Seth Dorfman
UCLA
Title: "Nature's Keys: Using Basic Plasma Physics to Unlock our World"
Abstract: Abstract: Plasma makes up 99.9% of the visible matter in the universe and is crucial to building a working fusion power plant, but many fundamental processes that occur in space and laboratory plasmas remain poorly understood. Interesting unsolved problems abound: Why is the outer layer of the sun (the solar corona) much hotter than the photosphere below, when from adiabatic considerations we would expect the reverse? How can we reduce losses to improve the performance of fusion plasmas? What determines the evolution of space weather that can damage our sensitive infrastructure? I will discuss fundamental plasma physics as the key to solving these and other problems, focusing primarily on the physics of Alfvén and related waves.
Alfvén waves are fundamental modes of a plasma with a magnetic field. The behavior of these waves may be key in contexts such as space weather and the scattering and loss of energetic particles in fusion devices. One important process with a long history of theoretical and simulation studies is a class of parametric instabilities in which a large amplitude Alfvén wave produces various daughter modes. I will show results from experiments at the Large Plasma Device at UCLA which represent the first observation of this type of instability in the laboratory [1]. I will also show results from measurements conducted upstream of the Earth's bow shock – here, energetic ions reflected from the shock generate Ultra Low Frequency waves in the Alfvén wave frequency range which can influence space weather all the way down to the ground. We recently measured the growth rate of these waves for the first time and plan to conduct future satellite studies on parametric instabilities [2].
[1] S. Dorfman and T. A. Carter, "Observation of an Alfvén Wave Parametric Instability in a Laboratory Plasma," Phys. Rev. Lett. 116, 195002 (2016). [2] S. Dorfman, H. Hietala, P. Astfalk, and V. Angelopoulos, "Growth Rate Measurement of ULF Waves in the Ion Foreshock," Geophys. Res. Let. 44 (2017).