High current positive ion source for Copernicus NBI based on a cold-cathode arc plasma generator

Abstract

The NBI system based on positive ions to be applied for TAE’s next-generation field reversed configuration experiment, Copernicus, has been designed. The beamlines are longer in the new system, so the required beam divergence smaller relative to the NBI system on TAE’s current device. This requirement motivates a change from slot-shaped apertures to circular in the plasma grid. The influence of changing the aperture shape on the divergence and total beam current across the extraction area has been examined. When considering spatial uniformity in calculations, it is expected that a beam current value of 173 A and a beam divergence angle of 17 mrad will be achieved, exceeding the required values by 15%. An octagonal-shaped ion source has also been developed for a future upgrade targeting 2.5 s long pulse operation, and the estimation indicates 83% source plasma uniformity with concurrent suppression of thermal loads. The development of multiple plasma diagnostics for assessing uniformity and proton ratios has been completed to validate these estimations and optimize the ion source dimensions.