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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.
Dr. Yang Zhang is a NASA Jack Eddy Postdoctoral Research Fellow at Princeton University. He earned his Ph.D. from Caltech in 2024. His research utilizes pulsed power plasma experiments and laser plasma experiments to explore fundamental phenomena in space physics and astrophysics, including magnetic Rayleigh-Taylor instability, solar flares, magnetic reconnection and plasma jets. In addition to his experimental work, Dr. Zhang is also advancing theoretical plasma astrophysics. His contributions include proposing that collisions between neutral and charged particles act as a mechanism for angular momentum transport in accretion disks and developing a magnetohydrodynamic (MHD) equilibrium model for braided magnetic flux ropes carrying a net current.
Location: N102