Studies of the compression dynamics of intermediate-density Z-pinches

The evolution of a constriction in a dense Z-pinch is studied in the Module A5-I installation (0.04 Omega output resistance, 1.3 MA load current, and 100 ns current rise time). Agar-agar fibers (2-3 mm in diameter) with a preformed constriction (0.1-0.5 mm in diameter) are used as a load. The fiber mass density is varied within a wide range from 10(-2) to 10(-1) g/cm(3). The conditions under which the constriction starts to develop are studied, and the parameters of the produced hot dense plasma are measured using various X-ray diagnostics. The configuration of the current channel is determined by simultaneously employing the laser shadow photography, the interferometric measurements with the visualization of images, and the measurement of the Faraday rotation of the plane of polarization of the probing laser beam. It is shown that, as a result of the onset of the neck instability, a hot, dense plasma with a temperature of 0.8-1.5 keV, electron density of 10(22) cm(3), and characteristic size less than 80 mu m is produced in the constriction.