A BEAM-LOSS MONITORING SYSTEM AT KEK
H. Nakagawa, S. Shibata, S. Hiramatsu, K. Uchino and T. Takashima
National Labolatory for High Energy Physics
Oho-machi, Tsukuba-gun, Ibaraki-ken, 305, Japan
1. Introduction

The beam-loss monitoring system with free-air ionization chambers wasinstalled in the Main Ring at KEK to get both spatial and temporal informationof beam losses. Two beam-loss monitoring system were used at KEK, scintil-1 )lation counter type detectors and ionization chambers with an argon mixture .
They had some troubles, careful maintenance was required. New system isalmost maintenance-free, because the material for ionize does not worsen andthere are no active electronic components in the tunnel. The signal processor
is advanced, the amount of beam losses can easy be measured. This system canobserve the beam-loss distribution varying with time in one cycle.
2. Monitoring system
The beam-loss detector of free-air ionization chamber has O.Sms resolution,
about 200~A saturation of curzynt at HT=SOOV. One detector, the type iscalled long radiation monitor , covers half cell (6m) and 56 chambers cover
all of the Main Ring. The signals from 56 chambers are integrated independently and operator or computer can read out at arbitrary timing without destroy
the information. We can also observe the integrated signal continuously at
any point. The system diagram is shown in fig.l.
The data from this system a3y processed and displayed on graphic terminal
by MELCOM-70 computer net-work .
3. Observation
Fig.2 (a)~(e) show beam-loss distributions which change at times. In thisaccelerator, typical beam losses happen 4 times in one cycle, injection,
acceleration start, phase transition, extraction. These 4 beam-loss patterns
are almost stationary. Sometimes, machine trouble, misoperation or mistuningcause different beam-loss distribution.
At the injection there were some beam losses in normal operation as shownin fig.2(a). At the acceleration start there were no beam losses in normal
operation. For example, beam losses caused by RF-station trouble are shown infig.2(b). At the phase transition beam losses occure at SF Q-magnets of eachsuperperiod, where holizontal dispersion function becomes maximum. Usually,maximum beam-loss location is SF of superperiod I as shown in fig.2(c). Whentuning of accelerator was not good, beam-loss location altered other SF, as
shown in fig.2(d). At the extraction it seems that the cause of beam losses
is extraction septum. Beam losses exist locally at near lD Q-magnet of superperiod II and III, where extraction septa were installed, as shown in fig.2(e).
We can estimate the extraction efficiency from this data.
This system can also use to study of the machine. Fig.3 shows the integrated signal of beam losses caused by phase transition at I-SF where the beamlosses are most heavy ~Y the time. The data is compared with the signal froma wall current monitor
which shows longitudinal distribution of bunch. It
seems that the beam losses at phase transition depend on longitudinal distribution of bunches.
From the facts described above, this monitoring system is very powerful for
operation and studies of the machine.
Reference
1) S. Hiramatsu et al. 2nd Syrnp. on Accelerator Science and Technology, Tokyo(1979) P.l27.
IEEE Trans. Nucl. Sci. NS-26 (1979) 3313.
2) R.L. Witkover
IEEE Trans. Nucl. Sci. NS-24 (1977) 1789.
3) T. Katoh et al.
4) H. Nakagawa et al. 2nd Syrnp. on Accelerator Science and Technology, Tokyo(1979) P.l17.
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TIME
FROM

TRIG.

Fig.l

IV
III
II
POSITON
Fig.2 (a) Beam losses at injection.

Block diagram of system.

~ACCELERATION
START

Fig.2 (b)POSITION
Beam losses at acceleration startwhen one of the RF-station could not run.

Fig.2 (d)POSITION
Beam losses at phase transition
When tuning is not good ..

PT

POSITION
Fig.2 ·(c) Beam losses· at phase transition (PT)in usual condition..

III
II
POSITION

Fig.2 (e)BEAM

~Beam losses and bunch shape ..

-174-IV

Beam losses at extraction ..

TRAJECTORY OF PARTICLESSSESTINT~ES

INTENSITY

Fig. 3INJECTIONMAGNIFIED FIGURE
OF A BUNCH