Relativistic magnetic flux amplification

Abstract

Summary form only given. The interaction of a plasma beam with curved or transverse magnetic field has been the interest of numerous investigators over the years. This interest stems from many different areas of plasma and astrophysics and it was shown already by Schmidt that a plasma can penetrate a transverse magnetic barrier through electrostatic self-polarization and subsequent E/B drift into the barrier and across magnetic field lines. Litwin et al. suggested particle acceleration by the electrostatic polarization field created when plasmoids impact with neutron stars and their associated magnetic field. The interaction of a plasma beam with a transverse magnetic field can be divided into several different categories. One classification is according to energy density; the kinetic energy density WK in the stream is compared to the involved electric and magnetic field energy densities WE and WB. A thin collisionless plasma does not contain enough energy to set up the required self-polarization electric field. If the plasma is far below this limit it will follow the magnetic field lines. Closer to and in a region above the limit, the plasma will react collectively by oscillations instead of penetrating. A very dense high energy plasma (βK>>1, where βK=WK/WB) on the other hand could penetrate the magnetic field ballistically by expulsion of the magnetic field. It is shown here that a plasmoid entering a region of transverse magnetic field at relativistic velocity can, under certain circumstances, amplify the magnetic field thus causing polarization fields that are much higher than those predicted by present theory. This effect is in complete contrast to the expulsion of the magnetic field from the plasma interior that can be expected in high βK plasmas. The amplification is shown to be caused by the relativistic motion of the space charge layers setting up the polarization field. Three dimensional electromagnetic particle-in-cell simulations that support this theory are presented.