Laboratory Experiments of Strong Alfvén Wave Interactions

Alfvénic turbulence is pervasive in the solar wind and thought to be common in astrophysical plasmas. The solar wind has allowed us to learn much about this turbulence, however, there are many open questions about how it works and shapes these systems. Lab experiments provide a controlled environment to test the basic physics of such turbulence. Here, we present an experiment on the Large Plasma Device, in which interacting low-frequency Alfvén waves at small k_⊥ρ_s are studied. We show that both counter-propagating and co-propagating waves result in a spectrum of new modes generated by their non-linear interaction. Estimated strength parameters, the wave frequencies involved, and their amplitude dependence on the initial waves, indicate the interaction to be in the strong regime – that applicable to space/astrophysical systems. The co-propagating waves produce a comparable spectrum to the counter-propagating ones, indicating a non-MHD interaction. We discuss a new non-linearity, that scales with k_⊥d_i, which may be responsible, and may also be important for understanding unexplained features of the solar wind. This experiment also allows other aspects of strong Alfvénic turbulence to be studied, such as residual energy, which will also be presented at this meeting.