Speaker
Nitin Shukla
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4010.pdf
Exploring astrophysical condition with ab initio kinetic PIC simulation
N. Shukla1 , J.Vieira1 , P. Muggli2 , G. Sarri3 , R. Fonseca1,4 and L. O. Silva1
1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de
Lisboa, Lisbon, Portugal
2 Max Planck Institute for Physics, Munich, Germany
3 Centre for Plasma Physics, School of Mathematics and Physics, Queen’s University of
Belfast, Belfast BT7 1NN, United Kingdom
4 DCTI/ISCTE, Instituto Universitario de Lisboa, Lisbon, Portugal
The fireball model allows for explaining the origin and amplification of magnetic fields in as-
trophysical settings [1]. A relativistic fireball consists of a flow of electrons and positrons in
an electronically quasi-neutral state. Interactions of these beams with the background plasma
are believed to trigger microinstabilities responsible for the field growth. Very recently, fire-
ball beams have been experimentally generated [2], thus providing a platform to explore such
processes in the laboratory.
In this work, we carried out a detailed numerical and theoretical study with multidimensional
particle-in-cell (PIC) simulations performed with the PIC code Osiris [3]. The aim of our work
is to determine the required laboratory conditions under which the fireball beam becomes un-
stable. In this work, we show that the ratio between the density of the fireball and background
plasma controls a transition between the current filamentation instability (CFI) and the compet-
ing transverse two-stream instability. When the density ratio is higher than unity the CFI can
grow as long as the beam expansion rate, caused by a finite emittance, is larger than the CFI
growth rate. We find that the longitudinal energy spread, typical of plasma-based accelerated
electron-positron fireball beams, plays a minor role in the growth of CFI. Finally, we investigate
the role of the transverse offsets between the centroids of the electron and positron beam spatial
distribution. We find that the CFI can also grow as long as the transverse offsets between the
beam centroids are smaller than a fraction of the beam transverse dimensions.
References
[1] P. Meszaros, M. Rees, ApJ. 405, 278 (1993). A. Gruzinov and E. Waxman ApJ. 511, 852
(1999). M. V. Medvedev et al ApJ., 618, L75 (2004).
[2] G. Sarri et al, Nat. Commun 6, 1 2015.
[3] R. A. Fonseca et al, LNCS 2331, 342 (2002); R. A. Fonseca et al., PPCF 50, 124034
(2008).
