Mechanisms of Plasma Production Using Folded Waveguide Antenna

Wave propagation and absorption of the wave power in an initial phase of plasma production by a folded waveguide antenna installed in the Large Helical Device were investigated by a ray tracing method. The calculated ray trajectory showed that a surface electrostatic wave propagates in a low-density and low-temperature plasma in the initial plasma production phase. Then a shear Alfven wave can propagate at a relatively higher density. The power absorption occurs through a collisional damping process in a wide range of density and at electron temperatures lower than 100 eV. Thus, propagation of a surface electrostatic wave and collisional damping seem to play important roles in the plasma production.