The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

DEVELOPMENT OF BEAM LOSS MONITOR SYSTEM IN THE J-PARC
LINAC, 3GEV RCS AND 50GEV MR
S.Lee A), T.Toyama A), D. Arakawa A), T.Miura A),
J. Kishiro , N. Hayashi B), S. Hiroki B), R. Toyokawa B), Y. Teruyama B), F. Hiroki B),
T. Tomisawa B), M. Tanaka B)
B)

A)

B)

KEK, Tsukuba, Ibaraki, 305-0801, JapanJAERI, Tokai, Naka, Ibaraki, 319-1195, Japan(e-mail:seishu.lee@kek.jp)

Abstract
The beam loss monitor system is designed to provide
quantitative loss data and investigate the loss mechanismin the J-PARC linac, 3 GeV RCS and 50GeV MR. Theloss monitor system is composed of scintillator,
3argon-methane/ He gas filled proportional counter and air
filled coaxial cable ionization chamber. It is necessary tomeasure wide dynamic range of loss intensity for various
beam energies. To prevent the activation and heat load byintense beam loss, fast time response of loss signals isrequired. The beam loss monitors play an essential role inmachine protection system (MPS). In this paper,construction and application of loss monitor system aredescribed in detail. Preliminary result of demonstration inthe KEK-PS and calibration with cobalt 60 γ -rayradiation source are also discussed.

BEAM LOSS MONITOR SYSTEM
The distribution of loss monitors in the J-PARC linac, 3
GeV RCS and 50 GeV MR is described in Table 1. Inorder to optimize the condition of chopper or otherequipments system, fast rise time of loss monitor isrequired. In addition, protection and prevention of magnet,
RF cavity and other equipment against the damage bydump of the beam, should be guaranteed before
thresholds are exceeded. The permitted delay timedepends critically on the relation between beam energyand materials.
Table 1: Expected beam loss and designed BLM systemin the JPARC linac, 3GeV RCS and 50 GeV MR. Time
response is determined by requirement of beam operationand MPS.

INTRODUCTION
The J-PARC (Japan Proton Accelerator ResearchComplex) project aims to provide the highest beam
intensity among the accelerators of such energies in theworld [1]. The 3 GeV and the 50 GeV proton synchrotron
ring designed to provide high intensity beams of 333µA(1MW) and 15µA (0.75MW), respectively. The potential
programs at the J-PARC are high-precision frontier, suchas materials and life science, and particle physics withKaons, Muons, and Neutrinos. However, the highintensity beam accelerator complex itself requires thesignificant progress of design study and hardware R&D.
Operational beam intensity should be limited by the beamloss and activation level of the equipment. Once the beamloss exceeds a criterion at outer environment, beam
intensity has to be decreased to prevent the further
activation. In order to investigate loss mechanism andsuppress the beam loss, a loss monitor system isdeveloped. The system will be essential component for
beam commissioning, tuning and machine protection inhigh intensity beam accelerators. The loss monitor system
employs the scintillator, gas filled proportional countersand coaxial cable ionization chamber, which detect γ -ray,
neutron and charged particles induced by lost particle [2].
In this paper, application and preliminary results ofevaluation for each loss monitors are discussed.

Required response

Expected loss level Flux particle Loss monitors<1µsec<2µsec for MPS

0.8kW chopper
3W/m average

n,g

S-BLM
P-BLM (3 He)~SDTL(100MeV) <10µsec<~15µsec for MPS

0.1W/mn,g

S-BLM
P-BLM (3 He)~3GeV ring

<10µsec<~60µsec for MPS

0.1~1W/m MEBT2 n,g,charged
1W/m average
particle

injection/extraction<10µsec

4kW

n,g,charged
particle

S-BLM 3P-BLM ( He)controlled loss

<10µsec

1W/m averagen,g,charged
particle

P-BLM (Ar/CH4 )AIC-BLM

uncontrolled loss <1msec

1W/m averagen,g,charged
particle

P-BLM (Ar/CH4 )AIC-BLM<100µsec

7.5kW slow ext.
1.1kW fast ext.
0.5W/m averagen,g,charged
particle

P-BLM (Ar/CH4 )AIC-BLM

uncontrolled loss <1msec

0.5W/m averagen,g,charged
particle

AIC-BLM

Linac~MEBT1P-BLM (Ar/CH4 )AIC-BLM

3GeV RCS

50GeV MR
controlled loss

The RFQ must be turned off within 2µsec for several
MeV low energy beam (up to MEBT1), which containdelay time at cable and interlock modules. Thus, fast time
response of less than a microsecond is required to loss
monitors. Because of above requirements, scintillator andphotomultiplier tube loss monitor (S-BLM) is provided at
low energy region. However scintillation andThe 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

photomultiplier efficiency will significantly decrease with
irradiation of accelerator operation. It is necessary tocorrect the sensitivity with other reliable (even if slow
time response) loss monitors. To calibrate the signal level
3of SBLM, He gas filled proportional counter (P-BLM) isemployed.
13Linac beam of 8.3×10 particles is injected into therapid cycle synchrotron (RCS) during 500µsec. In order
to confirm the efficiency of injection process, time
resolution of less than several microseconds is required,
which can survey the beam loss behaviour in eachrevolution period. Ar/CH4 (90/10%) gas mixture P-BLM
is prepared for 3GeV RSC and 50GeV MR by reason oftime response, lifetime, and feasibility of maintenance.
Although damage threshold is not so serious in RCS, hightime resolution is also required to avoid the activation atinjection. In addition, injected beam has to be aborted inthe 50 GeV MR, when anomalous loss is observed.
However, the degradation in gain of Ar/CH4 gas filled
P-BLM due to the deposit of polymerized material onwire was reported [3]. So that the air ionization chamber(AIC-BLM) is distributed in linac, 3GeV RCS and50GeV MR to correct the signal level of PBLM (Ar/CH4).
It is also used to observe the uncontrolled beam losses
around the 50 GeV MR.

EXPERIMENTAL RESULTS
S-BLM will be used to optimize the commissioning andtuning in the linac and is monitored during theinjection/extraction in RCS. Figure 1 shows an S-BLMloss signal of KEK-PS booster extraction. As can be seenin the Fig. 1, S-BLM could observe the extraction loss
oscillation with revolution frequency of about 6MHz.
PBLM also shows the rise time of several microseconds
for input impedance of 10 kΩ [1,4]. It can not be used toMPS at upper stream of linac. In addition, low energy loss
beam principally induces neutron and γ -ray [5,6]. So that3

the He gas filled P-BLM is applied to calibrate thescintillator efficiency of S-BLM. To satisfy the MPS
requirement of high energy beam, the Ar/CH4 (90/10%)
gas filled P-BLM is used at down stream of linac.
Sufficient signal level and time response could be
expected for high energy region.
Figure 2 shows that the preliminary results of P-BLM
calibration with cobalt 60 γ -ray radiation source. It was
confirmed that about 25% decreasing of sensitivity wereobserved for accumulated charge of 3.0 C. In order tocalibrate the signal level of Ar/CH4 gas filled P-BLM,
dual check system is performed. Air ionization chamber isdistributed to confirm the signal level. Furthermore,
detected signal of P-BLM during the all machine
operation should be recorded.

0.2Signal [V]

CT0.4

P-BLM

0.1
0-0.1-0.2-0.3-0.4

S-BLM

0-250
4030
20
10000.5

1

1.5
2
2.5
Accumulated Charge [C]

33.5

0

Figure 2: Gain degradation in argon-methane P-BLM
under cobalt 60 irradiation. The anode wire diameter andlength were 60 µm and 850mm.

-4

AIC-BLMS-BLM0-2-4

0.08
0.06
0.04
0.02
0200

250300350
Time[µsec]

400450500Figure 1: Current transformer and loss monitor signalsof the KEK booster extraction. In this study, extraction
bump magnet was excited to scatter beam paticles. In CTsignal, the delay time of 15 µsec is corrected

The AIC-BLM is made of coaxial cable, with the innerconductor supported by spiral polyethylene insulator.
About 500 V high tension is applied to the outer electrodeas the bias voltage for the chamber. One end of thecoaxial cable is used to pick up the signal, where the BNC
signal pin is connected to the detector inner conductor.
The other end is for the high tension terminal, where theHV-N connecter is attached to the outer conductor. Figure
3 shows the relation between the AIC-BLM signal and theloss intensity. Section I and II represent integral loss
signal of injection and extraction area of the KEK-PS
main ring. Although the accumulation of beam loss is
significantly different, sensitivity of AIC-BLMs aresimilar to each other. On the other hand, an ionizedelectron from an atom is easily captured by oxygen, andThe 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

2+2-

creates O and O ions [7]. Ion mobility and high tension
determine the delay time of AICBLM (about 0.1 msec).
Although AIC-BLM can not provide MPS interlock
signal due to slow time response, performs the sufficientreliability during twenty years operations.
25
sect ion I
sect ion II

9.7GeV

Integrated Signal [V]20

Argon-methane P-BLM are also employed to tune andinvestigate the loss mechanism around the RCS and 50
GeV MR, which provide alarm signal for abort system
when anomalous loss is observed. Coaxial cableAIC-BLM are placed at down stream of linac and RCS tocorrect the sensitivity of Ar/CH4 (90/10%) gas mixture
P-BLM. AICBLM also distributes in the 50 GeV MR toobserve the uncontrolled beam losses. The developmentof loss monitor system will support the MPS andcontribute a great deal to experiment and operation.
In order to evaluate the absolute sensitivity of each loss
monitors, further experimental studies are required in
315
5.5GeV1051.2GeV

000.51Loss particle [10 12 particle]

future. Efficiency, lifetime and other performance of Hegas filled P-BLM and various scintillators should also be
examined in the KEK-PS and cobalt 60 γ -ray irradiation
facilities. Especially, the correlation of loss monitor
signals and actual beam loss position have to be found toinvestigate the loss mechanism and realize the MPS.
Further investigation both experimental and numerical areindispensable to develop the BLM system in the J-PARC
linac, 3 GeV RCS and 50 GeV MR.

1.5

Figure 3: AIC-BLM integrated loss signals of theKEK-PS main ring. In this study, steering magnet wasexcited to scatter beam particles at injection (I) andextraction (II) area.

SUMMARY AND DISCUSSION
The beam losses with wide dynamic range of intensityand energy are expected in the J-PARC linac, RCS and 50
GeV MR. In order to pursue various phenomenon
concerning with high intensity beam loss, a diagnostic
system has been developed. S-BLM distributes along theupper stream of the linac and injection/extraction area of3RCS. He gas and Ar/CH4 (90/10%) gas mixture P-BLM
are installed in linac.

REFERENCES[1] Y. Yamazaki, eds. A ccelerator Technical Design R
eport for J-PARC, KEK Report 2002-13.
[2] G. F. Knoll, Radiation Detection and Measurem ent,rd3 Edition (John Wiley & Sons, inc, 2000).
[3] A. Smith and M.J.L. Turner, Nucl. Instr. and Meth.
192(1982)475.
[4] W. Bambynek, Nucl. Instr. and Meth. 112(1973)103.
[5] T. Nakamura, Radiation Physics and A ccelerator S
ndafety Engineering, 2 Edition (2001).
[6] W. R. Mills, Jr., R. I. Caldwell and I. L. Morgan, Rev.
Sci. Instrum., 33(1962)866.
[7] H. Nakagawa, S.Shibata, S. Hiramatsu, K. Uchino
and T. Takashima, Nucl. Instr. and Meth.
174(1980)401.