Research, Design, and Development Needed to Realise a Neutral Beam Injection System for a Fusion Reactor

Abstract

The ion temperature in the plasma in a fusion reactor must be sufficiently high that the fusion reaction (probably between D + and T +) will need to be high to ensure that the reaction rate is as high as is required. The plasma will be heated by the energetic alpha particle created in the fusion reaction, but it is widely accepted that additional (externally supplied) heating will also be required to ensure a sustained "burn" and, perhaps, to control the reaction rate. A reactor based on the tokamak confinement system requires a toroidal current to flow in the plasma. Most of that current will be created by the "bootstrap" effect, but an external method of driving current in the poloidal centre of the plasma is needed as the bootstrap current will be low, or zero in that region. Neutral beam injection is an efficient heating mechanism and it has the current drive efficiency required in a reactor. In this chapter the R&D required for an NBI system for a reactor, is considered against the background of the ITER NBI system design as the ITER beam energy and operating environment are reactor relevant. In addition the elements requiring most development are identified.

Surface production of negative ions from pulse-biased nitrogen doped diamond within a low-pressure deuterium plasma

“…In plasma-based sources, negative ions are produced using either volume production or surface-production processes, however surface production processes are typically dominant where a high current of negative ions are required [1,11,16]. Increasing the negative ion production from surfaces is typically achieved through the introduction of low work function metals such as caesium, which introduces complex engineering challenges [16,[19][20][21][22].…”