An intense neutral beam injected into thermonuclear plasmas plays important role in various stages of fusion reactor operations. The beam particles slow down, deposit most of their energy via Coulombic collisions, and create a tail (non-Maxwellian component) in velocity distribution function of the same ion species as the one injected. It is well known that for suprathermal ions, the nuclear elastic scattering (NES) by thermal ions contributes to the slowing-down process. According to the recent scaling up of the fusion experimental devices, the use of beam energy more than 1 MeV is considered. In this case, the NES effects on the slowing down process of injected beam particles may be important to understand device performance during plasma heating operations. The purpose of this paper is to quantitatively estimate the NES effect on neutral-beam-injection (NBI) plasma heating.

The NES is a non-Coulombic, large-energy-transfer (LET) scattering process. Recently we have derived the energy loss rate of high-energy ions due to the NES, including the LET knocking-up of background ions from thermal to higher energy range[1]. On the basis of the derived expression, we have estimated the NES effect on the fraction of beam energy deposited to ions. In this paper by solving the plasma power-balance and the particle conservation equations, we further estimate the NES effect on plasma startup process. It is shown that when the beam energy is higher than 1 MeV, the NES effects on NBI heating becomes appreciable.

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