Modeling of the recycling particle flux and electron particle transport in the DIII-D Tokamak

Abstract

One of the most difficult aspects of performing an equilibrium particle transport analysis in a diverted tokamak is the determination of the particle flux which enters the plasma after recycling from the divertor plasma, the divertor target plates or the vessel wall. An approach which has been utilized in the past is to model the edge, scrape-off layer (SOL) and divertor plasma to match measured plasma parameters and then use a neutral transport code to obtain an edge recycling flux while trying to match the measured divertor D α emissivity. Previous simulations were constrained by electron density ( n e ) and temperature ( T e ), ion temperature ( T i ) data at the outer midplane, divertor heat flux from infrared television cameras and n e , T e and particle flux at the target from fixed Langmuir probes, along with the divertor D α emissivity. In this paper, we present results of core fueling calculations from the 2D modeling for ELM-free discharges, constrained by data from the new divertor diagnostics. In addition, we present a simple technique for estimating the recycling flux just after the L-H transition and demonstrate how this technique is supported by the detailed modeling. We will show the effect which inaccuracies in the recycling flux have on the calculated particle flux in the plasma core. For some specific density profiles, it is possible to separate the convective flux from the conductive flux. The diffusion coefficients obtained show a sharp decrease near a normalized radius of 0.9 indicating the presence of a transport barrier.