Design Considerations for Unmagnetized Collisionless-Shock Measurements in Homologous Flows

Abstract

The subject of this paper is the design of practical laser experiments that can produce collisionless shocks mediated by the Weibel instability. Such shocks may be important in a wide range of astrophysical systems. Three issues are considered. The first issue is the implications of the fact that such experiments will produce expanding flows that are approximately homologous. As a result, both the velocity and the density of the interpenetrating plasma streams will be time dependent. The second issue is the implications of the linear theory of the Weibel instability. For the experiments, the instability is in a regime where standard simplifications do not apply. It appears feasible but non-trivial to obtain adequate growth. The third issue is collisionality. The need to keep resistive magnetic-field dissipation small enough implies that the plasmas should not be allowed to cool substantially.

Detailed characterization of laser-produced astrophysically-relevant jets formed via a poloidal magnetic nozzle

“…1D) expansion close to the target (z ∼ R spot ) and as a quasi-hemispherical (i.e. 3D) expansion at distances far from the target (z ≫ R spot ) [58,59], as we observe experimentally. We note that some previous work has referred to these flows as "jets" [60,61] due to their modest directionality.…”

Transition from Collisional to Collisionless Regimes in Interpenetrating Plasma Flows on the National Ignition Facility

“…With the advent of high energy, high power lasers, the study of high Mach number collisionless plasma interactions became possible in the laboratory [13][14][15][16], with a number of experiments observing non-Weibel mediated (electrostatic, etc.) collisionless shocks [17][18][19][20].…”

Filamentation Instability of Counterstreaming Laser-Driven Plasmas

“…Due to the long mean-free-path between ions in opposing streams, the streams interpenetrate, establishing supersonic counterstreaming conditions in the ion populations, while the electrons form a single thermalized cloud. Meanwhile, the plasma density is also sufficient so that the the ion skin depth d i = (m i /µ 0 ne 2 ) 1/2 , is much smaller than the system size L. These conditions allow the growth of an ion-driven Weibel instability, for which d i is the characteristic wavelength [14][15][16]. The Weibel-generated electromagnetic fields were observed with an ultrafast pro- ton radiography technique [17], and identified through good agreement with analytic theory [6] and particle-incell simulations, discussed below.…”