Proceedings of the 22nd Linear Accelerator Meeting in Japan

pp-40
L O S S M O N I T O R S Y S T E M F O R T H E JA E R I S U P E R C O N D U C T I N G R F L I N A C - B A S E D F E L
E.

J. Minehara, E.Tanaka, M . Sugimoto, M . Sawamura, R. Nagai, N . Kikuzawa and N . Nishim ori
Free Electron Laser Laboratory,
Department o f Reactor Engineering, Tokai Research Establishment,
Japan Atomic Energy Research Institute
2-4 Shirakata-shirane, Tokai, Naka, Ibaraki, 319-11 J A P A NAbstract
In order to reduce substantially high radiation level o f X - and gamma-rays at the J A E R I F E Lfacility, we have developed a beam current loss monitoring system being distributed along the beamline o f the JA E R I Superconducting rf Linac. Preliminary and experimental results showed thereduction o f about a few orders o f magnitudes in the J A E R I F E L experimental hall. Design optionso f the photon detectors and monitoring ways are reported briefly.

原研超伝導リニアックFELにおけるビームロスモニターシステム
In order to decrease substantially the hard X and gamma-rays radiation level at the JA E R I
F E L facility, we have developed a beam current
loss monitoring system being distributed alongways w ill be discussed.
In the F i g . l , a typical pulse shape from theloss monitor prototype o f Si-photo diode isshown to have a rise time o f 30jiis and a fall time

the beam line o f the J A E R I superconducting rf
linac. Usually, we first try to maximize ao f about one hundred |i,s. The rise time is thetransmission o f an electron beam through the rf

same with a beam pulse duration, and the falllinac by adjusting beam optical elements, and bytime an amplifier time constant. In the case o f themonitoring the beam current. Once we succeed

short pulse duration or gamma ray source, theto transport the electron beam with about a fullrise time is the same with the circuit rise time,transmission, and we can not use a current

and less than l|Lis. The pulse is taken about 2

monitor system to reduce a smaller amount o fmeters after the J A E R I superconducting rf-linac

the beam loss than a few %. In order to reducebased F E L driver along the beam line.

the beam loss smaller than 0.01% or less, wemonitor was fixed at the position o f about one

have to use a more sensitive monitor for theand half meter from the stainless-steel beam duct,

current loss than the current monitor.
Preliminary and experimental results showed
the reduction o f about one and half orders o fmagnitudes in the J A E R I F E L experimental hall.
Plastic, N al(Tl) crystal and Glass scintillators
have been used to reduce the radiation level. Inorder to monitor the radiation level induced by anelectron beam loss, we have developed a newsemiconductor radiation monitor using a Si-photo

Theand heavily-shielded with several 50mm-thick Pb
blocks on the floor. In the Fig.2, 2.5ms and 30\is duration components are shown in a typicalloss monitor pulse under beam acceleration. Thelong is the same with an rf pulse length o f thelinac, the short macro pulse. The long comesfrom the X-rays being originated from the fieldemitted electron bombardment, the short theelectron beam loss.

diode り，C s l or B G O scintillators and a chargesensitive hybrid a m p lifie r ，. In a heavy radiation References
1 ) Hamamatsu Photonics C o. "Si PIN Photocircumference, we used to remove thescintillation crystal or glass to reduce the monitor diode S 3 5 9 0 -0 5 '2) Hamamatsu Photonics C o. ’’a charge-sensitive
sensitivity, and reduce the bias voltage. Designoptions o f the photon detectors and monitoring

hybrid amplifier H4083, 丨.

T ek Run: IM S/sSampleilgglfgi

F i g . 1 : A typical pulse shape from a loss monitor prototype o f Si-photo diode is shown, and has arise time o f 30|is and a fall time o f about a few hundreds |is.

T e k gQSISI 50kS/s

Fig.2:

丨037 Acqs

Long and short duration components in the typical loss monitor output under beam

acceleration. The long one is 2.5ms long, the short 3 0 |lis long. The long comes from the X-rays
being originated from the field-emitted electron bombardment during the R F macro pulse, the shortthe electron beam loss.