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

Collisionless shock acceleration of protons and C^{6 +} ions has been achieved by the interaction of a 10²⁰ W /cm² , 1 μ 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 MeV /amu and energy spreads of 10%-20% with up to 3 ×10⁹ 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 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 MeV /amu can be produced using the same laser conditions.