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Author: Jeremy D Lore
Requested Type: Poster
Submitted: 2016-02-22 09:37:05

Co-authors: J-W. Ahn

Contact Info:
1 Bethel Valley Rd
Oak Ridge, TN   37831

Abstract Text:
The application of 3D magnetic field perturbations on NSTX has been observed to cause a detached divertor plasma on the low field side of the device to reattach [1]. When deuterium gas puffing is used to increase the plasma density the primary strike point can be again detached, however the outer heat flux peaks caused by strike point splitting remain. Further increasing the density causes degradation in the core confinement. This behavior is of concern for ITER operation, which is currently envisioned to require the simultaneous conditions of a partially detached divertor, applied 3D magnetic perturbations for ELM control, and good core confinement. The 3D fluid plasma and kinetic neutral transport code EMC3-EIRENE [2] is used to model these NSTX experiments. The simulations are able to reproduce the experimental trends, with an axisymmetric plasma transitioning to detachment at a lower density than a simulation with 3D fields. In the non-axisymmetric case the multiple heat flux peaks caused by the 3D (vacuum) magnetic field structure transition from sheath limited to high recycling to detached from the primary strike point outward. The outer heat flux peaks remain attached at a higher density than the primary strike point due to two effects: 1) the short connection length to the hot core plasma and 2) the transition of the primary strike point out of the sheath limited regime, which causes flux carried by cross-field transport to be diffusive radially outward. Quantitative comparisons remain challenging due to limitations and lack of constraints in the model, including the lack of heat flux limiters and volume recombination, and the freedom to assign the cross-field particle and heat diffusivities as a 3D function of space. Potential impacts of these effects and the status of model advancement are discussed.
Work supported by US DOE: DE-AC05-00OR22725, DE-AC02-09CH11466.
[1] J-W. Ahn, et al., PPCF 56, 015005 (2014).
[2] Y. Feng, et al., JNM 266, 812 (1999).