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Events on Monday, May 1st, 2023

Graduate Program Event
PhD Final Defense
Nanoscale Enhancement of Dipole Emission: Modeling Multi-Photon Effects and Microwave Emission from Small Josephson Junctions
Time: 10:00 am - 12:00 pm
Place: 4274 Chamberlin
Speaker: Colin Whisler, Physics Graduate Student
Abstract: The classical electric dipole acts as a source of electromagnetic radiation, and the power emitted can be modified significantly by optimizing the emitter's environment. This topic has numerous applications, as the electric dipole serves as an excellent representation for processes such as fluorescence from an atomic emitter in an excited state or radiation from a Josephson junction in the AC Josephson effect. Finite difference time domain (FDTD) simulations can provide powerful tools for analyzing these phenomena in arbitrary geometries. This dissertation first calculates the enhancement of two-photon spontaneous emission (2PSE) from trivalent and divalent rare earth ions in proximity to graphene and graphene nanoribbons for achievable experimental conditions using a combination of FDTD simulations and direct computation of transition rates between energy levels in rare earths. The second portion of the dissertation considers the enhancement of dipole emission in a nanoscale gap between an atomically sharp conducting tip and a metallic surface. This serves as a model for Josephson junction spectroscopy, in which the tunneling of Cooper pairs releases local microwaves at bias-dependent frequencies that can be absorbed by nearby molecules, causing DC current to flow. Our results suggest intriguing possibilities for new applications in quantum technology while also discussing the challenges that still must be overcome.
Host: Victor Brar
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Plasma Physics (Physics/ECE/NE 922) Seminar
Initial Results from the DIII-D Negative Triangularity Campaign
Time: 12:00 pm
Place: 2241 Chamberlin Hall
Speaker: Kathreen Thome, General Atomics
Abstract: Negative Triangularity (NT) is a potentially transformative scenario for fusion energy with its high-performance core, L-mode-like edge, and low-field-side divertors that could readily scale to an integrated reactor solution free of ELMs. Benefits of the NT shape were originally demonstrated on the TCV tokamak and high-performance has been previously achieved on DIII-D, which motivated the installation of graphite-tile armor on the low-field-side lower outer wall to attain high-power diverted plasmas with strong negative triangularity. In early 2023, a dedicated multiple-week experimental campaign was conducted to qualify the NT scenario for future reactors. During this campaign, high confinement (H98y,2≥1), high current (q95<3), and high normalized pressure plasmas (βN~3) were achieved at high-injected-power in strongly NT-shaped plasmas with δavg= - 0.5 and a lower outer divertor X-point during a dedicated experimental campaign on DIII-D that also demonstrated high normalized density (ne/nGW≤2) and a detached divertor, all while maintaining a non-ELMing NT-edge. Further results on performance, stability, transport, and core-edge integration will be presented.
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