Development of Spectroscopic Diagnostics for Assessing the Role Neutral Fueling Plays in the Production of High Density Helicon Plasmas*

Helicon plasmas capable of producing electron densities in the range of 10²⁰ m^-3 are being considered for use in next generation plasma wakefield particle accelerators. The ability to maintain the appropriate density with an axial uniformity on the order of <1% is a demanding requirement. The MARIA device at UW-Madison has been developed to study the role of neutral particle fueling in meeting these density requirements using non-invasive spectroscopic techniques. An improved algorithm based on collisional radiative modeling has been developed to assess the atomic populations of neutral argon as well as fundamental plasma parameters. Measurements of the electron temperature and the density ratio of the various metastable states is currently possible, while the ability to measure electron densities is under way. Additionally, laser induced fluorescence has been used to map the distribution of ion outflow and neutral inflow to the plasma. By combining these measurements, a picture of how a high-powered helicon plasma is fueled begins to emerge.