MICROPINCH ACTUATION IN THE SPEED-2 PLASMA-FOCUS

The occurrence of hot (kilo-electron-volts), dense (10(28) m(-3)) and short-lived (nanoseconds) substructures in pinch plasmas (micropinches ) is usually very erratic in space and time. On doping the deuterium d ischarge of the fast plasma focus SPEED 2 (180 kV, 1.5 MA, 400 ns) wit h argon, typically ten micropinches appear in an orderly manner along the axis of symmetry forming a straight chain of successive flashes wi thin 30 ns that starts near the anode and ends after 2 cm. Four frame pictures taken in the VUV (lambda < 20 nm) at different times during p inch formation and careful comparison with stronger filtered x-ray pin hole pictures (lambda < 2 nm) show that micropinches are actuated in n ecked pinch regions that preferentially undergo radiative collapse via bremsstrahlung and line radiation from argon. However, not every neck ing leads to micropinch formation so that necking is a necessary but n ot sufficient condition for micropinch actuation.