Design of the collective Thomson scattering diagnostics for Large Helical Device using a quasi-optical frequency tunable gyrotron as a radiation source

Summary form only given. Development of the Collective Thomson Scattering (CTS) diagnostic system for LHD is presented. High frequency, tunable (87-97 GHz), medium power ( /spl sim/100 kW) quasi-optical gyrotron will be used as a radiation source. We will show the detailed description of the system as well as initial calculations of the scattered microwave power from the LHD plasma. Using the quasi-optical gyrotron as a radiation source was inspired by the fact that this particular device has the ability of tuning of the operational frequency. Which is made it very attractive for using under the various scenarios for LHD plasmas. It is planned that the system utilize ´forward scattering schema´ of the experimental set-up. The calculation of the expected scattered power shows that (in the chosen frequency range and chosen values of the scattered angle) the dominant part of it came from the so-called ´ion-feature´. This is a situation when the incident radiation is mainly scattered by the ´shielded ions´ (by electron cloud). Other advantage for using gyrotron (not 10.6 /spl mu/m CO/sub 2/ laser) as a power source is as follows. Since for the typical scattering experiments under consideration scattered wave number is k /spl sim/ k/sub i/ sin(/spl theta//sub B//2). Thus for coherent scattering to occur, it is possible to significantly increase the scattered angle /spl theta//sub B/ as a wave length of the incident radiation increases from the short wavelength (CO/sub 2/ laser) through far-infra-red (FIR) wavelength to the millimeter wavelength of gyrotrons.