Numerical simulation of local and coaxial helicity injection in Pegasus-III

Non-inductive plasma startup techniques based on local helicity injection (LHI) and coaxial helicity injection (CHI) are being explored in Pegasus-III. Accurately simulating the nonlinear MHD behavior of these techniques is important for understanding their viability and scaling. New capabilities aim to improve the physical fidelity of LHI simulations for comparison with modern outboard injection experiments. They include modeling multiple injectors, the resistive wall, and vertical magnetic field programming. The setup and results of CHI computations are also presented and are being used to inform the design of discharge scenarios. Recent CHI computations for Pegasus-III include density and temperature evolution, subject to Ohmic heating, for increased fidelity. The bubble-burst current can be estimated for a given magnetic configuration if realistic thermal boundary conditions are used. Simulations have demonstrated 2D transient CHI, including discharges with significant flux closure which remain within Pegasus-III operational limits. The roles of extended MHD terms, particle density injection, radiation, and methods to optimize flux closure are being investigated.