BRAGG SPECTROSCOPY OF IMPURITIES DURING THE JET PRELIMINARY TRITIUM EXPERIMENT

Two Bragg spectrometers shared a shielded beamline, and monitored all significant plasma impurities throughout the Joint European Torus (JET) preliminary tritium experiment. The JET Active Phase Double Crystal Monochromator and a Bragg rotor spectrometer together monitored K-shell lines of Be, C, 0, and Cl, and L-shell lines from metals such as Ni and Zn, in the wavelength range 0.2-11 nm. Background radiation was recorded during and after discharges, to assess the signal-to-noise ratio, and to monitor any activation or tritium ingress. Bragg spectroscopy was shown to be suitable for all impurities in magnetically confined D-T plasmas, using a thin foil to isolate tritium, and a low f-number shielded beamline. Future improvements to the signal-to-noise ratio are discussed in the context of a next-step machine such as ITER.