Measuring ion velocity distribution functions in a compact, expanding helicon plasma

Laser Induced Fluorescence (LIF) measurements of ion velocity distribution functions (ivdf) in a compact, expanding helicon plasma were limited by optical access and laser power. LIF measurements in the Compact HElicon Waves and Instabilities Experiment (CHEWIE) determined the ivdf of a compact helicon argon plasma as a function of fill pressure, magnetic field, and partial pressure of argon. The LIF scheme used the ring dye laser to 611.662 nm (vacuum wavelength) to pump the Ar II 3d2G9/2 metastable state to the 4p2F7/2 state. The ion decayed to the 4s 2D5/2 level and the fluorescent emission at 460.96 nm was recorded as a function of laser frequency. RF power up to 450 Watts created steady state plasma in a 60 cm long, 7.5 cm diameter Pyrex tube source chamber. A 30 cm long, 15 cm diameter stainless steel expansion chamber was connected to one end of the source chamber. The magnetic field strength ranged from 0--550 Gauss. Argon ivdfs indicate the presence of an accelerated ion population for fill pressure less than 1.5 mTorr