Schlieren photography of plasma focus discharges with decreased magnetic insulation

Summary form only given. The dynamics of 6-kJ plasma focus discharges in deuterium at 5 Torr, with a 10% decrease of the magnetic insulation at the breech, was monitored with schlieren photography and other diagnostic methods. The resolution on the schlieren image was 33 line-pairs per mm, and the probed range of electron density gradients, with integration along the path of the ruby laser beam, was between 5 /spl times/ 10/sup 18/ cm/sup -3/ and 3 /spl times/ 10/sup 20/ cm/sup -3/. The duration of the typical Q-switched ruby laser pulse was 20 ns. Double and triple pulse generation made the measurement of the current sheath velocity possible. The average radial velocity was 1.2 /spl times/ 10/sup 7/ cm/s in the interval (-112 ns, -88 ns), the average axial velocity was 5 /spl times/ 10/sup 6/ cm/s and 8 /spl times/ 10/sup 6/ cm/s in the intervals (-4 ns, +96 ns) and (+96 ns, +126 ns), respectively. The data have been compared with those from discharges with normal level (no 10% decrease) of magnetic insulation at the breech. The current sheath fine structure in the region of high-density gradient was also monitored.