Speaker
Dr
Ryutaro Minami
(University of Tsukuba)
Description
The electron cyclotron heating (ECH) is essential for tandem mirror devices to achieve potential confinement and high electron temperature. A gyrotron is a powerful and an essential tool for ECH. Recent progress of the gyrotron has widened the use of gyrotrons for fusion research. High power and long pulse operations of the gyrotron and the efficient transmission of its output are quite important to achieve better plasma performances.
Recent ECH physics experiments require 28 GHz gyrotrons for plasma experimental devices. For the ECH systems of GAMMA 10/PDX and National Spherical Torus Experiment (NSTX) at Princeton Plasma Physics Laboratory (PPPL), a gyrotron with a 1.5–2 MW output for several seconds is required. For the Q-shuUniversity Experimental with Steady-State Spherical Tokamak (QUEST) ECH system at Kyushu University, a 0.4 MW CW gyrotron is needed. Therefore, the development of the higher power and CW operational gyrotron has been started as the collaborative research.
A 28 GHz 1 MW gyrotron developed for GAMMA 10/PDX achieved an output power of 1.38 MW in 2015 experiment after the power supply was improved. This gyrotron was applied to the 2013 QUEST plasma experiment campaign, and an over-dense plasma with a density at more than 1×1018 m-3 was produced, which is higher than cut-off density of 8.2 GHz, and EC-driven plasma current of 66 kA was non-inductively attained with the 28 GHz injection. These successful results lead to a 28 GHz gyrotron application program of NSTX-U.
The design study of a new 28/35 GHz dual-frequency gyrotron (2 MW 3 s and 0.4 MW CW) for QUEST, NSTX-U, Heliotron J and GAMMA 10/PDX has been completed and the fabrication of the gyrotron is in progress. The first test is scheduled from June 2016. This gyrotron has a sapphire double-disk window to enable CW operation. The frequency characteristic of a double-disk window is calculated by simulation of the three-layer structure of dielectrics and can be adjusted by varying the thickness of the center dielectric (fluorocarbon coolant). A fabricated double-disk window may have the reflection that is caused by manufacturing error and the permittivity error (dependent on frequency) of the sapphire disk and the fluorocarbon coolant. Before installing a double-disk window in the dual-frequency gyrotron, we measured the dependence of reflective power on the coolant thickness including the confirmation of the small reflective power less than 2 % by both cold test using a 1 W Gunn diode and the hot test using the gyrotron output power of 600 kW. The final fine adjustment of the coolant thickness will be performed after installing the double-disk window in the new gyrotron.
This work was partially supported by the NIFS Collaborative program (NIFS11KUGM050 and COD27077) and Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (26249141 and 15H05770A).
Primary author
Dr
Tsuyoshi Kariya
(Plasma Research Center, University of Tsukuba)
Co-authors
Prof.
Hiroshi Idei
(Kyusyu University)
Prof.
Kazuaki Hanada
(Kyusyu University)
Prof.
Kimiya Komurasaki
(University of Tokyo)
Mr
Kohei Tsumura
(University of Tsukuba)
Prof.
Masayuki Ono
(Princeton University Plasma Physics Laboratory)
Dr
Ryutaro Minami
(University of Tsukuba)
Dr
Tomoharu Numakura
(Plasma Research Center,University of Tsukuba)
Prof.
Tsuyoshi Imai
(University of Tsukuba)
Mr
Yoichi Endo
(University of Tsukuba)
Prof.
Yousuke Nakashima
(Plasma Research Center, University of Tsukuba)
Mr
Yuto Ebashi
(University of Tsukuba)
Peer reviewing
Paper
Paper files:
