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

LONG PULSE OPERATION OF THE ,JAERI SUPERCONDUCTING RF LINAC FOR FEL
E.J.Minehara, M.Sugimoto, M.Sawamura, R.Nagai, N.Kikuzawa, N.Nishimori and E. Tanaka*
Free Electron Laser Laboratory
Department of Reactor Engineering, Tokai research Establishment, Japan Atomic Energy Research Institute
2-4 Shirakata-shirane, Tokai-mura, Naka-gun, Ibaraki-ken, 319-11 JAPAN*Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
2-12-1 Ohokayama, Meguro, Tokyo, 152 JAPANA prototype for a quasi-cw or long-pulse, and highaverage power free electron lascr(FEL) driven by a 15 MeV60
supcrconduct-ing rf linac has been developed, andconstructed at Tokai, JAERI since 1989[ 1-8]. Cryogenic(50stand-by loss<3.5W at 4.5K) and accelerating fields'performances( Eacc < 8MV/m and Q < 2 xI 0+9) of four·v; 40
JAERI superconducting accelerator modules were realizedcI)
without any serious vibrational problem in the FELc 30I)
accelerator vault.
>
Since modification and related maintenance of the·~"ii 20cryogenic refrigerator system for the driver were completed~in the middle of October 1995, the system has run with
10no trouble, and the driver has been continuously run very
successfully up to now. The optical resonator system and0
related electron beam transport system were modified to33
63
93
123
realize larger acceptance than the old for both of theundulator radiation and energetic electron beam. An
Fig.l, Intermittent oscillation in the wavelength ofalignment and distance measurement system was newly
around 29 Jlm has been observed by using the Ge(Cu)developed, and successfully applied to actual preparatorydetectors and home-made fast current amplifier system.
measurement for lasing in the JAERI FEL. A far-infrared
light transport line and detector room was built to realize a References
low-loss and low-noise measurement ncar the accelerator[I] M.Sawamura et. al. ,N ucl. Instrum. Methodvault.
A318(1992) 127.
In order to realize the quasi-cw and long-pulse[2] M.Ohkubo et. al. ,Nucl. Instrum. Methods
operation, we have improved the electron gun grid pulscr
A296( 1990)270.
and high voltage power supply, and rf amplitude and phase [3]M. Takao, et al., in the Proceedings of Fourteenthcontrol systems for the JAERI superconduct- ing rf linac. International Free Electron Laser Conference, 1992, Kobe.
The improvements in the electron gun were nearly[4]M. Sawamura, et al., ibid.
finished, and the ones related with the rf system under way. [5]N. Kikuzawa, et al., ibid.
A beam test and commissioning of the JAERI[6]R. Nagai, et al., ibid.
superconducting rf linac as an FEL driver was successfully [7]M.Sugimoto, et al., ibid.
performed to get an electron beam ranging from 10 to 20[8]E.J.Minehara, et al., ppl59-161, in the proceedings of
MeV with a nearly full transmission and a full current, and Particle Accelerator Conference, 1995, Dallas.
relatively short macro pulse of 0.1 ms. Spontaneousemission and intermittent oscillation in the wavelength ofaround 29 Jlm have been observed by using the Ge(Cu)detectors and home-made fast current amplifier system. As
shown in Fig.l, a sudden increase of the light signal wereobserved after about 43Jlsec later from the beginning of
beam current pulse.

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