MAST neutral beam long pulse upgrade

Abstract Until summer 2003 two Neutral Beam Injectors (NBI), each equipped with one duopigatron ion source on loan from Oak Ridge National Laboratory (ORNL), were delivering up to 3 MW of deuterium neutral beam power into the Mega Amp Spherical Tokamak (MAST) plasma for a duration of up to 300 ms. The two ORNL injectors are now being replaced with JET type Positive Ion Neutral Injectors (PINIs). The MAST PINI design is a modification of the JET high current tetrode injector, with nominal deuterium beam voltage and current of 75 kV and 65 A, respectively. Each injector will deliver up to 2.5 MW of deuterium neutral beam power (in excess of 1 MW in hydrogen) for pulse lengths of up to 5 s. In addition to the replacement of the two injectors, many other components of the MAST NBI system are being replaced or modified. The various design issues of the upgraded MAST NBI system are addressed.