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McKee, G. R.

Publications and source records attributed to McKee, G. R..

22 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Impact of resonant magnetic perturbations on zonal flows and microturbulence

Results from a joint experimental and computational effort studying the effect of resonant magnetic perturbations (RMPs) on microturbulence levels and their connection to zonal flows in the DIII-D tokamak L-mode are presented. Beam emission spectroscopy measurements show a direct increase in density fluctuations at microturbulent scales with increasing RMP amplitude, suggesting that magnetic activity introduced by the RMP affects the regulation of microturbulence on DIII-D. This is analogous to how MHD-scale magnetic fluctuations arising from tearing modes have been observed in simulations to increase microturbulence levels in the reversed-field pinch (RFP). In the RFP, this is attributed to magnetic fluctuations eroding turbulence-limiting zonal flows; this work examines if a similar mechanism is present for DIII-D microturbulence. Gyrokinetic simulations find that the application of an RMP corresponds directly to a decrease in zonal flow levels, producing a similar increase of turbulent fluctuation levels over a range of RMP amplitudes as observed in the experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Collisionality driven turbulent particle transport changes in DIII-D H-mode plasmas

The results of the experimental dimensionless scan in this paper confirm that there is an increase in density peaking towards lower collisionality and that this can be partly linked to a shift in the turbulence regime from ITG towards TEM. However at the lowest collisionality, the changes in turbulence and transport are much more pronounced than expected from direct collisionality effect on the turbulence. In this paper, the collisionality, ν * is varied by a factor 5, while keeping ρ * , q , β , M , fixed. Additionally, a 3 Hz gas puff modulation is applied to modulate the electron density profile and extract the perturbed transport coefficients using two diagnostics. The transport analysis shows that the increase in density peaking at low ν * is linked to an increase in the inward particle pinch and not an increase in core fueling. These observations are not only in agreement with prior modeling scans of how turbulence changes as a function of collisionality and its impact upon the particle fluxes, but also with the multi-machine database (Fable E. et al 2010 Plasma Phys. Control. Fusion 52 015007) (Angioni C. et al 2003 Phys. Rev. Lett. 90 205003). The changes in turbulence across the collisionality scan were captured at large scale by the BES and at smaller scale by the DBS. A comparison with gradient-driven GENE simulations showed similar trends at both scales. Moreover, the changes observed in overall transport are in agreement with gradient-driven TGLF particle flux simulations. This indicates that TGLF/GENE when given the gradients as input, are able to reproduce the experimentally observed turbulence changes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗