K. Takahashi, K. Sakamoto, A. Kasugai, M. Tsuneoka, Yu. Ikeda, T. Imai, T. Kariya1, K. Hayashi2, Y. Mitsunaka2, Y. Hirata2, and Y. Okazaki1
RF Heating Laboratory, Department of Fusion Engineering Research Japan Atomic Energy Research Institute, Ibaraki, 311-01 Japan
1Electron Tube Division, Toshiba Co., Tochigi, 324 Japan
2R&D Center, Toshiba Co., Kanagawa, 210 Japan
A 170GHz, CW gyrotron is required for a large size fusion device like ITER. The development of the 170GHz gyrotron has been started since 1995 as R&D of ITER/EDA and mainly focused on higher order mode oscillation at cavity and output vacuum window. The oscillation mode of 170GHz gyrotron is high order volume mode(TE31,8) to reduce the heat load at the cavity wall. We demonstrated 1.1MW output with TE31,8 mode by using short pulse gyrotron. On the basis of the result above, a long pulse gyrotron which has a helix type mode converter inside has been fabricated and testing with collector potential depression(CPD) operation. We, so far, demonstrated high efficient operation of 40% and 0.18MW, 10sec and 0.5MW, 0.7sec operation. The most serious problem is heat deposition in the output window, through which the output wave beam passes. Sapphire and silicon nitride(Si3N4) have been used as gyrotron window. However, there is the difficulty of 1MW, CW operation with them. Lately, a large CVD diamond disk(f96 x2.23t) has been manufactured by industry. It is large enough for a gyrotron window and gives rise to the feasibility of 1MW, CW operation with Gaussian output. We have carried out the high power transmission experiment of the diamond window disk and confirmed that the disk has the outstanding physical properties: the thermal conductivity is extremely high (1800W/K) and tand at 170GHz is relatively low(<1.5 x10-4). We are going to fabricate the diamond window for a 170GHz, high power gyrotron.
We also have a plan of 170GHz, high power and long pulse transmission experiment for 40m long transmission line by using the 170GHz high power gyrotron. The transmission line consists of waveguides, miterbends, polarizers, waveguide switches and directional couplers. The aim of the experiment are to confirm the reliability of these components and to measure mode purity of transmitted millimeter wave and the transmission loss on high power and long pulse transmission. In this paper, we will present the recent activity on the development of 170GHz high power gyrotrons and transmission lines.