Orbit-modulated plasma transport and sources

Abstract

Using a general conservative gyrokinetic framework in axisymmetric magnetic geometry, the steady-state orbit-loss boundary fluxes are demonstrated to be predominantly determined by upstream transport (turbulent and collisional) and upstream sources and sinks. Within the framework, the details of the equilibrium orbits, even accounting for large but axisymmetric and time-independent electric fields and poloidal pressure gradients, are demonstrated to contribute only by modulating the upstream transport and source terms. This is true not only for gyrocenter fluxes, but also for any other moments that are expressible in terms of the adiabatic invariants that determine the orbits, such as parallel toroidal angular momentum. An explicit reformulation of the orbit-loss terms facilitates their evaluation via numerical diagnostics or reduced models. Additional contributions for realistic cases, including those of fast ions and time-evolving equilibria, are briefly discussed.