Y. Tatematsu, S. Kubo, M. Nishiura, K. Tanaka, N. Tamura, T. Shimozuma, T. Saito, T. Notake, Y. Yoshimura, H. Igami, H. Takahashi, T. Mutoh, K. Kawahata, K.Y.Watanabe, Y. Nagayama, Y. Takeiri, K. Ida, H. Yamada, O. Kaneko, A. Komori and LHD experimental Group
Development of Collective Thomson Scattering System using the Gyrotrons of sub-Tera Hz Region
Date of publication:
22 IAEA Fusion Energy Conference, FTP/P6-31
Collective Thomson scattering (CTS) system is being developed for fusion plasma and CTS measurement on the large helical device (LHD) plasma is discussed. Sub-terahertz frequencies are suitable to the probe beam for CTS on LHD. According to the feasibility study, frequency around 0.4 THz is best for the CTS measurement on LHD high density plasma, and power of 100 kW is required. Thus, only gyrotrons in the subterahertz range can meet these parameters. At the first stage of development, second harmonic gyrotrons have been developed. A sealed-off type of gyrotrons has been manufactured to improve a demountable one. Measured output power has increased to about 60 kW. In parallel with the development of gyrotrons, an actual CTS system using a 77 GHz gyrotron originally installed for heating is being developed as a benchmark of LHD CTS. A heterodyne receiver system of a fundamental mixer with a fixed frequency local oscillator was installed on the upstream of the transmission line. The probe beam is 100% power modulated at 50 Hz to separate the scattering component from background ECE. Signals that can be attributed to the CTS were obtained and the analysis method of these data is developed.