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Plasma Seminar
Understanding the plasma universe through laboratory experiments and related models
Date: Thursday, March 14th
Time: 1:00 pm - 2:00 pm
Place: B343 Sterling Hall
Speaker: Yang Zhang, Caltech
Abstract: Laboratory experiments and the models they inspire are powerful tools for studying the plasma universe. In this talk, I will present possible solutions to two big problems in the plasma universe, namely how solar flares are generated and how accretion disks transport angular momentum and generate astrophysical jets. Addressing the first problem, I will present observations from a laboratory experiment that simulates solar coronal loop physics. Transient, localized 7.6-keV X-ray bursts and a several-kilovolt voltage spike are observed to be associated with the breaking of braided magnetic flux ropes containing 2 eV plasma. These spikes occur when the braid strand radius is choked down to be at the kinetic scale by either MHD kink or magnetic Rayleigh–Taylor instabilities. The observed sequence reveals an MHD to non-MHD cross-scale coupling that is likely responsible for generating solar energetic particles and X-ray bursts. Addressing the second problem, I will present a first-principles angular momentum transport mechanism based only on collisions between neutrals and charged particles in the presence of gravitational and magnetic fields. I find that ions and electrons drift in opposite radial directions as a result of colliding with Kepler-motion neutrals. This reduces the ordinary angular momentum of neutrals and increases the canonical angular momentum of charged particles in a manner such that the net global canonical angular momentum is conserved. This process provides a gravitational dynamo converting gravitational energy into the electric energy that powers an astrophysical jet. The model predicts an accretion rate of 3 × 10−8 solar mass per year in good agreement with observed accretion rates. Finally, I will discuss my future research plans for using laboratory experiments and related models to study the plasma cosmos.
Host: Jan Egedal
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