Alternative principle and method in x-ray diagnostics for plasma electron temperatures

An alternative principle and method in x-ray diagnostics is proposed for measurements of plasma electron temperatures Tₑ. The method is different from widely utilized standard methods of x-ray pulse-height analysis and x-ray absorption. This proposal is based on three-dimensionally diffusing charges produced by x rays in a field-free substrate of a semiconductor detector, although these charges have been ignored for the x-ray measurements. This proposed theory corrects the standard conventional theory on a semiconductor response employed over the past quarter of the century for Tₑ analyses. Overestimations of Tₑ and misinterpretations of broader Tₑ profiles may result when the conventional theory is utilized. These lead to misunderstandings of pedestal structures in high confinement modes, electron-energy transport, as well as the misestimation of bootstrap currents and hence the misinterpretations of plasma physics itself. The proposed theory is extended to construct an alternative method for Tₑ measurements; this method is based on detection of the diffusion-charge distributions using a semiconductor depletion layer as a temporally changeable x-ray ``absorber'' during one plasma shot, in place of the conventional use of the depletion layer as an x-ray-sensitive region. X-ray signals in the conventional methods have a complicated dependence on plasma densities and Tₑ, while the proposed method is conveniently characterized by no effects of plasma densities on the signal analyses as well as no need of complicated systems for x-ray diagnostics. This method would be useful not only for providing a practical alternative but also for clarifying the physics essentials in the proposed theory through such practical examples.