Soft X-ray Analysis of HBT-EP Plasmas

Measuring soft x-ray emission is a useful and non-invasive diagnostic for studying internal plasma properties and MHD mode structure and dynamics. The HBT-EP tokamak is equipped with two multi-chord soft x-ray systems to study internal profile and fluctuation behavior. A 32-channel soft x-ray tomography system composed of discrete diodes with a thin film filter of Titanium, Zirconium, and Carbon coated directly on to the diode face is used to reconstruct 2-D plasma emissivity profiles at a single toroidal location. Resolution of the system is sufficient to measure the structure and evolution of edge (m,n) = (2,1) tearing modes. In addition, a 16-channel ``fan-array'' assembly based upon a linear diode array and a 400 nanometer Beryllium filter measures emission predominantly from the plasma core. Fan-array measurements of internal sawtooth and (m,n)=(1,1) mode activity will be presented. A planned upgrade to the fan-array for measuring temperature profiles using a multiple set of filters and additional diode arrays will be discussed.