A high-resolution soft x-ray spectrometer on the MAST tokamak

A curved crystal spectrometer in Johann configuration has been implemented on MAST to obtain values for electron temperature, ion temperature and toroidal velocity. The spectrometer is used to examine medium Z impurities in the soft x-ray region by utilising a Silicon (111) crystal, bent using a 4 pin bending jig, and a CCD detector (Δt=8 ms ) . Helium-like Argon emissions from 3.94 to 4.00 Å have been examined using a crystal radius of 859.77 mm . The Bragg angle and crystal radius can be adjusted with relative ease. The spectrometer can be scanned toroidally and poloidally to include a radial view which facilitates absolute velocity measurements by assuming radial velocity =0 . Doppler shifts of 2.3×10 −5 Å (1.8 kms −1 ) can be measured. The line of sight is shared with a neutral particle analyzer, which enables in situ ion temperature comparisons. Ray tracing has been used for the development of new imaging spectrometers, using spherical/toroidal crystals, planned to be implemented on MAST.