Speaker
Dr
Ryutaro Minami
(Plasma Research Center, University of Tsukuba)
Description
High-power millimeter-wave gyrotrons for fusion plasma applications are designed for continuous-wave or long-pulse operation. It becomes an indispensable tool for controlled fusion ECH and ECCD experiments. Recently, many studies[1,2,3] have devoted to high-power and long-pulse gyrotrons and multi-frequency gyrotrons are required for experimental flexibility and research collaborations. In the development of these gyrotrons, two of the important issues are the increase of the radiated power and to provide a stable operation in the single desired mode. To handle thermal losses, the resonators of these gyrotrons have a diameter much larger than a wavelength. It means that the gyrotrons operate in very high-order modes. The interaction of the electron beam with many modes and the mode competition during gyrotron startup are important. For the gyrotron development in the future plan, the computing code for the time-dependent and multimodes of the wave-guide-cavity gyrotron oscillators has been developed.
Several studies[1] have shown that the excitation of one or two parasitic modes is practically unavoidable. The mode competition during gyrotron startup is the important problem because the cyclotron resonance condition can be fulfilled for a large number of modes during the voltage rise from zero to its nominal value. The optimum design of the resonant cavity for gyrotron oscillators requires the analysis of the startup scenario. The present code calculates the cavity RF profile function by solving the set of the relativistic single-particle equations of motion and generalized telegrapher’s equations simultaneously to reach a self-consistent solution in the dynamic system that takes into account the effects of the electron beam in the field produced by a superposition of modes. The pitch factor and velocity spreads of the electron beams are calculated by the use of the electron trajectory code “EGUN”[4].
The computing code includes a time-dependent description of the electromagnetic field and a self-consistent analysis of the electron beams. The basic procedure is to solve the coupled equations in the cavity geometry by applying radiation boundary conditions. These coupled equations are integrated using the iterative predictor-corrector scheme and the Runge-Kutta integration scheme. The parallel algorithms are used for the required accuracy in calculation and the reduction of the computer time. We present the calculation results of the gyrotron for an application to the ECH system in GAMMA 10/PDX.
This work was partially supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (26249141).
[1] G. S. Nusinovich, Introduction to the Physics of Gyrotrons (Johns Hopkins University Press 2004).
[2] T.Imai et al., J. Plasma Fusion Res. 85 (2009) 378.
[3] T. Kariya et al., J. Infrared, Millimeter and Terahertz waves 32 (2011) 295.
[4] W. B. Herrmannsfeldt, SLAC-331-UC28, (1988).
Primary author
Dr
Tomoharu Numakura
(Plasma Research Center, University of Tsukuba)
Co-authors
Dr
Ryutaro Minami
(Plasma Research Center, University of Tsukuba)
Mr
Satoshi Kajino
(Plasma Research Center, University of Tsukuba)
Prof.
Tsuyoshi Imai
(Plasma Research Center, University of Tsukuba)
Dr
Tsuyoshi Kariya
(Plasma Research Center, University of Tsukuba)
Mr
Yuto Ebashi
(Plasma Research Center, University of Tsukuba)
Mr
kohei Tsumura
(Plasma Research Center, University of Tsukuba)
