Events at Physics |
Events During the Week of May 24th through May 31st, 2026
Monday, May 25th, 2026
- Academic Calendar
- Memorial Day
- Abstract: *Note: actual end time may vary.* University offices closed. CONTACT: admin@secfac.wisc.edu
Tuesday, May 26th, 2026
- Academic Calendar
- 3-week Summer Session Begins
- Abstract: *Note: actual end time may vary.* CONTACT: admin@secfac.wisc.edu
Wednesday, May 27th, 2026
- Thesis Defense
- Measurements of Electron Pressure Anisotropy during Laboratory Magnetic Reconnection
- Time: 10:00 am - 12:00 pm
- Place: B343 Sterling or
- Speaker: Cameron Kuchta, Physics PhD Graduate Student
- Abstract: The Terrestrial Reconnection EXperiment (TREX) at the Wisconsin Plasma Physics Laboratory (WiPPL) studies magnetic reconnection, a process in which magnetic energy can be converted to plasma energy creating flows, increased temperatures, and high energy particles. The reconnection studied in TREX is most relevant to Earth's magnetosphere that brings the Sun's solar wind plasma into the magnetic fields connected to Earth's poles. This thesis consists of three diagnostic developments that have enhanced our understanding of reconnection via more accurate measurements and access to new plasma parameters.
For driving reconnection, TREX applies a strong reconnection drive which includes the sudden energization of a system of coils encircling the plasma. Before the formation of the reconnection current layer, this reconnection drive produces a strong magnetosonic wave including a wave-front moving radially inward towards the center of the device. The propagation speed of this front is governed by the dispersion relation of the magnetosonic wave, directly related to the plasma density. We will discuss and show how the analysis of the wave propagation provides reliable density profiles which are consistent with measurements by Langmuir probes. These profiles characterize the initial plasma produced by an array of plasma guns, which is valuable for analyzing and understanding the plasma dynamics at later times during the plasma discharges.
Langmuir probes are commonly used for measuring plasma temperature, density, and potential. We have developed a number of techniques that optimize the functionality of multi-tip Langmuir probes used for measuring the full current-voltage characteristic at a 10 MHz sampling rate. These upgrades gives the probe increased signal-to-noise ratio, ability to measure lower plasma densities, and more accurate resulting measurements.
We have developed a pressure anisotropy probe that can measure plasma flows and temperature anisotropies during reconnection. TREX is in the collisionless kinetic regime in which we expect electron anisotropy effects to dominate the physics of the ion diffusion regime near the x-point of reconnection. Embedded jets, seen in laboratory data, are driven into the outflow as expected from spacecraft observation of the magnetosphere, theory, and simulations. This probe has successfully measured electron pressure anisotropy in the laboratory, validating the expected influence of kinetic effects during reconnection. - Host: Jan Egedal
Thursday, May 28th, 2026
- Thesis Defense
- Dynamical Imprints in Galactic Disks: Tracing History with Stellar Ages, Motions, and Structure
- Time: 10:30 am - 12:30 pm
- Place: 5280 CH
- Speaker: Lekshmi Thulasidharan, Physics PhD Graduate Student
- Host: Elena D'Onghia
Friday, May 29th, 2026
- Graduate Program Event
- Baryoid Dark Matter: Explaining the Dark Matter-Baryon Coincidence
- Time: 10:00 am - 12:00 pm
- Place: Chamberlin 5280 or
- Speaker: Dean Chen, Physics PhD Graduate Student
- Abstract: In this talk, I will discuss how the dark matter-baryon coincidence, namely the observation that the dark matter abundance is about five times the baryon abundance, can be explained if dark matter is a novel macroscopic baryonic state: baryoid. Starting from a spontaneously broken Z_N symmetry, the universe is divided into roughly equal numbers of domains occupying one of the N-fold degenerate vacua, leading to an approximate (N−1):1 baryon-abundance ratio between the false- and true-vacuum domains. Once the degeneracy is lifted by a QCD-triggered bias potential, the domain walls begin to collapse. Because baryons have reduced masses in the false-vacuum domains, they are efficiently trapped within the shrinking false-vacuum regions during non-relativistic domain-wall collapse, eventually forming stable baryoids. We show that this mechanism can successfully explain the dark matter-baryon coincidence and discuss potential experimental searches
- Host: Yang Bai