Planned Theory Contributions to the FY’2011 Joint Research Target on Pedestal Research R. J. Hawryluk Thanks to the Pedestal Working Group: C-S Chang, P. Diamond, R. Groebner, J. Hughes, R. Maingi, P. Snyder and X. Xu September 7, 2010

Joint Research Target for 2011 Experiment: Improve the understanding of the physics mechanisms responsible for the structure of the pedestal and compare with the predictive models described in the companion theory milestone. Perform experiments to test theoretical physics models in the pedestal region on multiple devices over a broad range of plasma parameters (e.g., collisionality, beta, and aspect ratio). Detailed measurements of the height and width of the pedestal will be performed augmented by measurements of the radial electric field. The evolution of these parameters during the discharge will be studied. Initial measurements of the turbulence in the pedestal region will also be performed to improve understanding of the relationship between edge turbulent transport and pedestal structure.

Joint Research Target for 2011 Theory: A focused analytic theory and computational effort, including large-scale simulations, will be used to identify and quantify relevant physics mechanisms controlling the structure of the pedestal. The performance of future burning plasmas is strongly correlated with the pressure at the top of the edge transport barrier (or pedestal height). Predicting the pedestal height has proved challenging due to a wide and overlapping range of relevant spatiotemporal scales, geometrical complexity, and a variety of potentially important physics mechanisms. Predictive models will be developed and key features of each model will be tested against observations, to clarify the relative importance of various physics mechanisms, and to make progress in developing a validated physics model for the pedestal height.

Solicited Input on Theory Contributions Input based on input from: Modeling– C. S. Chang regarding CPES – P. Snyder regarding EPED – X. Xu regarding BOUT/BOUT++ Comparison of Theory with DIII-D experiments Input from R. Groebner Looking for more contributions – Suggestions that can influence the experimental program – What can we test? – What is important in defining the pedestal width and height and what isnot? – What are the underlying physics mechanisms?

First Quarter Develop a preliminary research plan coordinated among the threefacilities, delineating the planned experiments aimed at developingunderstanding of the physics mechanisms responsible for the structureof the pedestal. Provide to the theoretical community a sample set of existingpreliminary pedestal data prior-to and following an ELM, including density and temperature, suitable for initial comparisons withsimulation. Develop a preliminary coordinated research plan for simulationactivities, delineating a planned set of simulations aimed at comparison with experiment. The theoretical community will begin the process of developing code interfaces to compare the code predictions with experimental data.

This Meeting is Part of the Effort to Develop a Coordinated Plan. Code interface requirements have been identified by X. Xu – Use a- and g-files from kinetic Efits and measured profiles from p-files – Will enable the transfer of experimental data to the theory/simulationcommunity Research Forums in December will further define and refine theexperimental plans. – One goal of the meeting is to foster the dialogue between the Theory andExperimental community to develop an effective plan.

Modeling Plans for First Quarter CPES: – Evaluate neoclassical ExB shear profile and pedestal structures(XGC0) – Analyze anomalous transport and its effect on ExB shear andpedestal structures (XGC0) – Compare with experiments to determine the role of neoclassical andanomalous effects in pedestal physics EPED: – Complete development of EPED2 – Continue comparing existing EPED, P-B and KBM models to existingdata BOUT/BOUT++ – Conduct BOUT/BOUT++ simulations for existing experimental data tocalibrate the size of electron viscosity/hyper-resistivity for ELMs sizes – May develop an empirical formula for dependence of hyper-resistivity onpedestal collisionality – Calculate turbulent transport due to viscous ballooning modes (or CDBM)in H-mode plasmas

Second Quarter Initial planned experiments will have been carried out on at least one of the three facilities and results conveyed to the theoretical community to inform the simulation program activities. Initial comparison of theory and experiment using the existing sample data set will have been carried out with at least two models. Results from the comparison will be conveyed to the experimental community to inform plans for remaining experiments.

Modeling Plans for Second Quarter CPES: –Calculate anisotropic ion distribution function in the pedestal, near LCFS, and in SOL (XGC0, XGC1) EPED: –Test EPED, P-B and KBM models on first quarter data BOUT/BOUT++ –Validate BOUT++ ELM simulations with data –Test the empirical formula for hyper-resistivity dependence on pedestal collisionality –Implement an analytical Diamond ETG model (if developed) for hyper- resistivity for self-consistent ELM simulations

Third Quarter Continue experiments accompanied by preliminary reduction of initial data, with results made available to the theoretical community. Comparison of theory and experiment will be extended to include a broader set of experimental conditions. Based on the results of experiments and simulations, remaining experimental plans will be adjusted and simulation models will be refined and extended.

Modeling Plans for Third Quarter CPES: –Calculate the role of neutral fueling on pedestal profile evolution (XGC0) EPED: –Test EPED, P-B and KBM models on additional data –Initial testing of EPED2 BOUT/BOUT++ –Validate the physics based hyper-resistivity ELM simulations with ELM data set –Validate the physics based hyper-resistivity turbulence simulations with H-mode data set

Fourth Quarter Complete experiments and simulations. Compare key features of relevant theoretical models against observations to clarify the relative importance of various physics mechanisms. Submit a report documenting completion of these activities, which includes summary data, simulation results, implications for future work, and a brief, preliminary assessment of the implications for ITER.

Modeling Plans for Fourth Quarter CPES: –Study pedestal structure under self-consistent turbulence (XGC1) –Compare turbulence fluctuation property and transport data with experiments across pedestal EPED: –Complete tests of EPED (both 1 and 2), P-B, and KBM models. BOUT/BOUT++ –Complete validations with ELM data set and draw possible conclusions Draw conclusions for ITER

Additional Theory-Experimental Comparisons Considered at DIII-D Test EPED and ELITE predictions Search for KBM –Vary magnetic shear and see if critical pressure gradient responds as predicted –Look for evidence that steepest part of pressure gradient experiences some flattening, perhaps in a bursty fashion Evaluate and test predictions of Paleoclassical Evaluate role of ExB shear in the pedestal to control transport Test Diamond’s model of Ti barrier width expansion in long ELM-free discharges Evaluate role of neutral fueling in density profile evolution (SOLPS, BOUT, GTEDGE, OEDGE…. Determine roles of neoclassical and anomalous transport (XGCO/ASTRA) Non-linear ELM evolution (BOUT/M3D) Measure and compute ion distribution function near LCFS or in SOL Compare with predictions from GYRO, TGLF, GEM….

Aspirations for This Meeting Identify additional physics mechanisms that can be tested in the upcoming run campaigns. –C-Mod and NSTX campaigns begin in October! Stimulate novel experimental ideas and diagnostics Identify specific experimental tests of theory and modeling predictions of pedestal transport and structure. –What other codes and analytic models can we apply to this problem? –Current list of theory contributions to the JRT is not meant to be all encompassing.