Micropinch actuation in the SPEED 2 plasma focus

Abstract

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