Events at Physics |
Events During the Week of December 4th through December 11th, 2022
Monday, December 5th, 2022
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Disruptive Tearing Modes In DIII-D IBS Discharges
- Time: 12:00 pm
- Place: 1610 Engineering Hall
- Speaker: Professor Emeritus James D. Callen, UW-Madison
- Abstract: In seeking maximum plasma performance in magnetically confined burning plasmas, physics parameters are pushed to conditions where neoclassical tearing modes (NTMs) can grow and precipitate major plasma current disruptions. In recent ITER baseline scenario (IBS) discharges in the DIII-D experiment, the “safety factor” q_95 is reduced to near 3 and plasma beta_N is increased to about 2 or more. The most problematic tearing instabilities occur at the q = 2/1 rational surface because they are the furthest out radially (and hence closest to the magnetic separatrix), and are the lowest m/n modes. Their induced growing magnetic island widths produce resistive wall drag, mode locking to the wall and ultimately plasma disruption. Recent benchmarking studies of IBS-type discharges in DIII-D demonstrate robustly growing 2/1 tearing instabilities that evolve into locked modes and then disruptions are pressure-gradient-driven NTMs which ultimately grow algebraically (~ t) in time. The inherently nonlinear NTMs are seeded by MHD transients (e.g., ELMs, sawtooth crashes, or three tearing mode resonances). Responses to them are correctly modeled by a modified Rutherford equation. [Classical tearing modes (CTMs) would grow quadratically in time ~ t^2 and are negligible]. In ITER, order of magnitude smaller MHD transients are predicted to seed 2/1 NTMs.
Bio
J. D. Callen is an Emeritus Professor in the Departments of Engineering Physics and Physics at UW-Madison. He received his B.S. and M.S. degrees in Nuclear Engineering at Kansas State University in 1962 and 1964, with the intervening 1963 academic year spent at the Technische Hogeschool Te Eindhoven in the Netherlands on a Fulbright fellowship. He received his Ph.D. in Nuclear Engineering from Massachusetts Institute of Technology (MIT) in 1968. Thereafter, he had a NSF Postdoctoral Fellowship at the Institute for Advanced Study in Princeton, NJ where Marshall Rosenbluth was his mentor. Then, he was an Assistant Professor of Aeronautics and Astronautics at MIT in 1969-1972, followed by 7 years in the Fusion Energy Division at Oak Ridge National Laboratory where in the last 4 years he served as the Head of the Plasma Theory Section. In 1979 he accepted an offer to become a Professor of Nuclear Engineering (coupled with a zero-time appointment in Physics) at UW-Madison. He became the D.W. Kerst Professor of Physics and Engineering Physics in 1986. Subsequently, he had sabbaticals as a Visiting Scientist at the JET project in England 1986-1987, and the TFTR project at Princeton Plasma Physics Laboratory 1991-1992. He retired from his academic role in 2003, but is still active in research. Throughout his career he has focused on theory, modeling and experimental validation of descriptions of magnetically confined plasmas, mostly tokamaks. Tuesday, December 6th, 2022
- Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
- Gravitational-wave signatures of dense matter in neutron star binary inspirals
- Time: 2:00 pm
- Place: Join Zoom Meeting Meeting ID: 912 3071 4547
- Speaker: Tanja Hinderer , Institute for Theoretical Physics, Utrecht University
- Abstract: The gravitational waves from merging binary systems carry unique information about the internal structure of neutron stars. Extracting and interpreting this information requires accurate models based on a detailed understanding of the interplay of matter with nonlinear gravity. I will outline recent progress on going beyond the dominant tidal deformability effects and discuss examples of the impact of incorporating more realistic physics. I will conclude with an outlook onto the remaining challenges and prospects for the coming years, as gravitational-wave science continues to move towards an era of precision physics.
- Host: Baha Balantekin
- Theory Seminar (High Energy/Cosmology)
- Electroweak Symmetric Balls
- Time: 4:00 pm - 5:00 pm
- Place: Chamberlin 5280
- Speaker: Mrunal Prashant Korwar, UW Madison
- Abstract: Electroweak symmetric balls are macroscopic objects with electroweak symmetry restored inside. Such an object can arise in models where dark sectors contain monopole or non-topological soliton with a Higgs portal interaction to the Standard Model. It could be produced in the early universe via phase transition or preheating mechanism, accounting for all dark matter. In a scenario where the balls are allowed to evaporate, the observed baryon asymmetry in our universe could be explained by a mechanism of “catalyzed baryogenesis.” In this mechanism, the motion of a ball-like catalyst provides the necessary out-of-equilibrium condition, its outer wall has CP-violating interactions with the Standard Model particles, and its interior has baryon number violating interactions via electroweak Sphaleron. Because of electroweak symmetric cores, such objects have a large geometric cross-section off a nucleus, generating a multi-hit signature in large-volume detectors. These objects could radiatively capture a nucleus and release GeV-scale energy for each interaction. The IceCube detector can probe dark matter balls with masses up to a gram.
- Host: George Wojcik
Wednesday, December 7th, 2022
- Physics Department Colloquium
- Moons, Planets, and Suns in Context: Environments & Evolutionary Pathways
- Time: 2:00 pm - 3:00 pm
- Place: Sterling 4421 or zoom:
- Speaker: Melinda Soares-Furtado, UW Madison
- Abstract: In early December we will be interviewing our very own Melinda Soares-Furtado for a tenure-track faculty position in the Departments of Astronomy and Physics. As part of the interview process, we have scheduled a special talk by Melinda as follows:
Moons, Planets, and Suns in Context: Environments & Evolutionary Pathways
The growing population of exoplanets and the expanding repertoire of instruments and analysis techniques make it possible to examine moons, planets, and suns within the context of their environments and evolutionary history. In this talk, I discuss how my team leverages stellar evolutionary models, observational survey data, and statistical methods to probe the interactions and evolution of moons, planets, and suns. More specifically, I present the effects of planetary collision, accretion, and engulfment on stellar hosts, identifying the ingestion-derived signatures that make it possible to detect such events. In the second part of my talk, I focus on my team’s investigations of young stars in co-moving groups and clusters. Since stellar systems are more dynamically active at early times, these environments offer important test beds to explore star-planet interactions. I present the results of my team’s efforts to characterize star-planet systems at early stages of evolution (< 500 Myr) and the value these data offer to the broader scientific community. Looking forward, infrared space-based missions will soon make it possible to detect transiting exomoons orbiting young (<5 Myr), free-floating planets. Such observations will help to constrain the formation pathways and dynamical histories of these extraordinary systems. In the last part of my talk, I discuss my team’s efforts to identify and characterize exosatellite populations and the broader implications of our anticipated results.
The talk will be at 2pm on Wednesday December 7th, in Sterling 4421.
Coffee and cookies will be served at 1:45pm. - Astronomy Talk: Melinda Soares-Furtado
- Moons, Planets, and Suns in Context: Environments & Evolutionary Pathways
- Time: 3:00 pm - 4:00 pm
- Place: 4421 Sterling Hall
- Speaker: Melinda Soares-Furtado, University of Wisconsin-Madison
- Abstract: The growing population of exoplanets and the expanding repertoire of instruments and analysis techniques make it possible to examine moons, planets, and suns within the context of their environments and evolutionary history. In this talk, I discuss how my team leverages stellar evolutionary models, observational survey data, and statistical methods to probe the interactions and evolution of moons, planets, and suns. More specifically, I present the effects of planetary collision, accretion, and engulfment on stellar hosts, identifying the ingestion-derived signatures that make it possible to detect such events. In the second part of my talk, I focus on my team’s investigations of young stars in co-moving groups and clusters. Since stellar systems are more dynamically active at early times, these environments offer important test beds to explore star-planet interactions. I present the results of my team’s efforts to characterize star-planet systems at early stages of evolution (< 500 Myr) and the value these data offer to the broader scientific community. Looking forward, infrared space-based missions will soon make it possible to detect transiting exomoons orbiting young (<5 Myr), free-floating planets. Such observations will help to constrain the formation pathways and dynamical histories of these extraordinary systems. In the last part of my talk, I discuss my team’s efforts to identify and characterize exosatellite populations and the broader implications of our anticipated results.
- Host: Richard Townsend
- GREAT IDEAS DEI Reading Group
- GREAT IDEAS Excursion to Sifting & Reckoning Exhibit
- Time: 5:00 pm - 6:30 pm
- Place: Meet in Chamberlin lobby to walk to Chazen museum
- Abstract: This will be a special GREAT IDEAS event, which will be an excursion to the Chazen Museum's Sifting and Reckoning exhibit (https://chazen.wisc.edu/exhibitions/sifting-reckoning-uw-madisons-history-of-exclusion-and-resistance/) as a group, followed by a short discussion. More details to be announced soon!
GREAT IDEAS stands for Group for Reading, Educating, And Talking about Inclusion, Diversity, Equity, & Advocacy in Science. It is a multimedia reading group dedicated to amplifying the experiences of underrepresented groups in science and academia in order to become better advocates for our peers. GREAT IDEAS is open to everyone (students/ faculty/ staff/ etc), and all are welcome and encouraged to engage with the material and contribute to the discussions. To keep a welcoming and safe environment for everyone, we ask that everyone understand and adhere to our community guidelines for the discussions. If you would like to submit an article for a future GREAT IDEAS discussion, you can do so on this form. - Host: GMaWiP and Climate and Diversity Committee (contact Jessie Thwaites or R. Sassella with questions)
Thursday, December 8th, 2022
- R. G. Herb Condensed Matter Seminar
- Spin-phonon effects in nitrogen-vacancy centers
- Time: 10:00 am - 6:00 pm
- Place: 5310 Chamberlin
- Speaker: Matt Cambria , UW-Madison
- Abstract: Spin-phonon interactions provide solid-state qubits with both a unique obstacle to long coherence times, as well as a useful property to exploit for quantum sensing. In this talk, we discuss our recent efforts to understand spin-phonon interactions in the nitrogen-vacancy (NV) center in diamond. In particular, we present measurements of phonon-limited relaxation rates within the NV center's electronic ground state spin triplet manifold. Informed by ab initio work, we determine that NV spin-phonon relaxation is dominated by interactions with phonons whose energies are centered at two characteristic frequencies. We adapt this observation into a semi-empirical model that provides excellent agreement with the experimental data. We discuss how a similar model can describe the NV center's zero field splitting, a quantity fundamental to NV-based thermometry schemes. Finally, we identify an NV qubit subspace that is immune to spin-phonon dephasing, and we predict that such a qubit could exhibit record NV electronic spin coherence times.
- Host: Alex Levchenko
- Preliminary Exam
- Constraining the Diffuse Flux of Ultra-High Energy Neutrinos with the Askaryan Radio Array’s Largest Analysis Ever
- Time: 2:00 pm
- Place:
- Speaker: Abigail Bishop, Physics Graduate Student
- Abstract: In the race to discover the first ultra-high energy neutrinos and zoom in on the ultra-high energy neutrino flux, the Askaryan Radio Array (ARA) is a frontrunner. Similar to the world renowned IceCube Neutrino Observatory, ARA deploys radio antennas in glaciers and searches for the ultra-high energy Askaryan emission radiating from cosmic neutrino interactions in the ice. Even though ARA can see neutrino interactions in volumes far greater than IceCube, the tremendously low flux of ultra-high energy neutrinos makes them even rarer to observe than the mid-high energy neutrinos IceCube detects. ARA has been operating for a decade and is composed of 5 separate stations, but historically each analysis has analyzed only one or two stations over the course of a few years. Presently, our collaboration is building the framework for a full 5 Station Analysis over every year of ARA operation and I am on the ground level of this effort. I propose a thesis project contributing to this leading edge, comprehensive neutrino search, performing an estimate of the diffuse neutrino flux considering every byte of ARA data, with personal emphasis on searching for unique signal topologies that can allow us to confidently identify neutrino candidates in, what used to be classified, as noise.
- Host: Albrecht Karle
- Astronomy Colloquium
- Linking Planet Formation to Exoplanet Composition
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Prof. Edwin(Ted) Bergin, University of Michigan
- Abstract: For the past decade we have begun to explore the origin of planetary compositions which are set in the natal protoplanetary disk. In this talk I will explore these links via two lenses that of giant planets formed far from their star and in smaller Earth-sized planets in the inner regions of planetary systems. For giant planets the primary link has been through the elemental C/O ratio. This is theorized to vary with position in the planet-forming disk as the main carriers of C and O (H2O, CO, and CO2) have spatially separated gas-ice sublimation fronts. I will outline the methodology via which the C/O ratio is traced within disk systems using data from the Atacama Large Millimeter Array (ALMA). I will then summarize the state of knowledge through a comparison of ALMA measurements of the C/O ratio to those measured with high accuracy in distant exoplanets and discuss what this means for the origins of these planetary systems. For the second part of my talk, I will explore the disposition of elemental carbon via new model of planet formation in the inner parts of the disk. This model relates the initial mantle composition of the planet to its formation zone around its star, factoring in the relative contributions of refractories (metals and silicates) and volatile components (solid state organics, water vapor/ice, and hydrogen-dominated nebular gas). We predict that a population of super-Earth’s and mini-Neptune’s will form in particular locations in their protoplanetary disks such that they receive significant inventories of organics, but very low amounts of water. As a result of geochemical equilibrium, the mantle of such a planet would be rich in reduced carbon but have relatively low oxygen (water) content. Outgassing would naturally yield the ingredients for haze production, which is widely observed in these systems. Although this type of planet has no solar system counterpart, it should be common in the galaxy.
- Host: Ke Zhang
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Treasure Maps for Detections of Extreme Energy Cosmic Rays
- Time: 4:00 pm - 5:00 pm
- Place: CH 4274
- Speaker: Anatoli Fedynitch, Academia Sinica, Taiwan
- Abstract: The origin of Ultra High Energy Cosmic Rays is a 60-year old mystery. We show that with more events at the highest energies (above 150~EeV) it may be possible to limit the character of the sources and learn about the intervening magnetic fields. Individual sources become more prominent, relative to the background, as the horizon diminishes. An event-by-event, composition-dependent observatory would allow a ``tomography'' of the sources as different mass and energy groups probe different GZK horizons. A major goal here is to provide a methodology to distinguish between steady and transient or highly variable sources. Using recent Galactic magnetic field models, we calculate ``treasure'' sky maps to identify the most promising directions for detecting Extreme Energy Cosmic Rays (EECR) doublets, events that are close in arrival time and direction. On this basis, we predict the incidence of doublets as a function of the nature of the source host galaxy. Based on the asymmetry in the distribution of time delays, we show that observation of doublets might distinguish source models. In particular the Telescope Array hotspot could exhibit temporal variability as it is in a ``magnetic window'' of small time delays. These considerations could improve the use of data with existing facilities and the planning of future ones such as Global Cosmic Ray Observatory - GCOS.
- Host: Lu Lu
Friday, December 9th, 2022
- Thesis Defense
- Physical structure of tooth enamel at the nano- and micro-scales, revealed by x-ray linear dichroism, and displayed by polarization-dependent imaging contrast mapping
- Time: 10:30 am - 6:00 pm
- Place:
- Speaker: Cayla Stifler, Physics Graduate Student
- Abstract: Tooth enamel is an extremely tough and wear resistant material, withstanding hundreds of Newtons of force every day during mastication. Enamel’s superior mechanical performance is especially important in animals that have particularly high biting forces or use their teeth to break hard materials like wood, nuts, bone, and shells. Enamel is hierarchical, meaning that it has different structures at different scales, from centimeter to Ångstrom. This hierarchy confers toughness and longevity to enamel, especially the micro- and nanoscale structure and crystal orientations. We developed Polarization-dependent Imaging Contrast (PIC) mapping of hydroxyapatite and fluorapatite (Ca10(PO4)6(OH)2) and Ca10(PO4)6F2), based on a physical effect we discovered: x-ray linear dichroism in all apatite crystals. With PIC mapping, we reveal for the first time the complex and diverse crystal orientations in enamel from modern and fossil animals, with nanoscale resolution. Crystal misorientation of adjacent pixels in PIC maps is converted to toughness, producing the first ever toughness maps. Surprisingly, T. rex, a dinosaur that had an extremely high biting force (15,000 N), has the least tough enamel of the 30 animals we measured. The toughest enamel is the saltwater crocodile, with the greatest biting force of all living animals (16,000 N).
- Host: Pupa Gilbert
- Thesis Defense
- New Frontiers in Collisionless Reconnection: Exploring Magnetosphere-Relevant Reconnection with Experiments and Custom Kinetic Simulations
- Time: 1:00 pm - 12:00 pm
- Place: B343 Sterling or
- Speaker: Samuel Greess, Physics Graduate Student
- Abstract: Magnetic reconnection is a ubiquitous phenomenon throughout the universe, but in terms of proximity, its occurrence at the day-side magnetopause is the instance that is closest to Earth both spatially and in importance to human life. At the day-side magnetopause, the solar magnetic field reconnects with the magnetic field of the Earth, beginning the process that results in the transfer of energized solar wind particles into the Earth's upper atmosphere. Usually, the result of these incursions is only the ethereal beauty of the auroras (borealis and australis); however, larger quantities of incident plasma can and have had devastating effects on terrestrial and space-based electronic systems. Predicting these geomagnetic storm events depends on an understanding of both how and when large quantities of plasma are emitted from the Sun (also a reconnection-based event) and how long it will take for these particles to enter the Earth's atmosphere via the magnetopause reconnection process. To that end, in addition to satellite missions created to measure the in situ process, experiments and simulations here on Earth are studying reconnection in the relevant parameter regimes, particularly in plasmas whose collisionality is low enough to mimic the space environment. One such experiment is the Terrestrial Reconnection EXperiment (TREX), which is based as the University of Wisconsin-Madison as a partner of the Wisconsin Plasma Physics Laboratory (WiPPL) collaborative research facility. TREX is designed to access the kinetic regime, which is typified by thin current layers, anisotropic pressure distributions, and fast reconnection. In conjunction with TREX, the newly developed Cylindrical VPIC (Vectorized Particle-in-Cell) code from Los Alamos National Laboratory has been used to simulate TREX in manner that preserves the experiment's cylindrical symmetry while optimizing computational efficiency. Different modified versions of the basic TREX VPIC setup have been successfully used to confirm and complement experimental findings, as well as to investigate plasma regimes the experiment cannot (presently) reach and to model different proposed TREX drive coil geometries. This thesis will present work from both the TREX laboratory and TREX VPIC simulations, with an emphasis on comparing the measured properties of reconnection in both scenarios and demonstrating how these data align with theoretical predictions about the kinetic reconnection parameter regime. Significant background to the construction and operation of TREX, Cylindrical VPIC, and relevant portions of the WiPPL facility will also be included.
- Host: Jan Egedal