The plasma lens solution for heavy-ion beam focusing

A new type of plasma lens using a «wall-stabilized» discharge has been investigated concerning its potential to fine-focus heavy-ion beams. The lens was tested in several runs at the GSI linear accelerator UNILAC with a beam energy of 2.2 GeV and a magnetic rigidity of 1.6 Tm. A remarkably high accuracy and reproducibility of the focusing was found. With a peak current of 22 kA a beam of 1 cm initial diameter was focused down to a spot diameter of below 300 μm at a distance of 90 mm behind the lens, in agreement with analytical calculations and Monte Carlo simulations of the focusing process. The focal spot size was mainly limited by the beam emittance and no lens-related aberrations could be detected. Plasma lenses are under consideration for use at the SIS/ESR facility of GSI to produce small beam spots on targets in order to achieve high energy density in matter. A design for a plasma lens focusing the beam from the SIS-synchrotron with a typical rigidity of 6 T m is proposed.