2.45 GHz microwave plasmas at magnetic fields below ECR

Abstract

Microwave plasmas (f= omega /2 pi =2.45 GHz, 200-1000 W) were excited and maintained at low static magnetic fields, B=300-450 G and gas pressures of 0.2-10 mTorr. Two modes were found and studied: low plasma density mode with Ne<Ncr=7.4*1010 cm-3, and high (overdense, Ne>Ncr) plasma mode. The resonance transition from low- and high-mode plasma was observed when the magnetic field near the microwave introduction (vacuum) window was Bw=435-440 G. It was attributed to the second gyratron harmonic resonance omega =2 omega BS. Mechanisms of microwave power absorption at B<Bce=875 G are discussed.