Rescaling methods and plasma expansions into vacuum

Abstract

The problem of a two-component, collisionless plasma expansion into vacuum is investigated from the viewpoint of the Vlasov–Poisson model. The set of equations is treated both analytically (through the rescaling transformations) and numerically, using a one-dimensional Eulerian code. In planar geometry, the rescaling allows to conjecture the existence of a self-similar expansion over long times. Numerical results subsequently confirm the conjecture and show that the plasma becomes neutral over a smaller and smaller scale. A few thermodynamical properties are studied: the temperature is shown to decrease as t−2; the polytropic relation (d/dt)(pn−γ)=0 (with γ=3) is verified asymptotically via a semianalytical argument. Finally, the same problem is studied in a spherical one-dimensional geometry. The time-asymptotic solution is again self-similar. Numerical simulations show that a non-neutral, multiple-layer structure appears, which is proved to be stable over long times.

Kinetics of the Collisionless Expansion of Spherical Nanoplasmas

“…4 (for the scenario of Fig. 3b), the electrons rapidly cool down and the charge buildup within the ion front decreases, until a ballistic regime is reached for both species [11]. In general, the electron dynamics strongly affects the energy spectrum of the ions, by reducing the repulsive electric field.…”

Ergodic model for the expansion of spherical nanoplasmas

“…10 [case (b)]. Asymptotically, the sphere enveloped by the expanding ion front encloses all trapped electrons, and a ballistic regime is reached for both species [7]. The self-consistent behavior of the electrons strongly affects the ion dynamics and their resulting energy spectrum.…”

“…In the present paper, for simplicity, only the ideal situation (commonly adopted in the literature [3,4,5,6,7]) of an initially neutral plasma with Maxwellian electrons is considered, in which all the information on the electron heating by the laser pulse is contained in the initial electron temperature, T 0 . The function g in Eq.…”

“…A remarkable example of numerical solution of the VP equations for the expansion problem in a spherical geometry can be found in Ref. [7], for the particular case in which the motion of both ions and electrons is purely radial.…”

“…Dawson in 1964 [1]. In the case of planar targets (employed for ion acceleration [2]), the physics of the expansion has been extensively studied under a variety of conditions, using different analytical and numerical approaches [3,4,5,6,7]. In contrast, the expansion of spherical plasmas [such as the nm-to µm-sized plasmas generated upon interaction of ultraintense lasers with atomic or molecular clusters (cf.…”