Events at Physics |
Events During the Week of November 15th through November 21st, 2026
Monday, November 16th, 2026
- Thesis Defense
- Dynamics of a pressure-driven collapse during high-density stellarator operation
- Time: 10:00 am - 12:00 pm
- Place: 4421 Sterling Hall
- Speaker: R. Sassella
- Abstract: High density stellarator operation is a promising scenario for a future fusion reactor. However, operating scenarios may be constrained by pressure-driven instabilities. The core density collapse (CDC) is a fast, pressure-driven loss of confinement that affects super-dense core (SDC) operation on the Large Helical Device. Previous work indicates that the CDC is triggered by a high-n ballooning mode in the bad-curvature region. The ballooning mode nonlinearly couples to a low-n mode in the core, and energy is inverse-cascaded into core mode, perturbing flux surfaces and causing the ejection of up to 50% of core density. To study high-resolution profile dynamics during the CDC, the instability was deliberately provoked with excessive pellet fueling of the core. Over 150 CDC events were produced. The first high-resolution temperature and density profile measurements of a CDC were made with a 20 kHz Thomson scattering diagnostic. A hot, narrow feature in the $T_e$ profile was observed during the CDC for the first time. The feature occupies about a quarter of the plasma diameter and lasts upwards of 150 $\mu$s before it collapses. This feature is hypothesized to be caused by either the transfer of kinetic energy from the ballooning mode to a core mode via nonlinear coupling or by an increase in localized NBI deposition caused by rapid changes to the density profile. The electron temperature feature is observed to collapse about 100 microseconds before core density, suggesting that multiple transport mechanisms may be at work. Density loss gradually propagates inward, from the transport barrier towards the magnetic axis. High resolution measurements of profile dynamics broadly agree with simulation predictions, although questions about the electron temperature feature and transport mechanisms remain. CDCs demonstrate that the ballooning mode places a hard limit on the accessible pressure gradient in stellarators.
- Host: Daniel Den Hartog
- Preliminary Exam
- Probing Element Specific Ultrafast Carrier and Spin Dynamics in Quantum and Magnetic Materials using X-FAST Instrument
- Time: 11:00 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: Aakankshya Mishra
- Abstract: Emerging quantum and magnetic materials host strongly coupled electronic, spin, and lattice degrees of freedom that can evolve on femtosecond timescales, making their nonequilibrium behavior important for understanding and ultimately controlling material properties relevant to future information and quantum technologies. This work uses X-ray Femtosecond Absorption Spectroscopy Tabletop (X-FAST), a laboratory-based extreme-ultraviolet (XUV) transient absorption instrument, to investigate these ultrafast processes with element specificity. X-FAST employs high-harmonic generation (HHG) to produce femtosecond XUV pulses that probe element-specific core-to-valence transitions following excitation by an ultrafast optical pump. This preliminary examination will introduce the motivation for studying emerging quantum and magnetic materials, the fundamentals and development of HHG-based tabletop XUV sources, and the experimental methodology and optimization of the X-FAST instrument. The capabilities of X-FAST will be demonstrated through measurements of 2H-MoTe₂ as a benchmark system and through studies of MnPtGa, where element-specific transient absorption provides insight into photoinduced carrier redistribution and its connection to the material’s magnetic electronic structure. In addition, the development and integration of a cryogenic sample environment will extend X-FAST toward temperature-dependent measurements, enabling the separation of electronic, magnetic, and lattice contributions and the investigation of phase-dependent ultrafast dynamics. Finally, future directions will focus on expanding the range of quantum and magnetic materials studied with X-FAST and advancing the instrument toward a versatile platform for probing and understanding nonequilibrium material behavior across ultrafast timescales and variable temperatures.
- Host: Uwe Bergmann
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Eulerian Energization in Reconnection and Turbulence
- Time: 12:00 pm - 1:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Jason Tenbarge, Princeton Plasma Physics Laboratory
- Abstract: Turbulence and magnetic reconnection are ubiquitous processes in space and astrophysical plasmas, and they play fundamental roles in transforming magnetic energy into kinetic and internal energies. Particle energization, especially in the context of reconnection, has frequently been examined from a particle, or Lagrangian, perspective employing guiding-center analyses to particle-in-cell (PIC) simulations. These analyses of PIC particles have suggested that Fermi (curvature drift) acceleration and direct acceleration via the reconnection electric field are the primary electron energization mechanisms. However, both PIC guiding-center analyses and spacecraft observations are performed in an Eulerian frame. We employ continuum kinetic simulations using the Gkeyll simulation framework and the Hybrid-Vlasov–Maxwell (HVM) code to re-examine energization from a continuum, Eulerian perspective. We separately examine the contribution of each drift energization component to determine the dominant energization mechanisms in a moderate guide-field Gkeyll reconnection simulation as well as in HVM turbulence simulations. We compare the Eulerian results with the wisdom gained from Lagrangian (PIC) analyses.
- Host: Rogerio Jorge
Tuesday, November 17th, 2026
- Graduate Program Event
- Prospective Grad Info Session (PhD)
- Time: 9:30 am - 10:30 am
- Place: Sign up for this session here:
- Speaker: Sharon Kahn, Graduate Program Manager
- Abstract: Prospective PhD-Physics applicants are invited to join faculty, staff and current students for this info session. This session will focus on PhD admissions and program details particularly relevant for applicants who are 1st generation college students or have faced barriers in their educational opportunities
Sign up for this session here: - Host: Sharon Kahn
- Condensed Matter Theory Group Seminar
- Microscopic origin of singlet and triplet tunnel couplings for readout in Si/SiGe Quantum Dots
- Time: 10:00 am - 11:00 am
- Place: Chamberlin 3290
- Speaker: Minyoung Kim, UW Madison
- Abstract: Pauli spin blockade (PSB) readout in silicon quantum dots relies on spin-dependent charge transitions between two-electron states. While conventional descriptions often assume a single-orbital model, strong electron–electron interactions, valley degrees of freedom, and alloy disorder can significantly modify the relevant tunneling processes. We investigate how Wigner-molecular correlations and valley physics influence the singlet and triplet tunnel couplings relevant to PSB readout. Using full configuration interaction, we construct a low-energy effective Hamiltonian and extract the singlet and triplet tunnel couplings and the exchange splitting at (0,2) charge configuration. We complement these numerical results with an analytical description connecting tunneling amplitudes to spatial wavefunctions and valley phases and examine how alloy disorder affects these effective parameters. This framework provides a microscopic description of spin-dependent tunneling beyond the conventional single-orbital model.
- Host: Elio Koenig-Tarasevich
Wednesday, November 18th, 2026
- Graduate Program Event
- Advances in Nonlinear X-Ray Spectroscopy and Instrumentation for Probing Ultrafast Processes
- Time: 4:30 pm - 6:30 pm
- Place: Sterling B343 or
- Speaker: Zain Abhari, Physics PhD Graduate Student
- Abstract: TBD
- Host: Uwe Bergmann
Thursday, November 19th, 2026
- R. G. Herb Condensed Matter Seminar
- Unconventional Superconductivity and Electron Crystals in Rhombohedral Graphene
- Time: 10:00 am - 6:00 pm
- Place: 5310 Chamberlin Hall
- Speaker: Long Ju, MIT
- Abstract: Crystalline graphene in the rhombohedral stacking order provides an ideal platform to study electron correlation effects. It hosts gate-tunable flat electronic dispersion and Berry curvatures. The internal degrees of freedom, spin and valley, further enrich the possibilities of symmetry-broken ground states. In this talk, I will show a range of superconductivities observed in rhombohedral graphene, featuring spin polarization and valley polarizations. On the other hand, the same flat dispersion create a fertile playground for electron crystals. I will also show the signatures of Wigner and metallic Wigner crystals.
- Host: Alex Levchenko
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Galactic Neutrino Emission: Revisiting Source Templates and Constraining the Hadronic Origin of Galactic Gamma-Ray Sources with IceCube Data
- Time: 2:30 pm - 3:30 pm
- Place:
- Speaker: Vittoria Vecchiotti, Norwegian University of Science and Technology (Norway)
- Abstract: IceCube has recently provided a high-significance detection of the high-energy neutrino emission from the Galactic plane. The observed signal is obtained by fitting the IceCube data with different spatial and spectral templates. Among the models, CRINGE provides a good description of the observed neutrino emission. This model accounts for both the diffuse neutrino emission, produced by cosmic-ray interactions during propagation through the interstellar medium, and the contribution from neutrino sources. However, the CRINGE model has some important limitations. First, it assumes that all sources that are unresolved in gamma-rays have hadronic origin. Second, it does not account for the possible contribution of resolved gamma-ray sources with a hadronic component to the Galactic neutrino signal. In this talk, I will revisit the modelling of unresolved gamma-ray sources and highlight some inconsistencies in their implementation in the CRINGE code. I will present a correct HEALPix template for the neutrino emission from Galactic sources , which can be used in IceCube data analyses. Furthermore, the CRINGE diffuse emission model adopts a cosmic-ray spectrum that is not consistent with recent LHAASO measurements of the proton spectrum. By using a diffuse emission model based on the new LHAASO measurement and comparing its prediction with the latest IceCube data, I will derive new constraints on the hadronic fraction of the Galactic gamma-ray source flux.
- Host: Matthias Thiesmeyer
- Astronomy Colloquium
- Study of Exotic Stellar Populations in Open Clusters and Galactic Fields
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Anju Panthi, Birla Institute of Astrophysics, India
- Abstract: Binary interactions can significantly alter stellar evolution, producing exotic populations that cannot be fully explained by single-star evolution. In this talk, I will present a multi-wavelength study of blue straggler stars (BSSs), yellow straggler stars (YSSs), and blue lurkers in open clusters, along with BSSs in the Galactic field. Using ultraviolet observations from AstroSat/UVIT together with multi-wavelength photometry, I search for hot white-dwarf companions and constrain the mass-transfer histories of these systems. I will also discuss time-domain studies using TESS and ZTF light curves to investigate variability and binarity. I will discuss how binary-evolution modelling with MESA can be used to trace the evolutionary history of the BSS–white dwarf system. Together, these complementary approaches provide insights into the formation pathways of exotic stellar populations and the role of binary interactions in shaping stellar evolution.
- Host: Bob Mathieu
Friday, November 20th, 2026
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Freeze-in Dark Matter: From the Seasons of the Early Universe to the Proton-Mass Window
- Time: 2:00 pm - 3:00 pm
- Place: Chamberlin Hall, Room 5280
- Speaker: Alessandro Lenoci, Hebrew University
- Abstract: tba
- Host: Nick Stone
- Physics Department Colloquium
- Emergent Quantum Phenomena in Graphene
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241 -
- Speaker: Long Ju, MIT
- Abstract: Condensed matter physics aims to explore and understand various quantum phenomena that emerge from the interactions between nuclei and electrons. Through synthesizing and investigating various crystals, this constructionism approach has led to the discovery of many amazing phenomena, especially when the principles of electron correlation and topology play important roles. The settings of such conventional crystals are often very complicated, making it hard to extract the essential ingredients and understand the underlying physics. In this talk, I will show our efforts on establishing a new paradigm, based on a material known as rhombohedral graphene, which is part of natural graphite. Rhombohedral graphene has the simplest chemistry and structure, yet can be controlled by a set of experimental knobs to exhibit many intriguing phenomena in condensed matter physics. Beyond phenomena that were familiar, I will focus on two newly observed quantum phases of matter, chiral superconductor[1] and fractional quantum anomalous Hall effect[2]. I will show their construction, phenomena, and implications for quantum many-body physics and applications. In the end, I will discuss new opportunities to be explored in this new paradigm. References: [1] Han, T., Lu, Z., Hadjri, Z. et al. Signatures of chiral superconductivity in rhombohedral graphene. Nature 643, 654–661 (2025). [2] Lu, Z., Han, T., Yao, Y. et al. Fractional quantum anomalous Hall effect in multilayer graphene. Nature 626, 759–764 (2024).
- Host: Alex Levchenko