335 / 2019-02-26 18:02:54

Multi-dimensional magnetohydrodynamic simulations of the laboratory astrophysics experiments on the PALS laser facility

Laboratory astrophysics,magnetosonic shocks,laser heated plasmas

全体主题 > Fundamental Physics at Extremes

Interaction of supersonic plasma jets with a plasma is of great importance for understanding of many astrophysical objects. The role of hydrodynamic instabilities and external magnetic fields in the shock formation and jet evolution needs to be understood. This paper presents analysis of the experiment conducted on the PALS facility in Prague on interaction of a laser-driven supersonic jet with an ambient plasma in a quasi-static magnetic field [1]. A jet of a density ~ 1018 cm-3 and velocity ~ 400 km/s was created by a laser pulse with energy of 20 – 100 J and duration of ~250 ps in interaction with a flat copper target. The ambient plasma of a comparable density was produced from an argon gas jet immersed in a magnetic field ~ 0 – 10 T perpendicular to the plasma jet propagation direction. Under such conditions magnetosonic and Alfvenic shocks may be excited and perturb the jet propagation through the background plasma.
In order to understand the physics of jet-plasma interaction and role of magnetic field, the experiment has been modelled with the multi-dimensional radiative Eulerian code FLASH [2] in pure hydro as well as in the magneto-hydrodynamic mode. According to the simulation results, in the case without external magnetic field, a hydrodynamic instability appears at the contact surface between the jet and the ambient plasma. The instability is accompanied with slowing down the jet, its radial expansion and creation of a turbulent zone near the contact surface. In contrast, the instability disappears when the jet enters in a magnetized ambient plasma. The magnetic field is strongly compressed near the contact surface thus preventing mixing of two plasmas. Moreover, the magnetic field expelled from the jet maintains its collimation for a longer time.
The combined effects of the radiation transport and magnetic field compression may explain strong collimation of the plasma jets observed in young stellar objects [1]. The simulation results will be discussed and compared to the experimental data.