Collective Thomson scattering of 77 GHz high power ECRH beam in LHD

The collective Thomson scattering (CTS) is one of the most promising methods for evaluating the ion velocity distribution function. LHD is equipped with eight gyrotrons and with well defined and steerable Gaussian beam injection antenna systems for the plasma production and heating. Such high power Gaussian beam is also attractive for the probing and receiving beams for CTS. One of the newly installed 77 GHz gyrotrons, in particular, can generate more than 1MW over 5 s. This gyrotron is connected to one of the Gaussian mirror antenna set. This antenna set includes one another Gaussian beam mirror suitable for receiving the scattered power from definite scattering volume. A receiver system is installed on the upstream of the transmission line. A heterodyne receiver system consists of a fundamental mixer with fixed local oscillator at 78 GHz. The receiver system of a harmonic mixer with dynamic local frequency tracking capability to the gyrotron frequency will also be installed in the system to improve the IF (intermediate frequency) stability. A notch filter with the 3 dB bandwidth of 300 MHz is used for the front end. First trial of the detection of scattering signal is successfully performed. The calibration and trial of deduction of the bulk ion temperature is reported. CTS using the higher frequency for the higher plasma density region is also under study. Advantages of using higher frequency are the lower expected ECE background and the higher spatial resolution. The gyrotron of the frequency range of 400 GHz is under development for this purpose in university of Fukui. Optimum injection and receiving systems using this gyrotron for CTS in LHD are under design.