Laboratory Studies of Nonlinear Alfv\'{e}n Interactions and Decay Instabilities*

Alfv\'{e}n waves, a fundamental mode of magnetized plasmas, are ubiquitous in lab and space. The non-linear behavior of these modes is thought to play a key role in important problems such as the heating of the solar corona, solar wind turbulence, and Alfv\'{e}n eigenmodes in tokamaks. In particular, theoretical predictions show that these Alfv\'{e}n waves may be unstable to various decay instabilities, even at low amplitudes ($\delta B/B < 10^{-3}$). The present work, conducted at UCLA's Large Plasma Device, represents the first fundamental laboratory study of the non-linear Alfv\'{e}n wave interactions responsible for Alfv\'{e}n wave decay instabilities. Experiments include the first laboratory observation of the Alfv\'{e}n-acoustic mode coupling at the heart of the Parametric Decay Instability [1]. More recently, efforts have focused on the non-linear decay of a KAW into daughter modes with frequencies and wave numbers that suggest co-propagating KAWs. The observed process is parametric, with the frequency of the daughter modes varying as a function of pump amplitude. Efforts are underway to fully characterize this set of experiments and compare with decay instabilities predicted by theory and simulations. \\[4pt] [1] S Dorfman and T Carter, Phys. Rev. Lett. 110, 195001 (2013).