Ray tracing calculation of shear Alfven wave on LHD

Y.Torii, R.Kumazawa1), T.Watari1), T.Mutoh1), T.Seki1), K.Saito1), N.Takeuchi, T.Watanabe1), F.Shimpo1), G.Nomura1), A.Kato1), Y.Zhao2), LHD Experimental Group1)

Nagoya University, Dept. of Energy Engineering and Science, Nagoya, 464-8403, Japan
1)National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
2) Institute of Plasma Physics, Chinese Academy of Science, PO Box 1126, Hefei

Using a folded waveguide antenna in the Ion Cyclotron Range of Frequency, a plasma production and heating experiment was carried out on the Large Helical Device in National Institute for Fusion Science, which was the first experiment in the torus system. In the 4th experimental campaign in 2000-2001, plasma of the average electron density up to 3×1018m-3 was produced with this antenna. In this campaign, pure hydrogen plasma were heated mainly using the frequency 25MHz in the field 2.6-2.8T. The relation between magnetic field strength and achieved density was explained using a propagation of a shear Alfven wave.
In order to understand mechanisms of plasma production, The ray tracing calculation of shear Alfven wave was carried out. In order to estimate the energy absorption, hot plasma dispersion relation was used.
Rays traveled along the magnetic line of force, which is a well known behavior of shear Alfven wave. Changing temperature and density, differences in trajectories and energy absorption were investigated. In collisionless low temperature plasma (<100eV), electron Landau damping did not occur. However, including electron collisional damping with ion or neutral, the shear Alfven wave was absorbed by electrons. Through ray tracing calculation, plasma production mechanism was clarified; In an early low density phase, electron-H0 collision effect was dominant. As density was risen, absorption through electron-H+ collision became stronger. And, in high temperature, plasma was heated through collisionless Landau damping.