ENHANCEMENT OF ION BEAM CHARGE STATES BY ELECTRON VORTICES IN A PLASMA OPTICAL DEVICE

Abstract

Electron vortex structures can be excited in cylindrically symmetric systems of finite length with crossed radial electric and longitudinal magnetic fields. In this paper, we consider the possibility of enhancing the ionization charge states of beam ions by such electron vortices. We show that the electron velocity in the vortices can be sufficiently large to increase the ionization charge states of beam ions. The cylindrical configuration that we consider here makes use of a number of ring electrodes along which an electric potential is distributed. We show that maximum ionization is achieved for minimum ion beam velocity through the vortex region. Though electron-ion collisions provide ionization, they also result in electron transport, in turn leading to reduced electron density. Increased magnetic field results in improved electron confinement. However, for large magnetic field the electron distribution is laminar, resulting in reduced ionization. For a given value of magnetic field, a specific number of discrete electrodes are required, along which the externally applied electric potential is distributed, or (alternatively) for a given number of the electrodes the maximum ionization is reached at a certain magnetic field. The experimentally observed dependence of electron density ne on magnetic field Ho has been analytically investigated. For Ho less than the optimum magnetic field Hopt the electron density increases with Ho; for Ho somewhat greater than Hopt, ne falls with increasing Ho; and for Ho much greater than Hopt, ne increases with Ho increasing. We consider the possibility of increasing the ionization charge states of beam ions by electron vortices self consistently excited in the plasma-optical system. The intensity of the excited vortex turbulence is proportional to magnetic field Ho, and the confinement of electrons is improved with increased Ho; thus the system calls for large Ho. It is necessary to use a certain minimum number of cylindrical electrodes, along which the electric potential is distributed, so that the radial distribution of electrons is not layered. A plasma-optical system for increasing the ionization state of ions from charge state n up to n+1 by electron vortices is considered. The system consists of three cylindrically symmetric segments located axially in the longitudinal direction (see Fig. 1). The configuration is of finite length located in the field of a chain of short coils, the sense of which is such as to create opposing magnetic fields Ho, and the separate segments trap electrons.