Tomographic 2-D X-ray imaging of toroidal fusion plasma using a tangential pinhole camera with gas electron multiplier detector

A tangential X-ray pinhole camera based on a gas electron multiplier (GEM) detector was installed on KSTAR to study high temperature plasmas emitting X-ray photons in the energy band of 4-15 keV. The camera system consists of a triple-GEM gas chamber with a readout printed circuit board and a pinhole to image the plasma in two dimensions (2-D). The advantages of this tangential camera system include its compactness, high efficiency, energy discrimination in bands, and selectivity of the photon energy range etc. This camera system allows a selection of the viewing area through a remote control of the entire setup. The Philips-Tikhonov algorithm for tangential reconstruction was used to visualize the poloidal cross-sectional images. Phantom tests were performed with synthetic D-shaped plasma images and a comparison with the magnetic equilibrium flux surfaces from the real-time EFIT code obtaining a good agreement between each other. The 2-D X-ray images of the KSTAR plasma were successfully acquired during sawtooth crash, electron cyclotron heating, vertical displacement event, and emissivity from the injected trace Ar impurity.