Events at Physics |
Events During the Week of April 16th through April 23rd, 2023
Monday, April 17th, 2023
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Schnack Memorial Seminar: Simulating Transient Excitation of Neoclassical Tearing Modes
- Time: 12:00 pm - 6:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Eric Howell, Tech-X Corporation
- Abstract: Disruption avoidance and mitigation strategies are needed for ITER and future fusion pilot plants. Neoclassical tearing modes (NTMs) are a leading physics cause of disruptions in present-day experiments, and predictive NTM models are vital for the success of burning plasma tokamaks. NTM growth is driven by a helical bootstrap current deformation that results from pressure flattening across an island. NTMs are metastable states that require a seed island to grow. The seed islands are generated by ELMs, sawteeth, and other transients. Nonlinear simulations study the transient excitation of NTMs. Simulations use reconstructions of DIII-D ITER baseline scenario discharges. The dominant neoclassical effects, including the bootstrap current drive, are modeled using heuristic fluid closures for neoclassical stresses. Magnetic perturbations are transiently applied to excite a growing NTM. These perturbations act as surrogates for ELMs. A Goldilocks effect is observed with regard to the applied perturbation amplitude. If the amplitude is too small, no NTMs grow. If the amplitude is too large, a 2/1 NTM grows robustly immediately following the pulse. If the amplitude is just right, then the 2/1 NTM grows in two phases: an initial slowly growing phase followed by a fast robustly growing phase. An energy transfer analysis shows that the early slow growth phase is partially driven by nonlinear interactions with higher-n core modes. The later robust growth phase is described by the modified Rutherford equation.
The work is funded by the US Department of Energy - Department Meeting
- Closed Department Meeting
- Time: 12:15 pm - 1:30 pm
- Place: VIRTUAL - link will be sent later.
- Speaker: Mark Eriksson, UW-Madison
- Closed meeting to discuss personnel matters—pursuant to Section 19.85(1)(c) of the Wisconsin Open Meetings Law Closed to all but tenured faculty
- Host: Mark Eriksson
Tuesday, April 18th, 2023
- Council Meeting
- Time: 3:00 pm - 4:00 pm
- Place: 2314 Chamberlin Hall
- Speaker: Mark Eriksson, UW-Madison
- Host: Mark Eriksson
- Outreach
- Astronomy on Tap
- Time: 7:00 pm - 8:30 pm
- Place: Working Draft Beer Company, 1129 E Wilson St, Madison
- Speaker: various, UW–Madison
- Abstract: Michael Nicandro Rosenthal, Hidden Monsters: Dusty Galaxies
[Future UW Physics faculty member] Melinda Soares-Furtado, Worlds Devoured by Suns
[physics affiliate faculty member] Sebastian Heinz, Bat Astronomy: Using X-ray Dust Echoes to Map the Galaxy
- Host: Astronomy on Tap Madison
Wednesday, April 19th, 2023
- Preliminary Exam
- Reconstruction of the Radial Velocity Field of the Universe with a joint CMB and Large Scale Structure likelihood analysis
- Time: 11:00 am - 6:00 pm
- Place: 4274 Chamberlin
- Speaker: Yurii Kvasiuk, Physics Graduate Student
- Abstract: We develop an optimization-based maximum likelihood approach to analyze the cross-correlation of the Cosmic Microwave Background (CMB) and the Large-Scale Structure (LSS) induced by the kinetic Sunyaev-Zeldovich effect. Our main goal is to reconstruct the radial velocity field of the universe. While the existing quadratic estimator (QE) is statistically optimal for current and near-term experiments, the likelihood can extract more signal-to-noise in the future. Our likelihood formulation has further advantages over the QE, such as the possibility of jointly fitting cosmological and astrophysical parameters. We implement an auto-differentiable likelihood pipeline in JAX, which is computationally tractable for a realistic survey resolution, and evaluate it on the Agora simulation.
- Host: Moritz Muenchmeyer
- Department Meeting
- Time: 12:15 pm - 1:15 pm
- Place: B343 Sterling Hall
- Speaker: Mark Eriksson, UW-Madison
- Host: Mark Eriksson
- Theory Seminar (High Energy/Cosmology)
- New inflationary probes of axion dark matter
- Time: 1:00 pm - 2:30 pm
- Place: Chamberlin 5280
- Speaker: Lingfeng Li, Brown University
- Abstract: If a light axion is present during inflation and becomes part of dark matter afterwards, its quantum fluctuations contribute to dark matter isocurvature. In this article, we introduce a whole new suite of cosmological observables for axion isocurvature, which could help test the presence of axions, as well as its coupling to the inflaton and other heavy spectator fields during inflation such as the radial mode of the Peccei-Quinn field. They include correlated clock signals in the curvature and isocurvature spectra, and mixed cosmological-collider non-Gaussianities involving both curvature and isocurvature fluctuations with shapes and running unconstrained by the current data. Taking into account of the existing strong constraints on axion isocurvature fluctuations from the CMB, these novel signals could still be sizable and potentially observable. In some models, the signals, if observed, could even help us significantly narrow down the range of the inflationary Hubble scale, a crucial parameter difficult to be determined in general, independent of the tensor mode.
- Host: George Wojcik
Thursday, April 20th, 2023
- Academic Calendar
- Deadline for Graduate students to request pass/fail or credit/audit options for a Spring term course
- Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, registrar@em.wisc.edu URL:
- Academic Calendar
- Deadline for Graduate students to change variable credits
- Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, registrar@em.wisc.edu URL:
- R. G. Herb Condensed Matter Seminar
- Driven-dissipative dynamics of coupled atomic clocks
- Time: 10:00 am - 11:00 am
- Place: 5310 Chamberlin
- Speaker: Emil Yuzbashyan, Rutgers
- Abstract: I will present the nonequilibrium phase diagram for the driven-dissipative dynamics of two ensembles of ultra-cold atoms coupled to a resonant cavity. We will see that this relatively simple system displays a range of remarkable phenomena beyond usual superradiance. These include periodically and quasiperiodically modulated superradiance, chaos via quasiperiodicity, and synchronized chaos.
- Host: Alex Levchenko
- Preliminary Exam
- Unraveling the Dynamics of the Milky Way: Investigations into the Asymmetries of the Galactic Disk
- Time: 11:00 am - 1:00 pm
- Place: 2124 Chamberlin or
- Speaker: Lekshmi Thulasidharan, Physics Graduate Student
- Abstract: "The Radcliffe wave (RW) is a recently discovered sinusoidal vertical feature of dense gas in the proximity of the Sun. In the disk plane, it is aligned with the Local Arm. However, the origin of its vertical undulation is still unknown. This study constrains the kinematics of the RW, using young stars and open clusters as tracers, and explores the possibility of this oscillation being part of a more extended vertical mode. We study the median vertical velocity trends of the young stars and clusters along with the RW and extend it further to the region beyond it. We discovered a kinematic wave in the Galaxy, distinct from the warp, with the amplitude of oscillation depending on the age of the stellar population. We performed a similar analysis in the N-body simulation of a satellite as massive as the Sagittarius dwarf galaxy impacting the galactic disk. When projected in the plane, the spiral density wave induced by the satellite impact is aligned with the RW, suggesting that both may be the response of the disk to an external perturbation. However, the observed kinematic wave is misaligned. It appears as a kinematic wave travelling radially, winding up faster than the density wave matched by the RW, setting its origins into question. If a satellite galaxy is indeed responsible for the presence of this kinematic wave, we predict the existence of a vertical velocity dipole that would be expected to form across the disk. The reality of this prediction may be measurable with the upcoming Gaia DR3 and DR4."
- Host: Prof. Elena D'Onghia
- Special Plasma Seminar
- The path to high-performance long-duration plasmas on Wendelstein 7-X
- Time: 12:00 pm - 6:00 pm
- Place: 1610 Engineering Hall
- Speaker: Prof. Thomas Klinger, IPP Greifswald, Germany
- Abstract: After a brief survey of the design and optimization principles of the superconducting stellarator device Wendelstein 7-X, the steps are described towards high-performance (in terms of density, temperature, confinement) and long-duration (in terms of stability, radiation, exhaust) plasmas. This is done along the lines of the present understanding of experimental observations and findings. The plasma in Wendelstein 7-X is turbulent, which has a strong impact on heat and particle transport. Methods to tame the turbulence are required for high-performance parameters. The heat and particle exhaust depends largely on the divertor functionality. The island divertor realized in Wendelstein 7-X shows allows for robust detachment and reasonable pumping. The full exploitation of Wendelstein 7-X is still in its beginnings, but the pathway towards fusion reactor relevant plasma operation becomes already visible.
- Host: Benedikt Geiger
- Physics Department Colloquium
- Hunting for new physics at CERN : Highlights and Prospects
- Time: 3:00 pm - 5:00 pm
- Place: 1313 Sterling
- Speaker: Niki Saoulidou, University of Athens
- Abstract: First we will make a brief introduction of the most complete theory to date, the Standard Model of Particle Physics, describing elementary particles and their interactions. Then, we will mention its shortcomings and limitations in the form of tantalizing anomalies and unknowns, that strongly point to new physics, waiting to be discovered. Efforts to resolve these now and in the near future are taking place with several different running and planned experiments worldwide. In this talk we will focus on the main two general purpose experiments, ATLAS and CMS, collecting data from proton-proton collisions at the CERN Large Hadron Collider (LHC). We will review status and prospects for discovering new physics at the LHC, trying to address the aforementioned open questions, with the data collected thus far in Run II and Run III, and also the ones anticipated at the High Luminosity (HL) LHC era. First, we will describe intriguing excesses seen by the ATLAS and CMS experiments in Run II, together with their status and follow-up plans in Run III. Next, we will focus on efforts targeting new and often more complex final states probing unexplored regions of new physics space enabled by i) new approaches to select and record events at the trigger level ii) novel reconstruction and identification techniques, and iii) powerful new analysis methodologies. Finally we we will briefly discuss prospects with the HL-LHC and give an overall outlook.
- Host: Kevin Black
- Astronomy Colloquium
- Mapping the circumgalactic medium with Lyα emission
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Dawn Erb, University of Wisconsin, Milwaukee
- Abstract: The circumgalactic medium modulates most of the key processes of galaxy evolution. Outflows powered by star formation drive gas out of galaxies and into the CGM, while new fuel for star formation may be accreted through the CGM, likely via dense, cold streams of gas. Ionizing photons that make their way out of the galaxy must also traverse the neutral hydrogen in the CGM. Because Lyα photons resonantly scatter from neutral hydrogen in the halos of galaxies, observations of Lyα emission can offer constraints on the properties of circumgalactic gas. I will present spatially extended integral field spectroscopic observations of Lyα emission in the circumgalactic medium of galaxies at z~2 from the Keck Cosmic Web Imager. In combination with new spatially resolved radiative transfer models, these data enable constraints on the kinematics and distribution of neutral hydrogen in the CGM on scales of tens of kiloparsecs.
- Host: Ke Zhang
- Graduate Program Event
- Disorder in the Kitaev Spin Liquid
- Time: 4:00 pm - 5:00 pm
- Place: 5310 Chamberlin
- Speaker: Wen-Han Kao, PhD graduate student in Physics at Univ of Minnesota
- Abstract: One of the long-standing open questions that recently attracted much attention is understanding how a quantum spin liquid (QSL) state responds to various forms of structural disorder that are inevitable in real materials. In the candidate compounds of the Kitaev spin liquid (KSL) system, it has been noted that quenched disorder plays a role in suppressing the long-range magnetic order but also makes the low-energy excitations puzzling. In my talk, I will introduce how the presence of vacancies and bond randomness modifies the density of states of Majorana fermion, which is one kind of fractionalized excitation of KSL. In the site-diluted model, the pileup of low-energy states leads to divergent specific heat, and the flux-sector crossover under magnetic fields provides an explanation for the puzzling experimental findings of a strong candidate material H3LiIr2O6. We also explored how the fractionalized degrees of freedom renormalize in the strong-disorder limit of bond randomness. Namely, we applied the strong-disorder renormalization group (SDRG) on the KSL system and found that strong-disorder criticality can appear differently on distinct fractionalized excitations. This points out further inquiries about the quenched disorder effects in frustrated magnetism.
- Host: Jaglul Hasan/Alex Levchenko
Friday, April 21st, 2023
- Academic Calendar
- Deadline for students to drop a Spring term course
- Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, registrar@em.wisc.edu URL:
- Academic Calendar
- Deadline for students to change Honors Optional course status
- Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, registrar@em.wisc.edu URL:
- Academic Calendar
- Deadline for students to add a Spring term course with department permission
- Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, registrar@em.wisc.edu URL:
- Academic Calendar
- Deadline for students (except Graduate) to withdraw from Spring term
- Abstract: *Note: actual end time may vary.* CONTACT: 262-3811, registrar@em.wisc.edu URL:
- Climate & Diversity
- Climate and Diversity Coffee Hour
- Time: 3:30 pm - 4:30 pm
- Place: foyer outside 2241 Chamberlin
- Speaker: Tulika Bose
- Abstract: The Climate and Diversity Committee invites the department to attend an informal coffee hour. We hope to engage in conversation about different aspects of the work of the committee and get feedback from the community about future initiatives. We hope you’ll stop by for coffee and a Greenbush doughnut (!) and to share your thoughts.
- Host: Climate and Diversity Committee
- Academic Calendar
- Graduate School Spring 2023: Request for all master's and doctoral degree warrants
- Time: 4:00 pm - 5:00 pm
- Abstract: CONTACT: 262-2433, gsacserv@grad.wisc.edu