|M.Sc Student||Asaf Lifshitz|
|Subject||Active Feedback Stabilization of the Flute Instability in|
a Mirror Machine Using Field-Aligned Coils
|Department||Department of Physics||Supervisors||Professor Emeritus Ron Amiram|
|Dr. Amnon Fisher|
|Full Thesis text|
Plasmas confined in mirror machines are unstable even at low beta (plasma pressure over magnetic pressure), mainly because of the flute instability. A method is suggested to stabilize the plasma by using active feedback to correct the plasma shape in real-time. The suggested feedback apparatus consists of six coils immersed in the plasma, outside of the hot core, aligned with the magnetic field. When current is driven through the coils, Alfven compression waves cause the plasma to move towards or away from the coils, and the electric field induced by the coils penetrates the plasma. First, an analytical model is used to find a robust feedback algorithm, resembling a PID feedback loop. For practical reasons, it is preferable for the feedback currents applied in response to a perturbation in the plasma to decay to zero after the perturbation is suppressed. It is found that the plasma’s rotation must be taken into account, in order to fulfill this requirement for zero residual currents. Then, a two-dimensional MHD simulation is used to test the suggested algorithm. It is found that indeed the system is stabilized with zero residual currents. Also, the parameters needed to achieve zero residual currents are with qualitative agreement with the ones derived in the analytical analysis. Lastly, the applicability of the suggested apparatus is discussed.