Layered synthetic microstructures for soft x-ray spectroscopy of magnetically confined plasmas (invited)

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Abstract
With the recent advances in layered synthetic microstructure (LSM) technology, it is now possible to build a simple, high‐throughput, near‐normal incidence soft x‐ray spectrometer as a diagnostic for magnetically confined plasmas. Such spectrometers could be used for radiative power loss measurements from intrinsic impurities, an impurity concentration monitor, or ion temperature measurements from Doppler broadening of high charge‐state metallic impurities. LSMs have been developed as either flat or curved multilayer mirrors (MLMs) or as coatings for conventional gratings. Flat multilayer mirrors can have near‐normal incidence reflectivities greater than 50% throughout the entire soft x‐ray region with bandpasses that can be less than 4 Å. Coated gratings are being developed that will combine the high soft x‐ray reflectivity of the LSM with the high resolution of the grating. Specific applications of LSMs as dispersive elements will be discussed. As an example, LSM‐based low‐resolution spectra of both a laboratory and tokamak plasma will be presented.