Laboratory studies of magnetic vortices. III. Collisions of electron magnetohydrodynamic vortices

Abstract

Magnetic vortices in the parameter regime of electron magnetohydrodynamics are studied in a large laboratory plasma. The vortices consist of magnetic field perturbations, which propagate in the whistler mode along a uniform dc magnetic field. The magnetic self-helicity of the spheromak-like field perturbations depends on the direction of propagation. Vortices with opposite toroidal or poloidal fields are launched from two antennas and propagated through each other. The vortices collide and propagate through one another without an exchange of momentum, energy, and helicity. The absence of nonlinear interactions is explained by the force-free fields of electron magnetohydrodynamic (EMHD) vortices.

Helicons in Unbounded Plasmas

“…It allows the superposition of fields from two or more antennas which has been verified earlier for counter-propagating whistler vortices [11]. Due to the uniformity in density and ambient magnetic field it is also valid to shift the antenna with its wave field to a different position.…”

Circular polarization of obliquely propagating whistler wave magnetic field

“…2,11 The textbook derivation of whistler waves shows that the wave electric field is right-hand circularly polarized when the propagation wavevector is parallel to the background magnetic field.…”

3D EMHD reconnection in a laboratory plasma

“…Since such fields exert no force on the electron fluid, they behave remarkably linear. No nonlinear interaction is observed when two EMHD vortices propagate along ±B 0 against each other (Urrutia et al, 2000). During the collision, the opposing (e.g., toroidal) fields annihilate.…”

“…When the vortex fields are smaller than the background field, the total field exhibits a twist and bulge/pinch but no null points. This is the linear regime of EMHD vortices which has been studied extensively (Stenzel and Urrutia, 1990;Rousculp et al, 1995;Urrutia et al, 2000). A brief summary of their interesting properties will be given prior to describing new observations of large-amplitude vortices with 3D null points.…”