Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 μ m lasers

Collisionless shock acceleration of protons and ${\mathrm{C}}^{6+}$ ions has been achieved by the interaction of a ${10}^{20}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$, $1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allows for systematic control of the plasma profile. This enables the production of beams with peaked spectra with energies of $10--18\text{ }\text{ }\mathrm{MeV}/\mathrm{amu}$ and energy spreads of 10%--20% with up to $3\ifmmode\times\else\texttimes\fi{}{10}^{9}$ particles within these narrow spectral features. The narrow energy spread and similar velocity of ion species with different charge-to-mass ratios are consistent with acceleration by the moving potential of a shock wave. Particle-in-cell simulations show shock accelerated beams of protons and ${\mathrm{C}}^{6+}$ ions with energy distributions consistent with the experiments. Simulations further indicate the plasma profile determines the trade-off between the beam charge and energy and that with additional target optimization narrow energy spread beams exceeding $100\text{ }\text{ }\mathrm{MeV}/\mathrm{amu}$ can be produced using the same laser conditions.