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Kasugai, Atsushi; Sakamoto, Keishi; Minami, Ryutaro; Takahashi, Koji; Imai, Tsuyoshi
Nuclear Instruments and Methods in Physics Research A, 528(1-2), p.110 - 114, 2004/08
Times Cited Count：23 Percentile：80.21(Instruments & Instrumentation)The development of the millimeter wave high power gyrotron with the development of a depressed collector, an over sized cavity and a synthesized diamond output window is under going in JAERI. The performances of 170 GHz, 0.9 MW for 9.2 s and 0.5 MW for 30 s were achieved up to now. It was clarified, however, that pulse extension of the gyrotron was limited by sudden outgassing due to stray RF power deposition to the bellows behind movable mirror. For suppression of stray RF power deposition, the structure of the bellows section was improved to avoid the direct power deposition and the surface of bellows was coated by copper for reduction of RF loss and increase of thermal conductivity. As a result of the modification, temperature increase of bellows was reduced to less than 1/10 and time constant of thermal diffusion shortened to 90 s from 270 s in comparison with before the modification. This indicates that the modification is quite effective for suppression of temperature increase.
Nishimori, Nobuyuki
Nuclear Instruments and Methods in Physics Research A, 528(1-2), p.34 - 38, 2004/08
Times Cited Count：1 Percentile：10.3(Instruments & Instrumentation)The sustained saturation in an FEL oscillator at zero detuning of an optical cavity (
=0) is studied analytically. The FEL field at =0 is characteristic of self-amplified spontaneous emission (SASE) FEL. For both cases, the field is composed of the forward incoherent and subsequent coherent states. The coherent field at =0 evolves with round trips due to the lethargy. The field at saturation is similar to that of the leading edge of SASE FEL with high electron beam density. It is found that the peak intensity and the pulse length of the saturation field scale with fundamental FEL parameter and an optical cavity loss.
Hajima, Ryoichi
Nuclear Instruments and Methods in Physics Research A, 528(1-2), p.335 - 339, 2004/08
Times Cited Count：20 Percentile：76.55(Instruments & Instrumentation)Dilution of electron beam emittance through a return arc is one of critical problems in the design of an energy-recovery linac for high-power FEL and a synchrotron light source. We present that the emittance dilution can be compensated by establishing the matching between the phase ellipse orientation and the CSR kick direction, and the effect of coherent synchrotron radiation on the beam emittance dilution can be estimated from simple calculation of transfer matrices.
Hajima, Ryoichi; Minehara, Eisuke; Nagai, Ryoji
Nuclear Instruments and Methods in Physics Research A, 528(1-2), p.340 - 344, 2004/08
Times Cited Count：1 Percentile：10.3(Instruments & Instrumentation)We propose a full-DC injector for an energy-recovery linac. The injector is based on a 2MeV DC accelerator commercially available (Dynamitron type) combined with a photo cathode. The bunched beam from the DC accelerator is merged into the ERL loop and injected to a superconducting buncher booster, which accelerates the beam up to 20MeV. The bunch booster is operated in "partial energy-recovery mode", in which we can reduce the capacity of RF main couplers down to 10kW level even for high-average current operation, 100mA. We present a result of beam dynamics simulation and RF system optimization.
Nagai, Ryoji; Hajima, Ryoichi; Sawamura, Masaru; Nishimori, Nobuyuki; Kikuzawa, Nobuhiro; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 528(1-2), p.231 - 234, 2004/08
Times Cited Count：2 Percentile：18.14(Instruments & Instrumentation)An optical resonator geometry of JAERI ERL-FEL is optimized to ensure the high-power operation. Efficiency of the FEL strongly depends on performance of the optical resonator such as an output efficiency and interaction mode volume. The resonator geometry is optimized by maxmization of the output efficiency and minimization of the interaction mode volume. The output efficiency and the interaction mode volume of the optical resonator is calculated by a simulation code using Fox-Li procedure. To search rapidly with various parameters, the simulation code is improved utilizing Fast-Fourie-Transform.
Nishimori, Nobuyuki; Hajima, Ryoichi; Nagai, Ryoji
Free Electron lasers 2003, p.II_21 - II_22, 2004/00
Free-Electron Laser (FEL) interaction with unbunched electrons at resonant energy induces a positive phase shift of the FEL field relative to the input phase. The positive phase shift corresponds to giving electrons positive energy detuning, and results in the FEL amplification. The zero small signal gain on resonance in low gain regime is related to the exponential growth in high gain regime by the positive phase shift.
Sawamura, Masaru; Hajima, Ryoichi; Kikuzawa, Nobuhiro; Minehara, Eisuke; Nagai, Ryoji; Nishimori, Nobuyuki
Free Electron lasers 2003, p.II_31 - II_32, 2004/00
no abstracts in English
Sekiguchi, Tetsuhiro; Baba, Yuji; Shimoyama, Iwao; Nath, K. G.
Free Electron lasers 2003, p.II_69 - II_70, 2004/00
no abstracts in English
