Laser-Induced Fluorescence and Probe Measurements on an Argon Helicon Plasma with Magnetic Nozzle

Summary form only given. Measurements are performed on an argon helicon plasma with magnetic nozzle field. The experimental apparatus consists of a 10-cm-diameter cylindrical Pyrex helicon source region connected to a 55-cm-diameter aluminum expansion chamber. The operating neutral pressure is up to 1 mTorr in the source region and 0.1 mTorr in the expansion region due to chamber cross-sections, a nozzle aperture, and differential pumping. The plasma is formed by an efficient half-turn double-helix antenna operating at 13.56 MHz with power scaling up to 3 kW of input power. A static axial magnetic field is generated, with source region fields up to 1 kG and magnetic nozzle peak fields of up to 1.5 kG. Laser-induced fluorescence (LIF) using a tunable diode laser centered around a vacuum wavelength of 668.614 nm is used to measure axial ion velocity distributions and to detect any acceleration resulting from plasma potential variations near the magnetic field gradient and in the magnetic field expansion region. An emissive probe consisting of a thoriated tungsten filament is used to determine the plasma potential gradient along the experimental axis in the magnetic nozzle region. Langmuir probe and 105 GHz microwave interferometry are used to determine the plasma density, which is measured up to 1 x 10¹³ cm^-3 in the source region. The wave magnetic field is measured using a B-dot probe to determine the helicon source wave structure. Mach probe measurements of ion drift are compared with LIF results. The character of the ion distribution and plasma potential variations in the expansion region are measured for a range of magnetic field gradients and plasma densities.