Simulation study of neutral beam injection heating in the HSX plasma

The Neutral Beam Injection (NBI) heating efficiency for the Helically Symmetric Experiment (HSX) plasma is studied by applying two simulation codes: HFREYA and GNET. HFREYA is employed to evaluate the birth profiles of the fast ions by the NBI into the plasma. GNET is used to solve the five-dimensional drift kinetic equation for the beam ions and to evaluate the heat deposition to the ion and electron. We vary the beam energy (15 - 30 keV) and the injection angle of the neutral beam. We also study the effect of the charge exchange loss by neutral particles on the NBI heat deposition. As a result, we obtain heat efficiency of up to 30% with the proper injection angles with the charge exchange loss. On the contrary, the heat deposition rate becomes very small (approximately 1%) in the perpendicular injections case. This small value of the deposition rate is due to the complex orbits of the trapped beam ions. We also find that no clear difference can be seen in the heat depositions between the QHS and Mirror configurations. Furthermore, the heat depositions in the deuterium beam case are smaller than those in the hydrogen beam case. (author)