Phil Snyder and Jerry Hughes (MIT) jointly presented a plenary talk on theoretical predictions of the Super H-Mode regime, and experiments to test those predictions and achieve high pedestal pressure at Alcator C-Mod, at last month’s US/EU Transport Task Force Workshop in Williamsburg, VA. The EPED pedestal structure model [Snyder NF2011], predicts that for strongly shaped plasmas above a critical density, the usual H-Mode pedestal solution splits into multiple solutions, including the H-Mode solution and a “Super H-Mode” solution at much higher pressure. The predicted Super H-Mode regime was first achieved on DIII-D [Solomon PRL14, Snyder NF15], employing feedback control of density to reach very high pedestal pressure at high density. The EPED model predicts that high triangularity discharges on Alcator C-Mod also have access to Super H-Mode at sufficiently low density and that low-n current driven modes will limit the pedestal in this regime. Experiments conducted on Alcator C-Mod employed I-Mode to H-Mode transitions triggered by a change in magnetic balance to enter a low density H-Mode. These discharges reached the predicted pedestal pressure for current-driven mode limited operation, and observed n=1 modes consistent with predictions. Raising the current to 1MA, and later to 1.4MA, enabled very hot, high pressure pedestals, in line with predictions. The 1.4MA discharge, based on preliminary analysis, entered the Super H-Mode regime and achieved a pedestal pressure of ~80 kPa, which appears to be the highest pedestal pressure ever achieved on any device, reaching ITER-like pedestal pressure at ITER-like toroidal and poloidal field.
Yueqiang Liu gave a plenary talk at the last TTF Meeting, entitled “Plasma response to RMP fields and consequences on momentum transport during ELM control”. He also reported new results on modeling the plasma density pump-out in DIII-D RMP experiments, using the recently updated quasi-linear code MARS-Q. It was found that the NTV particle flux, which is resonantly enhanced near the radial location of vanishing ExB flow during ELM suppression, plays a significant role in density pump-out.
O. Meneghini, S. Smith and B. Grierson gave a live demonstration at TTF of the suite of analysis and predictive transport capabilities that are publicly available to the community via OMFIT. The live demo included OMFIT-driven TRANSP interpretative and predictive runs, TGLF turbulent flux spectra and multidimensional sensitivity studies, and self-consistent core-pedestal predictions in TGYRO leveraging neural-network models. O. Meneghini also participated in a TRANSP users group meeting held at PPPL to discuss the possible inclusion of neural-network based models for the pedestal (EPED1-NN) and turbulent transport (TGLF-NN) in TRANSP. At the meeting, numerous presentations and interventions highlighted how the TRANSP module within the OMFIT framework is now the method of choice for the execution and post-processing of DIII-D and JET TRANSP runs. Amongst the most notable examples of the synergy between the two codes, it was reported that JET scientists are utilizing TRANSP runs driven by OMFIT for extrapolating JET experiments to D-T scenarios. Work towards expanding the support of TRANSP runs via OMFIT at C-Mod and EAST is in progress, and future plans for KSTAR were also discussed.
Emily Belli, Valerie Izzo, Brendan Lyons, and Gregorio Trevisan attended the 2017 International Sherwood Theory Meeting in Annapolis Md this week. Emily Belli presented a poster on her recent work on the “Influence of Sonic Toroidal Rotation on Gyrokinetic Stability”. Val Izzo described her work on “Shell-pellet modeling for disruption mitigation in DIII-D”. Brendan Lyons discussed work on “Understanding plasma response to 3D magnetic perturbations using automated and integrated magnetohydrodynamics modeling”, and Gregorio Trevisan described the investigations on the “Effects of 3D magnetic perturbation fields on the Small Angle Slot divertor”.
These highlights are reports of research work in progress and are accordingly subject to change or modification