Zavalov A. Space charge lenses for focusing beams of positive and negative ions

The dissertation is devoted to numeric studies of the space charge lenses for focusing beams of positive and negative ions. For that purpose self-consistent mathematical model was created which was used for the first time for numeric calculations of the phenomena taking place in plasma medium of such lenses. In frame of this model by the method of boundary leap the calculations of magnetic field of the system of permanent magnets with inserts and tips, as well as electric field of the system of ring electrodes, were performed. Modeling of the plasma medium was accomplished by means of P.I.C. (Particles-In-Cells) method for collision-less plasma. The distribution of space charge of the particles was calculated by means of С.І.С (Clouds-In-Cells) method. For the first time formation of layered electron structure in a volume of high-current plasma lens defined by finite dimensions of cylindrical fixing electrodes of the lens was determined. The effect of change of electric potential distribution and electron structure at the growth of the beam current was discovered. For the first time the studies were performed for the lens with positive space charge and the lens with new modernized design with additional source of the electron emission intended for focusing of negative ion beams. It was determined that required positive space charge in such lenses is formed due to inertia of the positive ions and removal of the electrons by longitudinal electric field.