Microwave heating power distribution in electron cyclotron resonance processing plasmas, experiment and theory

Summary form only given. We are currently investigating the mechanisms of microwave power absorption in an ECR plasma. The microwave electric field is detected with an antenna at the end of a shielded co-ax cable, connected to a bolometer for power measurements. Initial measurements have been 1-D along the axis of the plasma chamber. Later, 3-D profiles will be made of the microwave heating power distribution. The ECR vacuum chamber is 13 cm in diameter. Microwave energy at 2.45 GHz is injected parallel to the magnetic field. The magnetic field is produced by two coils. The microwaves are launched directly from a rectangular waveguide in TE/sub 0.1/ mode (no horn) through a quartz end plate. The power can be varied up to 1 kW, cw. By varying the current through the magnet coils and their positions, the 875 G resonance zone can be located anywhere in the first 20 cm from the window (the source region). Typical electron densities in this region are in the high 10/sup 11/ to low 10/sup 12/ cm/sup -3/ range. Plasma can then flow downstream for an additional 60 cm. Preliminary measurements of the microwave power absorption have been along the axis up to the quartz entry window (z=0 cm). Equal currents in the two field coils provide a flat magnetic field (within 20%) in the source region. Absorption profiles were done for different magnetic held strengths from 1085 G to 800 G. The position of the electron cyclotron resonance varied from z=21 cm to z=7 cm. A comparison of the experimental results with the theoretical microwave absorption will be presented. A ray tracing analysis of the propagating right hand wave will be given, including both collisional and collisionless absorption. Mode conversion effects are studied to explain why most of the power is absorbed at the entry window, especially the L wave power.