Soft x-ray diagnostics system for electron temperature measurement in the integrated commissioning phase of JT-60SA.

A soft x-ray (SX) diagnostic system has been designed and installed in JT-60SA for the first plasma. For quantitative measurement, the etendue of each viewing chord was evaluated analytically and numerically. The electron temperature is evaluated from the detected bremsstrahlung emission ratio between two detector arrays with two different thicknesses of Be filters. The two filter thicknesses were optimized to be 7 and 50 μm for the expected electron temperature range of 0-3 keV. The one-dimensional profile of SX emission is reconstructed from line integrated emission by the elliptic Abel inversion scheme. For a plasma discharge with a plasma current of 1 MA, a peaked electron temperature profile with about 800 eV at the center is obtained. The total bremsstrahlung power was also evaluated using the electron temperature profile and the absolutely evaluated etendue of each viewing chord. In this evaluation, the bremsstrahlung power is around 10% of ohmic heating power.