NIFS-996

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Author(s):

T. Imai, T. Kariya, R Minami, S. Kubo, T. Shimozuma, Y. Yoshimura, H. Takahashi, T. Mutoh, K. Sakamoto, Y. Mitsunaka4), Y. Endo, S. Ito, M. Ota and GAMMA 10 Group

Title:

Development of Over-1 MW Gyrotrons for the LHD and the GAMMA 10 ECH Systems

Date of publication:

Nov. 2010

Key words:

22 IAEA Fusion Energy Conference, FTP/P6-12

Abstract:

For the ECH upgrade program of LHD and GAMMA10, over-1 MW power gyrotrons have been developed in the joint program of NIFS and University of Tsukuba. The gyrotrons for LHD and GAMMA 10 have TE18,6 cavity and a diamond window at 77 GHz, and with TE8,3 cavity at 28 GHz, respectively. The maximum outputs obtained are 1.9 MW for 0.1 s on the 77 GHz LHD tube and ~ 1 MW on the 28 GHz one, which are the new records in these frequency ranges. The results of 1.8 MW for 1 s, 1.6 MW for 1.8s, 1 MW for 5 s, 300 kW for 40 min and 200 kW for 75 min were achieved at 77 GHz. In the long pulse operation, it is found that the stray RF is the major cause limiting the pulse length. Design improvements of the diffraction loss, the cavity and pitch factor ( = v bot / v_//) dispersion of the MIG have made the 77 GHz tube performance better, which have enabled to demonstrate 1.9 MW output and long pulse operation for more than 1 hour with 200 kW. The three 77 GHz gyrotrons have already been installed in the LHD ECH system and more than 3 MW has been injected into LHD plasma. In the 28 GHz long pulse operation, 400 kW for 1 sec has been obtained and it is found the higher and longer pulse operation would be possible with the operation optimization and conditioning.

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