Investigations of Electron Behavior in the Gamma 10 Tandem Mirror on the Basis of X-Ray Analyses Using a Novel Theory on Semiconductor Detector Response

Abstract

(i) A scaling law and its physics mechanism of potential formation for tandem-mirror plasma confinement are investigated. The first result of a generalized scaling covering over two typical plasma operational modes in the GAMMA 10 tandem mirror is presented; that is, a previously obtained potential-formation scaling in a plasma operational mode with a few-kV confinement potentials is found to be extended and generalized to a potential scaling in a hot-ion operational mode with thermal-neutron yield, when we take account of the dependence of potential formation on the ratio of the plug to the central-cell densities as well as the relation of electron temperatures in the central cell to thermal-barrier potentials. The finding of the existence of the same physics basis underlying in these two typical modes may provide the future possibility of simultaneously obtained hot-ion plasmas with high potentials. (ii) For these scaling studies, we have constructed the physics fundamentals of x-ray diagnostics; that is, we proposed a novel theory on the energy response of a widely utilized semiconductor x-ray detector. The theory solves a serious problem of a recent finding of the invalidity of the conventional standard theory on the response of such an x-ray detector; the conventional theory has widely been believed and employed over the last quarter of the century in various research fields including plasma-electron researches in most of plasma-confinement devices. The novel theory on the semiconductor x-ray response is characterized by the inclusion of a three-dimensional diffusion of x-ray-produced minority carriers in the field-free substrate of a detector, while the conventional theory is based only on the charges from an x-ray-sensitive depletion layer (i.e., the region of a p-n junction). Various and serious effects of the novel theory on the determination of electron temperatures and their radial profiles (i.e., the electron-temperature gradient) are also represented.