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Events During the Week of June 4th through June 11th, 2023

Monday, June 5th, 2023

Graduate Program Event
Thesis Defense
The Magellanic Corona and its Role in the Evolution of the Magellanic Stream
Time: 10:00 am
Place: 2241 Chamberlin or
Speaker: Scott Lucchini, Department of Physics Graduate Student
Abstract: The Magellanic System is the perfect opportunity to explore many aspects of astrophysics right on our Galaxy’s doorstep. The Large and Small Magellanic Clouds (LMC, SMC) are interacting with each other and with the Milky Way to form the Magellanic Stream, a multiphase gaseous tail of intertwined filaments trailing behind the Clouds. Here we can study galactic dynamics, gas dynamics, turbulent processes, gas cooling and mixing, metal transport, and more. However, there are two outstanding mysteries as to how the Magellanic System came to be -- its large amount of ionized gas, and the high mass of the LMC. To solve both these discrepancies simultaneously, we introduced the Magellanic Corona. This warm, ionized circumgalactic medium should surround the LMC as it interacts with the SMC and the Milky Way. Throughout my thesis work, I have used high-resolution numerical simulations of the formation of the Magellanic Stream to test this new model including the Magellanic Corona. We can account for both the neutral and ionized components of the Stream while also reproducing the present-day positions and velocities of the LMC and the SMC. We have also found a new family of orbital histories for the Clouds that result in the neutral Stream being significantly closer than previous models predicted. The Magellanic Corona seems to be the key to the formation of the Magellanic Stream and has many implications throughout galaxy evolution.
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Tuesday, June 6th, 2023

Graduate Program Event
Will gamma rays break superconducting quantum computers? And can surface encapsulation improve the performance of individual quantum bits?
Time: 9:00 am
Place: 4274 Chamberlin
Speaker: Sohair Abdullah, Physics Graduate Student
Host: Robert McDermott
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Dept of Physics - Cookie Potluck - Summer Edition
Time: 1:00 pm
Place: foyer outside 2241 Chamberlin
Speaker: Jarrett Rosenberg, Zachary Jerzyk, Sharon Kahn, Graduate Program
Abstract: We hope the summer has been off to a great start for everyone! In the spirit of community, PGSC, in conjunction with the department, will host a cookie potluck. This event is open to anyone who wants to hang out and eat cookies. We encourage the bakers out there to bring their favorite, home-baked cookies (please provide a list of ingredients for people with dietary restrictions), though this is not required. We hope you will join us!
Host: Jarrett Rosenberg, Zachary Jerzyk, Sharon Kahn
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Wednesday, June 7th, 2023

Graduate Program Event
Final Thesis Defense
Lundquist Number Scaling in the MST Reversed-Field Pinch
Time: 10:00 am
Place: B343 Sterling
Speaker: Steph Kubala, Department of Physics Graduate Student
Abstract: Nonlinear MHD fluctuations appear in both natural and magnetic confinement settings, such as the solar wind, self-organization dynamics in the RFP and spheromak, and current disruptions in tokamak plasmas. In this thesis, parameter scaling experiments oriented toward nonlinear MHD dynamics in RFP plasmas are presented. Experimental data have been gathered spanning a wide range of parameter space characterized by Lundquist number, S ∼ 104 −107, and density where is the empirical density limit. A new programmable power supply allows low-current, low-S operation, which overlaps with parameters available in numerical modeling. Experimental S scalings of magnetic fluctuation amplitude agree well with those from the nonlinear MHD codes DEBS and NIMROD. A transition from quasi-continuous activity to bursty relaxation having discrete sawtooth events is observed in going from low to high S, with a threshold at around S ∼ 105. The spectral properties of the magnetic fluctuations change at this transition, including a reduction in fluctuation phase velocity that suggests plasma flow and/or flow profile changes. Momentum transport and flattening of the flow profile are known features associated with sawtooth relaxation in RFP plasmas.
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Thursday, June 8th, 2023

R. G. Herb Condensed Matter Seminar
Diode effects in current-biased Josephson junctions
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Jacob F. Steiner, Caltech
Abstract: Current-biased Josephson junctions exhibit hysteretic transitions between dissipative and superconducting states as characterized by switching and retrapping currents. Common lore says that these currents become nonreciprocal (i.e., they depend on the direction of the bias current) if both time-reversal and inversion symmetry are absent. This so-called Josephson diode effect is used to experimentally probe for spontaneous time-reversal symmetry breaking. Recently, however, a Josephson diode effect was observed in a time-reversal symmetric Josephson junction involving a single magnetic adatom [1]. To resolve this apparent conflict, we develop a theory for diodelike effects in the switching and retrapping currents of weakly damped Josephson junctions. We find that while the diodelike behavior of switching currents is rooted in asymmetric current-phase relations, nonreciprocal retrapping currents originate in asymmetric dissipative currents. These different origins also imply distinctly different symmetry requirements: current-phase asymmetry requires broken time-reversal symmetry, in contrast asymmetric dissipation stems from broken particle-hole symmetry. In the case of magnetic-atom Josephson junctions the latter may be traced back to Yu-Shiba-Rusinov subgap states. While our theory [2] was inspired by the experiment [1], it relies on general principles only, and may provide significant guidance in identifying the microscopic origin of nonreciprocities in any Josephson junction. References: [1] Trahms et al. Nature 615 (2023) [2] Steiner et al. PRL 130 (2023)
Host: Alex Levchenko
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Friday, June 9th, 2023

No events scheduled