Colloquia

The Physics and Astronomy Colloquium Series is hosted on most Wednesdays from 2:30pm to 3:20pm in White Hall G09 on the WVU Downtown Campus.

• August 26: Title IX Training (WVU)
• September 9: Department Research Group Showcase
• September 23: Giuseppe Arrò, "Nonthermal particle acceleration by magnetic pumping in pulsating plasmas" (Plasma - University of Wisconsin, Madison)
• Abstract: The origin of high-energy particles in astrophysical sources is still debated, especially in high-beta plasmas, where magnetic energy is insufficient to cause nonthermal particle acceleration. However, high-beta plasmas are often embedded in large-scale compressible flows that could accelerate particles via magnetic pumping (MP), a mechanism where the plasma is energized by instabilities driven through cyclic compression and expansion (pulsation). In this work, we investigate particle acceleration by MP in high-beta "pulsating" plasmas, using fully kinetic simulations implementing a new "pulsating box" setup, showing for the first time that MP efficiently accelerates particles, producing nonthermal distributions with high-energy power-law tails. To interpret our results, we formulate a new generalized maximum entropy (GME) principle, extending the thermodynamic concept of maximum entropy to non-equilibrium plasmas. Numerical results are in excellent agreement with our model, accurately describing the evolution of the power-law index of distributions as a function of the injected energy. Our results are relevant for understanding particle acceleration in high-beta astrophysical plasmas, including planetary magnetosheaths, the intracluster medium of galaxy clusters, and accretion disks of compact objects.
• September 30: Joe Lazio (Astronomy - NASA Jet Propulsion Laboratory)
• October 7: Jyoti Katoch (Condensed Matter Physics - Carnegie Mellon University)
• October 21: Nehpreet K. Walia, "From solar wind to the boundary of our hemisphere" (Plasma - Princeton University)
• Abstract: This talk explores dynamic heliospheric processes and particle acceleration mechanisms from close to the Sun to the boundary of our heliosphere. First, we examine how successive 2012 and 2013 coronal mass ejections enhanced the pressure of the boundary of our heliosphere. These changes are measured using energetic neutral atom (ENA) emissions that are detected by NASA’s Interstellar Boundary Explorer (IBEX). These observations provide the direct link between solar wind changes and global heliospheric boundary dynamics. Second, we investigate nonthermal particle acceleration during asymmetric magnetic reconnection, a phenomenon relevant to recent Parker Solar Probe observations of the solar wind. Using kinetic simulations, we demonstrate that upstream density and magnetic field asymmetries reduce outflow speeds and yield softer energy spectra. The softer spectra result from the weaker acceleration caused by the misalignment between the magnetic curvature and the outflow jet in asymmetric reconnection. We propose a predictive theory relating initial asymmetries to the acceleration rate of particles, with broad implications for particle acceleration in the solar corona and Earth's magnetopause.
• Biography: Nehpreet Walia is a postdoctoral researcher at Princeton University specializing in heliophysics. She is currently involved in NASA’s Interstellar Mapping and Acceleration Probe (IMAP), a flagship mission designed to characterize our heliosphere, the protective bubble that shields us from galactic cosmic rays. Before joining Princeton, Nehpreet was at Los Alamos National Laboratory, where she analyzed data from NASA’s Interstellar Boundary Explorer (IBEX) to investigate the impact of solar wind on the boundary of our heliosphere. She also performed high-performance computing (HPC) studies using Particle-In-Cell (PIC) and hybrid simulations to examine particle acceleration in solar wind. Nehpreet earned her Ph.D. in Space Physics from the University of Tokyo, Japan.  Her doctoral research combined data from NASA’s Magnetospheric Multiscale (MMS) mission with hybrid HPC simulations to understand the structure and geometry of magnetic reconnection.
• November 4: TBD
• November 18: TBD
• December 2: Stella Ocker (Astronomy - California Institute of Technology)