Extended investigations of isotope effects on ECRH plasma in LHD

Abstract

Isotope effects of ECRH plasma in LHD were investigated in detail. A clear difference of transport and turbulence characteristics in H and D plasmas was found in the core region, with normalized radius <0.8 in high collisionality regime. On the other hand, differences of transport and turbulence were relatively small in low collisionality regime. Power balance analysis and neoclassical calculation showed a reduction of the anomalous contribution to electron and ion transport in D plasma compared with H plasma in the high collisionality regime. In core region, density modulation experiments also showed more reduced particle diffusion in D plasma than in H plasma, in the high collisionality regime. Ion scale turbulence was clearly reduced at  < 0.8 in high collisionality regime in D plasma compared with H plasma. The gyrokinetic linear analyses showed that the dominant instability  =0. 5 and 0.8 were ion temperature gradient mode (ITG). The linear growth rate of ITG was reduced in high D plasma than in H plasma. This is due to the lower normalized ion temperature gradient and density gradient. More hollowed density profile in D plasma is likely to be the key control parameter. Present analyses suggest that anomalous process play a role to make hollower density profiles in D plasma rather than neoclassical process. Electron scale turbulence were also investigated from the measurements and linear gyrokinetic simulations.

Observation of a reduced-turbulence regime with boron powder injection in a stellarator

“…This might be an effect of changes in the plasma profiles, in particular of the peaking of n e in the edge, by the combined effect of the extra electron source provided by the injected powder and the real-time reduction of recycling, finally resulting in a more hollow profile in the centre of the plasma. Hollow density profiles have been reported to increase the stability of ion temperature gradient modes in the LHD, reducing turbulence fluctuations 22,28 . Another possibility is turbulence being reduced by The experimental τ E is plotted against the predicted energy confinement time from the international stellarator scaling T E,ISS04 (ref.…”

“…In refs. 21,22 , similar phase-contrast imaging measurements were compared with gyrokinetic simulations, determining that the observed fluctuations are indeed due to ion temperature-gradient turbulence. Dedicated gyrokinetic simulations are needed to confirm this result for the cases discussed here and are planned for future work.…”

Observation of a novel reduced-turbulence regime with boron powder injection in a stellarator

“…In Refs. [17,18], similar PCI measurements were compared with gyrokinetic simulations, determining that the observed fluctuations are indeed due to ITG turbulence. Dedicated gyrokinetic simulations are needed to confirm this result for the cases exposed here, and are foreseen for future works.…”

“…plasma quantities, in particular of the peaking of n e in the edge, resulting in a more hollow profile in the center of the plasma. Hollow density profiles have been reported to increase ITG stability, reducing turbulence fluctuations [18,21]. Another possibility is turbulence being reduced by the increased effective charge Z ef f due to B injection, also referred to as plasma dilution.…”

W-band millimeter-wave back-scattering system for high wavenumber turbulence measurements in LHD

“…18 The ion scale turbulence observations have been compared with the gyrokinetic simulation (GKV 19,20 ) results. [21][22][23] The introduction of this electron scale turbulence measurement will allow for a more detailed comparative study.…”