Abstract
The toroidal force related to electron cyclotron heating (ECH) is investigated in large helical device (LHD) plasmas. When we apply the ECH to the plasma kept by neutral beam injection (NBI) heating, the radial profile of the toroidal flow velocity changes drastically in LHD. ECH-generated supra-thermal electrons can apply forces on the plasma through radial electron current and collisions. We investigate the perturbed electron distribution due to ECH by using the GNET code, which can solve the 5D drift kinetic equation. We also evaluate the electromagnetic force due to radial current and the collisional force driven by ECH. As a result, we find a comparable force driven by ECH to that by NBI heating. The direction of the force is the counter (co) direction radially inside (outside) from the ECH heating location, and these directions correspond with that of experiment results. Finally, we evaluate toroidal flows in ECH and NBI heated plasma solving the radial diffusion equation and compare them with that of experimental observations. We reproduce the co-rotating toroidal flow quantitatively in the balanced-NBI+ECH heated case, but we see a difference in the toroidal flow profiles in the co-NBI+ECH heated case.
Highlights
Many experiments suggest the important role of toroidal flow in turbulence transport
In the case where co-Neutral Beam Injection (NBI) heating and off axis electron cyclotron heating (ECH) are applied, the toroidal flow velocity decreases at the core region and increases outside of the ECH heating location
The purpose of this study is to clarify the effect of ECH driving force, so we select three sets of parameters (D, μ ) so that the obtained flows in the Co-NBI heating case have agreed reasonably
Summary
The toroidal force related to electron cyclotron heating (ECH) is investigated in large helical device (LHD) plasmas. When we apply the ECH to the plasma kept by neutral beam injection (NBI) heating, the radial profile of the toroidal flow velocity changes drastically in LHD. ECH generated supra-thermal electrons can apply forces on the plasma through radial electron current and collisions. We find a comparable force driven by ECH to that by NBI heating. The direction of the force is the counter (co) direction radially inside (outside) from the ECH heating location, and these directions correspond with that of experiment results. We evaluate toroidal flows in ECH and NBI heated plasma solving the radial diffusion equation and compare them with that of experimental observations.
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