Improvement of the active cylindrical plasma lens concept by a tapered discharge geometry

Recently an active current carrying plasma lens was introduced using a wall-stabilized discharge mode with remarkable focusing properties for high energy heavy ion beams. In this paper, a further improvement of focusing performance of a wall-stabilized plasma lens will be reported using a tapered geometry. The gradient of the focusing field is increased in z direction and the focusing power is increased compared to a cylindrical lens with the same length and discharge current. Aberration effects of this tapered lens were minimized by optimizing both shaping and discharge conditions. With the tested lens an argon ion beam of 15.4 MeV/amu was focused from an initial diameter of 10 mm down to a spot size of 160 μm. The results of the focusing experiments are compared with optical plasma diagnostics data allowing for an interpretation of the observed focusing behavior