Experimental Observation of Thin-shell Instability in a Collisionless Plasma

Abstract

We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balance between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.

General features of experiments on the dynamics of laser-driven electron–positron beams

“…This conclusion is inferred from simulations performed using HYADES [25], a commercial 1-D hydrodynamics Lagrangian code frequently used to estimate the conditions of a plasma in laboratory astrophysical studies (for examples, see Refs. [26,27]). As an example, we will discuss the experimental conditions presented in a recent publication [17].…”

Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds

“…In pure hydrodynamics, this imbalance results in a shearing flow along the corrugated sheet, accumulating materials at local extremities of the ripples and thus enhancing corrugation. This effect has been reported in many numerical simulations of collisions between molecular gas (Blondin & Marks 1996;Klein & Woods 1998;Hueckstaedt 2003;McLeod & Whitworth 2013) or unmagnetized plasma (Dieckmann et al 2015Ahmed et al 2017).…”

Increased hot electron production from the addition of a gas cell in sub-picosecond laser–foil interactions

“…Solving equation 7 for x, results in a cut off of about 3.5µm (it was found that the instability that get set up in the gas has a length scale of 4µm which further justifies this cut off). The maximal energy is therefore the integral of equation 6 up to this cut off: 8) which is over double the minimum energy needed for electrons to emit mostly > 100KeV photons. This final value is not too sensitive to small increases in the cut-off value (increasing the cutoff to 4µm increases peak energy to 5.2MeV).…”

“…Recently, experiments conducted at the VULCAN laser facility (Target Area West) at the Rutherford Appleton Laboratory, using thin foil targets with the rear surface in contact with a gas cell, have raised suspicion that the addition of the gas (or potentially the target geometry to achieve this) results in a significant increase in the production of hard (>100keV) x-rays able to exit the interaction chambers. Similar gas cells have been used in a number of prior experiments 5,7,8 . Figure 2 shows the radiation dose internal to the experimental area averaged over the experimental periods.…”