FLASH simulations of laboratory astrophysics experiments to study plasma jet collimation by a strong ambient magnetic field

The formation, morphology and propagation of plasma jets in external magnetic fields are fundamental problems applicable to many astrophysical systems. Laboratory astrophysics experiments have been developed in recent years for recreating scaled astrophysical systems by using powerful laser facilities like the OMEGA. The FLASH code is a parallel, multi-physics, adaptive mesh refinement and radiation magnetohydrodynamic code, which is used to simulate an experiment of collimated laser-driven plasma jet in strong applied magnetic fields. The simulation system consists of a polystyrene foil and washer, a 3ω laser beam delivers total energy of 5kJ on the foil within 10 ns to produce plasma. A 25 and 50 T magnetic field is applied in the direction of jet propagation. The sound speed, Alfvén velocity, Mach number and plasma beta are kept as the scale invariant between laboratory experiments and solar corona. Simulations show that collimated plasma jets can be produced by applying a strong external magnetic field in our designed experimental conditions and the collimation effect would be enhanced while the external magnetic field strength increases. The mechanism of collimation is magnetic fields are frozen in and pushed out by the plasma flow to form a high magnetic pressure region out of the jet edge, consequently the plasma jet is compressed by magnetic pressure difference to cause the magnetized jet collimation.