Tritium Operation of the JET Neutral Beam Systems and Tritium NBI Power Calculations

Abstract

Neutral beam injection (NBI) is a very flexible auxiliary heating method for tokamak plasmas, capable of being efficiently coupled to various plasma configurations required in the tritium and deuterium–tritium experimental campaign (DTE2) to be undertaken in the Joint European Torus (JET) device. In particular, experiments for high fusion yield and alpha particle studies require high-power NBI heating, and for maximum performance and optimum fuel mixture control in deuterium–tritium (D–T) plasmas, it is necessary to operate the JET NBI systems in both deuterium and tritium. The technical aspects of the JET NBI systems for compatibility with T operation are discussed, and the associated commissioning is described. The characterization of the JET NBI system in the tritium gas mode will be presented, with particular focus on the power and species mix measurements; this will be the first time that such data have been collected and analyzed for tritium neutral beams. Deuterium operation in the tritium gas mode was successfully carried out in 2019 with no loss in reliability. In this period of operation, the NBI power has been measured using beamline diagnostics and corroborated with plasma measurements. The species mix of the beam has been measured on the neutral beam test bed (NBTB) and also corroborated by plasma diagnostics on JET. These results will be presented alongside tritium NBI results allowing comparison of possible JET NBI performance between deuterium and tritium. Measurements of the NBI power in tritium show that there will be a higher neutralized fraction than in deuterium and a higher full energy fraction. When the effect of particle mass is also accounted for, this will lead overall to reduced beam penetration and lower particle flux per MW.