Prediction of divertor heat flux width for ITER using BOUT++ transport and turbulence module

Abstract

Investigation of turbulent transport dynamics in scrape-off-layer (SOL) and divertor heat flux width prediction is performed for ITER. Both BOUT++ transport and BOUT++ turbulence codes are applied to capture the physics on different temporal scales. Simulations start with an ITER 15MA baseline scenario profile generated by CORSICA (Kim et al 2015 Paper ITER_D_R9T8J9 v1.1). In BOUT++ transport code, the plasma parameters (, , ) and radial electric () profiles are evolved to steady state. The initial plasma profiles inside the separatrix are taken from CORSICA scenario studies. Transport coefficients are calculated by inverting the plasma profiles inside the separatrix. SOL transport coefficients are assumed to be constants connected to the separatrix. A parametric scan for the anomalous thermal diffusivity (, ) in the SOL is performed separately with and magnetic drift included, and without any drift effects. The results show that when the diffusivity is smaller than a critical , the heat flux width remains almost unchanged, which is roughly consistent with Goldston’s heuristic drift model (Goldston 2012 Nucl. Fusion 52 013009). Otherwise, it increases as a scaling resulting in a larger . BOUT++ six-field/two-fluid turbulence code is used to study pedestal and SOL turbulence dynamics and corresponding transport. In the turbulence simulation, pedestal is found to be peeling-ballooning unstable, which results in a larger . Pedestal structure is also found to be important in determining the effective thermal diffusivity and could lead to changes in the divertor heat flux width.