Events at Physics |
Events During the Week of September 12th through September 19th, 2021
Monday, September 13th, 2021
- Plasma Theory Seminar
- NO SEMINAR
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Applying Fast-Ion Transport Control Methods and Predictive Modeling in a Steady-State Tokamak Scenario
- Time: 12:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Cami Collins , ORNL
- Abstract: The viability of steady-state scenarios in ITER and future tokamak reactors relies on effective heating by energetic particles (EPs) to achieve high beta and bootstrap current. Experiments in the DIII-D tokamak show that a broadened fast-ion pressure profile and q-profile manipulation enables better control of performance-degrading Alfvén Eigenmodes (AEs), improves EP confinement, and allows access to new regimes with 15% higher normalized plasma beta than previously achieved in steady state scenarios with negative central shear and qmin>2. To clarify the impact of EP transport on thermal profiles, the TGLF-EP+Alpha critical-gradient model is used to calculate AE-induced EP transport. The model diffusion is used in TRANSP, reproduces the measured neutron rate within 5% in a wide range of evolving plasma conditions, and enables better thermal profile predictions. This has exciting applications in integrated modeling for scenario development and reactor scoping studies.
Tuesday, September 14th, 2021
- Theory Seminar (High Energy/Cosmology)
- The Geometric SMEFT description of curved Higgs Field Space(s)
- Time: 4:00 pm - 5:00 pm
- Place: Chamberlin 5280
- Speaker: Michael Trott, Niels Bohr Institute
- Abstract: In recent years, the effective field theory approach to the Standard Model, the SMEFT, has been used to study LHC data with ever increasing theoretical precision and sophistication. However, the complexity of this theory lead to several barriers to substantial theoretical progress. In particular, the explosion in the number of parameters in the SMEFT as a function of operator mass dimension, and the technical challenge or reformulating SM predictions consistently into the SMEFT were very serious problems, that called into question the possible success and value of the SMEFT physics program over the long term. I will discuss how these challenges have been overcome. The key point leading to this advance is the understanding that the projection of curved scalar field spaces generated by the Higgs onto a naive flat field space understanding implicitly embedded into the usual SMEFT Lagrangian was the root cause of many problems and confusions. Many outstanding issues have been remarkably addressed and immediately overcome by reformulating the SMEFT noting its curved scalar field space - in the Geometric SMEFT. Some examples of the benefits of this approach will be presented, and explained. Note: This is a hybrid event. A zoom link will be distributed via the seminar mailing list. To join, email the organizer.
- Host: Lars Aalsma
- Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
- The Milky Way is not special: accreted stars also inhabit the Spite Plateau
- Time: 5:00 pm
- Place:
- Speaker: Dr. Jeffrey Simpson, UNSW, Australia
- Abstract: The ESA Gaia astrometric mission has enabled the remarkable discovery that a large fraction of the stars within a few kiloparsecs of the Sun appear to be debris from a single in-falling system, the so-called Gaia-Sausage-Enceladus. One exciting feature of this result is that it gives astronomers for the first time a large sample of easily observable, unevolved stars that formed in an extra-Galactic environment, which can be compared to stars that formed within our Milky Way. In this talk I will discuss using these stars to investigate the "Spite Plateau" – the near-constant lithium abundance observed in metal-poor dwarf stars across a wide range of metallicities (-3 < [Fe/H] < -1). In particular our aim was to test whether the stars that formed in Gaia-Sausage-Enceladus show a different Spite Plateau to Milky Way stars that inhabit the disk and halo. Individual galaxies could have different Spite Plateaus – e.g., the interstellar medium could be more depleted in lithium in a lower galactic mass system due to it having a smaller reservoir of gas. We find that the Gaia-Sausage-Enceladus stars show the same lithium abundance as other likely accreted stars and in situ Milky Way stars, strongly suggesting that the "lithium problem" is not a consequence of the formation environment. This result fits within the growing consensus that the Spite Plateau, and more generally the "cosmological lithium problem" – the observed discrepancy between the amount of lithium in warm, metal-poor dwarf stars in our Galaxy, and the amount of lithium predicted to have been produced by Big Bang Nucleosynthesis – is the result of lithium depletion processes within stars.
- Host: Baha Balantekin
Wednesday, September 15th, 2021
- Wednesday Nite @ The Lab
- IceCube Turns Ten: Past, Present and Future for the World’s Biggest and Strangest Observatory
- Time: 7:00 pm - 8:15 pm
- Place: 1111 Biotech or sign up for zoom link:
- Speaker: Francis Halzen, John Kelly, and Lu Lu, Physics/WIPAC/IceCube
- Abstract: The IceCube Neutrino Observatory, dubbed “the strangest telescope in the world”, sits in a cubic kilometer of ice at the South Pole, Antarctica. IceCube detects signals from astrophysical neutrinos that interact in the ice, revealing previously hidden information about the universe. It has been 10 years since IceCube began full operations on May 13, 2011. Join us as we look back at the massive construction effort led by UW-Madison, highlight exciting discoveries uncovered by a team of nearly 400 scientists from 53 institutions in 12 countries, and give a glimpse into the future of this one-of-a-kind instrument.
- Host: Department
Thursday, September 16th, 2021
- Astronomy Colloquium
- Laboratory Astrochemistry
- Time: 3:30 pm - 5:00 pm
- Place: 4421 Sterling Hall, Coffee and Cookies at 3:30 pm, Talk starts at 3:45 pm
- Speaker: Gustavo Cruz Diaz, UW Madison
- Abstract: Dense and cold regions in space, such as protoplanetary disks and dark clouds, are regions where ice mantles can be observed. Ice mantles can be grown thanks to the deposition of simple volatiles like water, carbon monoxide, and carbon dioxide. These mantles are constantly exposed to a variety of energy sources processing the mantles changing their chemical composition. Over time, the ice mantles will change from a simple composition to a more complex one where organic molecules can be found. Using an ultra-high-vacuum chamber and a cryostat, dark clouds and protoplanetary disks conditions can be recreated in the lab. Energy sources like vacuum UV photons and high-energy electrons induce chemistry in the ice mantle and change their composition. What we are trying to answer is, how far can we go in space chemistry? Do we need specific environments like earth to produce organic molecules like the building blocks of life, or could they be produced in space?
Friday, September 17th, 2021
- Thesis Defense
- ITG Turbulence Saturation and Near-Resonant Heat Flux Reduction in Gyrokinetic Dimits-Shift Analysis
- Time: 9:00 am
- Place: zoom link below
- Speaker: Ping-Yu Li , Physics PhD Graduate Student
- Abstract: Microturbulence is caused by gyroradius-scale instabilities such as the Ion-Temperature-Gradient-driven (ITG) instability, Trapped Electron Mode (TEM), Kinetic Ballooning Mode (KBM), etc. Understanding how these instabilities saturate and form turbulence is important for the optimization of magnetic confinement fusion devices in the quest for sustained fusion energy. The objective of this thesis is to understand the important factors and mechanisms that saturate ITG turbulence and to utilize said understanding to build reduced models that capture key physical behavior as described by full-physics approach. Zonal-flow-catalyzed interactions that involve large-scale stable and unstable modes are crucial for the saturation of curvature-driven ITG turbulence. A corresponding saturation theory is built based on a fluid model and implemented and tested numerically. The crudest saturation theory drops the non-zonal interactions and also the nonlinear corrections to frequencies, it also truncates the wavenumber space to obtain scalings for the saturation level with the triplet correlation times with linear frequencies and coupling coefficients. It is then discovered that nonlinear interactions can cause nonnegligible modifications on the mode oscillations for systems with higher turbulence level. Furthermore, the kx direction in wavenumber space needs to be resolved in order to break the symmetry between modes and build up the zonal flow, which is shown in both time-dependent and time-independent research. Constructing a two-predator-prey model with no free parameter inputted base on the saturation theory is also demonstrated. This provides an idea how to build a predator-prey model from the first principle, which has the potential to help understanding the limit-cycle oscillations observed in L-H transition. The importance of large-scale stable modes and the triplet correlation time derived from the saturation theory are tested in gyrokinetics. Numerical results show that the resonance between the stable and unstable modes through the coupling of zonal flow corresponds to long nonlinear interaction life times, or large triplet correlation times, which increases nonlinear energy transfer and leads to strong turbulence suppression beyond any purely linear estimates. The triplet correlation time is further used to improve a highly reduced model for fast heat-flux prediction in gyrokinetics, which shows significant improvement in several cases that demonstrate heat-flux onset upshift from the linear critical gradient for gradient scans. The role of the coupling coefficient in gyrokinetics is still under investigation. Join Zoom Meeting Meeting ID: 325 961 7260 Passcode: 61T1p8
- Host: Paul Terry, Faculty Advisor
- Graduate Introductory Seminar (Physics 701)
- Intersection of Neutrino/Dark Matter Physics and Astrophysics with Quantum Information Science
- Time: 12:05 pm - 12:55 pm
- Place: 2241 Chamberlin
- Speaker: A. Balantekin, UW Madison Department of Physics
- Host: Sridhara Dasu
- Physics Department Colloquium
- Supermassive Black Holes and Merging Galaxies: Low-Frequency Gravitational Wave Detection with Pulsar Timing Arrays
- Time: 3:30 pm
- Place: 2103 Chamberlin Hall
- Speaker: Sarah Vigeland, UW-Milwaukee
- Abstract: Observations have shown that nearly all galaxies harbor massive or supermassive black holes at their centers. Gravitational wave (GW) observations of these black holes will shed light on their growth and evolution, and the merger histories of galaxies. Pulsar timing arrays (PTAs) use observations of millisecond pulsars to detect low-frequency GWs with frequencies ~1-100 nHz, and can detect GWs emitted by supermassive black hole binaries, which form when two galaxies merge. In this talk, I will discuss the current status of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) PTA, with an emphasis on results from our most recent search for the stochastic GW background. I will also discuss future prospects for detecting and characterizing GWs from individual supermassive binary black holes with PTAs.
- Host: Ellen Zweibel