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Parallel coupling: problems arising in the context of magnetic fusion

John R. Cary Professor, University of Colorado CEO, Tech-X Corporation. Parallel coupling: problems arising in the context of magnetic fusion. The nuclear fusion produces energy: D + T  (He 4 + 3.53 MeV) + (n + 14.06 MeV). Neutron energy (14 MeV) collected at walls.

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Parallel coupling: problems arising in the context of magnetic fusion

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  1. John R. Cary Professor, University of Colorado CEO, Tech-X Corporation Parallel coupling: problems arising in the context of magnetic fusion

  2. The nuclear fusion produces energy: D + T  (He4 + 3.53 MeV) + (n + 14.06 MeV) Neutron energy (14 MeV) collected at walls Alpha energy (3.5 MeV) deposited in plasma Courtesy of Don Batchelor, ORNL

  3. + + - B - Heat (to overcome repulsion) and hold particles in magnetic traps • Heat the particles so that the average energy is ~ 100,000,000F (plasma) • Contain plasma for many reactions to happen • Not overheat, which can lead to instability or confinement reduction Figures from Don Batchelor

  4. MHD codes compute growth of harmful structures • Particles move rapidly along field lines • Topology change means hot particle near inside can reach outside • Temperature flattens over width of island

  5. RF codes used to predict deposition of wave energy and momentum ICRF fast waves and mode converted ion Bernstein and ion cyclotron waves in Alcator C-Mod and ASDEX Upgrade. Full-wave LHRF field solutions at millimeter wavelengths over the entire tokamak cross-section. TORIC: • Solves both the ICRF and LHRF wave equation • Uses a mixed finite element - spectral basis representation. • Solves block tri-diagonal with Scalapack. • Scalable solver allows millimeter resolution http://psfcwww2.psfc.mit.edu/rf2005/

  6. Coupling RF and MHD can eliminate the harmful structures • Localized momentum deposition differential on the particles • Currents can be induced • Local: counteract current spike near island • Global: counteract island drive (D′, q) • Not much current required (IRF/Iplasma ~ 3%) Center island current out of plane

  7. Prediction of process requires coupling of very different parallel codes • TORIC: RF code computing • Toroidally fourier • Poloidally fourier • Finite element in minor radius • 1D decomposition • NIMROD: MHD evolution • Toroidally fourier • Finite elements radially and poloidally • 2D decomposition

  8. Spatial Domain Transformations All needed transformations are linear, and can be implemented as matrix-vector multiplication Code B representation Transformation to cylindrical coordinate system Possible Fourier synthesis MxN coupler Evaluation at Gauss quadrature points Possible Fourier analysis Mass matrix inversion to find representation for code B Transformation from cylindrical coordinate system Code A representation vgB(t) = FBCBvB(t) vgA(t) = GTABvgB(t) vA(t) = CA(MA)-1FAvgA(t)

  9. Questions • Should we be generic? • Is the performance hit of being generic excessive? • Should we do a particular problem first? • How will we overlap communication and computation? • How do we get there? • Is retrofitting old codes the way to go • Do we need a new framework for component management?

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