3D Modeling of impurity ion collection by a probe for application to data from the DIII-D tungsten ring campaign*

During the tungsten ring campaign on DIII-D, a collector probe system with multiple diameter, dual-facing collector rods was inserted into the far scrape off layer (SOL) near the outer midplane to measure the plasma W content. The deposition on these probes has been modeled using 2D OEDGE and the analytic model from [1]; however, it is challenging to experimentally validate the analytic model. In addition, 2D deposition measurements across the poloidal probe face are also available and these cannot be interpreted with the analytic model. An initial 3D Monte Carlo model of ion collection by a probe has been developed by modifying and enhancing the 3D capabilities of the LIM code [2]. Dynamic memory allocation, mirrored and absorbing boundary conditions, and new particle launch options were added. Collector probe simulations indicate greater deposition at the poloidal edges of the probe compared to the center which is similar to the experimental measurements. The simulated deposition on the collector probe is compared to the predictions from the analytic model.

[1] P.C. Stangeby, Physics of Fluids 30, 3262 (1987)

[2] P.C. Stangeby et al., Nuclear Fusion, 28(11), 1945 (1988)