Validation of simulation models for wall-connected scrape off layer currents during MHD activity in the HBT-EP tokamak

This program will investigate and validate numerical models for wall-connected currents in the Scrape-Off Layer (SOL) during disruptive events and MHD activity in the High Beta Tokamak – Extended Pulse (HBT-EP) using the NIMROD and PSI-Tet 3D extended MHD codes. Understanding currents flowing between the plasma and the first wall through the scrape-off layer during disruptive events, and MHD activity more broadly, is of critical importance to limiting structural loads due to halo currents to acceptable levels in ITER and next step devices. Developing a predictive understanding of these currents is a primary focus of investigation in the current HBT-EP program. This study is supported by a dedicated set of limiters, tiles, and other structures that are instrumented to measure current flowing from the plasma into the first wall with high spatial and temporal resolution. We propose to leverage this unique diagnostic capability to validate and improve present state of the art models for investigating and predicting halo and SOL currents in fusion devices. This will be done through: 1) Detailed validation of MHD models, including resistive wall models, for use in understanding and predicting SOL currents using experimental data from HBT-EP. 2) Quantifying the importance of geometric fidelity for 3D wall structures, such as ports, wall modules, and limiters. Linear and nonlinear simulations of HBT-EP discharges designed to study wall-connected currents will be performed and compared to experimental data using quantitative metrics. Varying levels of geometric fidelity will also be explored to quantify the importance of first wall and other structural components to the resulting current paths and dynamics.