Electron cyclotron heating scenario and experimental results in LHD

Abstract

A large helical device (LHD) experiment began at the end of March 1998. Fundamental and second harmonic electron cyclotron heating (ECH) are used as a plasma production and heating method with six gyrotrons whose frequencies are 82.6/84 and 168 GHz, respectively. Up to 0.9 MW power has been injected in LHD with long distance corrugated waveguide transmission systems. The maximum pulse width is achieved to 3.0 s/240 kW for the LHD experiments. Six antenna systems have been prepared at the horizontally and vertically elongated poloidal sections. The maximum stored energy using all six gyrotrons is 70 kJ at the averaged density of n̄ e=4×10 18 m −3. The maximum central electron temperature T e0=3.5 keV is achieved at n̄ e=3×10 18 m −3. The magnetic field structure in heliotron type devices like LHD, notably near the coil, is complicated. For this oblique injection, a wave is launched from the antenna, and then crosses the plasma in the complex field structure near the coil. The polarization ellipse of the wave is changed along the ray-path. The wave propagation in heliotron type devices has been analyzed in an ideal case that the magnetic field component along the propagation direction can be neglected. Even for perpendicular injection with our antenna systems, the field component along the propagation direction is not so small. Another treatment of the wave-propagation is introduced. Some calculations for the heating scenario with this treatment are shown.