Soft X-ray Tangential Imaging of the NSTX Core Plasma by Means of a MPGD Pin-hole Camera

Abstract

A fast X-ray system based on a Micro Pattern Gas Detector has been used for the first time, to investigate emission from the plasma core of the National Spherical Tokamak eXperiment (NSTX), at the Princeton Plasma Physics Laboratory. The results presented in this work demonstrate the capability of such a device to measure with a time resolution of the order of 1 ms, the curvature and the elongation of the X-ray iso-emissivity contours, under various plasma conditions. Also, comparisons with the magnetic surface structure calculated by the EFIT code show good agreement between reconstructed flux surface and the soft-X ray emissions (SXR) for poloidal beta values up to 0.6. For greater values of beta, X-ray iso-emissivity contours become circular, while magnetic flux surface reconstructions yield elongationThe X-ray images have been acquired with a (statistical) signal to noise ratio (SNR) per pixel of about 30. Thanks to the direct and efficient X-ray conversion and its operation in a photon counting mode, this new diagnostic tool allows the routine investigation of the plasma core with a sampling rate of 1kHz and extremely high SNR under all experimental conditions in NSTX.

Energy resolved fast two-dimensional x-ray imaging for MFE plasmas (invited)

“…Examples of these features have been shown in previous article. 4 The high dynamic range of this detector (510 5 measured in the NSTX shots) can be fully exploited because of the capabilities of this instrument to be tuned on the region of interest. Here we want to show deeper and stronger exploitation of the energy resolution coupled to 2D imaging.…”