Research, Design, and Development Needed to Realise a Neutral Beam Injection System… DOI: http://dx.doi.org/10.5772/intechopen.88724

Thus it is interesting to look at the expected efficiency of the ITER injectors to see where improvements must be made. Table 1 shows the expected performance of an ITER-like injector plus indications of possible performance changes that could lead to an injector operating on a fusion reactor. Each of the suggested changes is discussed in more detail below.

Before discussing the various items impacting the global efficiency, it is important to understand some of the more important constraints on the design of the injectors.

Firstly, the injectors will need to be commissioned after the first installation on the reactor and then maintained and recommissioned several times during their lifetime. Commissioning or recommissioning of all the injectors involves firing the neutral beam through the beamline components and into a beam dump, usually called a calorimeter. The overall process is that at the start of commissioning, the beam source is operated at low power and beam energy and for short pulse lengths, for example, 5–10 s. That ensures safe operation of the system even if the beam quality, such as the beamlet divergence, is not optimal. Once safe, good operation is achieved at the selected low power, the beam power, energy, and pulse length are gradually increased. This continues until full power and pulse length are achieved, always with the neutral beam being intercepted on the calorimeter. No system has yet been developed which allows commissioning of the high power beam system without a calorimeter. As it is almost certain that a calorimeter is required, it must be designed to withstand the power and power density it will be subjected to, and this has been demonstrated to be a restricting factor in the design of an injector for the ITER heating NB injectors. The calorimeter was one of the most difficult beamline components to be designed, and it can be reasonably considered that the power and power density handling of the ITER calorimeter design is close to the limit of what is technologically possible. Thus the beamline calorimeter sets a limit on the neutral beam power that can be produced by a neutral beam injector of ≈17 MW. In Table 1, the changes to be made for an injector to be used in a fusion reactor are such that this limitation is respected.

Table 1 gives a calculation of the global efficiency of an ITER-like heating neutral beam injector (HNB) and of a possible injector for a fusion reactor. Both deliver ≈17 MW of 1 MeV D0 to the plasma in the device. The calculations in Table 1 assume that for the injector on a fusion reactor:

I.The ion source and accelerator will be similar to those of the ITER-like injector.


A photon neutraliser will be used that has a neutralisation efficiency of 90% and a laser power of 800 kW, with a laser efficiency of 40%. A lower laser efficiency would be acceptable if the required laser power is <800 kW.
