Supersonic gas jets generated via a conical nozzle are widely applied in the laser wakefield acceleration of electrons. The stability of the gas jet is critical to the electron injection and the reproducibility of the wakefield acceleration. Here we discussed the role of the stilling chamber in a modified converging–diverging nozzle to dissipate the turbulence and to stabilize the gas jets. By the fluid dynamics simulations and the Mach–Zehnder interferometer measurements, the instability originating from the nonlinear turbulence is studied and the mechanism to suppress the instability is proposed. Both the numerical and experimental results prove that the carefully designed nozzle with a stilling chamber is able to reduce the perturbation by more than 10% compared with a simple-conical nozzle.

Magnetic reconnection driven by laser plasma interactions attracts great interests in the recent decades. Motivated by the rapid development of the laser technology, the ultra strong magnetic field generated by the laser-plasma accelerated electrons provides unique environment to investigate the relativistic magnetic field annihilation and reconnection. It opens a new way for understanding relativistic regimes of fast magnetic field dissipation particularly in space plasmas, where the large scale magnetic field energy is converted to the energy of the nonthermal charged particles. Here we review the recent results in relativistic magnetic reconnection based on the laser and collisionless plasma interactions. The basic mechanism and the theoretical model are discussed. Several proposed experimental setups for relativistic reconnection research are presented.

High-energy γ-photon generation via nonlinear Compton scattering and electron–positron pair creation via the Breit–Wheeler process driven by laser–plasma interaction are modeled, and a number of mechanisms are proposed. Owing to the small cross section, these processes require both an ultra-intense laser field and a relativistic electron bunch. The extreme conditions for such scenarios can be achieved through recent developments in laser technology. Photon emission via nonlinear Thomson and Compton scattering has been observed experimentally. High-energy positron beams generated via a multiphoton process have recently been observed too. This paper reviews the principles of γ-ray emission and e⁺e^? pair creation in the context of laser–plasma interaction. Several proposed experimental setups for γ-ray emission and e⁺e^? pair creation by ultra-intense laser pulses are compared in terms of their efficiency and the quality of the γ-photon and positron beams produced for ultrashort (15 fs) and longer (150 fs) multi-petawatt laser beams.