RF heating by cylindrical plasma waveguide modes

The authors have observed a global wave guide mode produced by injecting microwave power into a linear mirror machine - LISA. The stainless steel vacuum chamber has an inner diameter of 17cm and length 255cm. The magnetic field is operated around 1 kG/sub z/ which confines the helium plasma at 10/sup -4/ torr produced by a RF source of 2.45GH/sub z/ of 1 KW power. The microwave horn is mounted on the side of LISA. Wave propagation in a cylindrical guide with magnetized plasma has been investigated by many authors, but mode conversion and absorption have not been treated extensively. In a previous study it was shown experimentally that, in the presence of magnetic field, both TE and TM modes exist in the waveguide. For a vacuum wave guide, the dominant mode is TE/sub 10/ for rectangular or TE/sub 11/ for cylindrical geometry. When there is plasma, the modes are more complicated. In this work, taking the cold plasma dielectric tensor and using the electrostatic approximation, the authors solve the scalar potential phi in terms of the Bessel functions. The frequencies can be determined by the boundary condition at the wall. The analytical results are compared with the measured profiles. The authors show that the radio-frequency heating produces a dip on the plasma potential profile at the electron cyclotron resonance zone due to the preferential heating of the perpendicular temperature