First tritium operation of ITER-prototype VUV spectroscopy on JET

Abstract

Results from tritium operation of the VUV survey spectrometer on the JET tokamak are presented. The instrument, located outside the biological shield and offset from a direct plasma 1-o-s for maximum radiation protection, was operational during the trace tritium campaign (TTE) at JET. No discernible increase in detector background noise levels were detected for total neutron rates of up to 1 × 1017/s, demonstrating the shielding effectiveness of the configuration. Some tritium retention in the detector microchannel plate was measurable, but has not hampered subsequent operations. As a reference the unshielded detector of a close-coupled XUV instrument was operated during TTE (the spectrometer itself was valved off from the JET vessel). This was exposed to neutron fluxes of ∼109/cm 2 s, in excess of those predicted for the corresponding instrument on ITER (107-108/cm2 s). A corresponding increase in the background level equivalent to ∼5% of the detector dynamic range was measured. This demonstration of the shielding effectiveness of the SPRED configuration during DT operations, coupled with the tolerable noise levels measured in the SOXMOS detector, give confidence in the planned implementation of such instruments in ITER.