The PPPL code, called XGC, simulates behaviour of the ions, electrons and neutral atoms in the transport barrier region - or "pedestal" - between the ultra-hot core of the plasma that fuels fusion reactions and the cooler and turbulent outer edge of the plasma. The pedestal must be high and wide enough to prevent damage to the divertor plate that exhausts heat in doughnut-shaped tokamaks that house the fusion reactions. "How to create a high edge pedestal without damaging the divertor wall is the key question to be answered", stated C.S. Chang. "That is a prerequisite for achieving steady state fusion."
Among the team of nationwide experts developing this programme are PPPL physicists Seung-Ho Ku, Robert Hager and Stephane Ethier.
Selection of the PPPL code could help ready it for exascale development. "Computer architecture is evolving rapidly and these new pre-exascale computers have features that are quite different from some of the earlier petascale supercomputers", stated Amitava Bhattacharjee, head of the Theory Department at PPPL. Petascale machines operate in petaflops, or one million billion (1015) floating point operations per second.
Amitava Bhattacharjee heads a PPPL-led Exascale Computing Project that will integrate the XGC code with GENE, a code developed at the University of California, Los Angeles, to create the first simulation of a complete fusion plasma. Exascale supercomputers will perform exaflops, or a billion billion (1018) floating point operations per second.
The three new pre-exascale supercomputers are the following:
Also selected to participate in Cori's NERSC Exascale Science Applications Programme (NESAP) is the PPPL-led M3D-CI, an extended magnetohydrodynamics (MHD) code focused on simulation of plasma disruptions led by physicist Stephen Jardin, with support from physicists Joshua Breslau, Nate Ferraro and Jin Chen.
Two more PPPL-led codes, in addition to the 20 that included XGC and M3D-CI that were previously selected, will participate in the Cori NERSC programme. These programmes are GTC-P and GTS codes that model plasma turbulence in the plasma core and are headed by physicists William Tang and Stephane Ethier. Principal developer of the GTS code is PPPL physicist Weixing Wang. The GTC-P code is PPPL's version of the GTC code led by the University of California, Irvine.