Electron cyclotron heating scenario and experimental results in LHD

A large helical device (LHD) experiment began at the end of March 1998. Fun damental 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 m aximum 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 elon gated poloidal sections. The maximum stored energy using all six gyrotrons is 70 kJ at the averaged density of (n) over bar (e) = 4 x 10(18) m(-3). Th e maximum central electron temperature T-e0 = 3.5 keV is achieved at (n) ov er bar (e) = 3 x 10(18) m(-3). The magnetic field structure in heliotron ty pe devices like LHD, notably near the coil, is complicated. For this obliqu e injection, a wave is launched from the antenna, and then crosses the plas ma in the complex field structure near the coil. The polarization ellipse o f 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 co mponent along the propagation direction can be neglected. Even for perpendi cular injection with our antenna systems, the field component along the pro pagation direction is not so small. Another treatment of the wave-propagati on is introduced. Some calculations for the heating scenario with this trea tment are shown. (C) 2001 Elsevier Science B.V. All rights reserved.