Enx = 8.45 x 10·5 m rad) andEy =1.05 x 10· 7 m rad (Eny = 4.13 x 10·5 m rad).
These values are agreed with the result of the wirescanner.
IV. OPI'ICAL DESIGN FOR ATF
The cross section of the beain line at thescreen monitor is shown in Fig. 7. To protect theCCD camera from radiation damage, the camera
is set under the beam line. The distance of thecamera and beam line is about 1.5m. An object
lens of f=300mm(F4.5) and f=38mm(F2.8) macrolens as a x3 magnifier are used to make viewarea 10 x 7.5 mm. Achievable resolution of thissystem is following.
Deffraction limit
Reyleigh limit of the lens is indicated byf£=0.61-A..
hThe limit is£= -15 11m at the wave length A= 700
nm.
Resolution of CCD
The size of one cell of the CCD isorx = 10mm I 768cells = 13 11m andory = 7.5mm I 247ce11s = 30 J.Lm.
Thickness of screenWe calculate two effect of screen at the case of thethickness= 100 l.I.ID.
1) The effect of defocus to the light from deepest
area when the camera is focused on surface is O"d=-1.5 llffi.
2) The effect of view angle of 45 degree( it affectonly in X direction) is cra = -30 11m.
The overall resolution is about 50 11m.
V. OTR PROFILE MONITOR

Fig. 8 OTR profile monitor
Fig. 8 shows measuremen t scheme andtiming chart. A metal screen is used instead of thefluorescent screen to observe OTR. A fast camerawith image intensifier(HAMAMATSU C4078) has
3ns gate time and 1 x 106 of photon gain. The gate
is distinguisha ble each bunch in ATF. The
programma ble delay select gate timing
correspond to each bunch timing. At the point of
the downstream of analyzer magnet( 90 degreebend), this monitor will be installed to monitor
energy spread of each bunch.
VI. SUMMARY
Fluorescent screen profile monitor isdesigned and tested. The system resolution isabout 50 J.Lm. OTR profile monitor is designed tomeasure the each profile of the multi-bunch.
VII. ACKNOWLEDGMENTS
We would like to express our thanks toProfessors K. Takata and S.Takeda for theirencouragem ent. We acknowledg e Dr. K.
Furukawa for his help and Mr. T.Matsui(A.T.C.)
for his technical support of this experiment.
References[1) F.J.Decker, "Beam Size Measureme nt at
SLAC-PUB-5481
High Radiation Levels",
May 1991[2] H.Hayano, et. al, "WIRE SCANNER BEAMSIZE MONITOR FOR ATF", in thisproceedings[3] M.Ross et. al, "HIGH RESOLUTION BEAM
PROFILE MONITORS IN THE SLC", SLACPUB-3640 April 1985
[4] M.Ross et al, "AUTOMATED EMITTANCEMEASUREM ENTS IN THE SLC", SLACPUB-4278(1987)-375-