The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Beam Loss Monitoring in HIMAC with Fiber Optic Radiation Monitor
Toru OKA, Hirotsugu FUJIWARA, Yoshikazu TSUTAKA*, Teruo USAMI
Koji NODA**, and Hirotsugu OGAWA***
Industrial Electronics and Systems Laboratory, Mitsubishi Electric Corporation
Amagasaki, Hyogo, 661, JAPAN*Energy and Industrial Systems Center, Mitsubishi Electric Corporation
Hyogo-ku, Kobe, 652, JAPAN**National Institute of Radiological Sciences
Anagawa, Inage-ku, Chiba; 263, JAPAN***Accelerator Engineering CorporationAnagawa, Inage-ku, Chiba, 263, JAPANFiber Optic Radiation Monitor can measure theradiation distribution along the sensor. Time of Flight
Method is applied for distribution measurement, i.e., for thedetection of incident position of radiation. Figure1 shows
the principle of detection in Fiber Optic Radiation Monitor.
When radiation enters the scintillation fiber, theinteraction between core material and the radiation causes
scintillation within the core. Scintillation light pulse ispropagated towards both ends of the fiber, and received byeach photo-multiplier. As the propagation time depends onthe distance between the incident point of the radiation andthe photo-multiplier, it is possible to determine the incident
point of the radiation by measuring the propagation timedifference. [This method is known as the Time of Flight(TOF) method]. In addition, by counting all the opticalpulses, the radiation dose rate can be computed.

Abstract
Beam loss was measur-ed in HIMAC with Fiber Optic
Radiation Monitor. Fiber Optic Radiation Monitor canmeasure the radiation distribution continuously along thesensor cable made of scintillation fiber. Position andintensity of beam] loss were measured in various operatingcondition and time structure of beam loss was consistent
with the signal wave form from ripple monitor.

1Introduction

It is very important for an accelerator operation toreduce a beam loss as low as possible. The beam loss
monitor has been developed with Fiber Optic Radiation
Monitor 1•2 , which continuously detects the beam loss
position along the beam duct . The sensor of the monitor isa scintillation fiber with cable structure. It is installed on
the outer beam duct, and detects the radiation generated
when the beam hits the duct surface. The preliminary
experimental result in HIMAC 3 is reported in this paper.

2.2 Features and Specification

Beam loss monitoring with Fiber Optic Radiation
Monitor has following features.
(1) Reduction of beam adjustment time
With the detection of the beam loss position along the2 Fiber Optic Radiation Monitor

beam duct, the magnet which has to be adjusted is easily

identified and the result of adjusting is measured on realtime.

2.1 Principle ofdetection

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Time Difference Meter
ICounterI

Fig.1 Principle of Fiber Optic Radiation Monitor-145-IThe II th Symposium on Accelerator Science and Technology, Harima Science Garden City, I997

(2)Reduction of activation in facility
As beam duct is activated by high energy beam, thereduction of beam loss leads to the reduction of activationin the facility and of the exposure of operators.
(3)Non-destructive monitoring
The beam loss monitor is installed along the outside ofbeam duct and gives no influence to beam condition.
(4)Applicable to high-voltage and high frequency facility
Signals are transmitted in light pulse, soelectromagnetic noise immunity allows this monitor to be
applied in high-voltage or high-frequency facility.
Specification of the monitor is summarized at Table. I.
Table.l Specification
Specification
Item
X-ray or Gamma-ray
Type of radiation
Measuring Range
1 to 104uSv/h§nergy Range
600Ke V to 1.3MeV
Operating Temperature
pto 50 degree Celsius
Effective sensing length
20mSensor radius
15mmSensor cable length
60m
3 Experiment
The sensor was installed along the beam extraction
line in HIMAC synchrotron. It was chosen as themonitoring position of the beam loss, as shown in Fig.2,
because a beam is lost at the septum of the electrostatic
deflector(ESD).
The sensor and measuring unit were placed in theaccelerator area, the data processing unit in control room,and each unit were connected with co-axial cable.
Following tests were carried out in various operating
conditions with 290MeV/u Carbon beam.
(1) Beam loss detection with the insertion of ripple
monitor(RMON) or profile monitor(PRN).
Beam Ejection Line02345(2) Beam loss detection in the adjustment of steering
magnet and focusing magnet.
(3) In maximum beam intensity(4) Time structure of beam loss
4 Results and discussions

4.Jlnsertion of Profile monitor
Back ground level shows the peak at ESD position in
Figure.3 and this means that the wall has been activated by
the beam at ESD position.
The position and intensity of beam loss is shown in
Figure 4 in normal operation.
Beam loss was observed at the ESD position in normal
operation, because a part of the beam was lost (cut)inevitably by the septum of the ESD due to the resonantextraction process.
The position and intensity of beam loss in the insertionof profile monitor in normal operation is shown in Figure 5.
Beam loss was observed at near downstream of profile
monitor. Profile monitor has two aluminum-windows withthickness of 300um and two lattice-structure electrodes
with diameter of 20 and 50 urn, respectively. Thus beam
scattered by the profile monitor hits the beam duct atvarious magnet positions and X-ray and gamma-ray areemitted.

4.2 Adjustment of Focusing magnet
Figure 6 shows the beam loss m the condition offocusing magnet's power turning off.
Focusing magnet(QF) is designed to adjust the beamprofile. By turning Focusing magnet's power off, the beam
spreads out as it goes downstream; and beam loss wasdetected at about 4m downstream position in Fig.6.

/Cable Position '111/tBeam Direction
67891011 1213 1415 16Fig.2 Installing position of sensor-146-1718 19 20 mThe] 1th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997-"'>

time structure was consistent with the signal
from the ripple monitor.

10wave form

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2015

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-.1.--500

0500

1000

1500...

2000

Starting Measurement Time(ms)nI

Fig.7 Time structure of beam loss

1I!J ..

_..;~/____...,./"\.

510Position (m)15I ~'·~
20Fig.4 Beam loss in stable condition-~ 800510Posit ion (m)155 Conclusion
Fiber Optic Radiation Monitor with the detection .
length of 20m was installed on the beam extraction line inHIMAC synchrotron and the beam loss was measured.
It was possible to detect the position and intensity ofbeam loss by detecting the radiation emitted when the beamhits the beam duct.
Time structure synchronizing with the beam extraction
signal was also measured and consistent with the signal
wave form from ripple monitor.
Thus it was found that the beam loss monitor was
useful tool for beam tuning.

20References

Fig.5 Insertion of profile monitor?:: 2500~2000-.c~'-1500>

c-~(/)1000
-::t.

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£ soo-~--(~~-~~~-----~j\_.....!J_ ______ - - · - - - - - " " 1--·~--­·--14---------rl[l]S.IMAI et al., REV. SCI. INSTRUM., 62, 1093 (1991)[2]T.EMOTO et al., RADIATION DETECTORS AND
THEIR USES: KEK PROC., 94-7, 119 (1994)[3]E.TAKEDA et al., PROC. 5th EPAC, BARCELONA,
1996, p.2659-2661..

:-r \........-J~

oko=---~~~~==~=-~==~~--~~

510Position (m)1520Fig.6 Focusing magnet turning off

4.3 Time structure of beam loss

The time structure of beam loss is shown in Fig.7.
The beam was extracted at a cycle of 3.3 second. The
amount of beam loss was measured at an interval of 150ms
synchronizing with the extraction. The measurement of-147-