Sherwood 2015

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approved15_evans_sherwood_fv.pdf2015-04-28 09:28:32Todd Evans

3D Magnetic Perturbation Effects on Confinement during ELM Control Experiments

Author: Todd E. Evans
Requested Type: Consider for Invited
Submitted: 2015-02-06 12:58:18


Contact Info:
General Atomics
3550 General Atomics Ct
San Diego, California   92121

Abstract Text:
Experiments in Ohmic to L-mode and H-mode plasmas have demonstrated that the energy, momentum and particle confinement are significantly more sensitive to small 3D magnetic perturbation than theoretically expected. In Ohmic plasmas with relatively strong vacuum field stochasticity, the thermal diffusivity is increased by approximately 2 orders of magnitude in the edge stochastic region while the core energy confinement is maintained or moderately improved. In low triangularity H-mode plasmas, ion and electron temperatures can increase significantly in the core and slightly in the edge due to the applied 3D magnetic field perturbations, while the particle confinement in the edge is typically degraded. Moderate improvements in the particle confinement have also been observed inside psi_N=0.3-0.4 in some plasma configurations. These results contradict theoretical expectations based on the existence of an edge stochastic layer due to overlapping resonant magnetic islands as determined from vacuum magnetic field modeling. In H-mode plasmas, one hypothesis is that strong electron fluid poloidal flows in the pedestal region screen the resonant field components, which prevents the formation of a stochastic layer. If this is the case, then a mechanism is needed to explain the relatively large drop in the edge particle confinement while maintaining reasonably good H-mode energy confinement. Understanding the plasma response to these applied 3D magnetic perturbations has become a high priority in fusion research as a result of recent successes in stabilizing Edge Localized Modes (ELMs) with Resonant Magnetic Perturbation (RMP) fields. This talk will focus on experimental results found during the application of RMP fields in various tokamaks including changes in the particle, energy and momentum confinement during ELM suppression. Implications of these results for ITER and fusion energy research will also be discussed.


March 16-18, 2015
The Courant Institute, New York University