Space and time resolved electron density and current measurements in a dense plasma focus Z-pinch

Abstract

Plasma density and current profiles in a Z-pinch are important parameters to understand the implosion and radiation physics. This paper describes measurements of electron density and current at radii of /spl ges/200 /spl mu/m from the axis of a dense plasma focus (DPF) pinch plasma that is imploded by a /spl ap/0.3 MA current pulse. These measurements use laser interferometry and polarimetry. The electromagnetic wave propagating through a current carrying plasma will change its phase, polarization state, and propagation direction. Refraction by electrons bends the wave fronts and changes the propagation direction; Faraday rotation due to the magnetic field and electron density rotates the laser polarization vector. By measuring these quantities simultaneously, the magnetic field and electron density can be separately determined. Although the DPF used here is a low current device, the measured densities (/spl les/10/sup 20/ cm/sup -3/) and magnetic fields (/spl sim/100 T) are similar to values expected just outside higher current but larger radius Z-pinches, so this technique should be applicable there as well. The techniques described here do not require access to the core of the pinch to work; just outside these pinches the coronal density and self-magnetic field are high enough to give reliable data but not so high as to make the measurements difficult.