Understanding the impact of divertor configuration on neutral leakage and main-chamber recycling in DIII-D

Neutral Leakage (NL) estimated using Window-Pane (WP) analysis in different divertor geometry shows that open divertor produces more neutral particles compared to others. Previously, particle flux density (I_wall) was calculated using a single embedded probe in an axisymmetric surface of main chamber wall, called the window frame (WF). I_wall was estimated using the fitted radial decay length of neutral particle flux density using the probe. Here, a modified version of the WP analysis is used to calculate I_wall using three diagnostics in the WF: high resolution radiometer – Filterscope, pressure gauge and Langmuir probes. NL is calculated as the ratio of I_wall to neutral particle flux received at divertor plate (I_div). This ratio compares unique divertor geometry and its impact on NL over a range of discharge conditions. It also takes into account the conservation of particles in the WF. Higher NL causes main chamber recycling which leads to surface erosion and production of impurities. Estimating NL improves the understanding of neutral dynamics, particle sourcing and particle control system efficiency for DIII-D and future tokamaks.