Compact toroid injection for the MST experiment

We are developing experiments to inject compact toroid (CT) plasma into the Madison Symmetric Torus (MST) device and measure the plasma response with an emphasis on possible ion energization due to magnetic reconnection. CT injection has previously been experimentally tested for plasma fueling, rotation, and improved confinement. To understand the dynamics of a CT in a tokamak magnetic field, we adapt models that treat it as a moving spheromak plasmoid with an intrinsic magnetic moment. After injection into the tokamak, the modeled CT tilts and decelerates due to MHD wave drag. We expect magnetic reconnection to occur as it loses its kinetic and magnetic energy and dissipates in the background plasma. A high-order Runge-Kutta method is used to calculate CT trajectories in MST for different parametric cases and initial conditions. Using an injector developed for the Big Red Ball, CTs will be injected into MST at speeds of order 100 km/s. During tokamak operation, the MST device has a toroidal magnetic field strength of 0.13 T on the axis and electron densities of several times 10¹⁸ m^-3. Changes in ion temperature in the background plasma due to injection will be measured with passive Ion Doppler Spectroscopy. We also plan for experiments to inject CTs into RFP plasmas in the future.