Development Of A Hard X-Ray Profile Measurement System In The Tst-2 Spherical Tokamak

A compact hard X-ray measurement system was developed to measure bremsstrahlung of fast electrons generated by lower hybrid wave (LHW) in the TST-2 spherical tokamak. The system, which consists of an NaI scintillator, a photomultiplier tube, a curved acrylic lightguide, a lead collimator, and linear and rotational stages, enables us to measure the energy flux profile on the midplane with the energy resolution of 10 - 15 eV at 122 keV and with the energy range from a few tens to several hundreds of keV. Preliminary hard X-ray measurements were performed for LHW-driven TST-2 plasmas, and energy spectra were attained successfully. The typical effective temperature of the spectra is in the order of 10 keV, and we obtained the time evolutions of energy flux and effective temperature with a time resolution of 10 ms. Profile measurement showed that the flux at the inboard side is higher than that at the outboard side. (C) 2017 The Japan Society of Plasma Science and Nuclear Fusion Research