Generation of collisionless electrostatic shock waves in interaction between strong intense laser and near-critical-density plasma*

Weak and strong collisionless electrostatic shock wave (CESW) generated in the interaction between strong intense laser and near-critical-density plasma are studied by the one-dimensional particle-in-cell simulation in this work. And the effects of the ranges of plasma density profiles, non-relativistic and relativistic laser intensities on the generation of CESWs are also investigated. The non-relativistic weakly driven laser generates the weak CESW in the interaction between the laser and near-critical-density plasma. The electron spectra show double-temperature distribution because the non-relativistic driven laser cannot heat the electrons sufficiently. The low-temperature electrons have an important influence on the generation of weak CESW, and they can also cause the protons to be accelerated and reflected from the CESWs. The spectra of the weak CESW protons show a continuously distributed profile. When the range of plasma density up-ramp is large, the process can be observed that the post-soliton structure evolves into the ion acoustic wave and further into the weak collisionless electrostatic shock wave. When the driven laser intensity is relativistic, the electrons are heated sufficiently to a single relativistic temperature. The effect of the range of plasma density profile on the generation of CESW is further analyzed and it is found that 1) when the range of plasma density up-ramp is large, the potential barrier of ion acoustic wave is shielded by the hot electrons; 2) when the range of plasma density up-ramp is small, the effective distance (i.e. the Debye length) of accelerating field is larger and the endurance time is longer than when the range of plasma density up-ramp is large. This makes the ion acoustic wave structure more stable in its forward propagation process. When the difference in velocity between the ion acoustic wave accelerating protons and the target normal sheath accelerating protons satisfies the proton reflection condition of CESW, the ion acoustic wave further evolves into the strong CESW, the monoenergetic protons generated at the same time.