Theory Weekly Highlights for October 2016

October 28, 2016

Philip Snyder, Gary Staebler, Orso Meneghini, and Chris Holland attended International Tokamak Physics Activity (ITPA) meetings in Naka, Japan. Dr. Snyder presented two talks, one a summary and discussion of the ITPA Pedestal Structure Working group’s progress and activities, and another a response by the ITPA Pedestal group to requests from the Integrated Operating Scenarios (IOS) group for predictions of the ITER pedestal structure. This response included more than 15,000 predictions of ITER pedestal height and width from the EPED1 pedestal model for a wide variety of ITER parameters. Dr. Meneghini presented a report on the use of neural nets for core transport, and a talk on “Self-consistent core-pedestal coupled transport simulations with neural network TGLF-NN and EPED1-NN models.” Dr. Staebler presented talks on “Validating the multi-scale contribution to the L-mode shortfall problem,” and (with J.M. Park) on “Validation of the TGLF-SAT1 model on the DIII-D ITER-like current ramp data.” Dr. Holland presented talks on “Investigation of the shortfall issue using the new CGYRO code,” and “Comparison of GYRO and TGLF predictions to experiment for a DIII-D H-mode stiffness study.”

October 21, 2016

A number of people from the GA Theory group attended the 26th IAEA Fusion Energy Conference in Kyoto, Japan. At the meeting, Orso Meneghini delivered an oral presentation on “Integrated Fusion Simulation with Self-Consistent Core-Pedestal Coupling” summarizing the GA Theory effort on integrated modeling of the core and edge in tokamaks, and C. Holland gave a talk on “Demonstrating the Multiscale Nature of Electron Transport Through Experimentally Validated Simulations”. Rui Ding had a rapporteured presentation on “Advances in Understanding of High-Z Material Erosion and Redeposition in Low-Z Wall Environment in D”. In addition to Phil Snyder and Lang Lao attending as observers, posters covering recent transport and confinement work were presented by J. Candy on “Crucial role of zonal flows and electromagnetic effects in ITER turbulence simulations near threshold”, G.M. Staebler on “A Model of the Saturation of Coupled Electron and Ion Scale Gyrokinetic Turbulence”, and R.E. Waltz on “A critical gradient model for energetic particle transport from Alfven eigenmodes: GYRO verification, DIII-D validation, and ITER projection”.

October 14, 2016

A new zonal flow mixing saturation model for gyrokinetic turbulence, based on multi-scale GYRO simulations, has been validated with DIII-D L-mode data. The electron and ion temperatures were predicted with TGLF using the new model, taking the boundary condition very close to the separatrix. The shortfall in the predicted electron energy transport was reduced for the new model compared to the original one in all cases, due to enhanced electron scale streamer transport. However, there is still a shortfall for lower current and lower density L-modes. Additional multi-scale GYRO simulations are needed to more fully delineate the parametric dependencies of the zonal flow-mixing model.

October 07, 2016

As recently reported (see highlight from May 27 at Theory Weekly Highlights for May 2016), the growth rates for energetic particle (EP) driven local Alfven eigenmodes (AEs) from the TGLF reduced model have been found to be in excellent agreement with expensive GYRO gyrokinetic simulations when the high resolution wavefunctions are used in TGLF. This new TGLF capability provides a very efficient way to map out the local safety factor (q) and shear (s) dependence of the DIII-D critical gradient profile for AE-EP transport. An early phase of current penetration with qmin~4.5 has significant (50%) transport loss of central core EPs while the transport loss is negligible as the current fully penetrates with qmin dropping to 1.0.

These highlights are reports of research work in progress and are accordingly subject to change or modification