High throughput measurements of soft x-ray impurity emission using a multilayer mirror telescope

A 4in. multilayer mirror telescope has been tested on National Spherical Torus Experiment (NSTX) for high throughput measurements of the beam excited soft x-ray impurity emission. The design is aimed at imaging low-k turbulent fluctuations in the plasma core. The test device used curved and planar Mo∕Si mirrors to focus with ≈15% optical transmission and few angstrom bandwidths, the 135A Lyα line from injected Li III atoms, or the n=2–4 line from intrinsic C VI ions. As test detectors we used 1cm2 absolute extreme ultraviolet diodes, equipped with 400kHz bandwidth, low noise preamplifiers. With the available view on NSTX the telescope successfully detected small impurity density fluctuations associated with 1∕1 modes rotating at midradius, indicating that a high signal to noise ratio and cost effective core turbulence diagnostic is feasible based on this concept.