No abstract

We present results from fully kinetic particle-in-cell simulations of the transport of astrophysical relativistic jets in magnetized intergalactic medium. As opposed to magnetohydrodynamic simulations, the results show that a strong charge-separation electric field, induced by the different responses between jet electrons and ions to the magnetic fields, significantly enhances the energy exchange between different species of charged particles and electromagnetic fields, thus playing a key role in determining the collimation and shape of the jet spectral energy distribution (SED). It is found that when the magnetic field strength increases, the jet collimation also increases while the power-law slope of the jet SED decreases; this provides potential enlightenment on related astrophysical observations.

Knot structures exist ubiquitously in young stellar object (YSO) jets, which are a key tracer in astronomical observation to estimate the jet properties and eventually the YSO's parameters (age, size, mass and so on). Using 2D and 3D radiation magnetohydrodynamic simulations of the laser-produced plasma jets in external poloidal magnetic fields, we present a systematic analysis on the formation mechanism and characteristics of knot structures in collimated jets. The simulations demonstrate that the multi-knot pattern in jets can be formed by the oblique internal shocks in only single ejection. It is found that the distance L between different knots in jet is determined by the ratio of its thermal pressure to magnetic pressure β as L ∝ Dβ 1/2 , where D is the jet transverse diameter. There is a factor about 0.4-0.6 between the knot and jet velocities. And radiation cooling effect can alleviate the intensity of the external magnetic field required for collimating jets. These findings are scaled to the conditions of YSO jets, and can be applied to explore some characteristics of the astrophysical jets.

Magnetic reconnection, breaking and reorganization of magnetic field topology, is a fundamental process for rapid release of magnetic energy into plasmas that occurs pervasively throughout the universe. In natural circumstances, the plasma properties on either side of the reconnection layer are almost asymmetric, in particular for the collision rates that critically determine the underlying reconnection mechanism. To date, all laboratory experiments on magnetic reconnections have been limited to purely collisional or collisionless regimes. Here, we report a well-designed experimental investigation on magnetic reconnections in a hybrid collisional-collisionless regime by interactions between laser-ablated copper and plastic plasmas. We directly observe the topology evolutions of the whole process of this asymmetric magnetic reconnection by highly-resolved proton radiography. Through this, we show that the growth rate of tearing instability in such a hybrid regime is still extremely large, resulting in rapid formation of multiple plasmoids and generation of plasmoid-dominated current sheet.