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

2. 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

3. 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.

4. 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 > 10 20 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 

5. 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

6. 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

7. 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

8. 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.

9. 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

10. 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 10 -10 10 -2 10 4 10 0 CURRENT DIFFUSION 10 -8 10 -6 10 -4 10 2 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

11. 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)

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

13. 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

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

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

16. 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 http://swim.gat.com:8080/ Simulation of Wave Interactions with MHD (SWIM)

17. 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

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

19. 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.