Propagation of ultra relativistic fireball beam into plasma
Ab initio PIC simulations of astrophysical plasmas have provided new directions to identify the role of plasma instabilities in the formation of collisionless shock, the particle acceleration processes, and the generation of magnetic field structures compatible with the intense radiation bursts of synchrotron radiation.
It has been known that the interaction of ultra-relativistic beam with plasma drives several plasma instabilities. There are three possible main scenarios depending on the direction of the wave-vector respect to the flow; when the wave-vector is aligned to the flow, the purely two-stream instability driven by the peaked nature of the velocity distribution dominates; when the wave-vector is normal to the flow, the filamentation instability is excited; finally, if the wave-vector is at an arbitrary angle respect to the flow, then it is the oblique instability to play a role. As a consequence of all these instabilities, the beam breaks up into narrow and high current density filaments.
This movies shows what happens when a long fireball beam interacts with a static plasma composed of e− and e+ . It is possible to observe that the oblique instability grows faster than the filamentation instability due to the coupling between longitudinal and transverse modes, which reduces its growth. The instability generates an intense longitudinal electric field on the order of GV/m and drives a plasma wake. The beam further propagates inside the plasma and finally the instability saturates after 30 cm.
To reference this video, use Shukla, N. et al., Condition for the onset of the current filamentation instability of ultra-relativistic fireball bunches in plasmas, Bul. Am. Phys. Soc., 56th Annual Meeting of the APS DPP, 59, PO8.00066 (2014).