Events at Physics |
Events During the Week of February 22nd through March 1st, 2026
Monday, February 23rd, 2026
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Optical analogy for stellarators: Ridges as caustics and coils as singularities
- Time: 12:00 pm - 1:00 pm
- Place: Engineering Hall - 1227
- Speaker: Dr. Wrick Sengupta , Princeton Plasma Physics Laboratory
- Abstract: Abstract: A common feature of most numerically optimized stellarator geometries is the presence of sharp ridges on flux surfaces, irrespective of the rotational transform. Despite their importance, an analytical theory for their existence has been lacking. In this work, we demonstrate that ridges are not artifacts but mathematical necessities. We develop such a theory for devices with quasi-axisymmetry (QA). We demonstrate that QA exhibits close connections with the theory of geometrical optics, following Parker's ``optical analogy" (E.N. Parker 1989). By mapping vacuum QA to the eikonal equation of geometrical optics, we derive the conditions for ridge formation, identified as caustics where magnetic field lines focus. Furthermore, we prove a rigorous geometric theorem for stellarator coil design: filamentary coils must lie on the zero-determinant manifold of the magnetic gradient tensor. This topological constraint unifies the description of plasma ridges and external coils, providing a precise criterion for identifying valid coil locations and explaining the efficacy of the magnetic gradient (LgradB) norm as a coil optimization parameter. We demonstrate that as the device becomes more compact, sharp ridges naturally form on the inboard side in QA. We support our analytical theory with extensive numerical evidence.
Bio: I am interested in the theoretical aspects of plasma physics, particularly kinetic theory and magnetic confinement. I develop analytically tractable reduced models to provide insight into nonlinear interactions and geometry in confined plasmas. I focus on magnetic fields with hidden quasisymmetry, which could benefit next-generation stellarators, and I also explore plasma turbulence using solvable models.
PhD (2016) in plasma physics from the University of Maryland. Advisor: Adil Hassam, co-advisors: Bill Dorland, Tom Antonsen.
Post doc (2016-2021): Courant Institute of Mathematical Sciences. PI: Harold Weitzner and Antoine Cerfon
Associate Research Scientist (2021 - present): Department of Astrophysical Sciences, Princeton University, PI: Amitava Bhattacharjee
Tuesday, February 24th, 2026
- No events scheduled
Wednesday, February 25th, 2026
- No events scheduled
Thursday, February 26th, 2026
- R. G. Herb Condensed Matter Seminar
- APS March Meeting Practice Talks
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Students , UW-Madison
- Abstract: Students Presenting: Minyoung Kim, Longyu Ma, Gustav Romare,
Keenan Smith, Dmitry Zverevich - Host: Alex Levchenko
- Preliminary Exam
- Searches for heavy resonances decaying into two Higgs bosons (HH) in the bb tau tau final state using Run 3 data from the CMS experiment.
- Time: 11:00 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: Mitanshu Thakore
- Abstract: The talk will focus on searches for heavy resonances decaying into a pair of Higgs bosons predicted by beyond the Standard Model theories. The search targets final states where one Higgs boson decays into a pair of tau leptons and the other into a pair of bottom quarks: X→HH→bb ττ. The analysis uses proton–proton collision data at a center-of-mass energy of 13.6 TeV, collected with the Compact Muon Solenoid experiment at the Large Hadron Collider during Run 3 (2022–2026). These final states are particularly challenging because, for heavy resonances, the Higgs bosons are produced with large Lorentz boosts. As a result, their decay products are separated by a small angle in space and appear highly collimated in the detector. Due to this collimation, a single large-cone (AK8) jet is used to reconstruct the H→bb decay. For the H→ττ decay, the tau-lepton pair is also highly boosted and collimated. Depending on the event topology, the Taus may be reconstructed either within a single large jet or as two isolated tau leptons. The search is performed by scanning the distribution of the reconstructed resonance mass and looking for a local excess in data compared to the background prediction.
- Host: Tulika Bose
- Astronomy Colloquium
- Uncovering the Nature of Active Galactic Nuclei Accretion Disks with Radiation Magnetohydrodynamic Simulations, Machine Learning, and Laboratory Experiments
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Dr. Amy Secunda, Flatiron Institute/CCA
- Abstract: Active galactic nuclei (AGN) accretion disks fuel powerful AGN feedback and are important laboratories for studying accretion physics. Because AGN are generally too distant to resolve spatially, most of what we can learn about their accretion disks comes from studying the variability in AGN light curves. However, many mysteries remain about the source of variability in AGN light curves and what this variability can reveal about the structure, internal physics, and accretion rates of AGN disks. I will show how I use radiation magnetohydrodynamic simulations, long baseline AGN light curves, and machine learning tools to improve our understanding of AGN variability and model the structure of AGN disks. I will also briefly discuss my work using laboratory experiments to understand accretion more broadly.
- Host: Nicholas Stone
Friday, February 27th, 2026
- Physics Department Colloquium
- Materials that exceed classical thermodynamic bounds on properties
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241
- Speaker: Roderic Lakes, University of Wisconsin-Madison
- Abstract: Bounds on properties are useful in guiding design of heterogeneous materials and in understanding the distinction between effects that are physically reasonable and those that are not. Several bounds on physical properties can be exceeded by an appropriate choice of material. The reason is that the “proofs” of bounds contain either unstated assumptions about the material or assumptions that are couched in language that appears to be that of incontrovertible mathematics but that actually entails assumptions about the material. If those assumptions are relaxed, limits or bounds can be exceeded, as is demonstrated by analysis and experiments. For example, heat capacity, compressibility, electrical capacitance, and refractive index can be negative. Thermal expansion in composites can be larger or smaller than that of any constituent and can be negative. Materials and systems are known that are non-Hermitian or nonreciprocal. Currently, active fields of endeavor have arisen from such conceptual sources. Research efforts have led to the development of new materials and new classes of materials.
- Host: Alex Levchenko
Saturday, February 28th, 2026
- No events scheduled
Sunday, March 1st, 2026
- Graduate Program Event
- Ice Skating Social
- Time: 1:30 pm - 3:00 pm
- Place: Bakke Recreation and Wellbeing Center: Sub-Zero Ice Rink (1976 Observatory Drive | Madison, WI 53706)
- Abstract: The Physics Department will be hosting an ice skating social on Sunday, March 1, 1:30pm-3:00pm at the Sub-Zero Ice Rink in Bakke Recreation & Wellbeing Center.
- Host: Alice Kwok