Laboratory Study of Alfvén Wave Steepening

Alfvénic fluctuations - fluctuations with magnetic-field and velocity fluctuations perpendicular to the background magnetic field which are proportional to each other - are thought to be ubiquitous in magnetized astrophysical plasma environments and are observed across scales in our own solar wind. Recent theoretical work by Mallet et al [1] proposes a mechanism by which small-scale, oblique Alfvén waves undergo a one-dimensional nonlinear steepening process only at dispersive length scales smaller than the ion inertial length. This work presents the first laboratory tests of this steepening model, comparing predictions for the amplitude of the harmonic of a driven wave to experimental measurements from the Large Plasma Device (LAPD). These tests span highly inertial to highly kinetic conditions at low β to provide insight into turbulence in environments like the solar corona, where the usual counterpropagating Alfvén wave interactions may be suppressed.

[1] Mallet, Alfred, et al. "Nonlinear dynamics of small-scale Alfvén waves." arXiv preprint arXiv:2303.10192 (2023).

Funded by DE-SC0023326.