Collective Thomson Scattering of 77 GHz High-Power ECRH Beam in LHD

The measurement of the ion velocity distribution is especially important in reactor relevant plasmas. The collective Thomson scattering (CTS) is one of the most promising methods for evaluating the ion velocity distribution function. In spite of its potential, this method had long been suffered from the absence of adequate power sources. Recent development in the higher power, and higher frequency range of the gyrotron and the transmission technique enabled to realize the measurement of not only the bulk but also high energy component of the ion velocity distribution function. One of the newly installed 77 GHz gyrotrons in LHD that can generate more than 1 MW over 5 s and is connected to one of the Gaussian mirror beam launching antenna sets is used as a probing beam for CTS. A heterodyne receiver system of a fundamental mixer with 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 are developed (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)