A 2D Electron Density and Plasma Current Density Diagnostic for Opening Switches

Abstract

Abstract : A program to develop diagnostics for plasma opening switches has been completed. HY-Tech has investigated 2D interferometry using a short pulsed laser for determining the electron density distribution and multi-chord spectroscopic observations for determining the plasma current density. The electron density diagnostic used a short pulsed (10 ns) Nd:YAG laser to form interferograms using a Mach-Zehnder arrangement. These interference patterns were captured using a scientific grade CCD camera. HY-Tech developed computer algorithms to analyze interferometric fringe patterns using two dimensional fast Fourier transforms that could achieve a sensitivity to electrons of better than 6 X 10(exp 15) cm squared (10degrees at 1064 nm). The plasma current diagnostic is based on the spectroscopic observation of seeded ions in the POS plasma that are used to map out the magnetic field distribution. The magnetic field can be calculated by observation of Zeeman splitting or the acceleration of seeded ions, with each method best suited for opening switches operating in different regimes. The spectroscopic observation system included a McPherson 0.67 m imaging monochromatic and a Princeton Instruments ICCD camera. Numerous calculations and measurements were performed to optimize the injected material for the type of plasma. Details are included in this report.