Sub-Alfvénic plasma expansion

Abstract

A large ion Larmor radius plasma undergoes a particularly robust form of Rayleigh–Taylor instability when sub-Alfvénically expanding into a magnetic field. Results from an experimental study of this instability are reported and compared with theory, notably a magnetohydrodynamic (MHD) treatment that includes the Hall term, a generalized kinetic lower-hybrid drift theory, and with computer simulations. Many theoretical predictions are confirmed while several features remain unexplained. New and unusual features appear in the development of this instability. In the linear stage there is an onset criterion insensitive to the magnetic field, initial density clumping (versus interchange), linear growth rate much higher than in the ‘‘classic’’ MHD regime, and dominant instability wavelength of order of the plasma density scale length. In the nonlinear limit free-streaming flutes, apparent splitting (bifurcation) of flutes, curling of flutes in the electron cyclotron sense, and a highly asymmetric expansion are found. Also examined is the effect on the instability of the following: an ambient background plasma (that adds collisionality and raises the expansion speed/Alfvén speed ratio), magnetic-field line tying, and expansion asymmetries (that promotes plasma cross-field jetting).

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

“…The growth of flute-like instabilities affecting the plasma dynamics at intermediate levels of magnetization was also demonstrated [25,26]. We should note however that all these studies were conducted in a regime where only the electrons in the plasma were magnetized, the ions being not or weakly magnetized.…”

Investigation of flute instability in application to laboratory astrophysics and Z-pinch experiments

“…Similar phenomena can take place during Novae explosions (Zakharov 2003) and artificial magnetospheric releases, similar to the AMPTE magnetotail release (Bernhardt et al 1987;Ripin et al 1993).…”

Excitation of Electromagnetic Flute Modes in the Process of Interaction of Plasma Flow with Inhomogeneous Magnetic Field

“…During recent experiments on interaction of laser ablated plasma flows with the magnetic field created by the Zebra pulse power generator strong wave activity was detected in the region of plasma flow deceleration by the magnetic field (Presura et al, 2006). Similar phenomena can take place during Novae explosions (Zakharov, 2003) and artificial magnetospheric releases, similar to the AMPTE magnetotail release (Bernhardt et al, 1987;Ripin et al, 1993). To study its linear excitation and nonlinear evolution, a nonlinear set of equations for electrostatic potential, magnetic field, and density has been derived in the low frequency limit (ω ci ,where ω is the frequency of the excited mode and ci = ZeB 0z /M i c is the cyclotron frequency of the ion with charge Z and mass M i = μM p , M p being the proton mass) from two-fluid macroscopic equations which include gyroviscosity (Sotnikov et al, accepted by IEEE TPS, 2006).…”