Measuring the Alfvén wave Parametric Decay Instability Growth Rate in the Laboratory

Alfvén 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 Alfvén eigenmodes in tokamaks. In particular, theoretical predictions show that these Alfvén waves may be unstable to various parametric instabilities, but observational measurements of these processes are limited. We present an experiment on the Large Plasma Device at UCLA 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. This reduction in damping is the same order as the theoretically expected PDI growth rate and scales with the pump wave amplitude. Analysis is underway to more precisely compare the experimental results with PDI theory and to connect with related numerical simulations.