High Performance Computing in Magnetic Fusion Energy Research

1. High Performance Computing in Magnetic Fusion Energy Research Donald B. Batchelor RF Theory Plasma Theory Group Fusion Energy Division

2. Nuclear fusion is 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.

3. n + n n + n + n + n n n + + n The simplest fusion reaction – deuterium and tritium En= 14 MeV deposited in heat exchangers containing lithium for tritium breeding Ea= 3.5 MeV deposited in plasma, provides self heating About 1/2% of the mass is converted to energy (E = mc2 ) Remember this guy?

4. D T D D D T T D T D D T 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 that the temperature is much hotter than the sun ~100,000,000° PLASMA: electrons + ions • Then we hold the fuel particles and energy long enough for many reactions to occur • Lawson breakeven criterion:high enough temperature – T (~ 10 keV) high particle density – nlong confinement time –  neE > 1020 m-3s Nuclear thermos bottle

5. 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

6. R0 = 6 m ITER will take the next steps to explore the physics of a “burning” fusion plasma An international effort: Japan, Europe, US, Russia, China, Korea, India • Fusion power ~ 500MW • Iplasma = 15 MA, B0 = 5 Tesla T ~ 10 keV, E ~ 4 sec • Large – 30 m tall, 20k Tons • Expensive > $5B+ • Project staffing, administrative organization, environmental impact assessment • First burning plasmas ~ 2018 Latest news http://www.iter.org

7. What are the big questions in fusion research? • How do you heat the plasma to 100,000,000 degrees, and once you have it 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

8. We have SciDAC and other projects addressing separate phenomena and time scales Center for Extended MHD Modeling Gyrokinetic Particle Simulation Center • M3D code • NIMROD • XGC code • TEMPEST Center for Simulation of Wave-Plasma Interactions Edge Simulation Projects • GTC code • GYRO • AORSA code • TORIC • CQL3D • ORBITRF • DELTA5D

9. Petascale problems in wave heating and plasma control Objectives: understand heating of plasmas to ignition, detailed plasma control through localized heat, current and flow drive • AORSA uses Scalapack software to perform a dense matrix inversion. Have observed “perfect” scaling with processor number in the AORSA matrix inversions up to >8000 processors and we expect this scaling to persist. • AORSA has been coupled to the Fokker-Planck solver CQL3D to produce self-consistent plasma distribution functions. TORIC is now being coupled to CQL3D. Mode converted Ion Cyclotron Wave (ICW)

10. Petascale problems in extended MHD stability of fusion devices (M3D and NIMROD codes) Objectives: to reliably simulate the sawtooth and other unstable behavior in ITER in order to access the viability of different control techniques • M3D uses domain decomposition in the toroidal direction for massive parallization, partially implicit time advance, PETc for sparse linear solves • NIMROD spectral in the toroidal dimension, semi-implicit time advance, SuperLU for sparse linear solves

11. Phoenix (Cray X1E) Jaguar (Cray XT3 Earth Simulator (05) Phoenix (Cray X1) Jacquard (opteron+IB) Thunder (IA64+Quad) Blue Gene/L (Watson) Seaborg (IBM SP3) Seaborg (MPI+OMP) NEC SX-8 (HLRS) 10000 Latest vector optimizations Not tested on Earth Simulator 1000 Compute power (millions of particles) 100 10 1 64 128 256 512 1024 2048 4096 8192 16384 32768 Number of processors Petascale problems in particle based gyrokinetic simulation (GTC code) Objectives: Steady-state turbulence simulations including all relevant nonlinearities to determine device size scaling and isotope scaling of transport • Particles – 1 trillion particles on a 10,000  10,000  100 grid (100 particles/cell) for ITER-type plasmas with a grid size of the order of the electron skin depth, we need a 1 PF/s Jaguar at ORNL with 50,000 XT3 quad-core processors, assuming half the memory for storing particle data and the other half for grid data. • Field solve – toroidal domain decomposition is in place, radial decomposition near completion – 108 elements per plane • Production runs on IBM BlueGene/L using 32,768 processors (90 Tflops) Compute Power of the Gyrokinetic Toroidal Code Number of particles (in million) moved 1 step in 1 second

12. Contact • Donald B. Batchelor • RF Theory • Plasma Theory Group • Fusion Energy Division • (865) 574-1288 • batchelordb@ornl.gov 12 Batchelor_Fusion_0611