Operation of a lithium beam diagnostic in tritium and deuterium–tritium experiments at JET

Abstract A fast neutral lithium beam has been used at JET for more than 30 years to measure profiles of electron density in the pedestal and scrape off layer. The diagnostic was not designed for tritium operation. In this paper, we describe the modifications which were required to allow operation in tritium (T) and deuterium–tritium (D-T) fuelled pulses at JET in 2021 and 2023. Methods to allow remote startup and remote control of the beam were implemented. The vacuum pump and exhaust system had to be made tritium compatible. Radiation vulnerable electronics had to be removed from the torus hall. The observation system relied on regular in vessel mirror exchange. An in-vessel protection shield was installed close to the observation mirror to protect the mirror surface. Operation in T and D-T discharges, maintenance post tritium exposure, commissioning and the calibration of the diagnostic are discussed.