Exploration of Fusion Plasmas Using Integrated Simulations Jill Dahlburg, Naval Research Laboratory Presented by Dale Meade, Princeton University With contributions from: Steve Jardin Princeton University and Doug Post, Los Alamos & from FESAC Integrated Simulation & Optimization of Fusion Systems) Subcommittee Jill Dahlburg,* Naval Research Lab (Chair); James Corones, Krell Institute, (Vice-Chair); Donald Batchelor, Oak Ridge National Laboratory; Randall Bramley, Indiana University; Martin Greenwald, Massachusetts Institute of Technology; Stephen Jardin, Princeton Plasma Physics Laboratory; Sergei Krasheninnikov, University of California - San Diego; Alan Laub, University of California - Davis; Jean-Noel Leboeuf, University of California - Los Angeles; John Lindl, Lawrence Livermore National Laboratory; William Lokke, Lawrence Livermore National Laboratory; Marshall Rosenbluth; David Ross, UT - Austin; and, Dalton Schnack, Science Applications International Corporation Office of Science

Outline of Presentation Goals Issues and Challenges Examples of Current Work New Capabilities Required Future Plans

Experiments Diagnostics Integrated Simulation Theory Progress in Theory, Diagnostics, Experiments and Computer Capability make Large Scale Integrated Simulations Meaningful Capabilities Required to Make Progress in Fusion Science

A Tokamak Burning Plasma Experiment (ITER) Large - 30m tall, 20 ktonne expensive $5B + complex first burning plasmas 2018 An international effort (JA, EU, US, RF,CN, ROK) is underway negotiate a site and cost-sharing arrangement to build ITER. Latest news

An Integrated Simulation of Burning Plasmas is Needed Burning plasmas are complex, non-linear and strongly-coupled systems. highly self driven (83% self-heated, 90% self-driven current) plasmas are needed for power plant scenarios. Does a burning plasma naturally evolve to a self-driven state? A burning plasma simulation capability would be of great benefit to: Understand burning plasma phenomena based on existing exp’ts Refine the physics and engineering design for a BP experiment Provide real time control algorithm for self-driven burning plasma, and to optimize experimental operation Analyze the experimental results and transfer knowledge knowledge.

Elements of an Integrated Tokamak Plasma Model Sawtooth region q < 1 (MHD and global stability) Core confinement region (turbulent transport) Magnetic islands q = 2 (MHD and global stability) Edge pedestal region (edge physics, MHD, turbulence) Scrape-off layer (parallel flows, turbulence, atomic physics) Vacuum/Wall/Conductors/Antenna MHD equilibrium, RF and NBI physics Each of these different phenomena can be examined by an appropriate set of codes. Simplified models can be produced for use in the Integrated Modeling code, and can be checked by detailed computation

Typical Time Scales in FIRE SEC. CURRENT DIFFUSION ISLAND GROWTH ENERGY CONFINEMENT SAWTOOTH CRASH  FW RF Codes Electron Gyrokinetics Ion Gyrokinetics 2D MHD (Transport Codes) 3D Extended MHD Codes Telescoping in time is necessary because of the wide range of timescales present in a fusion device. Not possible to time-resolve all phenomena for entire discharge time as it would require or more time steps.  LH -1  ci -1  A  ce -1 ELECTRON TRANSIT TURBULENCE Burning Plasma Physics Spans Many Time Scales

These need to be integrated into one comprehensive simulation code. Major US Toroidal Physics Design & Analysis Codes Used by Plasma Physics Community * Examples of results follow. * * * * *

Example of Present Integrated Modeling Capability

Present capability: TSC (2D) simulation of an entire burning plasma tokamak discharge (FIRE) Includes: Ohmic heating Radio-Freq Wave heating Alpha-particle heating Microstability-based transport model L/H mode transition Sawtooth Model Evolving Equilibrium with actual coils and eddy currents in vessel

Additional Features are Needed for BP Simulation 2-D Physics including: model for density profile, plasma-wall interaction and pumping model for edge ion temperature - important for core transport model model for edge plasma- turbulence, parallel flow, atomic physics 3-D Physics including: MHD instabilities (local) - sawtooth, alpha driven, MHD instabilities (global) - kink - feedback stabilization, disruption fueling - pellet injection

From: D. Schnack, 2003 SIAM Conference on Computational Science and Engineering (Feb. 2003) The Beginning of Disruption Models Increase in neutral beam power Plasma pressure increases Sudden termination (disruption) Time dependence at disruption onset Growing 3-D magnetic perturbation Nonlinear evolution? Effect on confinement? Can this be predicted? Example: DIII-D shot 87009

3-D Nonlinear MHD SciDAC Codes Two major development projects for time-dependent models – M3D - multi-level, 3-D, parallel plasma simulation code Partially implicit Toroidal geometry - suitable for stellarators 2-fluid model Neo-classical and particle closures –NIMROD - 3-D nonlinear extended MHD Semi-implicit Slab, cylindrical, or axisymmetric toroidal geometry 2-fluid model Neo-classical closures Particle closures being debugged Both codes exhibit good parallel performance scaling. From: D. Schnack, 2003 SIAM Conference on Computational Science and Engineering (Feb. 2003) * *

Computational Challenges Extreme separation of time scales: –Realistic “Reynolds’ numbers” –Implicit methods Extreme separation of spatial scales –Important physics occurs in internal boundary layers –Small dissipation cannot be ignored –Requires grid packing or Adaptive Mesh Refinement Extreme anisotropy –Special direction determined by magnetic field –Requires specialized gridding operator is important Accurate treatment of (  Alfven transit <  sound transit <<  MHD evolution <<  resistive diffusion ) Inaccuracies lead to “spectral pollution” and anomalous perpendicular transport.

The fusion community is planning an integrated simulation capability: “The Fusion Simulation Project”

Fifteen-Year Goal: Fusion Plasma Simulator (FPS) Envisioned to be an integrated research tool that contains comprehensive coupled self-consistent models of all important plasma phenomena that would be used to guide experiments and be updated with ongoing results. Would serve as an intellectual integrator of physics phenomena in advanced tokamak configurations, advanced stellarators and tokamak burning plasma experiments. Would integrate the underlying fusion plasma science with the Innovative Confinement Concepts, thereby accelerating progress. This need was recognized at the 2002 Fusion Summer Study at Snowmass and in the report of the FESAC Development Path Subcommittee charged with identifying the requirements for the production of electricity from fusion energy in 35 years.

Fusion Simulator Project Priority is to Support Burning Plasma Experiments. Ray Orbach, Director, DOE Office of Science –“ITER (Burning Plasmas) is the number 1 priority project for the US DOE Office of Science. –Ultra-Scale Scientific Computing Capability is the number 2 priority for the US DOE Office of Science.” FSP logic: The Fusion Simulation Project is in the number 2 priority category supporting the number 1 priority Develop “predictive capability” for Burning Plasmas

A Specific Task: Control of a Burning Plasma (ITER) Real time control of the burning plasma will be essential to meet performance goals and avoid operational limits (e.g. disruptions) Use hierarchy of models in real time to interpret diagnostic data, control plasma actuators, feedback and feed-”forward” control algorithm predict plasma response Model all aspects of plasma behavior FSP Simulation Will optimize performance of burning plasma experiments Will facilitate rapid testing of models and theory with real experimental data Can unify computational, theoretical and experimental fusion communities

Full Burning Plasma Simulations will Require an Increase In Computing “Speed” by ~ 10 6, possible by 2015?

Focused Integration Initiatives The full extent of the 15-year project is expected to require on the order of $0.4B.

Concluding Remarks Numerical modeling has advanced to the stage where it plays an important role in understanding and predicting plasma behavior in existing experiments. Full predictive modeling of fusion plasmas will require cross coupling of a variety of physical processes and solution over many space and time scales. Plans are being made for an integrated fusion simulation activity, the Fusion Simulation Project (FSP). Full simulations of burning plasma experiments could be possible in the 5-10 year time frame if an aggressive growth program is launched in this area. A Fusion Simulator would have significant benefits to the fusion science program and to a Burning Plasma Experiment. Fusion simulation web site w3.pppl.gov/CEMM Talks for this session will be linked from