Design and investigation of a plasma lens for focusing a proton beam at LIGHT

An active plasma lens (APL) has been designed, constructed, and experimentally commissioned as a collimation device for laser-accelerated proton beams at the LIGHT beamline at GSI. The device consists of a 20 cm long, 4 cm diameter glass capillary filled with low-pressure argon and closed by thin Kapton entrance and exit windows, with coaxial ring electrodes and return conductors enabling a high-current discharge. A dedicated single-stage pulse-forming network based on a 9 µF to 27 µF capacitor bank was built and operated, delivering discharge pulses with peak currents of about 30 kA and microsecond duration, as confirmed by time-resolved current and voltage measurements under laboratory and beamline conditions at LIGHT. The lens has been integrated into the LIGHT beamline and operated during dedicated beam times; analysis of the resulting proton-beam data will be reported separately. A proton-transport simulation is employed as a design tool to define the required discharge-current range and to identify a 7.5 MeV to 8.5 MeV operating window relevant for post-acceleration at LIGHT. The paper focuses on the complete mechanical and electrical realization of a high-current APL for TNSA-driven proton beams and defines its operating parameter space for future detailed beam-transport studies.