Authors: S. Dorfman (Space Science Institute), T. Carter (UCLA), S. Vincena (UCLA), F. Li (New Mexico Consortium), S. Fu (New Mexico Consortium), P. Pribyl (UCLA), Y. Lin (Auburn University)

Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in our heliosphere. The non-linear behavior of these modes is thought to play a key role in important problems such as solar wind turbulence and the heating of the solar corona. Theoretical predictions show that these Alfvén waves may be unstable to various parametric instabilities, but in-situ satellite measurements of these processes are limited.

We present results from the Large Plasma Device aimed at diagnosing these instabilities in the laboratory where they can be studied in a well-controlled plasma environment. This includes:

1) The first observation of a shear Alfvén wave parametric instability in the laboratory [1]. When a single finite ω/Ωi, finite k⊥ Alfvén wave is launched above a threshold amplitude, three daughter waves are observed: two sideband Alfvén waves co-propagating with the pump and a low frequency nonresonant mode. The daughter modes are spatially localized on a gradient of the pump wave magnetic field amplitude in the plane perpendicular to the background field, suggesting that perpendicular nonlinear forces (and therefore k⊥ of the pump wave) play an important role in the instability process. Scaling studies show that this perpendicular parametric modulational instability (PPMI) is most active at the boundary between the inertial and kinetic Alfvén wave regimes, a parameter space highly relevant to the lower part of the Corona.

2) New studies aimed at measuring the Parametric Decay Instability (PDI) growth rate in the laboratory. In these experiments, a high amplitude δB/B0~0.7% pump Alfvén wave is launched from one end of the device and a smaller seed Alfvén wave in launched from the other side. When the frequency of the seed wave is chosen to match the backward wave expected from PDI, damping of the seed wave is reduced. Analysis is underway to compare this reduction in the damping to the theoretically expected PDI growth rate and to connect with results from related numerical simulations [2].

[1] S. Dorfman and T. A. Carter, Observation of an Alfvén wave parametric instability in a Laboratory Plasma, Phys. Rev. Lett. 116, 195002 (2016).

[2] F. Li, X. Fu, and S. Dorfman, Hybrid simulation of Alfven wave parametric decay instability in a laboratory relevant plasma, arXiv preprint arXiv:2205.04649, Under review at Physics of Plasmas (2022).