Radiofrequency initiation and radiofrequency sustainment of laser initiated seeded high pressure plasmas

Summary form only given, as follows. We have carried out experiments on radiofrequency initiated high pressure nitrogen and argon plasmas at pressures from 1-50 Torr. We have also carried out laser-initiated organic seed gases (2-6 milliTorr) and radiofrequency sustainment at pressures of 50-150 Torr. At 1 Torr with a 50/50 mix of nitrogen and argon a large volume plasma with a density of 5/spl times/10/sup 12//cm/sup 3/ and at sustained power densities of. 0.05 W/cm/sup 3/ is produced by means of a half-turn double helix which is superior to either gas alone at the same pressure. The measured antenna impedance is in agreement with our antenna coupling code. Optical spectra are measured to examine the mixed gas synergy in producing efficient plasmas. At higher pressures of 50-150 Torr, a 5-turn helix operating at 2.8 kW with a laser initiated organic seed gas (2-6 milliTorr) is used to produce 300-500 cm/sup 3/ plasmas at densities of 4/spl times/10/sup 12//cm/sup 3/ as measured by a 105 GHz interferometer. Recombination and ionization effects for the laser initiated gas mix are analyzed which allows a doubling of the pressure for sustainment compared to radiofrequency heating alone.