Design, installation and first measurements of a multi-energy soft x-ray (SXR) pinhole camera in the Madison Symmetric Torus (MST)

A multi-energy soft x-ray (SXR) pinhole camera has been designed and built for the Madison Symmetric Torus (MST) Reversed Field Pinch (RFP) to aid the study of particle and thermal transport, as well as MHD stability physics. This novel imaging diagnostic technique employs a pixelated x-ray detector in which the lower energy threshold for photon detection can be adjusted independently on each pixel. The local x-ray emissivity can be measured in multiple energy ranges simultaneously, from which it is possible to infer profile measurements of core electron temperature (T_e) and impurity density (T_e) with no a priori assumptions of plasma profiles, magnetic field reconstruction constraints, high-density limitations or need of shot-to-shot reproducibility. The maximum detector frame rate is 500 Hz with expected time and space resolutions of 2 ms and < 1 cm, respectively. Brightness measurements, and inferred spectral emissivity, during improved confinement (PPCD) and helical core (SHAx) scenarios are presented.

This work is supported by the U.S. Department of Energy, Office of Fusion Energy Sciences under Contract Number DE-AC02-09CH11466.