Finite-orbit effects on impurity sourcing in the pedestal of DIII-D Quiescent H-mode plasmas

Finite-orbit width effects on impurity sourcing and transport are assessed for the case of carbon (C) transport in the pedestal of Quiescent H-mode plasmas, to infer the electron particle source from ionization of the impurity ions. The latter has been shown to contribute to the dynamic evolution of the H-mode pedestal and is determined by the balance between transport and sources of carbon, both of which are challenging to determine experimentally. Recent dedicated DIII-D experiments leveraged outer gap sweeps to obtain spatial profiles of brightness from all charge states of C. Broad emissivity profiles well inside the plasma separatrix were observed from low charge states, possibly due to redistribution by finite orbit effects, expected to be significant for low collisionality, high temperature pedestal. Monte Carlo orbit calculations with the SPIRAL code [Kramer et al. PPCF 55, 2013, 025013] are used to assess the radial density broadening associated with drift orbit width for all carbon ion species, showing that a significant radial broadening is expected for C¹⁺ and C²⁺, which can strongly impact the impurity ionization balance profile. A basis-function approach to account for finite orbit broadening in 1D impurity transport models is introduced and discussed.