Electromagnetic and Centrifugal Effects on Plasma Acceleration in the Magnetic Nozzle

Abstract

Plasma flow and acceleration in the converging-diverging magnetic field configuration, such as magnetic nozzle in electric propulsion and open magnetic mirrors for fusion applications are considered. This work analyses plasma acceleration in the magnetic nozzle with an emphasis on the electromagnetic effects and centrifugal forces due to plasma rotation. Intrinsic coupling of the azimuthal rotation and azimuthal magnetic field is analyzed, and additional plasma acceleration due to the conversion of the energy of the azimuthal magnetic field and azimuthal rotation is demonstrated. For large expansion in the diverging magnetic field plasma flow velocities may approach and exceed the Alfvén velocity. In these regimes, stationary solutions for the transonic and trans-Alfvénic flows have been obtained that demonstrate the existence of the unique regular solution passing through all critical points within the MHD theory, i.e., the points where the plasma flow is equal to the signal velocities of the MHD modes: slow and fast magnetohydrodynamic waves and Alfvén wave. The time-dependent initial value simulations show that stationary equilibrium flows are robust and stable, so that time-dependent solutions converge toward stationary solutions.