Effect of electrostatic ion two-stream instability on the laser-driven collisionless shock ion acceleration in multi-ion species plasma

ABSTRACT The collisionless shocks are Ubiquitous in the various astrophysical environments such as in supernova remnants, pulsar wind nebulae etc. These shocks are thought to be responsible for the generation of high-energy cosmic rays. Thanks to the development of high-power and high-intensity lasers, it is possible to study the formation and evolution of collisionless shocks in laboratories. The numerical [1] and experimental [2] findings show that the laser-driven electrostatic collisionless shock can accelerate particles for possible applications such as proton radiography, cancer therapy, etc. In this paper, the 2D EPOCH particle-in-cell simulations are used to study the high-intensity laser-driven electrostatic collisionless shock ion acceleration in different target materials, such as CH and C2H3Cl, and pure H plasmas[3]. Our results indicate that, electrostatic collisionless shock is excited, and protons in the upstream region of the shock are reflected and accelerated by the shock potential. Ions in the upstream region expand with different velocities depending on their charge-to-mass ratios under the DC component of the sheath electrostatic field. In multi-ion species plasma, the excitation of electrostatic ion two-stream instability (EITI) [4] between the heavier and lighter ion populations occurs. This results in the deceleration of the expanding protons and appearance of a low-velocity component. An additional EITI between the reflected and expanding protons accelerates some of the protons to the higher velocity, which results in more protons being accelerated by the shock.

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