Laser-driven acceleration of a 94.8 MeV uniform proton beam enhanced by a thin axial absorber rod

Laser-based proton accelerators offer promising advantages for many sensitive applications due to their compact size. However, achieving uniform beams with a narrow energy spread remains a challenge. Here, a beamline simulation is performed using the racein and codes to optimize the spectral and spatial characteristics of a laser-driven proton beam. This beamline, comprised of four magnetic quadrupoles and equipped with a thin axial absorber rod in conjunction with an energy selection aperture for narrowing the energy spread, a carbon scatterer foil for beam spot smoothing, and an angular selection aperture for beam collimation, effectively transports a selected proton beam energy within the range of 50–250 MeV. In this work, laser-accelerated protons with a wide energy spread were transported through the proposed beamline, which was optimized for 109 MeV protons. The protons emerged well-collimated with a significantly narrowed energy spread of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>94.8</a:mn><a:mo>±</a:mo><a:mn>3.9</a:mn><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>MeV</a:mi></a:math> (a reduction from the intended 109 MeV due to passage through the scatterer) and a homogenized, 11 mm diameter beam spot while maintaining a transmission efficiency above 2.2%.