Global Gyrokinetic Particle-in-Cell Simulation

As the global energy economy makes the transition from fossil fuels toward cleaner alternatives, fusion becomes an attractive potential solution for satisfying the growing needs. Fusion energy, which is the power source for the sun, can be generated on earth, for example, in magnetically confined laboratory plasma experiments (called tokamaks) when the isotopes of hydrogen (e.g., deuterium and tritium) combine to produce an energetic helium alpha particle and a fast neutron-with an overall energy multiplication factor of 450:1. Building the scientific foundations needed to develop fusion power demands high-physics-fidelity predictive simulation capability for magnetically confined fusion energy (MFE) plasmas. To do so in a timely way requires utilizing the power of modern supercomputers to simulate the complex dynamics governing MFE systems-including International Thermonuclear Experimental Reactor (ITER), a multibillion dollar international burning plasma experiment supported by seven governments representing over half of the world's population. Currently, under construction in France, ITER will be the world's largest tokamak system, a device that uses strong magnetic fields to contain the burning plasma in a doughnut-shaped vacuum vessel. In tokamaks, unavoidable variations in the plasma's ion temperature profile drive microturbulence-fluctuating electromagnetic fields, which can grow to levels that can significantly increase the transport rate of heat, particles, and momentum across the confining magnetic field. Because the balance between these energy losses and the self-heating rates of the actual fusion reactions will ultimately determine the size and cost of an actual fusion reactor, understanding and possibly controlling the 508underlying physical processes is key to achieving the efficiency needed to help ensure the practicality of future fusion reactors. The associated motivation drives the pursuit of sufficiently realistic calculations of turbulent transport that can only be achieved through advanced simulations. The present paper on advanced particle-in-cell (PIC) global simulations of plasma microturbulence at the extreme scale is accordingly associated with this fusion energy science (FES) grand challenge [1,2].