Long Pulse Operation of the THz Gyrotron with a Pulse Magnet
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Long Pulse Operation of the THz Gyrotron with a Pulse Magnet T. Idehara & T. Saito & H. Mori & H. Tsuchiya & La Agusu & S. Mitsudo
Received: 29 October 2007 / Accepted: 13 November 2007 / Published online: 29 November 2007 # Springer Science + Business Media, LLC 2007
Abstract Long pulse operation up to 1 msec of a high frequency gyrotron with a pulse magnet has been successfully carried out in a frequency range including 1 THz. In the experiments, the timing of an electron beam pulse injection is adjusted at the top of the magnetic field pulse, where the variation of field intensity is negligible. The operation cavity modes seem to be TE1, 12 and TE4,12 at the second harmonics. The corresponding frequencies are 903 GHz and 1,013 GHz, respectively. Additionally several features of radiation measurement results of the gyrotron are described and brief considerations are presented. Keywords Gyrotron . Pulse magnet . Terahertz radiation . Gyrotron FU Series . Second harmonic operation
1 Introduction In the Research Center for Development of Far Infrared Region, at the University of Fukui (FIR FU) , we have developed high frequency gyrotrons covering a frequency range of subTHz during the last three decades by using high field superconducting magnets and high harmonic operations. [1–5] The long-term world record of high frequency operation of a gyrotron at 889 GHz was achieved in 1994 by our Gyrotron FU IVA. Similar studies are being advanced in MIT [6], University of Sydney [7, 8] and IAP-RAS [9]. Recently, we have succeeded to achieve the first experiment on a frequency breakthrough of 1 THz by a second harmonic gyrotron with a pulse magnet [10]. This is the first challenge to gyrotron operation at 1 THz. Development of high power THz radiation sources is quite important for development of high power THz technologies, for example, plasma diagnostics [11, 12], enhancement of NMR sensitivity using dynamic nuclear polarization (DNP) [13, 16], high frequency ESR T. Idehara : T. Saito : H. Mori (*) : H. Tsuchiya : L. Agusu : S. Mitsudo Research Center for Development of Far Infrared Region, University of Fukui (FIR FU), Bunkyo 3-9-1, Fukui-shi 910-8507, Japan e-mail: [email protected]
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Int J Infrared Milli Waves (2008) 29:131–141
spectroscopy [17] in nonlinear regime, communication in the frequency range of THz and so on. Among many radiation sources, the gyrotron is one of the most appropriate ones for such a objectives, because of high efficiency even in high frequency and high harmonics [4], stability of frequency and amplitude [18, 19] and possibility of long pulse or CW operation in long time. For application to such new high-power technologies in THz region mentioned above, we have already begun the development of CW gyrotrons, named “Gyrotron FU CW Series”. The development of the first gyrotron, Gyrotron FU CW I was completed and CW output of 1.75 kW was obtained at the frequency of 300 GHz. The cavity mode is TE22,8 at the fundamental operation. [20, 21] The second gyrotron, Gyrotron FU CW II [14–16] w
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