The Problem; the Successes; the Challenges

Lee A. Berry (lab@ornl.gov) Colleagues and Collaborators special thanks to Don Batchelor The Problem; the Successes; the Challenges HPC Users Forum Houston, TX April 6, 2011 IFP Discussion August 20, 2010

The Environment of Magnetic Fusion Simulation Is One of CollaborationAcknowledgements: • 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

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.

D T D D D T T D T = 1 breakeven  10  energy-feasible ∞ ignition D Pfusion Pheating D T  Q = T T T D T T T D D 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—. neE > 1020 m-3s Nuclear thermos bottle

Magnetic flux surfaces Minor radius  Magnetic axis 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

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

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.

The Computational and Mathematical Challenges Are Substantial • High dimensionality—6D plus time  Large numbers of unknowns 107  >1011 • Complex medium • spatially non-uniform • anisotropic • nonlocal • wide range of physics • highly non linear • Wide range of length scales involved – l ~ 100 x L  l << L, length scales can interact in localized plasma regions  mode conversion • Basic equations are non-symmetric and dissipative

We have been able to make progress by separating out the different phenomena and time scales into separate disciplines SLOW MHD INSTABILITY, ISLAND GROWTH CYCLOTRON PERIODce-1 ci-1 MICRO- TURBULENCE ENERGY CONFINEMENT, tE CURRENT DIFFUSION 10-10 10-8 10-6 10-4 10-2 100 102 104 PARTICLE COLLSIONS, tC SEC. ELECTRON TRANSIT, tT GAS EQUILIBRATION WITH VESSEL WALL FAST MHD INSTABILITY,SAWTOOTH CRASH RF Codes: wave-heating and current-drive Gyrokinetics Codes: micro-turbulence Extended MHD Codes: device scale stability Transport Codes: discharge time-scale

Nonlinear Gyrokinetic Vacuum & Conductors Linear Stability Gyrofluid MHD- + particles Ideal Non-Ideal global Flux tube Flux tube VACUUM low-n high-n low-n GYRO GS2 low-n high-n GRYFFIN VALEN PEST-I,II PEST-III HINST NOVA-K BALLOON Particle-in-cell Free Boundary Equilibrium global Flux tube NOVA MARS ORBIT CAMINO GTC SUMMIT DCON BALOOO Linear high-n gyrokinetic TEQ EFIT FP-Code GATO intermediate-n Antenna FULL TSCEQ ELITE CQL3D RANT3D 2D transport Inverse Equilibrium Plasma Edge RF Heating & CD 3D Nonlinear MHD TSC 2D plasma neutrals Static Time -Dependent TRANSP B2 AORSA JSOLVER DEGAS TORCH PIES M3D TOQ WHIST ORION LSC VMEC UEDGE EIRENE NIMROD ESC ONETWO TORIC FAR TORAY 3D plasma VMEC2D BOUT CORSICA METS CURRAY POLAR2D BALDUR CORSICA denotes parallel MPI code Major U.S. Toroidal Physics Design and Analysis codes (Dahlburg et al, Journal of Fusion Energy, 2001) DBB

High Power Radio Frequency Heating of ITER Theory Program Review

Energy Loss Is Dominated By Micro Turbulence • 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 Theory Program Review

Wall Street—Money Never Sleeps Theory Program Review

The Integrated Plasma Simulator (IPS):A Light-Weight Python Framework Theory Program Review

The SWIM Data Portal Has Proven to Be a (Near) Essential Tool for Monitoring/Debugging Simulations http://swim.gat.com:8080/ Simulation of Wave Interactions with MHD (SWIM) Theory Program Review

Time Can be Parallelized If We Are Willing to Use Cycles—Parareal : ~6x wall-clock improvement for 6x cycles: Parareal Plasma Turbulence Simulation Theory Program Review

Plasma-Wall Interactions Are Poorly Integrated: High Heat Fluxes, Erosion, Redeposition …. Theory Program Review

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.

The Problem; the Successes; the Challenges