Gubaryev S. Intense beams of heavy ions in a plasma lens

The thesis is devoted to investigation of manipulating wide-aperture intense beams of heavy ions with moderate energies (3-20 keV) by means of a plasma lens (PL), and also to studying beam-drift instability excited in the lens. Characteristics of the PL at operation with intense beams of heavy ions are studied. Due to diminishing momentum aberrations and minimizing spherical and dynamical ones in the PL, the values of ion beam compression coefficient at its focus are obtained, which significantly exceed those obtained earlier at operation with the beams of more lightweight hydrogen ions. On a basis of the model of two-component quasi-neutral plasma medium of the lens with anomalous diffusion of the electrons, an estimation of maximum achievable strength of driving electric field in the lens is made. Conditions of the beam-drift instability excitation in the PL defined by radial gradient of magnetic field strength, and its influence on the ion beam focusing are determined. Integral and dispersion characteristics of the oscillations due to mentioned instability are found, as well as their increments and frequencies. The excitation increment for such oscillations is shown to have its maximum at minimum values of axial wavenumber. For the first time, in a range of weak magnetic fields radical suppression of collective processes in the PL is discovered. At that, spherical and dynamical aberrations are diminished, and focusing features of the lens are essentially improved. For explanation of the improvement of focusing features of the lens in a range of weak magnetic fields, the model of plasma medium self-organization is proposed and considered, in which isodrift rotation of the electron cloud around its axis is formed in the lens, and there are no reasons for the development of beam-drift instability in it.