Expected performance of the ITER core x-ray crystal spectrometer (XRCS-Core) diagnostic including sensitivity to alignment and tolerancing

The ITER core x-ray crystal spectrometer (XRCS-Core)  has been simulated using advanced x-ray raytracing to study the effects of misalignment and thermal deformation on the  performance of the diagnostic. The XRCS-Core system will detect x-rays produced by the introduced impurity Xe and the intrinsic impurity W and spatially resolve the ion temperature and toroidal velocity profiles. The diagnostic utilizes a novel design that employs highly oriented pyrolytic graphite (HOPG) pre-reflectors to allow the crystals and detectors to be placed behind the bio-shield, while still being able to view x-ray sightlines covering the full minor radius of the plasma. In the operation of ITER, thermal expansion is expected to cause parts of the diagnostic to undergo translation and/or rotation motion, leading to misalignments of the crystals from the HOPG pre-reflectors. The effect of these rotations and translations on the throughput and energy bandwidth of the system were modeled using the XICSRT raytracing code. The use of actuators to pivot the crystals to maintain system alignment during thermal variations has been examined. Requirements for engineering, installation and alignment tolerances have been quantified and will be used as part of the continuing design efforts.