Speaker
Istvan Pusztai
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4004.pdf
Effects of impurities and electron trapping in collisionless electrostatic
shocks
I. Pusztai1 , A. Sundström1 , J. M. TenBarge2,3 , J. Juno4 , A. Hakim3 , and T. Fülöp1
1 Department of Physics, Chalmers University of Technology, Göteborg, Sweden
2 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08543, USA
3 Princeton Plasma Physics Laboratory, Prinecton, NJ 08543, USA
5 IREAP, University of Maryland, College Park, MD 20742, USA
Electrostatic collisionless shocks appear in various laboratory and space plasmas; and they are
also used in laser-plasma based acceleration schemes to produce mono-energetic ion beams [1].
We investigate the existence and properties of low Mach-number electrostatic collisionless
shocks, with particular emphasis on the effect of impurities and electron trapping. We use a
semi-analytical approach similar to Ref. [2, 3] to describe the vicinity of the shock. These shock
solutions show good correspondence to simulation results initialized with density discontinu-
ities with the fully kinetic, Eulerian Vlasov-Maxwell solver of Gkeyll[4].
We find that even a small amount of impurities can influence the shock properties signifi-
cantly, including the reflected light ion fraction, which can change several orders of magnitude.
We provide accurate analytical expressions for the reflected fractions of main ions and impu-
rities, which illuminate the different behavior of hydrogen, depending on its role as main ion
or impurity. The reflection of heavy impurities by a shock in a hydrogen plasma is vanishingly
small, while shocks in heavy ion plasmas – with relevance to laser-based ion acceleration ex-
periments – reflect most of the hydrogen impurity ions. When the electron distribution is flat
in the trapped phase space regions due to the downstream potential oscillations, bifurcation of
shock-like solutions is observed for low Mach-numbers.
References
[1] D. Haberberger et al., Nat. Phys. 8 95 (2012).
[2] I. Pusztai et al., Plasma Phys. Control Fusion 60, 035004 (2018).
[3] R. A. Cairns et al., Plasma Phys. Control Fusion 57, 044008 (2015).
[4] J. Juno et al., J. Comput. Phys. 353, 110 (2018).
