First-principles-based whole device modeling (WDM) of fusion devices is one of the great frontiers of computational plasma physics. Ultimately, success will enable the confident exploration of new ITER scenarios and new reactor concepts in silico, at greatly reduced cost and over a much wider range of possibilities. The challenges associated with connecting simulations of physical processes occurring at vastly different time and space scales to one another are immense and will require significant investments. In particular, success requires further intensive development of the most complex physics modules: the gyrokinetic turbulence kernels. Due in part to significant past SciDAC support, core tokamak ‘anomalous transport’ is no longer an intractable mystery. A validated predictive capability now exists for a range of conditions. However, important problems remain unsolved.
For example: The narrow transport barrier of the H-mode pedestal doubles tokamak energy confinement, but we cannot predict the conditions required to achieve it, its energy losses, or its scope for optimization. Internal transport barriers have proven to be equally challenging. Fluctuations coexisting on ion and electron gyroradius scales yield to heroic simulations today, but remain inaccessible on transport time scales and have not been explored in important parameter regimes. Electromagnetic fluctuations (including microtearing) can be simulated today, but not in the WDM context. Notably, each of these multiscale challenges is associated with high performance operating regimes that magnetic confinement fusion research seeks to exploit in the quest for fusion energy.