Effect of Magnetic Field Curvature on Penetration of the Magnetic Field into the Plasma

Abstract

The penetration of a magnetic field into a cylindrical plasma, in the time scale that is much longer than electron cyclotron period, is studied. A linear wave analysis is shown that the magnetic field penetrates rapidly into the plasma in radii smaller than the ion skin depth. Due to the axial symmetry, the problem reduces to a twodimensional problem. The magnetic field evolution is numerically calculated. The ion density is also calculated. It is shown that during the penetration of the magnetic field, a gap appears between cathode and plasma. At the early times, at the plasma boundary, electrons move radially, and coupling of the electron velocity and the electric field induces the magnetic field. Electrons then gain a drift due to the field curvature that results in fast penetration of the magnetic field into the plasma.