X-ray crystal spectrometer throughput, data treatment, and configuration over the JET DTE2 and DTE3 campaigns

The calibration of the JET x-ray spectrometer is presented. The absolute throughput, diffractor focusing, and instrument function of the spectrometer are presented, and the quality of the ion temperature measurement is re-assessed, particularly at the lower end. The addition of a second diffractor enables the simultaneous measurements of the spectra from H- and He-like nickel, which widens the spatial coverage of the core-ion temperature measurements for high-performance plasmas at a fixed Bragg angle range. A calculation of the absolute continua from the spectrum background from the second diffractor is analyzed for different JET plasmas. The spectrometer's narrow bandwidth makes it ideal as an "x-ray monochromator" that can sample a single energy channel (or two over the two crystal orders) within the free-free and free-bound x-ray continua. The measurable effect for impurity-seeded plasmas is explored as a means to determine the plasma concentration of the seeding impurities, which has the potential to be a robust method for high performance DT operations in reactor-class machines.