Gyrokinetic Particle Simulations of Fusion Plasmas

1. Gyrokinetic Particle Simulations of Fusion Plasmas SciDAC Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas (W.W. Lee, P.I., Princeton Plasma Physics Laboratory)

2. Mission of GPS Center: Study the effects of micro-turbulence in magnetic fusion plasmas • What role does micro-turbulence play in fusion plasmas? • It is believed to be the primary mechanism by which particles and energy diffuse across the confining magnetic field in toroidal fusion devices (energy loss = $$$) • We must understand this phenomenon in order to control it • We use global self-consistent gyrokinetic particle-in-cell (PIC) simulations to study micro- turbulence • Why “micro”? The term originates from small-scale structures of the order of ion gyroradius (~ 1 cm)

3. Our flagship code: The Gyrokinetic Toroidal Code (GTC) • State-of-the-art 3-dimensional PIC code • Solves the gyrophase-averaged Vlasov-Poisson equations • Guiding center Hamiltonian formulation for particles • Advances particles in magnetic coordinates • Global field-line following coordinates for the grid • Multi-level parallelism • Scales beyond 30,000 processors • Toroidal geometry

4. History of Scientific Discoveries through Advanced Computing 1993: First global gyrokinetic PIC simulation of ITG with 106 particles on Cray C90 • These simulations and experimental observations established the fact that ion temperature gradient (ITG) drift instabilities are one of the main causes for turbulent transport in tokamaks [Parker, Lee, Santoro, PRL1993]

5. 1998: Nonlinear zonal flow simulations by GTC with 108particles on Cray T3E • Nonlinearly generated zonal flows associated with ITG turbulence have been observed to break up the eddies and reduce transport in global simulations [Lin, Hahm, Lee, Tang, White, Science 1998]

6. 2002: First global ITER-size simulation using 109 particles on IBM SP 3 • Transition from Bohm to GyroBohm scaling was finally observed and the elusive GyroBohm scaling is finally found [Lin, Ethier, Hahm, Tang, PRL2002] • Data Streaming Technology to move terabytes of data from NERSC to PPPL [Klasky, Ethier, Lin, et al., SC2003] Good news for ITER!

7. GTC simulations show that turbulence spreading causes Bohm scaling • GTC: Turbulence spreading is responsible for transport Bohm scaling in small devices [Lin, Hahm, PoP2004] • ITG simulations using GTC for shaped plasmas have confirmed the nonlocal property of turbulent transport [Wang et al., PoP2006]

8. Convergence in ETG Simulations Scalability • Flux driven by particle noise is 1000 times smaller than ETG in global GTC simulation: noise does not affect ETG physics • Convergence: consistent ETGcewhen using 200-2000 particles/cell • GTC simulation calculates orbits of 4x1010 particles, 10000 time steps using ORNL Cray XT3, 6400 compute cores ETG flux c (reve2/LT) Noise flux Time (LT/Ve)

9. The Gyrokinetic Toroidal Code is ready for petascale computers • Runs on all major computing platforms [Ethier, 2006] • Scales beyond 30,000 processors • Highly efficienct (>95%) on multicore processors • Record performance on NCCS Cray XT3 Jaguar!

10. Scientific data management and visualization: critical tools for physics understanding Workflow automation to automate the process of data movement, data reduction, data analysis, and data visualization via SDM Center Kepler workflow

11. Advanced data analysis techniques using principal component analysis 1t • Transform to reducenon-linearity in distribution(often density-based) • PCA computed via SVD(or ICA, FA, etc.) • Constructionof component movies • Interpretation of spatial, time, and movie components • Pairs of equal singular values indicate periodic motion 2t ƒ (Xt) = S0 +1t S1 + … + kt Sk + Et S1 Ostrouchov ORNL EETG GTC Simulation Data (W. Lee, Z. Lin, and S. Klasky) Decomposition shows transient wave components in time

12. Contact Scott A. Klasky Lead, End-to-End Solutions Center for Computational Sciences (865) 241-9980 klasky@ornl.gov 12 Klasky_GTC_0611