Design of a Plasma neutraliser for a Fusion reactor or as an upgrade to the ITER heating neutral beam injectors

Abstract

The global efficiency of neutral beam injectors to be used on a fusion reactor needs to be of the order of, or greater than, 60 %, which is considerably higher than the efficiency of presently operating NBIs. The required efficiency can only be achieved by increasing the neutralisation efficiency from the ≈56 % obtained with the gas neutralisers currently used, which can be done using a plasma or photon neutraliser. This paper examines possible designs of a plasma neutraliser taking into account the many constraints imposed by operation in the environment around a fusion reactor, and a schematic design is proposed that meets those constraints. The design chosen uses a beam driven plasma neutraliser, which requires no additional power systems, diagnostics or interlocks.Using a plasma neutraliser is shown to improve the global efficiency to ≈55 %. Although that is below the desired value, reasons why that might be acceptable are discussed.This paper also discusses the possible use and benefits of such a neutraliser as an upgrade of the ITER heating neutral beam system.