Diagnostics and Computational Modeling of Argon, Helium, and Deuterium Helicon Plasmas in Nonuniform Magnetic Fields

Summary form only given. Radiofrequency helicon waves are excited in argon, helium, and deuterium at a frequency of 13.56 MHz with input RF powers of up to 2.5 kW using a half-turn double helix antenna. The effect on radial density profiles and ionization efficiency due to nonuniform axial static magnetic field profiles is investigated, with peak magnetic fields of up to 1 kG. The ionization efficiency in eV per electron-ion pair is calculated using measured density profiles and flow rates to determine the overall efficiency of plasma production in the source. Optimization of the magnetic field profile for maximum source efficiency is performed. Plasma density results obtained with a Langmuir probe are cross-checked with those obtained using a 105 GHz interferometer in helium and deuterium. Wave and optical measurements are obtained to investigate an abrupt transition marked by a sharp density increase and strong visual blue core observed in argon for higher powers and magnetic field strengths. Computational modeling is performed using the ANTENA2 code to predict and support plasma wave measurements for a variety of configurations