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Events During the Week of February 26th through March 5th, 2023

Monday, February 27th, 2023

Plasma Physics (Physics/ECE/NE 922) Seminar
Advances in Stellarator Optimization
Time: 12:00 pm
Place: 2241 Chamberlin Hall
Speaker: Sophia Henneberg, Max Planck Institute for Plasma Physics
Abstract: Recent improvements in stellarator optimization and new stellarator designs will be presented. Stellarators possess three-dimensional magnetic fields typically solely generated by the coils’ magnetic field. This reduces or even eliminates the need for generating toroidal plasma currents, which can lead to detrimental instabilities such as disruptions. However, the three-dimensionality can in general involve some drawbacks, e.g., more complicated coils are typically needed compared to the axisymmetric case. Nonetheless, with careful exploitation of the large design space via optimization, the apparent disadvantages can be diminished. In stellarator optimization studies, the boundary of the plasma is usually described by Fourier series that are not unique: several sets of Fourier coefficients describe approximately the same boundary shape. A simple method for eliminating this arbitrariness is proposed and shown to work well in practice. Additionally, we investigate the mathematical structure of the various inter-related calculations that underpin the integrated stellarator optimization problem to better understand how the equilibrium calculation, the coil calculation, and the optimization calculation communicate with each other. Furthermore, new exciting stellarator designs with better confinement properties will be presented. Lastly, I will describe ongoing and future work including ideas for a new university experiment and ways forward for generating simpler coils.
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Astronomy Colloquium
Thunder and Lightning: New Frontiers in Time-domain Astronomy
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Ben Margalit, University of California, Berkeley
Abstract: Advances in multi-messenger and time-domain astronomy provide a fresh view of the dynamic Universe and herald a new era in astrophysics. Through gravitational waves and across the electromagnetic spectrum, transient astrophysical phenomena hold enormous potential as probes of extreme physics and cosmic scales. In this talk I will give an overview of recent developments in time-domain astronomy. Focusing on two frontier research areas—neutron star mergers and fast radio bursts—I will illustrate how transients can be harnessed to study fundamental open questions with far-reaching implications. I will conclude by briefly discussing the future of the field and the opportunities ahead.
Host: Ke Zhang
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Tuesday, February 28th, 2023

Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
Reacceleration of Galactic Cosmic Rays Beyond the Knee at the Termination Shock of a Cosmic-Ray-Driven Galactic Wind
Time: 2:00 pm
Place: Join Zoom Meeting Meeting ID: 912 3071 4547
Speaker: Payel Mukhopadhyay , UC-Berkeley
Abstract: The origin of cosmic rays above the knee in the spectrum is an unsolved problem. We present a wind model in which interstellar gas flows along a non-rotating, expanding flux tube with a changing speed and cross-sectional area. Cosmic rays from Galactic sources, such as supernova remnants, which are coupled to the plasma via Alfvén waves, provide the main pressure source for driving this outflow. These cosmic rays are then subject to diffusive shock reacceleration at the Galactic wind termination shock, which is located at a distance ~200 kpc. Some of the highest-energy reaccelerated particles propagate upstream against the wind and can contribute to the PeV-EeV range of the spectrum. We analyze the conditions under which efficient reacceleration can occur and find that rigidities ~10-40 PV can be obtained and that the termination shock may account for half of the proton spectrum measured in IceCube/IceTop experiment. The highest-energy particles that escape downstream from our termination shock, and similar shocks surrounding most galaxies, can be further accelerated by intergalactic shock fronts.
Host: A. Baha Balantekin
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Wednesday, March 1st, 2023

Time: 12:15 pm - 1:15 pm
Place: Chamberlin 4274 or online
Abstract: We will be discussing the article, Creation of inclusive spaces with astromimicry. We will go over a brief summary and welcome attendees who have not had a chance to read the article.

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)
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Theory Seminar (High Energy/Cosmology)
Machine Learning for String Compactifications
Time: 1:00 pm - 2:30 pm
Place: Chamberlin 5280
Speaker: Anthony Ashmore, U. Chicago
Abstract: The mysterious nature of Calabi-Yau metrics and hermitian Yang-Mills connections has been a persistent challenge in mathematics and theoretical physics for decades. These elusive geometric objects play a critical role in deriving semi-realistic models of particle physics from string theory. However, with no explicit expressions for them, we are left unable to compute basic quantities in top-down string models, such as particle masses and couplings. Recent breakthroughs in machine learning have opened up a new avenue for tackling this problem. In this seminar, we will explore the potential of machine learning for computing these elusive objects. Starting with a review of their relationship to effective field theories, we will then delve into the latest progress in using machine learning to calculate Calabi-Yau metrics and hermitian Yang-Mills connections numerically. Finally, we will give examples of practical applications of this new data, including a test of the so-called "swampland distance conjecture".
Host: George Wojcik
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Thursday, March 2nd, 2023

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
WIPAC-astro discussion
Where are Milky Way’s Hadronic PeVatrons?
Time: 2:30 pm - 3:30 pm
Speaker: Takahiro Sudo, Ohio State University
Abstract: Observations of the Milky Way at TeV–PeV energies reveal a bright diffuse flux of hadronic cosmic rays and also bright point sources of gamma rays. If the gamma-ray sources are hadronic cosmic-ray accelerators, then they must also be neutrino sources. However, no neutrino sources have been detected. Where are they? We introduce a new population-based approach to probe Milky Way hadronic PeVatrons, demanding consistency between diffuse and point-source PeV-range data on cosmic rays, gamma rays, and neutrinos. For the PeVatrons, two extreme scenarios are allowed: (1) the hadronic cosmic-ray accelerators and the gamma-ray sources are the same objects, so that bright neutrino sources exist and improved telescopes can detect them, versus (2) the hadronic cosmic-ray accelerators and the gamma-ray sources are distinct, so that there are no detectable neutrino sources. The latter case is possible if hadronic accelerators have sufficiently thin column densities. We quantify present constraints and future prospects, showing how to reveal the nature of the hadronic PeVatrons
Host: Lu Lu
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Plasma Physics (Physics/ECE/NE 922) Seminar
Life Cycle of Magnetized Plasmas in the Universe
Time: 2:30 pm
Place: B343 Sterling Hall
Speaker: Young Dae Yoon, Asia Pacific Center for Theoretical Physics
Abstract: Magnetized plasmas are ubiquitous in the Universe and are important because many of the events therein are governed by their dynamics. Understanding their nature is thus crucial in various contexts including nuclear fusion, space, and astrophysics. Magnetized plasmas typically undergo three cyclic processes: “generation” of magnetic fields by the plasma, “relaxation” of the system to an equilibrium, and “explosion” of the stored magnetic energy back into the plasma. In this talk, I will present recent results in selected sub-processes within these categories, namely magnetic reconnection, ion energization, wave-particle interaction, and current sheet relaxation. I will then briefly discuss my vision for future work that calls for continued and expanded investigations of these processes.
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Friday, March 3rd, 2023

Graduate Program Event
Prospective Visit Days
Time: 8:30 am - 5:30 pm
Place: all over Chamberlin
Speaker: Sharon Kahn, Graduate Program
Abstract: This weekend, we'll host 28 prospective PhD student visitors to the department. Please welcome them as you see them around Chamberlin!
Host: Sharon Kahn
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Machine Learning and its Applications in IceCube
Time: 2:00 pm - 3:00 pm
Place: CH4274/Join Zoom Meeting
Speaker: Claudio Kopper, Michigan State University/Friedrich-Alexander-Universität Erlangen-Nürnberg
Abstract: In this talk, I will be discussing the fascinating world of machine learning (ML) and its applications to the IceCube neutrino telescope. The field of machine learning has become increasingly important over the last years and now constitutes a vital contribution to the physics output of experiments such as IceCube. I will present recent IceCube results that were made possible by machine learning techniques and highlight the challenges we face when applying ML to IceCube data. The key challenges to be solved in IceCube are background suppression, particle identification, and event reconstruction, all of which can benefit from the implementation of ML techniques. I will be showcasing the ways in which ML can help with these challenges, and how it has been widely adopted within IceCube, not only to tackle these issues but also in the development of analysis methodology. Overall, the talk will provide an overview of ML techniques, how they are applied in IceCube, and the exciting recent results based on ML.
Host: Albrecht Karle
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Physics Department Colloquium
The Cool Copper Collider
Time: 3:30 pm - 4:30 pm
Place: 2241 Chamberlin Hall
Speaker: Emilio Nanni, SLAC, Stanford University
Abstract: The goal of a next-generation e+e- collider is to carry out precision measurements to percent level of the Higgs boson properties that are not accessible at the LHC and HL-LHC. In this talk we will present the study of a new concept for a high gradient, high power accelerator with beam characteristics suitable to study the Higgs boson, the Cool Copper Collider (C^3), with the goal of significantly reducing capital and operating costs. C^3 is based on the latest advances in rf accelerator technology and utilizes optimized cavity geometries, novel rf distribution and operation a cryogenic temperatures to allow the linear accelerator to achieve high accelerating gradients while maintaining overall system efficiency. We will present the latest demonstrated performance of prototype accelerators and highlight the future development path for C^3.
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