Chekh Y. Static and dynamic characteristics of wide-aperture plasma lenses with permanent magnetic fields

Wide-aperture plasma lenses with permanent magnetic fields (in particular, the lenses with minimized magnetic field gradients) are investigated at the focusing of the pulsed medium-energy (~ 20 keV) high-current (up to 0,5 А) beams of heavy ions (Сu, Pb), generated by multi-aperture vacuum-arc ion source. Both the static and dynamic characteristics of the focused ion beams, as well as the parameters of the plasma medium in the lenses enable to determine the main factor, which determines the restriction of the maximum compression factor of the ion beams at low magnetic fields. Also the physical processes, which determine the peculiarities of the operation of the lenses with permanent electric and magnetic fields and the possibility for electron vortices to be generated in the plasma lens medium are studied. The regimes of large current density in the focus (up to 250-390 mA/cm2) are shown to be reached at low magnetic fields. At the same time, the degree of noise modulation and emittance, correspondingto 50 % of total beam current, are almost not effected. At these conditions the maximum current density in the focus is found to be limited by the initial phase volume of the beam. It is established, that the presence of medium generated by self-maintained glow discharge, causes the essential improvement of lens focusing properties. It is shown that large-scale electron vortices in the plasma lens are generated in the presence of strong radial gradient of electron density. It is established, that deviation from the condition of longitudinal confinement results in the restriction of amplitude of vortices.