Space-Time Resolved Mach-Zehnder Interferometer Measurements of Cross-Sectional Electron Distribution in theta-Pinch Plasma

摘要

In theta-pinch deuterium plasmas instabilities are studied extensively and related to end losses, axial density minima, and neutron production. Non-rotating flute and flute-like instabilities form in the first quarter-cycle in all reverse biased plasmas. Mode numbers and evolution characteristics are highly dependent on reverse bias strength. Kink instabilities rotating near 1 rev/micro sec always develop near or after the time of peak-B for -2.7 to -4.0 kG and in certain cases for -1.3 kG bias. For 0.04 to 0.10 Torr a Mach-Zehnder interferometer illuminated by a 175 MW (6943 A) giant pulse ruby laser and axially coupled to the plasma yields space-time resolved cross-sectional electron distributions. A digital computer technique employs information extracted from the interference fringe patterns to determine the total number of electrons present. Plasma luminosity viewed axially through a Kerr cell shutter is deduced to be highly representative of electron distributions. He-Ne laser coupled resonator data agree to within + or - 30 percent to the interferometer data. Numerical predictions of a modified Hain-Roberts digital computer code agree with the experimentally deduced trends. (Author)