OPTICAL MEASUREMENTS OF PLASMA DYNAMICS IN CARBON-FIBER Z-PINCHES

A series of experiments has been carried out on the Mega Ampere Genera tor for plasma Implosion Experiments (MAGPIE) generator in order to st udy the dynamics of carbon fiber Z-pinches. The generator was operated at 1.4 MV, with a peak current of 1 MA, and a rise time of 150 ns. In some shots, a current prepulse of about 30 kA was provided to Study i ts influence on the dynamics of the fiber pinch. Carbon fibers of 7, 3 3, and 300 mu m diameter were used during these experiments. The diagn ostics employed were a self-referencing interferometer, a two-frame Sc hlieren system, an optical streak camera, and a four-frame X-ray frami ng camera. A novel feature of these measurements is the employment of an optical streak camera with a set of four slits arranged along the f iber axis and displaced in the radial direction. This permitted the st udy of the temporal evolution (axial and radial) of the plasma regions emitting in the visible part of the spectra. Correlation between thes e regions of the plasma and the location of X-ray hot spots is discuss ed. In carbon fibers of 33 mu m diameter, the radial expansion velocit y measured from Schlieren images was 3.6 x 10(6) cm/s and 5.5 x 10(6) cm/s for shots with and without prepulse, respectively. The dominant a xial wavelengths of instabilities in the coronal plasma were between 0 .05 and 0.2 cm, which correspond to ka values between 10 and 20, where k is the wavenumber of the instability and a is its amplitude. The dy namics of carbon fibers of different diameters are compared.