Events at Physics |
Events During the Week of October 1st through October 8th, 2023
Monday, October 2nd, 2023
- Plasma Physics (Physics/ECE/NE 922) Seminar
- The High-field Stellarator Path to Fusion Energy pursued by Type One Energy
- Time: 12:00 pm - 1:15 pm
- Place: 1610 Engineering Hall
- Speaker: Thomas Pederson, Type One Energy
- Abstract: Stellarators offer substantial advantages as fusion power plants, including intrinsic steady-state operation, low recirculating power, benign heat loads onto the plasma-facing components (PFCs), and the absence of complications associated with runaway electron beams. These benefits have been shown in a number of experiments, in particular Wendelstein 7-X, which also has shown substantial reduction of neoclassical transport through a careful computational optimisation of the magnetic topology. New optimisation codes are producing stellarator magnetic configurations which are substantially better, in particular with respect to fast-particle confinement.
Owing to the relatively small amount of plasma-generated magnetic field, they are also less self-organized than many other fusion concepts, making their performance more predictable.
Due to these advantages, and recent technological advances allowing substantially higher magnetic field strengths and much more rapid production of the highly three-dimensional hardware needed for stellarators, a fast path to a net-power-producing high-field stellarator first-of-a-kind power plant appears feasible.
This talk will start with a brief introduction to stellarators, then review recent advances in stellarator science and technology, and give an update on Type One Energy’s plans for commercializing stellarator fusion energy.
Biography:
Thomas Sunn Pedersen received his PhD in 2000 from MIT, working on soft-x-ray diagnostics and impurity transport on Alcator C-Mod, advised by Robert Granetz and Miklos Porkolab. That same year he joined the Columbia University faculty, where he oversaw the conception, design and construction of the CNT stellarator, which went into operation in 2004, dedicated to the studies of non-neutral plasmas confined on magnetic surfaces, and the effects of ExB drifts on the confinement of particles in a classical stellarator. In 2011, he left Columbia University to take on the position as Director of Stellarator Edge and Divertor Physics at the Max Planck Institute for Plasma Physics, working on the Wendelstein 7-X stellarator, and teaching as a Professor of Physics at the University of Greifswald, Germany, to a fully cooled, quasi-steady-state capable device in 2022. At the start of 2023, he joined the Type One Energy Group as Chief Technology Officer, pursuing a rapid path to high-field stellarator-based fusion net energy production. - Host: Prof. Steffi Diem
Tuesday, October 3rd, 2023
- Graduate Program Event
- Intermittency in the Dimits Regime of Toroidal Ion Temperature Gradient Driven Turbulence
- Time: 11:00 am - 1:00 pm
- Place: B343 Sterling
- Speaker: Augustus Azelis, Department of Physics Graduate Student
- Abstract: In toroidal ion temperature gradient (ITG) driven turbulence, it remains a challenge to understand heat flux reduction at and above the threshold of linear instability for a range of driving gradients called the Dimits regime. A known but unexplained feature of this regime is the observation of temporally intermittent turbulent fluctuations and resulting transport. Preexisting theory for the Dimits shift successfully attributed heat flux reduction to resonance in mode coupling, but this analysis was based on a cumulant-discard method which neglected intermittency and also did not produce any bifurcation demarcating variation in transport with driving gradient above and below the nonlinear critical threshold. In this work, weak turbulence closures are employed to produce dynamical equations for a fourth order cumulant as well as the heat flux itself. The former predicts conditions under which intermittent behavior may develop while the latter is a direct attempt to model said phenomenon. Preliminary analysis has found strong cumulant growth near the linear threshold which can be attributed to resonances in triplet correlation times and nonlinear coupling coefficients. This suggests possible coincidence between the mechanism responsible for heat flux suppression and the inherent non-Gaussian tendencies of the Dimits regime. Analytical work is compared against solutions of the reduced two-field fluid model for toroidal ITG driven turbulence from the numerical solver Dedalus.
- Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
- Primordial Black Holes as a dark matter candidate
- Time: 2:00 pm
- Place: Join Zoom Meeting Meeting ID: 912 3071 4547
- Speaker: Prof. Anne Green , U of Nottingham, UK
- Abstract: Historically the most popular dark matter candidates have been new elementary particles, such as WIMPs and axions. However Primordial Black Holes (PBHs), black holes formed from over-densities in the early Universe, are another possibility. The discovery of gravitational waves from mergers of ~10 Solar mass black hole binaries by LIGO-Virgo has generated a surge in interest in PBH dark matter. I will overview the formation of PBHs, observational probes of their abundance and the key open questions in the field.
- Host: Baha Balantekin
Wednesday, October 4th, 2023
- No events scheduled
Thursday, October 5th, 2023
- Astronomy Colloquium
- On the Comparison of AGN with GRMHD Simulations: Sgr A* and M87
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Richard Anantua, University of Texas at San Antonio
- Abstract: With the advent of the sub-mm imaging of two distinct black hole shadows in 2019 and 2022 by the Event Horizon Telescope, we are now in position to infer the physical properties of such systems using phenomenological models. Models of magnetized plasma in the jet (or outflow)/accretion flow/black hole (JAB) system Sagittarius A* based on turbulent heating and deviations from the equipartition of particle and magnetic energies are input into a High Accuracy Relativistic Magnetohydrodynamics (HARM) simulation. Spectra, movies and light curves simulating hourly timescales show that these models aggregate into four quasi-stationary types: 1.) thin, asymmetric photon ring with best fit spectrum; 2.) coronal boundary layer with thin photon ring and steep spectrum; 3.) thick photon ring with flat spectrum; and 4.) extended outflow with low frequency spectral knee. For M87, a self-similar, stationary, axisymmetric jet model based on a force-free flow in a HARM jet simulation is used to generate Stokes maps at Very Long Baseline Array (VLBA, 43 GHz) and Event Horizon Telescope (EHT, 230 GHz) scales. The model varies plasma content from ionic (e-p) to pair (e-e+). Emission at the observed frequency is assumed to be synchrotron radiation from electrons and positrons, whose pressure is set to be constant fractions of the local magnetic pressure. The cleanest observational signature in the Stokes maps is the vanishing of circular polarization for increasing positron content. Positrons are also incorporated into the general relativistic ray tracer IPOLE to display positron effects on general relativistic magnetohydrodynamic simulations, showing stark differences in polarization signatures between standard and normal evolution (SANE) and magnetically arrested disk (MAD) accretion modes due to Faraday effects. The inclusion of electrons, positrons and protons in our radiative transfer pipeline thus provides a powerful probe of the composition of JAB systems
- Host: Ke Zhang
Friday, October 6th, 2023
- Physics Department Colloquium
- Neutrino Tomography: A journey into the interior of Earth
- Time: 3:30 pm - 5:00 pm
- Place: Chamberlin 2241
- Speaker: Sanjib Kumar Agarwalla , Institute of Physics, Bhubaneswar, India and Physics Department and WIPAC, University of Wisconsin-Madison
- Abstract: Neutrinos produced in cosmic ray interactions in the atmosphere provide a unique and independent probe to explore the internal structure and composition of the deep Earth, which is complementary to traditional seismic and gravitational measurements and pave the way for multi-messenger tomography of Earth. I will discuss the two different approaches to perform Earth tomography with neutrinos: (i) neutrino absorption tomography, based on partial absorption of a high-energy TeV-PeV neutrino flux as it propagates through Earth and (ii) neutrino oscillation tomography, based on Earth matter effects due to the coherent forward scattering of multi-GeV neutrinos with the ambient electrons modifying neutrino oscillation patterns. I will subsequently show how well the DeepCore detector, a densely instrumented sub-array of the IceCube neutrino observatory at the South Pole, can observe these Earth matter effects in atmospheric neutrino oscillations using 9.3 years of data. We will further demonstrate that these matter effects in oscillations of atmospheric neutrinos can be used to establish the layered structure inside Earth and measure the mass of Earth and mass of core. I will conclude my talk discussing the remarkable physics reach of a new extension of DeepCore to be deployed in the Antarctic summer 2025/26, called the IceCube Upgrade.
- Host: Prof. Francis Halzen