Bulletin of the American Physical Society
2018 Annual Meeting of the Far West Section
Volume 63, Number 17
Thursday–Saturday, October 18–20, 2018; Cal State Fullerton, Fullerton, California
Session B02: Atomic, Molecular, Optical and Plasma Physics |
Hide Abstracts |
Chair: Alla Safronova, University of Nevada, Reno Room: Titan Student Union Gabrelino |
Friday, October 19, 2018 2:00PM - 2:12PM |
B02.00001: Spatial Phase Reconstruction for Plasma Diagnostic by TW-class Laser in the Proton Driven Plasma Wakefield Acceleration Experiment, AWAKE, in CERN Valentina Lee, Joshua Moody, Patric Muggli The spatial phase of a TW-class laser was reconstructed for establishing the laser initial conditions for the ionization and propagation process in a ten meter Rubidium vapor source. The near field intensity and the intensity at the entrance of the vapor source were unitized to reconstruct the spatial phase by a modified Gerchberg-Saxton algorithm. The other two downstream intensity profiles were taken for examining the reconstructed phase by propagating the beam with the reconstructed phase for five and ten meters. A defined root mean squared error between the reconstructed intensity profile and the entrance intensity data has been demonstrated decreasing as the algorithm iterates. The agreement between the downstream data and the reconstructed profiles increases as the algorithm iterates as well. |
Friday, October 19, 2018 2:12PM - 2:24PM |
B02.00002: Establishing a Laboratory Benchmark to Diagnose Astrophysical Plasmas using the Fe/Ni Intensity Ratio Ryan Childers, Alla Safronova, Victor Kantsyrev, Ishor Shrestha, Austin Stafford Plasma is an ionized, collectively-behaving gas that constitutes >95% of observable matter in the universe. Through laboratory-produced, high-energy-density (HED) plasmas and high-resolution spectroscopy, the ability to probe physical parameters of astrophysically relevant plasmas is now feasible in a controlled, experimental setting. Astrophysical plasma analysis involves computational spectroscopic modeling to infer electron plasma temperature, density, distribution function, etc. In the absence of these computational models, diagnostics to investigate HED plasmas are relatively incomplete. In this talk, I present a theoretical benchmark to diagnose plasma parameters in lieu of computational models using the Fe/Ni intensity ratio. Fe and Ni are chosen due to their relative abundance in the universe which resembles their relative composition in stainless steel alloy wires used in the production of HED Z-pinch plasmas. Theoretical line intensities are produced with the Spectroscopic Collisional-Radiative Atomic Model and Fe/Ni ratios tabulated for a range of plasma parameters. An example of the application to experimental HED plasma data is presented. |
Friday, October 19, 2018 2:24PM - 2:36PM |
B02.00003: Effects of target parameters on electron energy gain during laser-driven acceleration in a hollow-core target Katherine Chin, Zheng Gong, Alexey V Arefiev The structure of the hollow-core target exhibits the ability to prevent laser diffraction which allows the focusing effect to enhance the laser longitudinal electric field. When the laser propagates inside the target, electrons can be injected into the channel by the transverse laser electric field. For forward moving electrons, the force from the self-generated quasi-static transverse electric field is compensated by the force of the azimuthal magnetic field, allowing for purely longitudinal acceleration. This process will terminate once electrons slide out of the favorable accelerating phase due to the difference between phase velocity (vph) and longitudinal velocity of the electrons, where vph depends on the density of injected electrons and the size of the channel. We have performed a series of 2D particle-in-cell simulations for different hollow-core radii to self-consistently determine the phase velocity and corresponding maximum electron energy. The considered setup offers an attractive possibility of generating beams of highly collimated energetic electrons with near-critical density. |
Friday, October 19, 2018 2:36PM - 2:48PM |
B02.00004: Highlights of experiments with Al and W DPWAS on the University of Michigan's Linear Transformer Driver Christopher J Butcher, Victor Leonidovitch Kantsyrev, Alla Safronova, Veronica V Shylaptseva, Ishor Shrestha, Austin Stafford, Paul C Campbell, Stephanie M Miller, David A Yager-Elorriaga, Adam M Steiner, Nick M Jordan, Ryan D McBride, Ronald M Gilgenbach Results of joint UNR/UM experiments with low-Z Aluminum (Al) and high-Z Tungsten (W) Double Planar Wire Arrays (DPWA) at the UM low-impedance Linear Transformer Driver (LTD) MAIZE generator (0.1 Ω, 0.5–1 MA, and 100–250 ns) are presented. The DPWAs consisted of two wire planes of micron-scale sized Al and W wires, spaced 3-6 mm apart. Current from the machine causes the DPWA to ablate, creating two sheets of plasma that pinch in the center of the arrays. As the DPWA begins to implode, radiation in a broad range is emitted, and then detected using a PCD (>2.4 keV) and Si-diodes (>1.4 keV), x-ray pinhole cameras, spectrometers, and a fast, visible light camera which captures plasma evolution via self-emission. The differences and similarities of Al and W DPWAs are summarized. The research was supported by the NNSA under DOE grant DE-NA0003047. |
Friday, October 19, 2018 2:48PM - 3:00PM |
B02.00005: Probing the inner workings of single molecules with atomically terminated, nanoscopically smooth metallic tips via tip-enhanced Raman Spectroscopy Alexander Hart, Benjamin Taber, Joonhee Lee, Ara Apkarian In the past two decades, tip-enhanced Raman spectroscopy has emerged as a powerful technique for nanoscale chemical analysis. Central to this technique is the fabrication of metallic tips as mediators between the incident light and the chemical response of the sample. In this regard, we employ a process of electrochemical polishing and field-directed ion sputtering to develop atomically sharp and nanoscopically smooth tips capable of achieving subatomic spatial resolution. These tip characteristics are believed to be necessary for their function as minimum-loss antennas that channel incident light into localized surface plasmons at the tip apex. The confinement leads to electromagnetic field enhancement in excess of 108, sufficient to detect the Raman scattering signal from single molecules. The design and batch production of these tips will be discussed, and their utility illustrated via studies of adsorbed benzene on an atomically flat copper surface, within an ultra-high vacuum scanning tunneling microscope. The studies underscore the potential of this method to probe the inner workings of individual molecules – a new frontier in chemical science. |
Friday, October 19, 2018 3:00PM - 3:12PM |
B02.00006: Assessing Protein-Ligand Binding Modes Via Ensemble Molecular Dynamics Parker Bremer, Walter Alvarado, Angela Choy, Aingty Eung, Eric Sorin Molecular dynamics (MD) simulations of biomolecular phenomena require extensive sampling. Fortunately, advances in computational hardware and algorithmic efficiency facilitate the acquisition of ensemble datasets and there is a growing need for analytical approaches to assess datasets of this nature. In this study, we characterize conformations of butyrylcholinesterase (BChE) in complex with a number of inhibitors. The Folding@Home distributed computing network allowed for the acquisition of over 100 μs of all-atom MD sampling for each of thirteen BChE-inhibitor complexes and the enzyme sans inhibitor, yielding a total simulation time of nearly 1.5 ms. For each complex, post-equilibration structures were characterized by the magnitude and type of contact between inhibitor functional groups and BChE residues. These descriptors were then clustered via K-means and the resulting clusters were described via contact tables, which convey the results of massive datasets in a comprehensive, concise manner accessible to our collaborators, who have provided experimentally measured KI values for the studied inhibitor. This approach, in tandem with ensemble-level sampling, provides a novel atomic-level picture perspective, improving our capacity to propose more efficacious inhibitors. |
Friday, October 19, 2018 3:12PM - 3:24PM |
B02.00007: Properties of Koopman operator and its approximations for dynamical systems with symmetries. Anastasiya Vladimirovna Salova, Jeffrey V Emenheiser, Adam Rupe, Raissa M D'Souza, James Crutchfield We investigate the properties of Koopman operator governing the evolution of observables for dynamical systems with point symmetries. Koopman operator approximations such as extended dynamic mode decomposition (EDMD) are a powerful tool for studying nonlinear dynamical systems with unknown underlying dynamics directly from data. We consider the properties of the EDMD approximation of Koopman operator for such systems and propose a modification of the algorithm that utilizes the properties of the isotypic decomposition of dynamical systems with symmetries. |
Friday, October 19, 2018 3:24PM - 3:36PM |
B02.00008: Probing and Visualizing Spin-Exchange Interactions Between Two Single Magnetic Molecules Using Scanning Tunneling Microscopy and Spectroscopy Gregory Czap, Peter Wagner, Jiang Yao, Wilson Ho Over the last decade single-molecule functionalized scanning probe tips have been shown to provide novel sensing capabilities at the nanoscale, such as visualization of chemical structures and bonds as well as electrostatic fields. However, the use of magnetic molecules to sense spin densities and quantify spin-spin interactions has yet to be demonstrated. Here we show that a single S = 1 nickelocene (NiCp2) molecule attached to a scanning tunneling microscope tip can be used to probe spin-spin interactions with other magnetic entities on the surface using inelastic electron tunneling spectroscopy. When the NiCp2-tip is positioned above another NiCp2 molecule, antiferromagnetic superexchange interactions act across the vacuum gap which are sensitive to sub-Ångström scale changes in the intermolecular separation. Using this sensitivity, we demonstrate the ability to image contours of spin-spin interaction strength and provide a means to visualize spin density with a molecular probe tip. Our results extend the capabilities of molecule-functionalized tips to the detection of continuously-tunable magnetic interactions with other objects in the local environment. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700