Gas puffing for creation of high density, quiescent and uniform plasmas in the Large Plasma Device at UCLA

A large (38.5 cm diameter) Lanthanum Hexaboride source has replaced a Barium Oxide cathode in the LAPD device at UCLA. Traditional gas feed using mass flow controllers produced plasmas that had radial and axial density temperature variations. The gas feed was replaced with two piezoelectric valves creating gas puffs (H, He, Ar..) at the radial edge of the cathode and located 10 cm from the moly anode. Gas puffing has produced plasmas with flat density profiles and little axial density variation over the 19 m long plasma column. Densities as high as 2X10¹³ cm^-3 have been achieved. Electron density was measured with Langmuir probes, spectroscopically using ratios of neutral line emission , a 100 GHz microwave interferometer and Thomson scattering. The electron temperature ( .5 < Te < 12 eV) was measured using probes, Thomson scattering and line ratios. The ion temperature ( .5 < Ti < 9 eV) in helium was obtained spectroscopically using the 640.56 nm ion line with a 1.3 m monochromator, with a 2400 l/mm grating and thermoelectrically cooled phototube. The higher densities were confirmed from the dispersion of shear Alfvén waves launched with a RMF antenna and received by a pair of B-dot probes. Measurements of these quantities as a function of space and time and input discharge power will be presented.