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Nishimori, Nobuyuki; Hajima, Ryoichi; Nagai, Ryoji; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 483(1-2), p.134 - 137, 2002/05
Times Cited Count：7 Percentile：44.29(Instruments & Instrumentation)We made a systematic measurement of efficiency detuning curves at several gain and loss parameters. The absolute detuning length (dL) was measured within the accuracy of 0.1 um around the maximum efficiency by a method of pulse stacking with an external laser. The FEL gain was controlled by the undulator gap instead of bunch charge, because rapid change of the gain is possible with keeping the same electron bunch condition. At the high gain and low loss region, the maximum efficiency is obtained at dL = 0um and has a larger value than the theoretical scaling law in the superradiant regime, while at the low gain region the maximum efficiency is obtained at dL shorter than 0um and has similar value with the scaling law. We will present the results of the systematic measurement.
Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki; Kikuzawa, Nobuhiro; Sawamura, Masaru; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 483(1-2), p.129 - 133, 2002/05
Times Cited Count：7 Percentile：44.29(Instruments & Instrumentation)An intense ultrashort pulse is generated at the perfect synchronism of optical-resonator length in the JAERI far-infrared free-electron laser. At wavelength of 22.5 
m, second-order optical autocorrelation measurements show that the FEL pulse duration is 250 fs and less than four optical cycles which is consistent with numerical calculation result. The pulse energy ranges up to 100 J. The second-hermonic generation in a 2 mm thickness Te crystal is used to provide the nonlinear autocorrelation signal. In the various desynchronism of optical-resonator length, the way of appearing of the sub-pulse corresponded to the calculation result well, too.
Hajima, Ryoichi; Nishimori, Nobuyuki; Nagai, Ryoji; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 483(1-2), p.113 - 118, 2002/05
Times Cited Count：8 Percentile：47.85(Instruments & Instrumentation)It has been verified experimentally in JAERI-FEL that a high-gain FEL oscillator has the maximum extraction efficiency at the perfect synchronism of optical-cavity length. The simultaneous measurement of FEL efficiency and absolute cavity length for various gain and loss parameters has clearly shown that the steep peak of detuning curve at the perfect synchronism appears only in high-gain and small-loss regime and the FEL extraction efficiency exceeds the scaling law of short-bunch FEL oscillators. A numerical analysis indicates that the lasing at the perfect synchronism is quasi-stationary superradiance with random fluctuation. It is also found that shot-noise in the electron bunch is inevitable to simulate the lasing at the perfect synchronism. Second-order autocorrelation measurements show that FEL pulses shorter than four optical cycles are successively generated for a number of round trips at the perfect synchronism, which is consistent with numerical results.
Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 483(1-2), p.8 - 13, 2002/05
Times Cited Count：21 Percentile：77.32(Instruments & Instrumentation)In order to realize a tunable, highly-efficient, high average power, high peak power and ultra-short pulse free-electron laser(FEL) as a supertool [1]of the 21st for all , the JAERI FEL group and I have developed an industrial FEL driven by a compact, stand-alone and zero-boil-off super-conducting rf linac[2] with an energy-recovery geometry as a conceptual design. Our discussions on the supertool will cover market-requirements for the industrial FELs, some answers from the JAERI compact, stand-alone and zero-boil-off cryostat concept and operational experience over these 8 years, our discovery of the new, highly-efficient, high-power, and ultra-short pulse lasing mode[3], and the energy-recovery geometry.
Morimoto, Iwao; Zheng, X. D.*; Maebara, Sunao; Kishiro, Junichi*; Takayama, Ken*; Horioka, Kazuhiko*; Ishizuka, Hiroshi*; Kawasaki, Sunao*; Shiho, Makoto
Nuclear Instruments and Methods in Physics Research A, 475(1-3), p.509 - 513, 2001/12
Times Cited Count：0 Percentile：0.01(Instruments & Instrumentation)no abstracts in English
Shizuma, Toshiyuki; Hajima, Ryoichi; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 475(1-3), p.569 - 573, 2001/12
Times Cited Count：1 Percentile：12.96(Instruments & Instrumentation)no abstracts in English
Nishimori, Nobuyuki; Hajima, Ryoichi; Nagai, Ryoji; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 475(1-3), p.266 - 269, 2001/12
Times Cited Count：15 Percentile：71.15(Instruments & Instrumentation)no abstracts in English
Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki; Sawamura, Masaru; Kikuzawa, Nobuhiro; Shizuma, Toshiyuki; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 475(1-3), p.519 - 523, 2001/12
Times Cited Count：5 Percentile：38.96(Instruments & Instrumentation)no abstracts in English
Hajima, Ryoichi; Nagai, Ryoji; Nishimori, Nobuyuki; Kikuzawa, Nobuhiro; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 475(1-3), p.43 - 46, 2001/12
Times Cited Count：11 Percentile：61.93(Instruments & Instrumentation)no abstracts in English
Hajima, Ryoichi; Nishimori, Nobuyuki; Nagai, Ryoji; Minehara, Eisuke
Nuclear Instruments and Methods in Physics Research A, 475(1-3), p.270 - 275, 2001/12
Times Cited Count：20 Percentile：77.9(Instruments & Instrumentation)no abstracts in English
