We report experimental results on a megawatt power level, 140-GHz coaxial gyrotron oscillator. The gyrotron has an inverted magnetron injection gun (IMIG) designed for operation at up to 95 kV and 88 A. The IMIG has an inner grounded anode which extends from the center of the gun down through the entire length of the tube including the cavity and collector. The IMIG was tested at up to 105 kV and 93 A in 3 /spl mu/s pulses, achieving an electron beam power of 10 MW. The output power from the coaxial gyrotron cavity was transported to an internal mode converter and a single mirror that coupled the power out transversely from the tube axis. A maximum output power of up to 1 MW was obtained in the TE/sub 27,11/ mode at 142 GHz at an efficiency of 16%, about one half of the design efficiency. The reduced efficiency was attributed to nonuniformity of the cathode emission and the sensitivity to the relative alignment of the electron gun, coaxial insert, and cavity. The cathode emission over the azimuthal angle was measured for two cathodes and was shown to be nonuniform due to both temperature and emitter work function nonuniformity. The gyrotron was also tested in two alternate configurations: 1) with the internal mode converter removed (axial output), and 2) with both the internal converter and the coaxial insert removed (empty cavity). In operation in the empty cavity configuration, which is equivalent to a conventional gyrotron oscillator, output power of up to 0.9 MW was observed.

Experimental investigation of a 140-GHz coaxial gyrotron oscillator

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.

Long Pulse Operation of the THz Gyrotron with a Pulse Magnet

Submillimeter wave ESR spectrometer using Gyrotron FU series as electromagnetic wave radiation sources and the pulse magnet for high field up to 40 T has been developed. The ESR spectrometer has been successfully applied to several ESR measurements. ESR measurements were performed under the pulsed magnetic fields up to 40 T at the temperature of 4.2 K in CsFeCl 3 single crystal. The frequency-field diagram of ESR absorptions was obtained.

/pdf/high-field-esr-measurements-using-gyrotron-fu-series-as-bbebmqpwph.pdf

High Field ESR Measurements Using Gyrotron FU Series as Radiation Sources

Gyrotron FU CW VII, one of the FU CW Series Gyrotrons, has been designed, constructed and completed operational tests successfully in the Research Center for Development of Far Infrared Region, University of Fukui (FIR FU). The gyrotron operates at around 200 GHz for the fundamental cyclotron resonances and at around 400 GHz for the second harmonics. These radiation frequencies will be applied to 300 MHz and 600 MHz DNP enhanced NMR spectroscopy.

pdf/gyrotron-fu-cw-vii-for-300-mhz-and-600-mhz-dnp-nmr-2i2nra2hf0.pdf

Gyrotron FU CW VII for 300 MHz and 600 MHz DNP-NMR Spectroscopy

Gyrotron FU II has been successfully applied as a submillimeter wave radiation source to plasma scattering measurements on the Compact Helical System (CHS) in National Institute for Fusion Science (NIFS) in Japan. The gyrotron operates in a long pulse mode (the pulse width is about 600 ms) at a frequency of about 350 GHz (the corresponding wavelength is 0.85 mm). The output power is about 110 W. The output power is transmitted along a circular waveguide system and converted to a Gaussian-like beam by a quasi-optical antenna. After that, the beam is directed onto the CHS plasma and the scattered signal is detected by a homodyne detection system. The frequency and the wave number of the scattered signal are analyzed. The results suggest that a broad band low frequency (several tens to several hundreds kHz) density fluctuation is excited in the CHS plasma only during neutral beam injection (NBI) or ion cyclotron resonance (ICR) heating.

/pdf/application-of-the-gyrotron-fu-ii-submillimeter-wave-4a1tegfnne.pdf

Application of the gyrotron FU II submillimeter wave radiation source to plasma scattering measurements

Stabilization and modulation of the output power of submillimeter wave gyrotron

The gyrotrons developed at Fukui University ("Gyrotron FU series") are high frequency, medium power devices, covering a broad frequency band in the millimeter and submillimeter wavelength region. The gyrotrons from the FU series were successfully used in plasma scattering experiments, electron spin resonance (ESR) spectroscopy and in in-depth studies of mode competition and mode cooperation. In the paper, we illustrate some of the achievements of the Gyrotron FU series.

Present status of submillimeter wave gyrotrons (FU series) development and their applications

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Stabilization and modulation of the output power of submillimeter wave gyrotron

Present status of submillimeter wave gyrotrons (FU series) development and their applications