JAERI-Conf 95-021

PB05
Fast Wire Scanner at the KEK-PS
Kiyomi KOBA *, Dai ARAKAWA, Jun-ichi KISHIRO
Katsuhiko MIKA WA, Hikaru SATO, Masashi SHIRAKATA
Takeshi TOYAMA and Masahito YOSHIINational Laboratory for High Energy Physics, KEK
1-1, Oho, Tsukuba, Ibaraki, Japan

Abstract
The KEK 12GeV proton synchrotron isscheduled to serve an intense beam for aneutrino oscillation experiment. This experimentis foreseeing about two times higher proton
intensity than the current one, and acceleratormachine studies are going on to improve thecurrent proton intensity. The most important
machine study is the investigation of anemittance blow up mechanism during theinjection/acceleration period. An observation ofa fast transverse emittance blow up is one of thekey issue in this machine study and a flying wire
monitor is now developing at KEK-PS.

during the injection/acceleration period. A single
photo-multiplier mounted beside the rotator
detects the secondary particles produced by theproton/wire interaction. Figure 1 shows amechanical device.

1. Introduction•Fig.1 Mechanical device

A transverse beam profile provides somany information related to the blow up
mechanism, such as orbit miss matching,strength of resonances, space charge effect etc.
The beam profile varies turn by turn during theacceleration. The slow profile change is caused
from, for instance, weak resonance andadiabatic damping etc. It can be detectable byemploying a residual gas ion monitor I)' whichcollects the ions produced from the ionization of
the residual gas by circulating proton. However,this type of monitor has ambiguity due to thespace charge and the finite ion drift time to theelectrode. A flying wire profile monitor is one ofthe candidate to check each other and to observe
the fast profile change during the acceleration2)-

SControl0
KEK 12GeV PROTON
SYNC~ffiOTRON5).

The KEK-PS flying wire monitor isdesigned to observe the vertical beam profile byrotating a thin Aluminum wire (25J..Lm<!>) into thebeam bunch by a speed of 20m/sec. Then thecrossing time duration is about 3msec and makeit possible to observe the fast profile variation

Fig.2 Instrument position-260-2. Flying wire mechanism

JAERI-Conf. Flyin~ Wire monitor is installed justbehmd a lattice defocus magnet as shown inFig.2. It consists of the low inertia U -shapefork, the high precision potentiome ter and thehigh power DC servo motor. The U-shape fork
has a gap of 66mm with an aluminum wire of
25~m diameter stretched. The fork spacing andlength are determined to cover whole beam sizeat the location where the wire is installed. Thefork is placed aiming to observe the verticalbeam profile and it crosses the circulating beamfrom up to down with the maximum velocity of20m~sec usin~ a DC servo motor. An angle ofrotatmg fork IS detected by the potentiome ter
which is connecting to DC servo motor bypulley. The fork velocity is automatica lly
c_ontrolled by col!lparing the motor driving
signal and the rotational angle signal.
Collision between the proton beam andthe wire material produces secondary particles,
number of which is proportional to the protondensity in the beam bunch.

95-021(WS) through a 16 bit parallel l/0 which cantransmit them by 4Mbyte/sec.

and photo-multipliers1gnal when three bunches were injected.

F~g.4 Tagging signal

Photo-multiplier.

data:.::trigger

Fig.3 System block diagramn~~~il~ IIIII~'IIIII"""~~::;Ill

3. Data acquisition,,_Figure 3 shows a block diagram of the.
signal flow. The photo-multiplier signal and thepotentiometer signal are digitized simultaneously
by a_~ave _Form ~igitizes(WFD). The photomultiplier signals 1s a pulse train each of which
has a length of about lOOnsec and varied
according to the acceleration RF frequency from
6.0MHz to 7.8MHz. Therefore the sampling
rate should be at least 200Msample/sec to obtain
20samples . for lOOnsec. Total memory of
0.6Mbyte IS necessary to cover all the times
where the wire crosses the whole beam crosssection. Since the harmonic number of theKEK-PS main ring is nine, a tagging signal isnecessary in addition to two signals mentioned
above in order to identify each bunch. The WFD
stores thre~ signals in lMbyte/cha nnel memory,and transmits them to a high speed Work Station

Fig.5 Potentiometer signal
The data from the WFD is analyzed by a high~peed \YS. Photo-mul tiplier signal express themtegrauon of number of secondary particles.
The peak of photo-mul tiplier signal ispro~ortional to the number of secondary
particles produced when a bunch hits the wire.
The analysis program of the WS looks for thepeak value ?f the e~tch ~unch signal and plot iton the Y-ax1s as a function of the wire rotation
angle on the X-axis. Since the bunch
identification by the tagging signal is carried out,
the beam profile of each bunch can be alsodedu~e~. Th_e tagging signal and the photomuluplter s1g~al are shown in Fig.4, andpotentiometer signal shown in Fig.5.

-261-

JAERI-Conf 95-021

4. Heating of the wire
and the emittance blow up
Beside the high energy secondary
particle shower detected by the photo-multiplier,the beam/wire interaction also causes a multiple
scattering of the circulating proton and theproton losses its energy at the same time. The
temperature rise of the wire material, ~ T, isassumed to be caused by every loss of theproton without considerlatio n of the energy
transfer to the secondary particle etc.

the incident particle, d and LR are the thickness
and the radiation length of scattering medium,respectively. Typical circulatingbea m emittance,
E, is 45mm-mrad. Dependence of the emittanceblow up on the wire materials is estimated asshown in Table 2. It is obvious that W(tungsten)causes about 10% blow up, then we don't useit.

Table 2.
d[J.Lm]w
AI~T dE/dX dm Cvc(1)1025
10~E[mm-mrad]( 500MeV)
4.24640.279220.25911~E[mm-mrad]( 12GeV)
0.131170.0086182
0.0079973

~E/E

[%]
9.437
0.620
0.576

where dE/dX, m, d and Cv are the minimum
ionization loss, mass, thickness and specificheat of the wire, respectively.
Temperature rise is estimated by using
eq.(l) and that of all wire materials is much lessthan the melting point as shown in Table 1.

By the taking account of thetemperature rise and the emittance blow up, wedecided to use aluminum wire which is moreeasy to stretch on the fork than a carbon wire.

Table 1.

5. Conclusionw
AIcd[J.Lm<!>]102510~T[K]
433.92435.02829.435

Design of the fast wire scanner at theKEK-PS main ring was described. This flying
wire has just installed on early September. Afeasibility study and the software development
are now going on. The result of the study will
be presented at the Symposium.

melting point
[K]
3660
993
3773

The emittance blow up, ~E. is describedas*Miyazaki University
1-1, Nishi, Gakuenkibanadai, Miyazaki, Japan

where ~y is the vertical beta function, d isthickness of the wire, e is the rms value ofmultiple scattering angle and n is the number ofrevolution, respectively. eis estimated6) byedlogw(LR)r::--[1+1 (3)9R

20[MeV/c]~p~where P, ~and Zinc are the momentum (inMeV/c), Lorentz factor and a charge number ofReferences
1) T.Kawakubo, Nucl.Instru.& Methods
A302(1991)397
2) Ch.Steinbach and M.van Rooij, 1985 IEEE
Transaction on Nuclear ScienceVol. NS-32, No.5, p.1920
3) J.Gannon et al, 1989 IEEE Particle
Accelerator Conference Vol.3 p.68
4) S.Hancock et al, 1991 ABI Proceedings
Vol.l p.126
5) J.Bosser et al, 1987 IEEE Particle Accelerator
Conference Vol.2 p.783
6) Particle Properties DATA Booklet-262-