THE PROBLEM; THE SUCCESSES; THE CHALLENGES HPC Users Forum Houston, TX April 6, 2011 Lee A. Berry Colleagues and Collaborators special thanks to Don Batchelor IFP Discussion August 20, 2010

2Managed by UT-Battelle for the Department of Energy The Environment of Magnetic Fusion Simulation Is One of Collaboration Acknowledgements:  Sponsors: –NSF, DOE (Offices of Science and Advanced Computing)  Collaborators: –MIT, Princeton Plasma Physics Laboratory, General Atomics, ITER, TechX, CompX, Lodestar, U. of Alaska, Fairbanks, U. Carlos III Madrid, Lehigh, U. Tennessee Knoxville, …  Resources: –NERSC, NCCS, PPPL, ARSC, ITER, TechX, MIT, GA, … Theory Program Review

3Managed by UT-Battelle for the Department of Energy Nuclear fusion: The Process of Building up Heavier Nuclei by Combining Lighter Ones It is the process that powers the sun and the stars and that produces the elements.

4Managed by UT-Battelle for the Department of Energy We can get net energy production from a thermonuclear process.  We heat a large number of particles so the temperature is much hotter than the sun, ~100,000,000°F.  PLASMA: electrons + ions  Then we hold the fuel particles and energy long enough for many reactions to occur. Lawson breakeven criteria:  High enough temperature—T (~ 10 keV).  High particle density—n.  Long confinement time— . n e  E > m -3 s Nuclear thermos bottle T T T T T T T T T T T D D D D D D D D D D = 1  breakeven  10  energy-feasible ∞  ignition Q = P fusion P heating 

5Managed by UT-Battelle for the Department of Energy We Confine the Hot Plasma Using Strong Magnetic Fields in the Shape of a Torus  Charged particles move primarily along magnetic field lines. Field lines form closed, nested toroidal surfaces.  The most successful magnetic confinement devices are tokamaks. DIII-D Tokamak Magnetic axis Minor radius  Magnetic flux surfaces

6Managed by UT-Battelle for the Department of Energy ITER: Understand the Science and Engineering for Fusion Power Practicality  500 MW of fusion power, Fusion /Auxiliary Power = 10  Seven party collaboration between EU, US, Japan, China, Korea, India  Sited at Cadarche, France

7Managed by UT-Battelle for the Department of Energy ITER: Understand the Science and Engineering for Fusion Power Practicality  500 MW of fusion power, Fusion /Auxiliary Power = 10  Seven party collaboration between EU, US, Japan, China, Korea, India  Sited at Cadarche, France

8Managed by UT-Battelle for the Department of Energy The Big Questions in Fusion Research  How do you heat the plasma to 100,000,000°F, and once you have done so, how do you control it? –We use high-power electromagnetic waves or energetic beams of neutral atoms. Where do they go? How and where are they absorbed?  How can we produce stable plasma configurations? –What happens if the plasma is unstable? Can we live with it? Or can we feedback-control it?  How do heat and particles leak out? How do you minimize the loss? –Transport is mostly from small-scale turbulence. –Why does the turbulence sometimes spontaneously disappear in regions of the plasma, greatly improving confinement?  How can a fusion-grade plasma live in close proximity to a material vacuum vessel wall? –How can we handle the intense flux of power, neutrons, and charged particles on the wall? Supercomputing plays a critical role in answering such questions.

9Managed by UT-Battelle for the Department of Energy The Computational and Mathematical Challenges Are Substantial  High dimensionality—6D plus time  Large numbers of unknowns 10 7  >10 11  Complex medium –spatially non-uniform –anisotropic –nonlocal –wide range of physics –highly non linear  Wide range of length scales involved –  ~ 100 x L  << L, length scales can interact in localized plasma regions  mode conversion  Basic equations are non-symmetric and dissipative

10Managed by UT-Battelle for the Department of Energy We have been able to make progress by separating out the different phenomena and time scales into separate disciplines SEC. Transport Codes: discharge time-scale CURRENT DIFFUSION CYCLOTRON PERIOD  ce -1  c i -1 SLOW MHD INSTABILITY, ISLAND GROWTH ENERGY CONFINEMENT,  E FAST MHD INSTABILITY, SAWTOOTH CRASH MICRO- TURBULENCE ELECTRON TRANSIT,  T GAS EQUILIBRATION WITH VESSEL WALL PARTICLE COLLSIONS,  C RF Codes: wave-heating and current-drive Gyrokinetics Codes: micro-turbulence Extended MHD Codes: device scale stability

11Managed by UT-Battelle for the Department of Energy 10/4/2015 DBB 11 Major U.S. Toroidal Physics Design and Analysis codes ( Dahlburg et al, Journal of Fusion Energy, 2001)

12Managed by UT-Battelle for the Department of Energy High Power Radio Frequency Heating of ITER Theory Program Review

13Managed by UT-Battelle for the Department of Energy Energy Loss Is Dominated By Micro Turbulence Theory Program Review  ITG (ion temperature gradient) driven turbulence is the most robust and fundamental microturbulence in a tokamak plasma  Whole-volume, full-f ITG simulation for DIII-D  XGC1 scales efficiently to the maximal number of Jaguar cores

14Managed by UT-Battelle for the Department of Energy Wall Street—Money Never Sleeps Theory Program Review

15Managed by UT-Battelle for the Department of Energy The Integrated Plasma Simulator (IPS): A Light-Weight Python Framework Theory Program Review

16Managed by UT-Battelle for the Department of Energy The SWIM Data Portal Has Proven to Be a (Near) Essential Tool for Monitoring/Debugging Simulations Theory Program Review Simulation of Wave Interactions with MHD (SWIM)

17Managed by UT-Battelle for the Department of Energy Time Can be Parallelized If We Are Willing to Use Cycles—Parareal : ~6x wall-clock improvement for 6x cycles: Theory Program Review Plasma Turbulence Simulation Parareal

18Managed by UT-Battelle for the Department of Energy Plasma-Wall Interactions Are Poorly Integrated: High Heat Fluxes, Erosion, Redeposition …. Theory Program Review

19Managed by UT-Battelle for the Department of Energy Summary/Observations (mine)  Advances in simulation capability are providing the tools needed to understand fusion plasmas.  Multiphysics simulations (including materials) and GPU-based HPCs are changing the game.  Partnerships of applied mathematicians, computer scientists and physicists are enabling these advances.