Study of hot spot phenomenon in Z-pinches

Summary form only given. A vacuum spark discharge was studied experimentally with a set of X-ray diagnostics including dosimetry, pin-holes cameras, time resolved X-ray spectrometry and X-ray line polarization measurements, as well as laser interferometry, shadowgraphy and Faraday rotation diagnostics. Consecutive phases of the discharge with iron electrodes are discussed. In the ignition phase the electrons extracted from the trigger plasma are concentrated on the anode tip providing vaporization and pressure rising in the anode-cathode gap. In the starting phase collision ionization prevails and the arc discharge begins. During the MHD phase anode and cathode necks are formed due to initial inhomogeneities of the discharge plasma radius and linear concentration along the z-axis. As a result a Bennet pinch O0.2/spl times/1 mm is formed with n/sub e//spl sim/10/sup 21/ cm/sup -3/ and T/spl ap/50 eV. Hot spots (micropinches) having dimensions O40/spl times/150 /spl mu/ in the spectral region near 1 keV and decaying on 2-3 smaller micropinches O3/spl times/10 /spl mu/ inthe spectral band h/spl nu/>3 keV are formed mainly in the anode neck. The plasma parameters in the micropinch are: n/sub e//spl ges/10/sup 22/ cm/sup -3/ and T/spl sim/1 keV. The micropinches emit up to 10 J of X-ray radiation within the band 0.5-1.5 keV and /spl sim/10/sup -3/ J in h/spl nu/>3 keV in the pulse /spl tau//spl les/2 ns.