Total-f XGC study of electromagnetic turbulence effect on divertor heat-load width

Understanding the underlying physics of the divertor heat-load width, λ_q, is one of the most important issues for reliable operation of ITER. Previously, predictions from the total-f multi-physics simulation in XGC agreed with the “Eich” all-machine regression formula #14, but predicted 12 times wider turbulence-enhanced λ_q for the full-current ITER [1]. However, the simulations were electrostatic, and the electromagnetic turbulence effect remained as a question. Recently, an electromagnetic algorithm utilizing the mixed-variable and pull-back transformation methods was installed on the total-f gyrokinetic code XGC [2]. XGC has been simulating the electromagnetic physics while retaining all the total-f capabilities that self-consistently include neoclassical physics, turbulence physics, neutral particle recycling, heat and torque sources, nonlinear Fokker-Planck collisions, logical sheath, etc. Here, we report the heat-flux width study for DIII-D and ITER H-mode plasmas using electromagnetic XGC simulations. XGC finds that the electromagnetic effect makes little difference to the divertor heat-load width in DIII-D, but makes a noticeable widening of λ_q in ITER. Data analysis and physics details will be presented.