Numerical Study of FRC Stabilization in C-2W with External Actuators

TAE Technologies, Inc. is pursuing fusion energy using steady state, magnetically confined plasmas in the field-reversed configuration (FRC). The company's experimental platform, C-2W, has demonstrated unprecedented FRC stability through a combination of external actuators which include neutral beam injection (NBI), core fueling, and electrode biasing. Here we discuss 3d, whole device simulations performed with the open-source particle-in-cell code WarpX, in which the necessity of these actuators to achieve long-lived FRCs are demonstrated. Focus is given to the stabilizing effects from NBI, leading to the formation of high energy, large Larmor orbit ions, and electrode biasing which leads to sheared thermal ion rotation. Both actuators are captured in hybrid-PIC simulations. A sheath model is used to impose appropriate boundary conditions for electrode biasing and NBI is simulated through binary collisions used to capture charge exchange of injected high energy neutral particles. Fully kinetic electrostatic simulations are also discussed showing the impact of electrode biasing on the electron temperature. The electrostatic simulations employ a semi-implicit Poisson solver to enable whole device simulations to be evolved up to several ion crossing times. Successful validation of WarpX through comparisons to C-2W results allows us to predict the required actuator specifications in next generation machines, thereby reducing technical risk associated with the program.