MEASUREMENT OF PLASMA DENSITY IN A FAST AND COMPACT PLASMA FOCUS OPERATING AT HUNDREDS OF JOULES

Abstract

It is known that there are plasma parameters that remain relatively constant for plasma focus facilities operating in a wide range of de energy, from 1kJ to 1MJ, such as: electron density, temperature and plasma energy density. Particularly the electron density is of the order of 1025m?3. Recently the experimental studies in plasma focus has been extended to devices operating under 1kJ, in the range of hundreds and tens of joules. In this work an optical refractive system was implemented in order to measure the electron density in a plasma focus devices of hundred of joules, PF-400J (880 nF, 30 kV, 120 kA, 400 J, 300 ns time to peak current, dI/dt?4×1011 A/s. The plasma discharge was synchronized with a pulsed Nd-YAG laser (?6ns FWHM at 532nm) in order to obtain optical diagnostics as interferometry and Schlieren. An electron density of (0.9±0.25)×1025m?3 was obtained at the axis of the plasma column close to the pinch time. This value is of the same order that the obtained in devices oparating in the energy range of 1kJ to 1MJ.