Measurements of Slow Theta Pinch Plasma by Mach-Zehnder Interferometer with Giant Pulse Ruby Laser

Spase and time resolved Mach-Zebnder interferometer is applied to study a slow theta pinch plasma. Methods of timing operations and experimental arrangements are described. The plasma is pinched in the third half cycle of discharge period. The interferogram shows that the peak electron density varies from about 1 x 1016 to 1 x 1017 cm-3 as the filling gas pressure is varied from 25 to 400 mtorr. The radial distribution of shell structure is observed when a small reverse bias field is added. The relaxation time of this field is longer at the lower gas pressure. In the pressure range of higher than 40 mtorr, a flute-type instability appears. But no drift motions are observed. Interferograms show various modes of instabilities. The loss rate of the total number of electrons is estimated and the result is in good agreement with a theoretical model of steady magnetohydrodynamic fluid.