INDUCED MAGNETIC-FIELD EFFECTS IN INDUCTIVELY-COUPLED PLASMAS

In inductive plasma sources, the rapid spatial decay of the electric f ield arising from the skin effect produces a large radio frequency (RF ) magnetic field via Faraday's law. It was previously shown that this magnetic field leads to a reduction of the electron density in the ski n region, as well as a reduction in the collisionless heating rate. Th e electron deficit leads to the formation of an electrostatic potentia l which pulls electrons into restore quasineutrality. Here the electro n density calculation is extended to include both the induced and elec trostatic fields. If the wave frequency is not too low, the ions respo nd only to the averaged fields, and hence the electrostatic field is o scillatory, predominantly at the second harmonic of the applied field. The potential required to establish a constant electron density is ca lculated and compared with numerical orbit-code calculations. For time s short compared to ion transit times, the quasineutral density is jus t the initial ion density. For timescales long enough that the ions ca n relax, the density profile can be found from the solution of fluid e quations with an effective (ponderomotive-like) potential added. Altho ugh the time-varying electrostatic potential is an extra source of hea ting, the net effect of the induced magnetic and electrostatic fields through trapping, early turning, and direct heating is a significant r eduction in collisionless heating for parameters of interest. (C) 1996 American Institute of Physics.