Radial profiles of neutral argon in a helicon source

Summary form only given. Ion-neutral and electron-neutral collisions can be important mechanisms for Alfven wave damping, ion cyclotron wave damping, and flow thermalization in helicon sources. The phenomenon of neutral pumping, leading to reduced neutral pressures on axis, has been suggested to play an important role in the physics of cylindrically symmetric helicon sources. However, the spatial distribution, temperature, and flow of neutral atoms in helicon sources are poorly understood quantities. We have obtained laser induced fluorescence (LIF) measurements of argon neutrals, helium neutrals, and argon ions as a function of radial position with a low power, tunable diode laser in the Hot hELIcon eXperiment (HELIX) at West Virginia University. Using radial profile measurements of electron density and electron temperature, the neutral (or ion) density profile can be extracted from spatially resolved LIF measurements of the interrogated species. LIF neutral density profiles are compared to neutral density profile measurements obtained through spatially resolved, passive emission spectroscopy measurements.