X-ray raytracing of Bragg reflections from Highly Oriented Pyrolytic Graphite (HOPG) in support of the ITER XRCS-Core diagnostic*

The ITER core x-ray crystal spectrometer (XRCS-Core), which  measures core profiles of the ion-temperature and toroidal rotation in ITER, is a primary diagnostic that provides critical measurements for the ITER physics program. The ITER spectrometer utilizes a novel design with Highly Oriented Pyrolytic Graphite (HOPG) pre-reflectors that allow the spectrometer to be placed 9 meters away from the device. A complete raytracing model has been developed for ITER to study the expected performance of the XRCS-Core diagnostic. As a result, a new x-ray raytracing model for Bragg reflections from Highly Oriented Pyrolytic Graphite (HOPG) has been created using the XICSRT raytracing code. A key component is the accurate and efficient modeling of reflections from the HOPG reflectors. A set of simple reflection models have been developed and their performance is evaluated and compared to previous modeling efforts. Additionally, a set of laboratory experiments have been designed to allow direct validation of the HOPG raytracing models. Simulations of the expected results for these experiments will be presented, which can be compared to future experimental measurements.