Measurements of electron density and energy content in the VX-30 helicon discharge

We have observed plasma conditions at several locations in the VASIMR experiment, VX-30, a 20 kW helicon plasma expanding into a nozzle. A three frequency interferometer (70, 90, 110 GHz) provided electron densities at these locations. We made absolutely calibrated spectroscopic measurements of He I and He II lines in the UV, visible, and near IR. A comparison with a collisional radiative model suggested that the actual electron density distribution function was not a Maxwellian, but rather was significantly underpopulated at higher electron energies. We will present preliminary results comparing our measurements with a spectral model using a non Maxwellian distribution.