Events at Physics |
Events on Monday, October 5th, 2026
- Theory Seminar (High Energy/Cosmology)
- Probing Cosmic Neutrinos & Free-Streaming Radiation with the Cosmic Microwave Background
- Time: 11:30 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: Gab Montefalcone, University of Wisconsin-Madison
- Abstract: The cosmic microwave background (CMB) provides a unique window onto fundamental physics, allowing us to study particles and interactions that are otherwise extremely difficult to probe in laboratory experiments. One important example is the cosmic neutrino background, which influences the evolution of the early Universe, primarily through gravity despite interacting only very weakly with ordinary matter. In this talk, I will discuss how the free-streaming nature of neutrinos is expected to leave a subtle but distinctive imprint on the CMB by inducing a phase-shift in the acoustic oscillations of the photon–baryon plasma prior to recombination, providing a clean and robust probe of neutrino physics. I will present a framework to extract this effect directly from CMB observations, and show that current data from Planck, ACT, and SPT detect it with high significance, consistent with the Standard Model prediction of three free-streaming neutrino species. I will then discuss how the same measurement can be used to test beyond standard model scenarios in which neutrinos interact more strongly, delaying their decoupling from the primordial plasma. By directly relating the observed phase shift to neutrino interactions, cosmological data can place competitive constraints on new neutrino physics using this single, well-understood observable and without the need for dedicated model-dependent analyses.
- Host: Joshua Foster
- Plasma Physics (Physics/ECE/NE 922) Seminar
- STAR_Lite: Hampton University’s flexible, table-top quasi-axisymmetric stellarator for testing resilient divertors
- Time: 12:00 pm - 1:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Shibabrat Naik, Hampton University
- Abstract: STAR_Lite is a stellarator under construction at Hampton University whose primary purpose is to test divertor resilience, specifically non-resonant divertors (NRDs), to magnetic field error and plasma current. The first coil configuration, STAR_Lite-A, is a two-field-period quasi-axisymmetric configuration with 0.5 m major radius and mean field strength on the axis of 87.5 mT, the field being set by 2.45 GHz electron cyclotron heating (ECH) from two 15 kW magnetrons. Six modular coils of two distinct shapes are wound from 4/0 copper cable around stainless-steel spines bent to the design curve, a method chosen so the coils can be made in-house. A key feature of this design is its operational flexibility, and our analysis will also demonstrate that the X-point structure remains resilient to both equilibrium changes and real-world manufacturing errors. I will present the magnetic topology of STAR_Lite-A including analysis and optimization for the X-points, their stable and unstable manifolds, last closed flux surface (LCFS), and related divertor structure, EMC3-Lite heat flux calculations on two candidate vacuum vessels, and a Monte Carlo study of coil fabrication errors using Gaussian-process perturbations. Quasisymmetry and the existence of the X-points are robust to errors up to 1cm manufacturing error and I will discuss what that implies for field correction. I will close with a new approach to combined X-point and vessel optimization that has produced single X point, parabolic, and snowflake divertor candidates for future STAR_Lite coil configurations. STAR_Lite is primarily built by the undergraduate students who wind the coils on bent steel spines, perform electrical characterization of the coils, test and assemble the pulsed-power system, and will run the Hall-probe field-mapping campaign. STAR_Lite is funded through DOE FAIR, RENEW and the Simons Foundation, with the stated aim of building a fusion workforce pipeline at Hampton University.
Biography
Shibabrat Naik joined Hampton University in September 2023 as a faculty member in the Department of Mathematics and as a member of the Center for Fusion Training and Research. His research interests are in theory and applications of nonlinear dynamics, chaos, computational science and engineering, and magnetic confinement of plasma. Along with collaborators and co-investigators, he has secured $1.46 million in research funding from DOE for training and developing a fusion workforce at Hampton University. Currently, he co-supervises a team of 10 undergraduate students from mathematics, engineering, and computer science. He obtained his Ph.D. in Engineering Mechanics from Virginia Tech and trained as a postdoctoral researcher in engineering at Drexel University and University of Pennsylvania, applied mathematics at University of Bristol and University of Warwick. His interdisciplinary research articles on nonlinear dynamical systems and computational science have appeared in Physical Review E, Nonlinearity, Royal Society’s PCCP, Chaos, Commun. Nonlinear Sci Numer. Simul. - Host: Rogerio Jorge