Lower-hybrid drift instability and macroscopic flow of colliding magnetized plasmas

Abstract

Microscopic instability and macroscopic flow pattern resulting from colliding plasmas are studied analytically in support of laboratory experiments. The plasma flows are assumed to stream radially from two separate centers. In a quasi-planar (2D) geometry, they may arise from an Ohmic explosion of two parallel wires, but similar configurations emerge from other outflows, e.g., colliding winds in binary star systems. One objective of this paper is to characterize the flow instabilities developing near the flow stagnation line. An exact solution for the Buneman-type dispersion equation is obtained without conventional simplifications. The unstable wave characteristics are key to anomalous resistivity that determines the reconnection rate of opposite magnetic fields transported with each flow toward the stagnation zone. The second objective of the paper is to calculate the stream function of the plasma shocked upon collision. We addressed this task by mapping the flow region to a hodograph plane and solving a Dirichlet problem for the stream function. By providing the instability growth rate, responsible for anomalous transport coefficients, and the overall flow configuration, these studies lay the ground for the next step. From there, we will examine the field reconnection scenarios and emerging mesoscopic structures, such as radial striata observed in the experiments.

Instabilities, Anomalous Heating and Stochastic Acceleration of Electrons in Colliding Plasmas

“…Spatio-temporal characteristics of the instabilities and associated turbulent motion is another objective of this study. The analytic and numerical studies in [1,2] have indicated that plasmas that stream against each other from two ohmically vaporized wires may indeed mix in a relatively thin layer, in accord with the preceding experiments [5]. The shocked corona layer is separated from the inflowing material by a pair of termination shocks (for supersonic flows), and the plasma pressure inside the layer reaches its maximum at the flow stagnation point.…”

“…To produce such deflection, the electrostatic potential, Φ, must reach the level of where u is the speed of plasma upstream of the collision layer, and M is the ion mass. In more detail, a twodimensional flow that emerges from the collision of two concentric outflows has been studied using the hodograph transformation in [1]. The magnetic field carried to the collision layer with the flows is assumed to have no substantial effect on the ion motion since the flow ram pressure is typically about an order of magnitude higher than the magnetic pressure [5].…”

“…Even if it does, it will quickly thermalize and mix up the electron populations before the much heavier ions start responding to this instability. The modified two-stream instability, in which electrons ExB drift in the wire direction, has been considered [1]. It should produce a similar effect of electron preheating.…”

“…This paper will consider microscopic instabilities and electron heating in interpenetrating plasmas using unmagnetized plasma approximation near a symmetry plane of collision. The collision regime of magnetized electrons and unmagnetized ions has been addressed in [1] along with the macroscopic two-dimensional flow emerging from the collision. Macroscopic instabilities of this flow have been studied numerically in [2] in hydrodynamic approximation.…”

“…This work is directly relevant to laboratory experiments with explosively-created laser or z-pinch plasmas but may also elucidate naturally occurring plasma collisions in astrophysical or space physics contexts. In the previous publications [1,2], we have studied, analytically and numerically, the flow emerging from interpenetrating coronas launched by two parallel wires vaporized in a vacuum chamber. The main foci of the studies have been on the general flow pattern and lower-hybrid and thin-shell instabilities that under certain conditions develop in the collision layer.…”