Development of THz Gyrotrons for Plasma Diagnostics

T. Idehara, H. Tsuchiya, H. Mori, O. Watanabe, S. Mitsudo, I. Ogawa and T. Saito
Research Center for Development of Far Infrared Region, University of Fukui,
Bungyo 3-9-1, Fukui-shi 910-8507, Japan
Abstract. Sub-THz gyrotron series named ‘ Gyrotron FU Series’ developed in Research Center for Development of Far Infrared
Region, University of Fukui (FIR FU) has achieved the maximum frequency of 889 GHz with the output power of several
hundred watt and has been successfully applied to plasma diagnostics and material physics. Recently, a THz gyrotron with a
pulse magnet has been designed, constructed and operated in FIR FU. The gyrotron has achieved the first experimental result for
high frequency operations whose radiation frequency exceeds 1 THz. In this paper, the design detail and the operation test results
for sub-terahertz to terahertz range are described. The second harmonic operation is confirmed experimentally at the expected
frequency of 1.01 THz due to TE6,11 cavity mode at the magnetic field intensity of 19.1 T.
Key words: Gyrotron, pulse magnet, Terahertz radiation, Gyrotron FU Series, Second harmonic operation
PACS: 52.70.-m, 84.40.lk
1. Introduction
Medium power, high frequency gyrotrons are being developed in several institutions in the world1),2). High
magnetic field and higher harmonic operations are used for increasing operation frequency. Such gyrotrons have
already covered wide frequency range in millimeter to submillimeter wavelength region and been applied
as submillimeter wave radiation sources for wide fields including plasma diagnostics, electron spin
resonance (ESR) specroscopy, new medical technology, and so on. These gyrotrons are only one high
power stable sub-THz radiation source and will be important and useful in future for development of high
power sub-THz technologies.
Our gyrotrons developed in FIR FU named Gyrotron FU Series belongs to the second type gyrotrons,
that is, medium power high frequency gyrotrons. The series has achieved following items, 1) frequency
step-tuneability in wide range in millimeter to submillimeter wavelength region (from 38 to 889 GHz), 2)
highest frequency (889 GHz) corresponding to the wavelength of 377

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