Speaker: Prof. Paul Gibbon（Institute for Advanced Simulation, Jülich Supercomputing Centre, Germany）

Chair Person: Prof. Bin Qiao

Date: July 21, 2016, 15:00

Place: Room 434 COE Mechanics Building

Report Introduction:

Numerical modeling of plasmas often demands a kinetic approach to handle extreme nonlinearities, wave-particle interactions and other non-Maxwellian phenomena.  Mathematically this requires the ab initiosolution of the relativistic Vlasov-Boltzmann equation for the plasma constituents together with the appropriate Maxwell equations for the electromagnetic fields.  Currently the model of choice is the particle-in-cell (PIC) code, a highly versatile, robust, finite-difference discretization of the Vlasov equation for the particle distribution function f(x,p).  State of the art three dimensional PIC simulations involve up to 1012 particles on 105 cores on modern supercomputers and have, for example, become an indispensable tool for exploring the complex physics behind laser-based particle beam and radiation sources.   

Despite these successes, PIC simulation still has its limitations: the necessity of transferring information to and from the spatial grid makes it inherently noisy, collisional regimes are only accessible via ad-hoc extensions, and some form of adaptive mesh refinement is required to handle geometrically complex problems.   Recently a new modeling paradigm has been established – mesh-free plasma simulation – in which fast summation techniques replace the solution of the field equations on the mesh.  The key innovation behind this development is the hierarchical tree algorithm, a rapid O(N log N) technique for evaluating mutual (Coulomb) forces due to an ensemble of charged particles.  At JSC we have developed a parallel tree-code (PEPC) capable of running on the entire 458k processors of the BlueGene/Q supercomputer JUQUEEN, a milestone which makes it feasible to perform first principles simulation of collective and collisional plasma phenomena in a variety of physical settings using well over 109 particles. 

Recent work at the Jülich Supercomputing Centre on the development of the above two paradigms will be presented with regard to present and future supercomputer architectures. Examples of their respective application in various areas will also be discussed, including the generation of attosecond electron bunches with high-intensity, few-cycle lasers, plasma-wall interactions in ITER-like environments, and a fully kinetic treatment of the Kelvin-Helmholtz instability in a magnetized plasma sheath.

About Speaker:
　　Paul Gibbon received the B.Sc. degree in physics from the University of Bristol, Bristol, U.K., in 1985 and a Ph.D. in plasma physics from Imperial College London, London, U.K. in 1988 under the supervision of A. R. Bell. He continued working in the field of high-intensity laser–matter interactions at several European institutes, including Darmstadt University of Technology, Germany, CEA Saclay, and the University of Jena, Germany. Since 2001, he has been with Forschungszentrum Jülich GmbH, Jülich, Germany, where he now heads the Computational Science Division of the Jülich Supercomputing Centre. His current research interests are centred on the application of high-performance computing to topical challenges in plasma physics, ranging from laser-driven particle acceleration and radiation sources, to tokamak edge physics – subjects on which he has authored 2 text books and over 100 peer-reviewed publications. Recently he has been appointed Associate Professor at the Katholieke Universiteit Leuven, where he teaches computational methods in physics. Since 2009 he has been Topic Speaker of the Helmholtz Association’s Supercomputing Programme. Further information about Paul Gibbon’s research group can be found here: http://www.fz-juelich.de/ias/jsc/slpp