Generation of relativistic ions, electrons and positrons in high-intensity short-pulse laser-solid interactions

The newly-commissioned Orion laser facility at AWE Aldermaston can deliver intense ($10^{21}$~W/cm$^{2}$), short (0.6~ps) laser pulses at $1\omega$ (1~$\mu$ m) and 3$\times10^{20}$~W/cm$^{2}$ at $2\omega$ with pulse contrasts of $10^{7}$ and $10^{13}$, respectively, in addition to ten $3\omega$, 500~J long-pulse ($\sim$ns) beams. All can be delivered to target synchronized to $\sim20$~ps. We report on the production and characterization of multi-MeV protons, ions, positrons and electrons at the Orion facility using 500~J, 0.6~ps, $1\omega$ pulses and 100~J, 0.6~ps, $2\omega$ pulses onto both thin (20~$\mu$ m) and thick (1~mm) gold targets. Laser intensities were scanned from $10^{19}$ to $10^{21}$~W/cm$^{2}$ by altering pulse energy and length while maintaining a consistent focal spot size of 10~$\mu$. Particle energies were recorded by use of a magnetic and a Thomson spectrometer, with X-ray emissions imaged using a time-integrating pinhole camera in addition to time-integrating crystal spectrometers. The implications for future experiments such as investigations into electron transport mechanisms and proton heating are briefly discussed.