Development of a plasma lens operating at Hz-frequencies for laser-driven proton acceleration

An active plasma lens is a device used to focus charged particle beams by means of a gas discharge initiated in a capillary aligned with the beam axis. The high current carried by the discharge plasma generates a strong azimuthal magnetic field, causing the charged particles traversing the plasma to experience a focusing Lorentz force.

Plasma lenses are particularly suited for laser-accelerated ions, which exhibit high divergence and broad energy spectra. By adjusting the discharge current, the focal strength can be tuned to target specific particle energies. A key advantage of plasma lenses is their symmetric focusing in all transverse directions, in contrast to quadrupole magnets.

For technical implementation of the plasma lens a pulse forming network (PFN) is necessary, which can deliver discharge currents of several kiloamperes —depending on lens geometry, distance to the ion source, and ion energy. To ensure a homogeneous discharge and uniform current density, argon is used as the working gas due to its low thermal conductivity. Moreover, the operating frequency of the PFN must be synchronized with the repetition rate of the laser-driven ion source. Another challenge is the confinement of the working gas within the capillary without obstructing the ion beam. To address this, a pulsed gas injection system is proposed, eliminating the need for physical sealing.