| Co-Investigator(Kenkyū-buntansha) |
MITSUDO Seitaro Fukui University, Research Center for Development of Far-Infrared Region, Associate Professor, 遠赤外領域開発研究センター, 助教授 (60261517)
IDEHARA Toshitaka Fukui University, Research Center for Development of Far-Infrared Region, Professor, 遠赤外領域開発研究センター, 教授 (80020197)
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| Research Abstract |
High frequency, medium power gyrotrons (Gyrotrons FU series) achieved the highest frequency of 889 GHz for single mode operation at the second harmonic (N=2) and the frequency step-tunability from 38 to 889 GHz using the fundamental, second, and third harmonic operation. Output powers of several hundred watts at the fundamentals and several ten watts at second harmonics have been achieved.
As a result of the feedback control of the anode potential we succeeded to reduce the fluctuation level of the cw output power (f=301 GHz, P=20 W) from 3.7% to 1.5%. The fluctuation level could be decreased down to 0.6% by reducing fluctuation level of the cathode potential below 3 V. As a result of the control of the anode potential we succeeded to modulate the gyrotron output with a modulation frequency up to 20 kHz.
The conversion system consists of a quasi-optical antenna, sequence of two ellipsoidal focusing mirrors and a spatial filter. It is intended to convert four TEィイD21nィエD2 mode outputs of the Gyrotron FU IVA (TEィイD212ィエD2, 170 GHz; TEィイD213ィエD2, 271 GHz; TEィイD214ィエD2, 372 GHz; TEィイD215ィエD2, 472 GHz) into gaussian-like beams with waist size of wィイD2x"ィエD2=wィイD2y"ィエD2=16.3 mm as well as three TEィイD20nィエD2 modes (TEィイD202ィエD2, 223 GHz; TEィイD203ィエD2, 323 GHz; TEィイD204ィエD2, 423 GHz) into bigaussian-like beams with waist sizes of wィイD2x"ィエD2 =23.5 mm and wィイD2yo"ィエD2=16.4 mm. Compared with the earlier system capable of converting only one operating mode the novel one is more versatile and is compatible with frequency tunable gyrotrons such as the Gyrotron FU IVA. In spite of the truncation of the sidelobes of the beam by the spatial filter most of the image source power is transferred to the final waist. As a result, intense high-quality beams in the submillimeter wavelength range can be produced.
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