Search

We present the detection of directional muon beams produced using a PW laser at the Lawrence Berkeley National Laboratory. The muon source is a multi-GeV electron beam generated in a 30 cm laser plasma accelerator interacting with a high-Z converter target. The GeV photons resulting from the interaction are converted into a high-flux, directional muon beam via pair production. By employing scintillators to capture delayed events, we were able to identify the produced muons and characterize the source. Using theoretical knowledge of the muon production process combined with simulations that show outstanding agreement with the experiments, we demonstrate that the multi-GeV electron beams produce muon beams with GeV energies and fluxes, at a few meters from the source, up to 4 orders of magnitude higher than cosmic ray muons. Laser-plasma-accelerator-based muon sources can therefore enhance muon imaging applications thanks to their compactness, directionality, and high fluxes which reduce the exposure time by orders of magnitude compared to cosmic ray muons. Using the Geant4-based simulation code we developed to gain insight into the experimental results, we can design future experiments and applications based on LPA-generated muons.

We measure the high intensity laser propagation throughout meter-scale, channel-guided LPAs by adjusting the length of the plasma channel on a shot-by-shot basis, showing high quality guiding of 500 TW laser pulses over 30 cm in a hydrogen plasma of density $n_0 \approx 1 \times 10^{17} \, \mathrm{cm^{-3}}$. We observed transverse energy transport of higher-order modes in the first $\approx 12 \, \mathrm{cm}$ of the plasma channel, followed by quasi-matched propagation, and the gradual, dark-current-free depletion of laser energy to the wakefield. We quantify the laser-to-wake transfer efficiency limitations of currently available PW-class laser systems, and demonstrate via simulation how control over the laser mode can significantly improve accelerated beam parameters. Using just 21.3 J of laser energy, and triggering localized electron injection into the accelerator, we observed electron bunches with single, quasimonoenergetic peaks, relative energy spreads as low as 3 % and energy up to 9.2 GeV with charge extending beyond 10 GeV.