Improvement of Faraday Rotation and Its Application in Preconditioned Single-Wire Z-Pinch Plasma

Abstract

Magnetic field measurement in Z-pinch plasma has drawn considerable interest because it is a key problem in the research of dynamic behaviors and the coupling of magnetic field and plasma. In this study, the measurement sensitivity of the rotation angle in Z-pinch plasma was improved by considering the second polarization effect caused by optical elements. The magnetic field distribution of preconditioned single-wire Z-pinch plasma was determined by this method. The Faraday rotation of the 1064-nm probe laser was measured by the beam-splitting polarization method when the plasma acted as a Faraday medium. A second polarization effect on the rotation angle was realized by taking the different transmittances and reflectivities of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$s$</tex-math> </inline-formula> components of the beam splitters into account. This configuration doubled the sensitivity of the Faraday rotation measurement. The diagnostic errors produced by the techniques and data processing were quantified. The early stage of the preconditioned imploding plasma was monitored, and the distributions of areal electron density, Faraday rotation, and magnetic field were measured. The experimental results demonstrated that the current distribution can be divided into three parts by two dense shells. The majority of the current was distributed outside the dense shell which existed inside the coronal plasma. In addition, only a small amount of current was distributed in the wire core.