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Events on Monday, December 11th, 2023

Plasma Physics (Physics/ECE/NE 922) Seminar
Fusion-relevant studies using the LAPD: ICRF and mirror physics
Time: 12:00 pm - 1:15 pm
Place: 1610 Engineering Hall
Speaker: Dr. Troy Carter, Director of Basic Plasma Science Facility (BaPSF) at UCLA
Abstract: The Basic Plasma Science Facility (BaPSF) at UCLA is a US national collaborative research facility for studies of fundamental processes in magnetized plasmas supported by DOE FES and NSF. The centerpiece of the facility is the Large Plasma Device (LAPD), a 20m long, magnetized linear plasma device. LAPD has been utilized to study a number of fundamental processes, including: collisionless shocks, dispersion and damping of kinetic and inertial Alfvén waves, compressional Alfvén waves for ion-cyclotron range of frequencies heating, flux ropes and magnetic reconnection, three-wave interactions and parametric instabilities of Alfvén waves, turbulence and transport and interactions of energetic ions and electrons with plasma waves. An overview of research using the facility will be given, followed by a more detailed discussion of fusion- and mirror-relevant studies. These include our "ICRF Campaign," focused on wave physics and parasitic effects relevant to ion cyclotron range of frequencies (ICRF) heating and current drive in fusion devices. This includes high power (~ 200kW) fast wave excitation (ω ∼ 2−10Ωci) experiments that have the structure and scaling of RF sheaths, the formation of convective cells and associated density modification, as well as low power experiments documenting parasitic coupling to the slow mode and the interaction of high-harmonic fast waves (or helicon waves) with filamentary structures to study turbulent scattering processes. LAPD has a flexible magnetic field configuration, allowing for mirror configurations with variable mirror ratio, including periodic (many cell) mirrors. Changes to turbulence and turbulent transport have been documented as a function of mirror ratio. In a single-celled mirror, density and magnetic field fluctuation amplitudes decreased with increasing mirror ratio, while potential fluctuation amplitudes remained similar. The cross-phase between potential and density fluctuations varies with increasing mirror ratio, suggesting a shift in the underlying linear instability as the mirror ratio is increased and magnetic curvature is introduced.

Troy Carter is a Professor of Physics at the University of California, Los Angeles. Prof. Carter is the Director of the Basic Plasma Science Facility (BaPSF), a national user facility for plasma science supported by DOE and NSF. He is also the Director of the Plasma Science and Technology Institute (PSTI), an organized research unit at UCLA. His research into waves, instabilities, turbulence and transport in magnetically confined plasmas is motivated by the desire to understand processes in space and astrophysical plasmas as well as by the need to develop carbon-free electricity generation via nuclear fusion. Prof. Carter led the DOE FESAC Long Range Planning process that resulted in the 2021 report “Powering the Future: Fusion and Plasmas.” He is a Fellow of the APS and is a recipient of the APS DPP John Dawson Excellence in Plasma Physics Research Award and of the Fusion Power Associates Leadership Award. Prof. Carter received BS degrees in Physics and Nuclear Engineering from North Carolina State University in 1995 and a PhD in Astrophysical Sciences from Princeton University in 2001.
Host: Prof. Steffi Diem
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Thesis Defense
Discovery, Demographics, and Dark Matter Implications of Faint Dwarf Galaxies in Wide-area Optical Surveys
Time: 12:00 pm
Place: B343 Sterling
Speaker: Mitch McNanna, Physics PhD Graduate Student
Abstract: The combined sky coverage and depth of modern wide-area ground-based optical imaging surveys, in particular the Dark Energy Survey, have made possible the discovery and cataloging of the least luminous known galaxies. The demographics of faint dwarf galaxies throughout our local environment and the properties of the smallest individual ultrafaint galaxies have broad implications for astrophysics. I have designed and implemented search algorithms to identify faint dwarf galaxies both within the gravitational influence of the Milky Way and beyond out to the edges of the Local Group. The census of ultrafaint Milky Way satellites has placed competitive constraints on several alternative dark matter models, established the importance of the Large Magellanic Cloud in the formation of our local galactic environment, and increased our understanding of the connection between the smallest galaxies and the dark matter halos that host them. The search for faint field dwarf galaxies beyond the Milky Way uncovered one of the most diffuse dwarf galaxies ever discovered, the largest galaxy known at its luminosity. By comparing the current catalog of nearby dwarf galaxies to the results of searches over simulated versions of the Local Group, I conclude that we have likely exhausted the power of searches for resolved stellar populations in current wide-area sky coverage. Looking forward, this work informs what we might expect to discover in future surveys covering new areas of sky or with deeper data and how these discoveries will change our understanding of the particle properties of dark matter and the nature of galaxy formation.
Host: Keith Bechtol
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