Simulations of magnetic field reversal by neutral beam injection in a mirror-confined plasma

In the Norm experiment at TAE Technologies, a reversed field configuration (FRC) is formed by reversing the magnetic field of a mirror configuration using neutral beam injection. An FRC is formed and sustained in a steady state by the diamagnetic current of the thermal plasma and the azimuthal current provided by fast ions. In the present paper, we present numerical simulations of FRC formation using the Q2D code. Q2D is a code that couples 2D MHD equations with separate ion and electron temperatures, a fluid model for the neutral gas, and a 3D Monte Carlo module, which is used to calculate neutral beam injection, fast ion orbits, and their interaction with the thermal plasma and neutral fluid. We use Q2D to simulate the FRC formation and sustainment by neutral beam injection, and we study the effects of different beam injection angles, impact parameters, equilibrium magnetic fields, and neutral beam current. We analyze the different types of fast ion orbits and their contribution to the diamagnetic current. The simulations show that the fast ion current can reverse the magnetic field if the current density is sufficiently high. Equilibria with higher magnetic field require higher diamagnetic current density for FRC formation.