Ion acceleration in electrostatic collisionless shocks is driven by the interaction of the high-power laser with specially tailored near-relativistic critical density plasma. 2D EPOCH particle-in-cell simulations show that the ion acceleration is dependent on the target material used. In materials with low charge-to-mass ratio $⟨Z/A⟩$, proton beams with high flux and low energy spread are generated. In multi-ion plasmas the ions with different $⟨Z/A⟩$ acquire different velocities under a non-oscillating component of electrostatic field in the upstream region. This relative drift between the protons ($⟨Z/A⟩=1$) and the lower $⟨Z/A⟩$ ions leads to the excitation of electrostatic ion two-stream instability. This in turn generates a low-velocity component in the upstream expanding protons. The velocity distribution of the upstream expanding protons is further broadened toward the higher velocity by the electrostatic ion two-stream instability between reflected protons, which results in large number of protons being accelerated by the shock.

• Received 1 October 2018

DOI:https://doi.org/10.1103/PhysRevAccelBeams.22.043401

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Published by the American Physical Society