Laboratory Scaling Studies of a Shear Alfvén Wave Parametric Instability*

Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in space plasmas.  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.  Recent results from the Large Plasma Device at UCLA have recorded the first observation of a sheer Alfvén wave parametric instability in the laboratory [Dorfman and Carter, PRL 2016]. When a single finite ω/Ω_i, 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.  To shed light on the physics responsible, scaling studies are underway to determine how the instability physics changes with plasma and antenna parameters.  Parameters required for the instability will be compared to those expected in the near-Sun solar wind region to be visited by Parker Solar Probe.