Bulletin of the American Physical Society
Four Corners Section 2022 Meeting
Volume 67, Number 14
Friday–Saturday, October 14–15, 2022; Albuquerque, New Mexico
Session B01: Plasma Physics and Condensed Matter I |
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Chair: Paul Schwoebel, UNM Room: UNM PAIS 1010 |
Friday, October 14, 2022 10:00AM - 10:24AM |
B01.00001: Stronger, Faster, Better: Plasma-Based Particle Accelerators Invited Speaker: Michael D Litos Plasma-based particle accelerators offer an opportunity to significantly reduce the size and cost of high-energy particle beams for applications ranging from ultrafast electron diffraction, to X-ray free electron lasers, to high-energy particle colliders. These applications in turn serve users in a variety of research fields by permitting access to ultrafast dynamics at atomic scales, or even fundamental particle interactions. Plasma wakefield accelerators (PWFAs) can sustain accelerating electric fields that are orders of magnitude greater than conventional metallic accelerating structures due in part to the fact that the plasma medium cannot itself be destroyed by the fields, in contrast to metallic structures. Researchers have shown that PWFAs can provide the promised large rates of acceleration to electron bunches, and the next great challenge for the field is to is to preserve the quality (i.e. emittance) of the accelerated bunches. This will be achieved by utilizing the plasma source itself to precisely focus the electron bunches into the PWFA, matching the natural divergence of the electron beam to the strong focusing force experienced in the plasma. Experiments planned at the currently-commissioning FACET-II facility at SLAC National Accelerator Laboratory aim to accomplish this alongside other tangential research goals utilizing relativistic particle beams and plasmas. |
Friday, October 14, 2022 10:24AM - 10:36AM |
B01.00002: A statistical approach to Stark broadening for complex ions Kelsey Adler, Thomas A Gomez, Nathaniel R Shaffer, Charles Starrett, Stephanie B Hansen Lineshapes encode a wealth of information about the plasmas that produce them, including plasma composition, density, temperature, motion and rotation, and magnitude of electric and magnetic fields. In particular, Stark broadening encodes information about the electric microfields generated by neighboring ions in a plasma and is a valuable density diagnostic. Producing lineshapes for complex atoms with 3 or more active electrons using standard perturbation theory can have prohibitively high computational costs. We present a simple and computationally straightforward heuristic model that can be used for ions of any complexity. Our statistical approach uses transition energies, energy shifts, and radial density distributions from a self-consistent average atom code to produce Stark-broadened lineshapes. We present comparisons to standard line-broadening methods for lines from one-and two-electron aluminum ions. |
Friday, October 14, 2022 10:36AM - 10:48AM |
B01.00003: Simulating ICH on ions in a VASIMR Benjamin Miera, Phil Matheson Ion Cyclotron Heating (ICH) is used to heat a plasma and create thrust in a Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine. An ICH Radio Frequency (RF) antenna is placed near the throat of a magnetic nozzle. It produces a localized circularly polarized electric field near the ion cyclotron frequency. An ion is accelerated by pumping its magnetic moment, μ, which is the ratio of perpendicular kinetic energy to the magnitude of the B-field. Outside the antenna region, μ is conserved and the additional kinetic energy is converted into thrust as ions traverse the nozzle into the region of expanding and weakening B-field . This study looks at the efficiency of the pumping process by simulating individual ions generated from an initially cool Maxwellian distribution and looking at the average increase in total energy of ions as they pass through the engine. The resulting heated distribution of ions may be used to estimate the specific impulse and efficiency of the VASIMR engine. Since the model does not yet incorporate any collisional losses, it represents an upper limit on heating efficiencies for a given ICH input. Computational checks on the instantaneous and average value of μ serve to verify the energy and power inputs to the plasma. |
Friday, October 14, 2022 10:48AM - 11:00AM |
B01.00004: Terahertz gain and collective fluctuation modes in microcavity lasers Matthew E Spotnitz, Nai-Hang Kwong, Rolf Binder In a semiconductor microcavity laser, coherence forms spontaneously among the inverted populations of electrons (e) and holes (h), and the emitted photons. One method of describing the coherent e-h states is the BCS approach, adapted from the Bardeen-Cooper-Schrieffer theory of superconductivity.[1] The spectral properties of the BCS state include the formation of conduction and valence intra-band BCS gaps. The direct measurement of the BCS gap can be challenging in high-Q cavities. However, far detuned from the order parameter, the BCS gaps can be measured with a terahertz probe beam.[2] The THz probe excites new angular momentum components, and mixes coherently with the laser frequency to excite the fluctuation spectrum. The fluctuations modes, which include collective modes (related to, but distinct from, Higgs modes[3]), lead to THz gain, with possible technological applications. |
Friday, October 14, 2022 11:00AM - 11:12AM |
B01.00005: Evolution of Magnetic Domain Morphology for Co/Pt Thin Films with In-Situ Field John J Ray, Michael Vaka, Carson J Richards, Olav Hellwig, Karine Chesnel Thin ferromagnetic films with perpendicular magnetic anisotropy show potential for being used as ultra-high-density recording devices because they exhibit a high density of magnetic domains with out-of-plane magnetization. We have found that multilayered cobalt/platinum (Co/Pt) thin films can exhibit domain densities at remanence up to 1000 domains/100 μm2 when the Co thickness is optimized [1] and even remanent densities beyond 2000 domains/100 μm2 for optimized number of layers. [2]. From previous studies of these films, we understand how density and morphology of their domains at remanence respond to previously applied magnetic field [1] [3] and sample composition [2]. Now we examine these changes while applying a magnetic field in-situ during MFM imaging. We examine this behavior for various numbers of layers (N), from 9 to 20, and various Co thicknesses (X) for N=20, from 10 Å to 30 Å. In these investigations, we collect MFM images at distinct in-situ field values, up to various maximum field values. We find, in agreement with previous work [2], that maximum domain density is achieved with N=20 and X=30 Å, at a maximum applied field of ~7 kG, or ~70% of its saturation point. Under these conditions, domains form a hexagonal lattice of dot states. As N, X, and the applied field vary from this optimal point, domain density decreases as domains connect to form stripes and isotropic mazes. Most often, this loss in density happens gradually as the applied field descends from the optimal density point back to remanence. |
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