Calibration of a two-color soft x-ray diagnostic for electron temperature measurement

The two-color soft x-ray (SXR) tomography diagnostic on the Madison Symmetric Torus is capable of making electron temperature measurements via the double-filter technique; however, there has been a 15% systematic discrepancy between the SXR double-filter (SXR_DF) temperature and Thomson scattering (TS) temperature. Here we discuss calibration of the Be filters used in the SXR_DF measurement using empirical measurements of the transmission function versus energy at the BESSY II electron storage ring, electron microprobe analysis of filter contaminants, and measurement of the effective density. The calibration does not account for the TS and SXR_DF discrepancy, and evidence from experiments indicates that this discrepancy is due to physics missing from the SXR_DF analysis rather than instrumentation effects.