Simulation Analysis of Charge-Exchange Losses During Neutral Beam Injection on EAST

Abstract

Neutral beam injection (NBI) is one of the most effective heating methods on modern tokamak. As one of the two main losses during the NBI discharge, the charge-exchange (CX) losses are hard to measure due to their scattering. In this paper, through the simulation analysis with NUBEAM and ONETWO, CX losses have been investigated to obtain a rough evaluation by comparing to the shinethrough losses or the beam power. Firstly, according to the simulation results, the ratio of CX losses to the shinethrough losses varies from 0.28 to 1.87 in the scanning of plasma and NBI parameters. Thus, CX losses should not be ignored in the evaluations of the Low–High power threshold and beam torque in beam-heated discharges. Secondly, when T _e (0) > 1 keV, CX losses have little relationship with the increasing temperature and can be roughly estimated as 17 % of the beam power or 85 % of the shinethrough losses. Finally, in the high collisional plasma, CX losses and shinethrough losses increase with the injected 80 keV neutral beam power. However, the ratio of them is almost similar. Thus, CX losses can be estimated as about 30 % of the shinethrough losses. On the other hand, scans of injected 4 MW neutral beam energy show that the beam energy has little effect on CX losses, which can be approximately estimated as 5 % of the beam power. Therefore, based on the simulation results, for EAST-NBI-1, when the line-average density $\bar{n}_{e} = 3 \times 10^{19} /{\text{m}}^{3}$, P _NBI  = 2 MW and E _NBI  = 50 keV, the total beam losses (CX losses and shinethrough losses) are about 30 % of the beam power. These conclusions will be valuable for the experimental analysis of beam-heated discharges on EAST.