Characterization of an Inductively Coupled Plasma Preionization Device Using Optical Emission Spectroscopy

Abstract

A rotamak device uses a rotating magnetic field (RMF) to initiate and confine a field reverse-configuration (FRC) plasma. However, depending on the gas used, the pressure, and the geometry of the system, the rotating magnetic field may be insufficient to initiate the FRC. This problem creates the need for a preionization system to provide sufficient seed electrons for FRC formation. In this thesis, a helical coil ICP system is designed and constructed based on previous literature and COMSOL simulations. The electron densities and temperature produced by the ICP system were then estimated at a variety of pressures and powers using optical emission spectroscopy and a collisional radiative model. The initial experiments and characterization of plasma were done using argon. It was found that two discharges were produced simultaneously within the system, the primary one of inductive nature and the secondary hypothesized to be of capacitive nature. Using the collisional radiative model and the line-ratio method, the system was determined to produce electron densities on the order of 109 𝑐𝑚−3 with electron temperatures ranging from 2.5 to 5.0 eV in pressures from 31 to 100 Pa with 60 to 120 W of input power in the secondary discharge. This is comparable with previous literature for a capacitive-coupled discharge. Further testing is needed to characterize the primary inductive plasma.