Princeton Center for Heliophysics Seminar

Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous throughout our heliosphere. The non-linear behavior of these modes may play key roles in the physics of the turbulent solar wind, heating of the solar corona, and the behavior of more distant astrophysical plasmas. In order to gain insight into the nature of non-linear Alfvén wave behavior, we aim to isolate the key physical processes in the laboratory for detailed study. In this seminar, I will present several examples of experimental work on the Large Plasma Device (LAPD) at UCLA as well as theoretical studies aimed at understanding fundamental non-linear Alfvén wave physics. One focus of our work is Alfvén wave parametric instabilities, which bound the solar wind parameter space [Bowen, et. al. 2018]. LAPD experiments show the first lab observation of an Alfvén wave parametric instability, including features not yet predicted by theory [Dorfman and Carter, PRL 2016]. We also recently conducted a proof-of-principle experiment to measure the growth rate of the standard Parametric Decay Instability (PDI) in the laboratory. Current work also includes theory and experiments focused on the observation of residual energy in the solar wind -- the inertial range of the turbulent cascade has more energy in the magnetic than the velocity fluctuations, but an MHD Alfvén wave has equal amounts of energy in each. Another recent theoretical result is the discovery of non-linear Hall effects at small scales (k⊥*di ≳ 1) which allow co-propagating modes to interact and enable dispersive Alfvén wave steepening; not only is this testable in LAPD, but these effects may be especially important in the region currently being explored by Parker Solar Probe and Solar Orbiter, which is dominated by outward-traveling Alfvén waves, with only a relatively small inward-traveling component [Mallet, et. al. 2023]. After examining these various examples of non-linear Alfvén wave behavior, I will discuss the prospects of a new Solar Wind Machine aimed at producing magnetized plasma turbulence in the laboratory for detailed study [Dorfman, et. al, NASA Decadal White Paper 2022].