Ripple transport in helical-axis advanced stellarators: a comparison with classical stellarator/torsatrons

Abstract

Calculations of the neoclassical tEUiSpofi rates due to particles trapped in the helical ripples of a stellarator's magnetic field are carried out based on solutions of the bounce-averaged kinetic equation. These calculations employ amodel forthe magnetic field strength, B, whichir. m accurate approximation to the actual B far a wide variety of stellarator-type devices, amone, which are Helical-Axis Advanced Stellmtors (Hdizs) as well as conventional stellarators and torsatrons. Comparisons are cmied out in which it is shown that the Helias concept leads to significmt reductions in neoclassical transpolt rates throughout the entire long-mean-free-path regime, with the reduction being particularly dramatic in the U-' regime. These findings an:wnhrmed by numerical simulations. Further, it is shown that the behaviour of deeply trapped particles in Helias c3n be fundamentally diffemnt from that in classical_stellaratqr/torsatrons; a?; a consequence, the beneficial effects of a radial electric field on the transport make themselves felt at a lower collision frequency than is usual.

Gyrokinetic turbulent transport simulation of a high ion temperature plasma in large helical device experiment

“…The simulation results are 15%-50% lower than that in the experimental values which include both the anomalous and neoclassical contributions to the transport. If we subtract the neoclassical part calculated by the GSRAKE code, 23 the simulation results agree well with the anomalous part of P i , such that the observed differences are less than 10% for q ¼ 0:46; 0:65, and about 30% for q ¼ 0:83 (see also Table I for the ion heat diffusivity v i ). Figure 3 shows the poloidal wavenumber spectra of the turbulent density fluctuation obtained from the PCI measurement and the simulation, where k y is treated as the poloidal wavenumber in the coordinates used in the simulation.…”

Turbulence Response in the High Ti Discharge of the LHD

“…Power balance analysis was conducted using the PROCTR code [4], and neoclassical transport coefficients were calculated using the GSRAKE code [5]. In stellarator/heliotron devices, neoclassical transport is strongly af- fected by the radial electric field (E r ).…”

Core electron-root confinement (CERC) in helical plasmas

“…For the simplest picture of helical devices, the transport scales either as ν 1/2 or ν, depending on whether collisions or drifts are responsible for removing the particles from local ripples. It is possible to determine the mono-energetic diffusion coefficient, D, in each of these three lmfp regimes from asymptotic solutions of the kinetic equation and the scalings obtained may be summarized as [6,12,13] , , ,…”