Simultaneous measurements of temporally and spatially resolved ion and electron temperatures using a semiconductor detector array in a single plasma discharge

Abstract

A method is proposed for obtaining radial profiles of both plasma ion (Ti) and electron temperatures (Te) simultaneously using a semiconductor detector. This method for semiconductor Ti diagnostics is proposed on the basis of an alternative “positive” use of a semiconductor “dead layer” as an energy-analysis filter. Filtering dependence of charge-exchange (cx) neutral particles from plasmas on the thickness on the order of a nanometer-thick SiO2 layer is used for analyzing Ti in the range from hundreds to thousands of electron volts. Even under the circumstances of simultaneous incidence of such particles and x rays along the same lines of sight of a semiconductor detector array, it is found that the different dependence on their penetration lengths and deposition depths in semiconductor materials makes it possible to distinguish cx neutral particles for Ti diagnostics from x rays for Te diagnostics. Experimental verification of this concept of the simultaneous Ti and Te diagnostics is carried out in the GAMMA 10 tandem mirror by the use of a matrix-type semiconductor detector. The detector is characterized in terms of compact formation of six rows with different thicknesses of thin dead layers (SiO2) on its surface. Each row has seven channels (columns) for measuring radiation profiles in the radial direction of plasmas so as to make tomographic reconstructions for attaining the actual emissivity profiles in the plasmas. These various SiO2 layers are proposed to be applied as “unbreakable ultrathin radiation-absorption filters” having various thicknesses to distinguish x rays from neutral particles simultaneously.