Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Plasma Physics
Volume 64, Number 11
Monday–Friday, October 21–25, 2019; Fort Lauderdale, Florida
Session YP10: Poster Session IX: Supplemental Posters (9:30am-12:30pm) |
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Room: Exhibit Hall A |
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YP10.00001: A conservative implicit PIC scheme for the hybrid kinetic-ion fluid-electron model on curvilinear meshes Luis Chacon, Adam Stanier, Guangye Chen The quasi-neutral hybrid model with kinetic ions and fluid electrons is a promising approach to model multi-scale problems in space and laboratory plasmas. However, current explicit schemes suffer from a number of key algorithmic issues related to the stable propagation of whistler waves, and finite-grid instabilities for cold ion beams due to non-conservation of discrete momentum or energy. Here, we present a novel particle-based non-linear hybrid algorithm that features discrete conservation of mass, momentum and energy. Recently, the basic algorithm has been extended to allow the efficient treatment of multi-scale problems in generalized curvilinear geometries, using a fluid moment-based preconditioner to accelerate convergence when stepping over fast normal modes. A number of test problems are presented to demonstrate the correctness of the implementation, the unique conservation properties, and the favorable stability properties of the new scheme. [Preview Abstract] |
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YP10.00002: Laser-cooled Be$^{\mathrm{+}}$ for sympathetic cooling of e$^{\mathrm{+}}$ for Antihydrogen formation Niels Madsen, Daniel Thomas Maxwell, Jack McCauley Jones, Joanna Peszka Antihydrogen, the antimatter counterpart of hydrogen, is an exciting system for testing fundamental symmetries such a CPT (Charge, Parity and Time) and the weak equivalence principle. The ALPHA collaboration has in recent years made the first precision measurements of both the ground state hyperfine splitting and the ground (1S) to first excited stated (2S) two photon transition in antihydrogen. In addition, ALPHA has recently expanded its discovery potential by adding an apparatus allowing for direct tests of the gravitational acceleration of antihydrogen, thus testing the weak equivalence principle. These initial measurements have benefitted from increased trapping rates of antihydrogen achieved principally by using colder positrons. We present the result of an effort to load and laser-cool Be$^{\mathrm{+}}$ ions in the challenging environment of an apparatus used for antihydrogen formation and trapping. The laser-cooled Be$^{\mathrm{+}}$ ions are used to sympathetically cool positrons, to achieve even colder positron plasmas than possible through strategies based on cyclotron cooling in the strong magnetic fields used in these experiments. Experimental evidence suggests that even a small reduction in the temperature of the positrons used for antihydrogen formation will greatly enhance the antihydrogen trapping efficiency, suggesting that this approach could increase the amount of antihydrogen available for experimentation by at least an order of magnitude. [Preview Abstract] |
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YP10.00003: Investigation of ion acoustic turbulence in tokamak start-up stage. Jian Chen, Alex Khrabrov, Igor Kaganovich Generally, tokamak start-up driven by pure Ohmic heating consists of the gas breakdown, burn-through, and current ramp-up phases. During the current ramp-up stage, plasma has already been fully ionized. The ramp-up is expected due to acceleration of electrons and ions by the induced toroidal electric field. However, the actual rate of current rise may be controlled by an instability triggered by increasing relative velocity between ions and electrons. In this study, we employed an electrostatic particle-in-cell code (1D EDIPIC) to simulate the current ramp-up. Initially (after gas breakdown) electrons and ions are both warm, with assumed Maxwellian distributions in velocity. Periodic boundary condition was adopted for both the particle motion and the electric field. A constant induced electric field was applied in addition to the self-consistent field occurring in the plasma. Simulation results show that ion acoustic instability grows from the initial noise and saturates after several ion plasma periods. The instability could slow down the acceleration of electrons and heat the ions, which can be identified as an anomalous resistivity mechanism. Growth of ion temperature eventually damps the instability. The saturation level of the electrostatic oscillations can be high enough to create phase-space structures known as ion holes, which have been observed in our simulations. [Preview Abstract] |
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YP10.00004: 3-D Particle Simulations of Nonlinear Lower Hybrid Drift Instability Zhenyu Wang, Yu Lin, Xueyi Wang, Liu Chen Previously, we investigated 3-D linear instabilities of Harris current sheet under a realistic ion-to-electron mass ratio and a finite guide field. The excitation and 3-D properties of lower hybrid drift instability (LHDI), kink, sausage and a streaming instabilities were demonstrated. In the present poster, we study the nonlinear properties of current sheet instabilities by employing Gyrokinetic electron and Fully kinetic ion (GeFi) particle simulation code. It is found that part of the energy of the LHDI modes penetrates to the current sheet center in the nonlinear stage. The saturation level of magnetic field at the current sheet center is an order of magnitude smaller than that at the current sheet edge. The nonlinear GeFi simulation results are compared with nonlinear fully kinetic PIC simulations. [Preview Abstract] |
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YP10.00005: Ion-dust streaming instability in microgravity dusty plasma Evdokiya Kostadinova, Martin Lechuga, Joshua Padgett, Constanze Liaw, Peter Hartmann, Lorin Matthews, Truell Hyde Streaming instabilities are a likely mechanism for planetesimal formation in protoplanetary disks. Due to the presence of charged dust particles in dense interstellar and circumstellar environments, charging processes are likely to affect the onset of such instabilities. Here we investigate ion-dust streaming instabilities in microgravity dusty plasmas using data from the Plasma Kristall-4 facility on board the International Space Station. Specifically, we examine how dust charging and ion wakefield formation affect the onset of the streaming instability and identify the parameter space where these instabilities are most likely to occur. The analysis reveals that above a critical dust particle concentration, the onset of ion-dust streaming instability is highly sensitive to variations in plasma density and gas pressure, which makes it a useful indicator of (controlled or unexpected) changes in the system conditions. [Preview Abstract] |
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YP10.00006: Measurement of Electrical Potential Profile in Collisional Plasma Shock Samuel Langendorf, Tom Byvank Collisional plasma shocks are expected to contain self-generated electric fields that modify the diffusion of plasma species across the shock front [1]. We perform experiments on the Plasma Liner Experiment (PLX) to create collisional plasma shocks between coaxial-gun-produced plasma jets, and study the electrical potential profile across the shock using a multi-tip Langmuir probe. The probe tip dimensions are minimized below the plasma ion-ion mean free path to prevent standing shock fronts from forming on the probe tips and supports. Results will be compared to theory and simulation and inform ongoing efforts to incorporate detailed models of shock formation into plasma simulation codes.\\ $^1$ Jaffrin, M. Y., Probstein, R. F. The Physics of Fluids 7.10 (1964): 1658-1674.\\ [Preview Abstract] |
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YP10.00007: Extraordinary field emission diamond film using Microwave Plasma Jet Chemical Vapor Deposition Jing-Shyang Yen, Chun-Yu Lin, Jwo-Shiun Sun, Chi-Wen Liu, Chii-Ruey Lin, Hua-Yi Hsu, Ming-Chieh Lin The research and development of a microwave plasma jet chemical vapor deposition for diamond film growth have been carried out in this study. A 3D adaptive finite element method electromagnetic model of microwave plasma interactions is constructed to get more understanding of the operating characteristics of diamond film growth. The whole system has been simulated self-consistently. In addition, a thin diamond film has been successfully fabricated according to the identical conditions predicted in the simulations. The SEM image shows that the deposited diamond particles are uniformly distributed on the substrate with the size of 1um. The field emission from the diamond film grown from this MPJCVD shows extraordinary properties, i.e., extremely low turn-on voltage and high current density. This work is promising in surface hardening and bright field electron emission sources. [Preview Abstract] |
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YP10.00008: Rigorous derivation of the self-force and momentum of a charged particle in the hyperbolic motion Teyoun Kang, Min Sup Hur The problem of the classical electrodynamics is that the equation of motion including the self-force of a charged particle is still incomplete. For examples, there are a few popular theory models such as Lorentz-Abraham-Dirac and Landau-Lifshitz equations, but the causality violation or contradiction is not avoided in those models. In particular, the radiation reaction from a point charge in the hyperbolic motion has not been described successfully; the reaction term vanishes, although it actually radiates, leading to apparent violation of the energy conservation. Furthermore, the self-force of a point charge is strongly related to the renormalization, which is still unclear in QED system. Owing to the recent development of ultra-intense laser facilities, great interest in this problem is emerging rapidly, as the radiation reaction of charged particles is expected to be observed in much stronger fields. In this poster, we present a unique charge distribution that we named `point-like conductor (PLC),' with a derivation of the self-force and momentum of PLC by applying the Rindler coordinates. Eventually we suggest a modified equation of motion for a point particle by assuming the particle and PLC are equivalent, and we explain the difference between previous and modified results. [Preview Abstract] |
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YP10.00009: Tunable Metallic Nanocrystal Generation using Laser-Driven Proton Irradiation Patrizio Antici, Marianna Barberio, Simone Giusepponi, Simon Vallieres, Massimiliano Sciscio, Massimo Celino Laser-driven proton acceleration, as produced during the interaction of a high-intensity (I\textgreater 1x10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}})$, short pulse (\textless 1 ps) laser with a solid target, is a prosperous field of endeavor for manifold applications in different domains, including astrophysics, biomedicine and materials science. These emerging applications benefit from the unique features of the laser-accelerated particles such as short duration, intense flux and energy versatility, which allow obtaining unprecedented temperature and pressure conditions. In this paper we show that laser-driven protons are perfectly suited for producing, in a single sub-ns laser shot, gold nanocrystals with tunable diameter ranging from tens to hundreds of nm and very high precision. Our method relies on the intense and very quick proton energy deposition, which induces in a bulk material an explosive boiling and produces nanocrystals that aggregate in a plasma plume composed by atoms detached from the proton-irradiated surface. The properties of the obtained particles depend on the deposited proton energy and on the duration of the thermodynamical process. Suitably controlling the irradiated dose allows fabricating nanocrystals of a specific size with low polydispersity that can easily be isolated in order to obtain a monodisperse nanocrystal solution. Molecular Dynamics simulations confirm our experimental results. [Preview Abstract] |
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YP10.00010: MHD modeling of deuterium-filled dense plasma foci with prescribed noble gas impurities Jeff Narkis, Fabio Conti, David Housley, Daniel Lowe, Farhat Beg Dense plasma foci are an efficient source of fusion neutrons. Though the stagnation physics are highly kinetic, MHD simulations can estimate useful quantities like peak temperature, density, and thermonuclear yield, and provide information related to the axial run-down dynamics, e.g. stability. Presented here are HYDRA simulations for DPFs using two configurations: the driver of the first configuration delivers 1.3 MA in 5 $\mu $s to the load and the device has geometry similar (z \textasciitilde 60 cm, anode and cathode radius of r$_{\mathrm{a}}$ \textasciitilde 5 and r$_{\mathrm{c}}$ \textasciitilde 8 cm, respectively) to that used on Gemini at the Nevada National Security Site. The driver of the second configuration delivers 800 kA in 160 ns to the load and has much shorter electrodes (z \textasciitilde 2-3 cm) at smaller radii (r$_{\mathrm{a}}$ \textasciitilde 1.25 cm, r$_{\mathrm{c}}$ \textasciitilde 2.5 cm) to account for the much faster rise time. The effect of impurities (Ar, Kr and Xe) on dynamics, stagnation conditions, and thermonuclear neutron yield is also discussed. [Preview Abstract] |
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YP10.00011: Diamagnetic-like states in self-gravitating fluids in curved spacetimes Felipe Asenjo It is shown that a self-gravitating fluid can be casted in a plasma-like formalism when its own gravity is a perturbation of a given spacetime background. In this case, the scalar part of the perturbed metric acts as an electric field, while the vectorial parts behave as an effective magnetic field. This allow us to find equilibrium solutions where the self-gravitating fluid behaves as an effective diamagnetic plasma. Thus, it can be shown that the gravitational field of the fluid can have analoguos properties to a superconducting medium. [Preview Abstract] |
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YP10.00012: Modeling and Interpretation of Laboratory Experiments of Magnetized Collisionless Shocks Zhenyu Wang, Anatoly Spitkovsky, Channing Huntington, Hye-Sook Park, Frederico Fiuza, Bradley Pollock, Steven Ross, Dmitri Ryutov We present the modeling and interpretation of laser experiments designed to generate high Mach number magnetized collisionless shocks on OMEGA-EP facility. In the experiment, a laser-produced high velocity plasma collides with a magnetized, pre-ablated plasma. Proton radiography shows a moving region of proton deficit followed by a sharp enhancement of proton density. These features are produced by gradients in propagating compressed magnetic field. We compare the data to the results of 3D PIC simulations, explain the oblique moving features introduced by density gradients in expanding plasma and by curvature of the imposed magnetic field, and identify the narrowing of proton deficit region width with a signature of strong magnetic overshoot. We determine the boundary of pre-ablated background plasma by comparing with radiography of laser shots with only background plasma present. We measure the strength of MIFEDS field by magnetic deflection. We conclude that our experiments have reproducibly achieved magnetized shocks with Alfvenic Mach number 3 to 9 in laboratory conditions. [Preview Abstract] |
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YP10.00013: Using Research in Plasma Physics and Astrophysics to Increase Freshmen Retention Dereth Drake Many university physics programs struggle with increasing or retaining freshmen students. At Valdosta State University, historically the retention rate in physics has been very low, \textasciitilde 33{\%}. In Fall 2017, our department started examining ways to increase our retention rate by using first year research opportunities. That year, two freshmen female students were invited to participate in research. Both students were retained to their sophomore year. With the limited success that year, in Fall 2018 we invited 7 of the 15 incoming freshmen to participate. The students participated in five projects throughout the year in astrophysics and plasma physics. All seven students were retained to their second year. Of the eight who did not participate only a fraction were retained. This presentation will describe the program in more detail, discuss the challenges faced during implementation process, and show the programs goals and plans for the current and next academic year. [Preview Abstract] |
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YP10.00014: Fusion breeding and the scientific prototype for midcentury, carbon free, sustainable power, Wallace Manheimer For 20 years now the author has argued that the MFE program would be much better off switching from pure fusion to fusion breeding. This way the MFE program would be prosing something it might actually accomplish in a reasonable time. He also argued that the best course of action for the US MFE program is to build the ‘scientific prototype’ a tokamak like TFTR, having Q~1, running steady state in DT and breeding its own tritium. Papers on this have appeared in the fusion literature [1,2], a literature with limited readership. More recently a summary has been published in a well-regarded IEEE journal [3]. This poster will discuss these points with interested visitors. 1. W. Manheimer, Fusion Technology, 36,1, 1999 2. W. Manheimer, J. Fusion Energy 2014, (open access), https://link.springer.com/article/10.1007/s10894-014-9690-9 3. W. Manheimer. IEEE Access 2018 ,(open access) https://ieeexplore.ieee.org/document/8502757 [Preview Abstract] |
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YP10.00015: Bandwidth broadening of waveguide circulator for industrial dual-band magnetrons Kaviya Aranganadin, Hua-Yi Hsu, Ming-Chieh Lin An RF waveguide circulator is a ferromagnetic passive device with three or four ports which is used to protect other RF components from excessive signal reflection. This paper focuses on the design and development of a partial height ferrite circulator with wider operating bandwidth of minimum 100 MHz with the frequency centered at 2.45 GHz to replace the present industrial waveguide circulator which has 50 MHz bandwidth because the circulator with bandwidth broadening from 50 to 100 MHz can serve as a low-cost but high-efficiency protection device for two magnetrons operating concurrently at different frequencies of 2430 and 2480 MHz. Hence, increasing the bandwidth of a circulator reduces the number of units used from two to one for the dual frequency magnetrons. The validation of the design is performed using the finite element method simulations. A preliminary optimization using a small signal approximation of ferrite tensor shows that the overall operation ranges from 2340 to 2550 MHz with the insertion loss less than 0.24 dB, reflection, and isolation better than 20 dB can be achieved. The detailed design, simulation, optimization, and manufacturing plan will be discussed. [Preview Abstract] |
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YP10.00016: Denying Unmanned Aerial Vehicle Invasion using High Power Electromagnetic Waves Jing-Shyang Yen, Xuan-De Huang, Chia-Wei Lin, Kaviya Aranganadin, Jwo-Shiun Sun, Hua-Yi Hsu, Chii-Ruey Lin, Ming-Chieh Lin A unmanned aerial vehicle (UAV) or simply a drone has no onboard human pilot. In recent years, UAVs are well developed and made commercially available. Several countries have operational, domestic UAVs, and many more have imported drones or have development programs under way. Airport control or public security might be endangered by intended invasion or accidental activities. A UAV might be used to carry aircraft ordnance such as missiles and is used for drone strikes. These drones are usually under real-time human control, with varying levels of autonomy, speeds, and payloads. Thus, denying this type of invasion is not a trivial task. In this work, electromagnetic effects on a UAV are studied using a 3-D conformal finite-difference time-domain simulation in order to find some solutions to mitigating a UAV invasion. The 3-D model of a commercially available drone has been built and investigated. [Preview Abstract] |
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YP10.00017: X-ray Phase-Contrast Imaging of Strong Shocks. Nigel Woolsey, Luca Antonelli, Matt Khan, Robbie Scott, Kevin Glize, Wolfgang Theobald, Phil Nilson, Arnab Kar, Riccardo Betti, Stefano Atzeni, Dimitri Batani, Alexis Casner, Luke Ceurvorst, Jocelain Trela, Francesco Barbato We demonstrate x-ray phase contrast enhanced imaging (XPCI) on OMEGA EP as a new imaging platform that offers exceptional spatial and material interface resolution. Phase-contrast enhanced imaging requires an x-ray source with some spatial coherence. This is possible with a laser produced incoherent and broadband x-ray source by matching the source size and the energy spectrum with the distance between the source and the object. We describe the application of XPCI on OMEGA EP and how the challenges of an incoherent source and the close proximity of the source to object are managed. It is necessary to minimize the spatial extent of the source whilst ensuring a sufficient photon flux to make a measurement. This is possible by using short pulse laser, such as OMEGA EP, to provide a bright x-ray source and limit the source size with either a pinhole or a free-standing mass-limited foil target with the foil edge pointing towards the object. We apply the XPCI platform to study a shock wave launched using OMEGA EP long pulse beams. [Preview Abstract] |
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YP10.00018: The Relation Between The Quantum Entanglement In Theoretical Physics As A New Insight Into The Cancer Biology Sorush Niknamian Quantum entanglement is a phenomenon in theoretical physics that happens when pairs or groups of particles are generated in ways that the quantum state of each particle cannot be described independently of the others, even when the particles are separated by a large distance. Instead, a quantum state must be described for the system as a whole. Based on the introduction of cancer as an evolutionary metabolic disease (EMHC), each cancerous cell are eukaryotic cells with different metabolic rate from healthy cells due to the damaged or shut down mitochondria in them. Assuming each human eukaryotic cell as a particle and the whole body as a quantum entangled system, is a new perspective into the description of the cancer disease and this link between theoretical physics and biological sciences in the field of cancer therapies can be a new insight into the cause, prevention and treatment of cancer. Additionally, this perspective admits the Lamarckian evolution in the understanding of the mentioned disease. We have introduced each human eukaryotic cell containing mitochondria as a QES, also, the whole body containing healthy and normal cells as a QES as well. The difference between the entropy of the healthy and cancer cells has been mentioned in this research as well. [Preview Abstract] |
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YP10.00019: Determinism, Muonium, Regge Beta Decay, Yang-Mills Unification, Anti-Matter Plasmas, and Endothermic Ordering Entropy Escape Quark Fusion Stephen Sharma Predestination is a philosophy attributed to eras of the past, however, deterministic geodesics generate Hamilton-Jacobi equations. Laplace and Poincar\'e believed, a sufficient intelligence predicts the universe. As such, the production of exotic materials, like a muon orbiting a proton, anti-hydrogen, and the DT plasma seem like tangible classical problems. This means that the uncertainty principle is neglected in the MHD, relativity, and Fokker-Planck relations. Extrapolating this analytic dissonance to new Regge theory, the beta decay is explained by a spectrum of rotational energy, non-negligible in the production of a Ferm-Curie deconvolution. Yang-Mills frequencies further angular corrections of an old theory. Mathematical tools that describe rotation, symmetry, abstract amplitude functions, and strings in the spacetime Riemann metric unify. Analysis leads to prime number distributions in Dirac’s gamma matrix dimensions generating the simplified standard model as the surface of a quantum observable. Unification simplifies expressions, helpful for analyzing turbulent motion. Unified physics promises a utpoia; fusion through endothermic quark ordering can be done in theory. [Preview Abstract] |
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YP10.00020: First Measurements of Multi-scale Density Fluctuations and \textbf{\textit{E}}x\textbf{\textit{B}} Velocity via Doppler Backscattering in the C-2W Field-Reversed Configuration M. Tuszewski, L. Schmitz, M. Beall, R. Smith, H. Gota, T. Roche, C. Lau, T. Tajima, M. Binderbauer An advanced multi-channel combined Doppler Backscattering (DBS) diagnostic has been installed at the C-2W Field-Reversed Configuration (FRC) device. First measurements of intermediate wavenumber density fluctuations 2$\le k_{\mathrm{tor}}\rho_{\mathrm{s}}\le $10 and \textbf{\textit{E}}x\textbf{\textit{B}} velocity in the FRC core plasma (outside the null field region) and in the scrape-off layer are presented. Plans and preparations for the first tests of Cross Polarization Scattering [1] (CPS, for the measurement of perpendicular magnetic field fluctuations from the DBS scattering volume) are also discussed. GENRAY ray tracing predicts that magnetic fluctuations with 2$\le k_{\mathrm{tor}}\rho _{\mathrm{s}}\le $ 30 can be accessed in the FRC core and scrape-off layer (SOL). DBS data from the previous C-2U FRC experiment [2] already show the absence of ion-scale density turbulence in the FRC core. Global gyrokinetic simulations attribute core stability to Finite Larmor radius effects, short fieldline connection length, and favorable magnetic field gradient. In contrast, multi-scale turbulence including short-scale electron modes has been observed in C-2U via DBS in the mirror-confined SOL plasma, also in agreement with global gyrokinetic simulations which predict unstable drift-interchange modes for $k_{\mathrm{tor}}\rho_{\mathrm{s}}\ge $1.5. [1] X.L. Zou et al., Phys. Rev. Lett. 75 1090-93 (1991); [2] L. Schmitz et al., Nature Comm. 7 13860 (2016). [Preview Abstract] |
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YP10.00021: Tomography System for Density Profile Reconstruction in HIT-SI3 and Ion Doppler Spectroscopy K.W. Lee, A.C. Hossack, C.J. Hansen, D.A. Sutherland A tomography system has been installed to assess the symmetry of spheromak plasma density in the HIT-SI3 spheromak experiment. The tomography diagnostic consists of four toroidal chord fans and three sets of three poloidal fans that provide 3D plasma emission information. Each fan expands from a wide-angle lens with130 degree field of view coupled to bundles of fiber optics. The light collected by the fiber optics is split into two paths, filtered at 668 nm and 728 nm, and imaged by a high-speed camera. Since the ratio of the 668/728 nm emission has a strong plasma density dependence within the range of typical HIT-SI3 plasma parameters, the 3D emissivity profiles constructed by inverting line-averaged emissivity along chords can be related to the plasma density profiles. The reconstruction of emissivity profiles constitutes a highly underdetermined and ill-posed inversion problem and the maximum entropy method was chosen to find the most physically informed solution. Additionally, a multi-chord ion Doppler spectroscopy system for measuring impurity ion velocity and temperature is presented. [Preview Abstract] |
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YP10.00022: Augmented Reality Visualization of EMPIRE Simulations for Transmedia Learning Elaine M Raybourn, Keith L Cartwright, Brad Carvey, Daniel Gomez, Chris Moore, Nick Roberds, Tim Pointon, Peggy Christenson We demonstrate how guiding principles from transmedia learning information visualization, and cross-reality were used to develop augmented reality (AR) visualizations of high-fidelity simulations of photoelectrically generated cavity plasma experiments. The simulation results are generated using EMPIRE, an electromagnetic plasma physics application being developed for exascale simulation on next-generation hardware architectures. Our effort focused on the use of augmented reality (AR) to facilitate a deeper understanding of scientific phenomena via transmedia learning, a scalable system of messages that represents a core experience that unfolds from the use of multiple media. we used AR to superimpose digital assets onto the real-world environment to facilitate understanding of complex information. We outline how we developed an iOS and Android augmented reality application from high-fidelity EMPIRE simulation results by using commercial technology such as Houdini, Unity game engine, Adobe Premiere, and the Wikitude SDK. Participants will take away a deeper understanding of the role of visualization in high performance computing from the perspectives of learning, productivity, and communication through our examples from simulations of x-ray driven cavity plasma experiments conducted on the Z Machine and at the National Ignition Facility (NIF). [Preview Abstract] |
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YP10.00023: Using Machine Learning to Automate Mesh Management for HYDRA Simulations Christopher Yang, Jay Salmonson, Christopher Young, Sujay Kazi, Joseph Koning, Jayson Peterson Multi-physics HYDRA simulations for inertial confinement fusion (ICF) experiments at the National Ignition Facility use mesh relaxation directives to manage the state of the arbitrary Lagrangian-Eulerian (ALE) mesh and prevent entanglement. Generating an effective meshing strategy throughout a full ICF laser-driven hohlraum simulation is a laborious process that to date must be done by hand. Machine learning techniques are well-suited to address this challenge. We take a supervised learning approach that uses semantic segmentation via DenseNet103 [1] to imitate existing, expert-labeled mesh management strategies for 2D hohlraum simulations. DenseNet103 achieves high (98.73\%) prediction accuracy on test data, and we demonstrate successful control over ALE mesh management in a HYDRA hohlraum simulation. We also investigate adversarial autoencoders for generating a smooth latent space inside the semantic segmentation algorithm, in preparation for fine-tuning the mesh management policy with reinforcement learning. Thus, this approach may be improved upon and extended to handle new use cases such as 3D hohlraum simulations. [1] S. Jégou et al. ``The One Hundred Layers Tiramisu: Fully Convolutional DenseNets for Semantic Segmentation.'' PROC CVPR IEEE (2017) [Preview Abstract] |
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YP10.00024: Simulations of the Direct Laser Acceleration of Electrons Including the Use of a Customized Field Solver and Quasi-3D Geometry Kyle Miller, Fei Li, Xinlu Xu, Nuno Lemos, Felicie Albert, Chan Joshi, Warren Mori There is interest in generating moderately relativistic electrons (10--100 MeV) to produce X-rays for the probing of hot, dense material. One way to produce such hot electrons involves using a \textunderscore high-intensity picosecond laser, which generates relativistic plasma waves and goes unstable due to self-modulational and Raman scattering instabilities. In this configuration, energetic electrons are generated due to a combination of plasma wakefield acceleration and direct laser acceleration (DLA). The electrons then radiate X-rays due to their betatron motion. Recent work has shown that much of the energy contribution to hot electrons can be from the DLA mechanism, but properly determining this contribution is challenging due to numerical issues found in most particle-in-cell codes. We present a customized finite-difference field solver designed to minimize errors in the dispersion relation of light waves in vacuum and to take into account the time-staggered electric and magnetic fields. Single-particle tests show that the new solver is much more accurate when compared to theory. We present preliminary results on the acceleration mechanisms of electrons for a variety of laser pulse durations, using both three-dimensional and quasi-3D simulation geometries, with and without the new solver. [Preview Abstract] |
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YP10.00025: \textit{Probing the Boiling Point of the Vacuum of Quantum Electrodynamics at the EU.XFEL} Ishay Pomerantz LUXE (Laser Und XFEL Experiment), is an experiment planned to be installed in Hamburg using the high-quality and high-energy beam of the European XFEL and a powerful laser. The scientific objective of the experiment is to study quantum electrodynamics in the regime of strong fields, close to and beyond the Schwinger critical field. Within a strong electromagnetic field, the vacuum itself is expected become unstable and spark with spontaneous creation of electron-positron pairs. This experimentally largely untested regime is relevant to a variety of phenomena in Nature, e.g. in the areas of astrophysics, collider physics or atomic physics. It is anticipated with the planned setup that the LUXE experiment will access values three times larger than the critical field, and pioneer this regime of quantum physics. I will report on the science case and the experimental setup, which requires in particular modifications to the European XFEL accelerator complex, the installation of a powerful laser with sophisticated diagnostics, and an array of precision detectors optimized to measure electrons, positrons and photons. [Preview Abstract] |
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YP10.00026: Cross phase of drift-resistive plasma fluctuations Chang-Bae Kim Knowledge of the cross phases between the fluctuations is crucial in the turbulent transport of the plasma particles and the thermal energy. The cross phase plays an important role in the determination of the turbulence level because the fluctuations in the drift plasma turbulence are driven by the turbulent fluxes across the plasma profiles. In the presentation the cross phase between the electrostatic potential and the electron density is analyzed based on the numerical simulations of the two-dimensional Hasegawa-Wakatani model. In the presence of the zonal flow $V$ (ZF) the cross phase $\delta$ is strongly distorted by the ZF. Where the flow curvature $V''$ (the gradient of the zonal vorticity) is positive, $\delta$ is reduced at the saturated state if the electron response is nearly adiabatic. Turbulence is localized where $V$ is in the direction of the electron diamagnetic drift and $V''>0$. The cross phase is found negative where the turbulence is weak. Results of two separate numerical simulations of ZF being either sinusoidally imposed or dynamically generated will be discussed at the presentation. [Preview Abstract] |
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YP10.00027: EMPIRE Simulation of the RKA Electron Beam in a Gas Cell Brandon Medina As part of a continued validation effort for Sandia's new plasma code, EMPIRE, we have modeled and are simulating the RKA beam experiment. Specifically, we have begun simulations of the RKA diode into the gas cell. The current EMPIRE (informal) validation effort is ultimately concerned with the electron-beam transport (e.g. electron-neutral chemistry) through an Ar-filled gas cell at various pressures from vacuum to \textasciitilde 1 Torr. In the current work, we will compare our simulations to CEA results and test a possible explanation for why the CEA/CESTA is seeing asymmetric burn-through on their cathode foil. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology {\&} Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. [Preview Abstract] |
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YP10.00028: Plasma collision in a gas atmosphere Sebastien Le Pape, laurent divol, gael huser, Joe Katz, Andreas Kemp, J. S. Ross, S. Wallace, S. Wilks Plasma collisions are present in a large range of conditions which impact the characteristics of the collision. We present a study on the impact of a gas atmosphere on the collision of two counter propagating plasmas (gold and carbon). Imaging optical Thomson scattering data of the plasma collision with and without helium in between have been obtained on the Omega laser facility. We observed the presence of gold ions across the entire field of view in the vacuum case. Once Helium is added, the two plasmas remain separated. The dramatic difference in ionic temperature is consistent with a reduction of the maximum flow velocity from M$=$7 to M$=$4 due to the presence of helium. This reduction of a factor 1.75 in peak velocity implies a reduction by a factor of \textasciitilde 10 of the mean free path of gold ions into ablated carbon. The presence a small amount of helium is enough to transition from an interpenetrating regime to a regime in better agreement with a hydrodynamic description of the system. [Preview Abstract] |
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YP10.00029: Long-gap pulse discharge in air at atmospheric pressure. Jiri Schmidt, Alexandr Frolov, Petr Hoffer, Karel Kolacek, Jaroslav Straus Nowadays experimental works show that not only lightning flashes in thunderstorms but also long high-voltage (HV) discharges in air under laboratory conditions generate high-energy radiation and particles. The processes in these types of discharges are not satisfactorily explained and are still the subject of research. We have designed and assembled an experimental device which helps us to investigate the time evolution of long HV discharges in the air. Our designed apparatus consists of oil insulated 8-stage Marx generator (pulse voltage up to 1.5 MV), water-filled pulse forming line which is connected by a spark gap to HV electric bushing. Firstly, basic measurements of voltage (based on capacitor-resistor divider) and current (by Pearson current monitor) were re-calibrated. In the next step, we have generated short gap discharges (from 5 up to 35 cm long). These discharges were observed optically by a digital photo camera with the suitable filter. Measurements of X-ray emission (with the help of scintillators and photomultipliers) have been in a progress as well. In this paper we will present a description of our experiment with long-gap laboratory HV discharge at atmospheric pressure and its recent results. [Preview Abstract] |
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YP10.00030: Measurement of Hot-spot Velocity and Ion Temperature in Inertial Confinement Fusion Implosions Using Fused-silica Cherenkov Detectors. Alastair Moore, Edward Hartouni, David Schlossberg, Mark Eckart, Cory Waltz, Michael Rubery, Gary Grim Uniform symmetric drive is critical to optimizing inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF). Drive imbalance can result in motion of the hot-spot and residual kinetic energy upon stagnation which degrades the implosion performance. At the NIF the neutron time-of-flight (nToF) detector suite has been upgraded to include fused-silica Cherenkov detectors on each of four collimated lines of sight. Cherenkov nToF detectors exceed the performance of traditional scintillators by providing an energy thresholded measurement of gamma rays emitted by the target and a short (sub-ns) instrument response function that reduces systematic uncertainties in analyzing the neutron spectrum. Measurements from cryogenic deuterium-tritium (DT)-layered implosion experiments are analyzed to obtain hot-spot velocity, ion temperature and fuel density via the down-scattered neutron spectrum. Results from a range of DT-layered implosions are presented and compared to independent measurements from existing scintillator nToF detectors. LLNL-ABS-786737 Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
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YP10.00031: Improved Convergence for the LoDestro Method at Marginal Stability Alex Friedman, Lynda L. LoDestro, Jeffrey B. Parker We present recent progress on a method for multiple-timescale coupling of global gyrokinetic simulations with a transport solver, to evolve a self-consistent temperature profile $T(x)$. This requires implicit advancement of the transport difference equation for $T$ over an interval $\Delta t$. The original LoDestro method [1] has been successfully employed with GENE microturbulence simulations via the Tango solver [2]. However, near marginal stability of the underlying turbulence model, the dependence of the turbulence-generated flux on $\nabla T$ becomes extremely stiff; in such cases, Tango-GENE studies confirm that strong under-relaxation of the iteration employed is needed, resulting in slow convergence. We have formulated and tested a revised, more robust iteration that (on a model problem) overcomes this difficulty and promises major savings in computational effort. The new technique and our results to date are presented. [1] A. Shestakov, L. L. LoDestro, et al., J. Comp. Phys. 185, 399 (2003). [2] J. B. Parker, L. L. LoDestro, D. Told, G. Merlo, L. F. Ricketson, A. Campos, F. Jenko and J. A. F. Hittinger, Nucl. Fusion 58, 054004 (2018). [Preview Abstract] |
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YP10.00032: Inferring the apparent ion-temperature from MagLIF implosions using a forward-fit technique Jedediah Styron, Gary Cooper, Carlos Ruiz, Gordon Chandler, Michael Mangan, Sara Pelka, Colin Weaver, Clark Highstrete, Jose Torres, Gary Whitlow A high-resolution neutron transport model has been developed in MCNP to simulate neutrons produced from MagLIF experiments conducted at Sandia National Laboratories' Z-Machine. Results of these simulations show that neutron interactions in the complex load hardware and bremsstrahlung shielding directly in the line-of-sight broaden the neutron time-of-flight signal, which can lead to an overestimation of the average ion-temperature by as much as 500 eV for nominal MagLIF conditions at the 9.5m detector location. A family of potential nToF signals at different source conditions were generated in MCNP and convolved with an instrument response function and compared to experimental data. Using this technique, it is feasible to infer the apparent ion-temperature, Be liner areal density and neutron yield from a single measurement. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 [Preview Abstract] |
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YP10.00033: Testing Charge-, Sign- and Energy-Dependence of Cosmic-Ray Solar Modulation with AMS-02 observations during cycle 24. Ian McKinnon, Ilias Cholis Our basic theoretical understanding of the sources of cosmic rays and their propagation through the interstellar medium is hindered by the Sun, that through the solar wind affects the observed cosmic-ray spectra.This effect is known as solar modulation. However recently released cosmic-ray data and publicly available measurements of the solar wind properties from ACS and the Wilcox observatory allow us to test the analytical modeling of the time-, charge- and energy-dependence of solar modulation. Using the well established time-dependence of solar modulation we will show clear evidence for its charge and energy dependence. [Preview Abstract] |
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YP10.00034: Plasma velocity profile during merging by using regularized reconstruction technique Tara Ahmadi, Hiroshi Tanabe, Yasushi Ono A standard method to derive local emission profile from the optical fibers line of sight is tomographic inversion. Such an inversion is burdensome due to its ill conditioned state and the dependency of reconstructed profile quality not only on measurement but also on the reconstruction algorithm used. To overcome these limitation, full Helmholtz decomposition theorem along with analytical (Max. Entropy duality with Max. Likelihood Estimation) and algebraic(linear iterative reconstruction and solution based regularization) reconstruction methods have been proposed to carry inverse reconstruction problem for TS-6 merging plasma. Combining these methods along with solution regularization method made it possible to obtain radial velocity profile from data received from multiple angles with high accuracy which is not in reach by other algorithms. This method showed good capacity in inversion problem,but needs improvement in solution regularization. The uniqueness of the achieved solution should be proved as the assumption regarding plasma incompressibility may affect the final solution. However, the evidence of existing another solution has not been observed TS-6 data test. After,gathered emission profile will be used as training for neural network for fusion tomography. [Preview Abstract] |
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YP10.00035: Tests of a Discontinuous Galerkin scheme for Hamiltonian systems in non-canonical coordinates Rupak Mukherjee, Noah Mandell, Ammar Hakim, Gregory W. Hammett A discontinuous Galerkin scheme for the solution of a general Hamiltonian system written in arbitrary non-canonical coordinates is presented. Examples of such systems are the Vlasov-Poisson equation, the incompressible Euler equations and the gyrokinetic equations. Our algorithm builds on a previous algorithm[1] by introducing an arbitrary coordinate transform in phase-space, with explicit appearance of coordinate metrics in the Poisson bracket operator. We show that a proper discretization of the metric, combined with a continuous representation of the Hamiltonian, leads to a scheme that conserves the total energy (in the time-continuous limit) exactly. We will show tests of the scheme in simpler 2D settings and outline potential extensions needed to solve the full electromagnetic gyrokinetic equations[2] in arbitrary, multi-block X-point geometries using field-aligned coordinates.\\ [1] A. Hakim, G. Hammett, E. Shi, N. Mandell, arxiv:1908.01814 [2] N. R. Mandell, A. Hakim, G. W. Hammett, M. Francisquez, arxiv:1908.05653 [Preview Abstract] |
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YP10.00036: Intense relativistic electron beam-plasma interactions and parameter estimation M.A. Jaworski, K.A. Schultz, M.E. Schulze Intense relativistic electron beam (IREB) propagation through plasmas is a common phenomenon with a range of applications from astrophysical gamma ray bursts, to inertial confinement fusion, to electron beam welding. Previous work indicates that IREB energy transfer transitions from collision-dominated processes at near-solid density, to a regime where plasma collective effects play a significant role[1]. In our experiments, we produce a plasma via isochoric heating of a thin, solid, high-Z target with an IREB. A simple expansion model is used to develop order-of-magnitude estimates for plasma parameters and evaluate instability growth rates within this plasma. Prototypical experiments on a molybdenum foil utilize visible imaging to characterize the plume and indicates nearly constant velocity expansion of several [mm/$\mu$s]. These measurements are an initial exploration of IREB transport in the transition from collision-dominated to collective-effects dominated phenomena. [1] C. Deutsch, \emph{et al.}, \emph{Phys. Rev. Lett.} \textbf{77} (1996) 2483. [Preview Abstract] |
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YP10.00037: A Kinetically Driven Magnetic Reconnection Laboratory Experiment Timothy Tharp A novel experiment is proposed to investigate magnetic reconnection in a laboratory plasma. Rather than quickly ramping currents through wires to induce magnetic reconnection, we will rapidly move a permanent magnet through a steady-state plasma in a configuration analogous to the astrophysical system of the Earth encountering the solar wind. The proposed experiments are capable of investigating the energy dissipated by magnetic reconnection as plasma parameters are varied, and may provide significant new insights into the role of boundary conditions in magnetic reconnection. [Preview Abstract] |
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YP10.00038: Supporting IMAS actors and the European Transport Solver in OMFIT O. Meneghini, S.P. Smith, J. Ferreira, Michele Romanelli, Stuart Henderson, Jeff Candy, Lang Lao The OMFIT framework [https://gafusion.github.io/OMFIT-source] and OMAS library [https://gafusion.github.io/omas] are used to facilitate the execution of the European Transport Solver (ETS) [https://wpcd-workflows.github.io/ets.html]. A distinguishing feature of ETS is that physics components exchange data between each other via ITER IMAS data structures, while the transport simulation itself is orchestrated by the Kepler workflow manager. The interface between OMFIT and ETS is mediated by the OMAS Python library, which simplifies the interface of Python codes and IMAS. In this scheme, OMFIT enables loading the experimental data of different devices into IMAS, and provides ETS with a convenient user interface to facilitate setting up and executing the simulation within Kepler. Since OMFIT can cast data in IMAS data structures independently of the experiment of origin, we were able to seamlessly carry out JET and DIII-D transport simulations in ETS. Importantly, this approach can be easily extended to execute any existing IMAS Python actors and Kepler workflows within OMFIT. Such developments illustrate how physicists can leverage the versatility of the OMFIT environment to drive the large set of Python IMAS actors that are being developed by EUROFUSION and the ITER organization. [Preview Abstract] |
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YP10.00039: Scaling Physics of Reconnection Heating and Acceleration in Tokamak Merging Experiments Yasushi Ono, H. Tanabe, S. Kamiya, H. Tanaka, Y. Cai, Q. H. Cao, X. Junguang, M. Gryaznevich, S. Usami, R. Horiuchi The high-power reconnection heating of merging tokamak plasma has been developed in TS-3, TS-4 and MAST experiments. This unique method is based on the promising scaling of ion heating energy that increases with squire of reconnecting magnetic field B\textunderscore rec. We studied mechanisms for this scaling of reconnection (ion) heating mainly using TS-3U (TS-6) experiment and PIC simulations and found the following features: (i) the ion heating energy is as high as \textasciitilde 40-50{\%} of poloidal magnetic energy of two merging tokamak plasmas, (ii) the ion heating energy is not affected by (guide) toroidal field B\textunderscore t$_{\mathrm{,}}$ in the region of B\textunderscore t/ B\textunderscore rec \textgreater 1 under two conditions: (a) compression of current sheet to the order of ion gyroradius and (b) full-isolation of the merging tokamak plasmas from coils and walls. The sheet compression to ion gyro radius was found to be a key condition to realize the fast reconnection as well as the high power ion heating consistent with the B\textunderscore rec\textasciicircum 2-scaling prediction. Under this condition, the ion heating energy is determined uniquely by B\textunderscore rec \textasciitilde B\textunderscore p not by B\textunderscore t in the conventional tokamak operation region: B\textunderscore t/ B\textunderscore rec \textgreater 1. This promising scaling realized ion temperature as high as 2.2keV in 2019 and is expected to realize the burning ion temperature \textgreater 10keV (under electron density n\textunderscore e\textasciitilde 1.5x10\textasciicircum 19$^{\mathrm{\thinspace }}$[m\textasciicircum -3]) just by increasing B\textunderscore rec over 0.6T. [Preview Abstract] |
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YP10.00040: Development of a QH-mode scenario on ASDEX Upgrade Eleonora Viezzer, Joerg Hobirk, Emilia Solano, Hendrik Meyer, Pilar Cano, Marco Cavedon, Diego Cruz, Mike Dunne, Javier Gonzalez, Tim Happel, Marc Maraschek, Antoine Merle, Theresa Wilks For future magnetic fusion devices, the mitigation or even full suppression of edge localized modes (ELMs) is required to avoid erosion of the divertor target plates from the heat and particle fluxes caused by a type-I ELM. The QH-mode has recently regained attention as alternative scenario as it is naturally ELM-free. The onset of the QH-mode is characterized by the edge harmonic oscillation (EHO) which increases the edge particle transport to allow natural stability against an ELM. Here we report on the development of the QH-mode in the all-metal AUG tokamak. The experiments were carried out in forward and reversed Ip/Bt. For the first time, low collisionality plasmas with up to 6 MW NBI heating were achieved in reversed field. In forward field, the most promising scenario has been identified in upper single null. Transient QH-mode phases up to 400ms have been obtained showing signatures of the EHO in various diagnostics. Analysis of the pedestal structure show that high ExB rotational shear was achieved at low density and high temperature, situating the pedestal close to the kink-peeling boundary. [Preview Abstract] |
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YP10.00041: Absolute Temperature Calculation Using a Multispectral Thermal Infrared Camera and n-Color TES Image Processing Benjamin Saute, Alexandrine Huot, Serge-Olivier-Adam Gnessougou, Martin Lariviere-Bastien Two-color pyrometry is a non-contact point temperature measurement technique that utilizes two distinct, closely-spaced narrowband filters to collect radiance measurements. The ratio of these radiance measurements is then used to compute the absolute temperature of the object without requiring prior knowledge of the material emissivity. Telops is developing an algorithm called n-color TES that extends two-color pyrometry principles to generate absolute temperature maps from multispectral thermal infrared imaging data. Processed image quality is highly dependent upon the use of appropriate spectral filters, with best results being observed from the use of two narrow, closely-spaced wavebands with no overlap in spectral range. Telops is working to extend this algorithm by incorporating radiance data from $n$-wavebands (up to 8) in order to optimize the accuracy of the absolute temperature values generated for each pixel. In this work, the Telops MS-M100k was used to collect in-band radiance (IBR) measurements on a flame-heated steel plate for use in n-color TES calculations. The MS-M100k is equipped with a fast-rotating filter wheel capable of 6000 rpm rotation which, when synchronized with camera acquisition, allows for collection of 8-channel thermal imagery at 100 fps per channel. The multispectral thermal images and n-color TES images are presented along with a discussion on initial attempts to characterize the accuracy of temperature values generated by n-color TES. [Preview Abstract] |
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YP10.00042: Plasma Potential Measurements Using an Emissive Probe in Diverse Plasmas. Amanda Ready, Douglass Endrizzi, Ken Flanagan, Cary Forest Making accurate plasma potential (V p) measurements is critical to the Wisconsin Plasma Physics Laboratory (WiPPL), which conducts a variety of plasma experiments. We present a simple yet robust emissive probe capable of making V p measurements in a diverse number of environments. This probe was tested with varying levels of Joule heating current, verifying that the probe makes accurate V p measurements. We will present the design of the probe, data verifying its emissive nature, measurements showing the probe collecting current from the plasma to bring it to the emissive point, and a cusp region scan of WiPPL's Plasma Couette Experiment (PCX).. [Preview Abstract] |
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YP10.00043: Assessment of the role of molecules in divertor plasma detachment for tokamak devices using the multi-fluid code UEDGE A. Holm, T. D. Rognlien, W. H. Meyer The importance of molecules for onset and degree of plasma detachment is demonstrated for a one-dimensional and a two-dimensional slab geometry. Plasma detachment, experimentally observed for $T<3$~eV [1], decreases the particle and heat fluxes incident on the divertor due to volumetric recombination. Molecular processes become relevant at temperatures relevant to detachment [2], and may result in sub-eV plasma temperatures, when electron-ion recombination become large. Equipartition of hydrogen ions and atoms with molecules cools the ions and atoms, and the decreased ion temperature diminishes the electron heating due to electron-ion thermal coupling. When the collisionality becomes sufficiently high, the ion temperature decreases below the electron temperature due to ion-molecule equipartition and ion-electron equipartition becomes an electron energy sink. It is shown that this electron energy sink results in sub-eV electron temperatures, yielding high electron-ion recombination rates and, subsequently, high degrees of plasma detachment not observed in simulations without molecules.\\\\\noindent[1] D. Eldon, et al., {\it Nucl.~Fusion} {\bf57}, 066039 (2017).\\\noindent[2] U. Fantz, et al., {\it J.~Nucl.~Mat.} {\bf290}, 367 (2001). [Preview Abstract] |
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YP10.00044: The Role of Spontaneous Parity-Time Symmetry Breaking in the Kelvin-Helmholtz Instability Yichen Fu, Hong Qin Parity-Time (PT) symmetry is an active research topic in both quantum and classical physics. It was recently pointed out [Qin et al., Physics of Plasmas 26, 032102 (2019)] as a general principle that conservative classical systems admit PT-symmetry, and become unstable when and only when PT-symmetry is broken spontaneously. In the present study, we demonstrate that this is indeed the case for the Kelvin-Helmholtz instability in a shear flow system with a smoothly varying flow profile. The nontrivial PT-symmetry of the system is identified, and numerically calculated eigenmodes show that the PT-symmetry is preserved for stable modes and spontaneously broken for unstable modes. The method of PT-symmetry physics enables new tools in the study of instabilities in classical fluids and plasmas. [Preview Abstract] |
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YP10.00045: Overcoming the laser wakefield acceleration dephasing limit using multiple driver pulses James Sadler, Christopher Arran, Hui Li, Kirk Flippo The electric field in laser-driven plasma wakefield acceleration is orders of magnitude higher than conventional radio-frequency cavities, but the energy gain is limited by dephasing between the ultra-relativistic electron bunch and the wakefield, which travels at the laser group velocity. We present a way to overcome this limit within a single plasma stage, by using a train of laser pulses in a modulated density profile. This creates a succession of acceleration sections, where the pulses' wakefields combine constructively, and non-resonant drift sections, where the wakefield disappears and the electrons rephase. In a two-dimensional particle-in-cell simulation, electrons were accelerated to over three times the energy obtained from a uniform plasma. Minimising laser depletion limits the scheme to sub-relativistic laser intensities. [Preview Abstract] |
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YP10.00046: Dispersion relations of parallel propagating electromagnetic waves in magnetized quantum electron plasmas with finite temperature Chang Ho Woo, Min Ho Woo, Cheong Rim Choi, Kyoung Wook Min In the present paper, parallel propagating electromagnetic waves in magnetized quantum electron plasma are discussed. The dispersion relations are derived using the quantum Vlasov equation for the Fermi Dirac distribution with finite temperature. It is shown that inclusion of finite temperature increases the group and phase velocities for the upper L and R waves whereas it decreases the velocities in the case of lower R waves. We present the dispersion relations in analytic forms for the long wavelength limit in both the low and high degeneracy cases, and compare them with numerical solutions. We also discuss the effect of finite temperature and the quantum mechanical effect on the Landau damping. [Preview Abstract] |
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YP10.00047: The new reconstruction method for velocity profile in TS6 device: Phantom and initial results Tara Ahmadi, Hiroshi Tanabe, Yasushi Ono The field related to computer tomography of experimental measurements needs constant progress as the popular methods like ME have serious flaws. To overcome these limitation, full Helmholtz’s decomposition theorem along with analytical (Maximum Fisher and max. likelihood) and algebraic(linear iterative reconstruction and solution based regularization) reconstruction methods have been proposed to carry inverse reconstruction problem for TS-6 merging plasma data to calculate velocity components of flow. Combining these methods along with solution regularization method made it possible to obtain radial velocity profile from data received from multiple angles with high accuracy which is not in reach by other algorithms. The Vr profile has maximum in the outflow jet which is predicted by simulation.The number of channels necessary for this method is several times less than the necessary number for analogous methods. Reconstructed phantom profile showed good capacity of proposed method for ring-like emissivity profile compared to Fourier and ME methods with exact numbers of channels. However, before using this method to analyze experimental data, a set of simulation data with well-known velocity profile will be used to double check the method. [Preview Abstract] |
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YP10.00048: Physics-Informed Neural Networks for Solving PDEs in Plasma Physics Nick McGreivy Physics Informed Neural Networks (PINNs) [1] have been recently introduced as a means of solving PDEs, where the solution is represented by a neural network. Partial derivatives are calculated using automatic differentiation, allowing the neural network to find the solution to the PDE without ever discretizing the solution space. Here, a PINN is used to solve a number of problems in plasma physics, thereby illustrating the strengths and weaknesses of this approach. [1] M. Raissi, P. Perdikaris, and G. E. Karniadakis. Physics informed deep learning (part I): Data-driven solutions of nonlinear partial differential equations. CoRR, abs/1711.10561, 2017. [Preview Abstract] |
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YP10.00049: Zettawatt-Equivalent Ultrashort Pulse Laser System (ZEUS) at the University of Michigan A. Maksimchuk, I. Jovanovic, G. Kalinchenko, C. Kuranz, J. Nees, A.G.R. Thomas, L. Willingale, K. Krushelnick The past two decades have witnessed the development of revolutionary light sources having the unprecedented ability to probe and control matter with atomic scale precision. The University of Michigan has been at the forefront in the development of this high-power laser technology, with the HERCULES laser presently operational at peak powers up to 500 TW. The ZEUS facility to be constructed will include a dual-beamline 3 PW laser system that will provide unique new capabilities. The name ZEUS (Zettawatt-Equivalent Ultrashort pulse laser System) refers to the interaction of a PW laser pulse colliding with a GeV energy electron beam generated by one of its two beamlines. This geometry provides the equivalent of a "Zettawatt" power laser interaction (10$^{\mathrm{21}}$ Watts) in the rest frame of the electron beam. It will consequently allow exploration of fundamental questions regarding non-linear quantum electrodynamics in relativistic plasmas and electron-positron pair production mechanisms. Further experiments enabled by this facility will include pump-probe experiments using femtosecond x-rays to probe material dynamics, the production of GeV ion beams, the exploration of vacuum polarization effects and relativistic astrophysical shocks. Once completed, the ZEUS laser system will be the highest-power laser system in the US and will be a user facility for US scientists and wider international research community. [Preview Abstract] |
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YP10.00050: Verification of the delta-f kinetic electron physics in XGC pallavi trivedi, Julien Dominski, Michael cole, alexey mishchenko, Stephan Brunner, Laurent Villard, Choong-Seock Chang The High-Fidelity Whole Device Modeling project aims at delivering a core-edge coupled simulation including kinetic electron physics. XGC and GENE have been cross-verified for electrostatic ion temperature gradient instabilities with adiabatic electrons [Merlo et al Phys. Plasmas 25, 062308 (2018)]. In the present work, XGC kinetic electron physics will be cross-verified against the gyrokinetic PIC code ORB5. Indeed, ORB5 and GENE have already been specifically benchmarked with kinetic electrons [J. Dominski, et al. Phys. Plasma 2017]. Moreover, ORB5 and XGC being PIC codes, a particular care will be given to the particle sampling noise problem. [Preview Abstract] |
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YP10.00051: Current Sheet Structure in Anti-Parallel Driven Magnetic Reconnection Chio Cheng, Shizuo Inoue, Yasushi Ono, Hiroshi Tanabe, Ritoku Horiuchi Solutions of the particle dynamics, the density profiles and flow structures of electrons and ions in the reconnecting current sheet during quasi-steady phase of anti-parallel driven magnetic reconnection are presented. The theory provides understanding of the particle dynamics and heating/acceleration processes as observed in the PIC simulations. In particular, the increase of ion temperature is due to the electrostatic potential drop which is proportional to the square of the upstream Alfven velocity.. [Preview Abstract] |
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YP10.00052: Single-shot ultrafast visualization of plasma dynamics and nonlinear index of refraction in flexible glass using frequency domain holography Dennis Dempsey, Garima Nagar, Christopher Renskers, Rostislav Grynko, James Sutherland, Bonggu Shim We measure the nonlinear index of refraction (n$_2$) and investigate plasma dynamics in flexible Corning\textsuperscript{\textregistered} Willow\textsuperscript{\textregistered} Glass using single-shot Frequency Domain Holography (FDH) [1,2]. Flexible glass has received a lot of attention recently due to various applications such as 3-D photonics [3] and wearable devices. Femtosecond laser micromachining (FLM) is a viable tool to fabricate these devices because of minimal thermal effects and thus enables fabrication of small and clean 3-D structures. To control and understand the underlying dynamics of FLM, ultrafast visualization of plasma and optical Kerr effect is important. FDH is a robust femtosecond time-resolved technique in which chirped reference and probe pulses centered at 404 nm are used to measure and visualize the plasma and Kerr effect produced by an intense, ultrashort pump pulse centered at 808 nm. Using FDH, we study laser-matter interactions in Willow Glass and measure its n$_2$ to be 3.41$\pm$0.08$\times 10^{-16}$cm$^2$/W and visualize the plasma dynamics. [1] S. P. Le Blanc et al., Opt. Lett. 56, 764-766 (2000). [2] Kim et al., APL, 88 4124-4126 (2002). [3] S. Huang et. al., OFC 1-3 (2014). [Preview Abstract] |
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YP10.00053: Global ion heating characteristics of magnetic reconnection during two tokamak plasma merging experiment Haruaki Tanaka, Hiroshi Tanabe, Tara Ahmadi, Qinnghong Cao, Yasushi Ono The global and fine structures of ion temperature have been studied during magnetic reconnection of two high-guide-field merging tokamak plasmas: in TS-6 merging experiment. The new extensive/high-resolution ion Doppler measurement enables us to measure the global ion temperature profile of entire magnetic flux tube. In the past, the ion heating was measured just around current sheet. However, we recently found the negative electrostatic potential well exists globally in the whole downstream area of the two merging tokamak plasmas. We measured the global characteristics of ion heating in the merging tokamak area using Ar and H gases. In the case of Ar gas, Ar ions are energized up to 200eV prevailing around the whole downstream area, suggesting ion acceleration by negative potential well in global downstream region in sharp contrast with our previous results. In the case of H gas, H ions are heated in global region similarly but the external compression force cannot compress the current sheet to the order of its small Larmor radius unlike the Ar case, losing a chance to trigger fast reconnection. Its slow reconnection causes its ion heating power much lower than the Ar case. [Preview Abstract] |
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YP10.00054: Hybrid Fission-Assisted Fusion Dense Plasma Focus (DPF) For Space Applications Paul Stockett, Robert Bean, Chan Choi Engineering feasibility for a manned mission to Mars with a dense plasma focus (DPF) had been studied earlier [1]. The current work seeks to investigate the use of a fission-powered magnetic fusion thruster, dense plasma focus device, with the emphasis on creating a very near-term propulsion system, by utilizing present-day technology and adapting methods of nuclear electric and nuclear fusion propulsion. When analyzing a new mission with a critical time of flight for a manned mission, a porkchop plot [2] was created to depict the various delta-V's necessary to complete the mission in a set period of time. The derived delta-V requirements along with the reference thrust-to-weight ratio provided a target performance which was assessed through numerical simulation of the fusion reactions for the fission-assisted fusion propulsion system. The fission-assisted propulsion system for DPF with D-T and D-$^{\mathrm{3}}$He fuels demonstrates near-term solutions with the thrust-to-weight ratio greater than a reference value, 0.2, along with extended specific impulse. \\ $[1]$. Choi, C. K., ``Engineering Considerations for the Self-Energizing Magnetoplasmadynamic (MPD)-Type Fusion Plasma Thruster,'' Tech. Rep. PL-TR-91-3087, Purdue Univ., Lafayette, IN. School of Nuclear Engineering, February 1992. \\ $[2]$. Juan Luis Gonzalo, Universidad Polit\'{e}cnica de Madrid (Technical University of Madrid) [Preview Abstract] |
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YP10.00055: Simple and accurate impact-excitation cross-sections including plasma density effects Jean-Christophe Pain, Djamel Benredjem We propose a simple and accurate approach for the computation of the electron-impact excitation (EIE) cross-section in the Plane Wave Born (PWB) approximation. The formalism relies on the screened hydrogenic model. The generalized oscillator strength involved in the collision strength is expressed in terms of integrals which can be calculated analytically. In order to remedy the fact that the PWB approximation is not correct at low energy (near threshold), we also investigate the accuracy of different correcting factors (Elwert-Sommerfeld, Cowan-Robb, Brookes and Kilcrease). Finally, we study the impact of plasma density effects (such as ionization potential depression) of the EIE cross-section, through the inclusion of energy shifts due to electrons. For that purpose, a new expression of the electronic shift is proposed and compared to other formulas recently published by Li et al. [Preview Abstract] |
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YP10.00056: Computing the shape gradient of coil complexity with respect to the plasma boundary with an adjoint method Arthur Carlton-Jones, Elizabeth Paul, William Dorland A major challenge associated with the stellarator concept is obtaining coils which can produce the desired configuration. Coil complexity metrics can be obtained from REGCOIL, which computes coil shapes using a linear least squares method based on a current potential approximation. We extend REGCOIL to compute derivatives of the objective function with respect to parameters describing the boundary. We represent the surface using a single Fourier series to describe the radial distance from an axis. This representation is advantageous over the VMEC representation, as it only requires a single cosine series rather than a sine and cosine series. It also uses a uniquely defined poloidal angle, which eliminates a null space in the optimization. When computing the derivatives, the adjoint method is used to obtain analytic derivatives. Rather than solving the linear least-squares system for every Fourier amplitude, it is only necessary to do this twice. This results in low computational cost and elimination of noise in comparison with finite-differences. These derivatives are used to obtain a shape gradient of the objective function, which describes the sensitivity to perturbations in the plasma shape. This can be used to optimize the plasma boundary to obtain simpler coils. [Preview Abstract] |
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YP10.00057: Improving thrust density of electrohydrodynamic propulsion michael thompson, Mubarak Mujawar Dielectric fluids may be accelerated with the electrostatic forces generated during controlled electrical discharge. Charged particles collide with molecules of the ambient fluid and propel them along the electric field generated between two opposite sources of electric potential. Electrohydrodynamic (EHD) thrusters capitalize on this phenomenon by linearizing the flow of propelled molecules. In this work the performance of single-stage thrusters with wire-to-cylinder and ring-to-cylinder electrode geometries were characterized. Extremely high thrust-to-power ratios of 20 N / KW have been achieved making the technology a viable form of atmospheric propulsion for small aircraft, however, low achieved thrust densities of approximately 10 N / m\texttwosuperior means that compact propulsion systems are not yet feasible. Multi-staged thrusters that add intermediary electrodes in order to ``stack'' thrusters are also considered in order to improve thrust density. Emitter-to-collector electrode radius ratios are tested for improved thrust density performance. Results indicate that increased thrust density can be achieved by decreasing the emitter-to-collector ratio at the cost of thrust-to-power efficiency. [Preview Abstract] |
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YP10.00058: Characterization of the collisional transport of a high-$Z$ impurity in a Wendelstein 7-X Electron Cyclotron Resonance Heated plasma Albert Moll\'en, Novimir A. Pablant, Peter Traverso, H{\aa}kan M. Smith, Andreas Langenberg, Thomas Wegner, Benedikt Geiger, Rainer Burhenn, Golo Fuchert, Sergey Bozhenkov, Hannes Damm, Ekkehard Pasch, Jos\'e Manuel Garc\'ia-Rega\~na, Jos\'e Luis Velasco, Stefan Buller A concern for stellarators is the central accumulation of high-$Z$ impurities driven by the radial electric field, expected to point inwards at reactor relevant conditions. Here we study the radial transport of tracer Ar16+ impurities in an ECRH plasma from the last campaign of the W7-X stellarator [Klinger et al. Nucl. Fusion 59 (2019) 112004], and compare results from collisional transport calculations to experimental values inferred from X-ray Imaging Crystal Spectrometer measurements. The calculations are performed with three radially local drift-kinetic equation solvers, SFINCS [Landreman et al. Phys. Plasmas 21 (2014) 042503], EUTERPE [Rega\~na et al. Nucl. Fusion 57 (2017) 056004] and KNOSOS [Velasco et al. arXiv:1908.11615]. These tools include effects such as advanced collision operators and potential variations along flux-surfaces which can be important when studying high-$Z$ impurities. We find that the radial collisional transport of Ar16+ is dominated by convection, and that the collisional transport can at most account for $\sim$10\% of the observed transport. [Preview Abstract] |
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YP10.00059: Acceleration of low-divergence quasi-mono-energetic electron bunches to MeV-scale energies at 1 kHz with few-cycle laser pulses Fatholah Salehi, Manh Le, Luke Pascale, Howard Milchberg We demonstrate acceleration of quasi monoenergetic electron bunches with a small divergence angle to MeV-scale energies at 1 kHz repetition rate using laser pulses with \textasciitilde 5fs duration and \textasciitilde 2.5mJ energy focused on a near-critical density gas target. Our previous experiments using 30fs laser pulses showed that using a near-critical density gas jet lowers the critical power for relativistic self-focusing sufficiently to enable MeV-scale electron acceleration using a high repetition rate laser system with mJ-scale pulse energy.................[1]. Those electron bunches, accelerated in the self-modulated wakefield regime, had a large energy spread and divergence angle. Using few cycle laser pulses, generated through a hollow core fiber as the drive pulse and operating in bubble regime led to quasi-mono-energetic beams with smaller divergence angle and varying shot to shot stability of the beam pointing depending on the laser beam focusing geometry.....[2]. In this work, employing supersonic hydrogen jet targets with sharp boundaries, along with the 5fs drive pulses, we accelerate quasi monoenergetic electron bunches with superior energy spread, transverse beam profile, and pointing stability. [1] F. Salehi, A. J. Goers, G. A. Hine, L. Feder, D. Kuk, B. Miao, D. Woodbury, K. Y. Kim, and H. M. Milchberg, Opt. Lett. \textbf{42}, 215 (2017). [2] F. Salehi, High Repetition Rate Laser-Driven Electron Acceleration to Mega-Electron-Volt Energies, University of Maryland College Park, 2019. [Preview Abstract] |
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YP10.00060: Spectroscopic Investigations of Power Flow Plasmas on the Z-Machine at Sandia National Laboratories Mark Johnston, Sonal Patel, George Laity, Michael Cuneo, R. Doron, E. Stambulchik, V. Bernshtam, Y. Maron Investigations are underway to study plasmas formed in the power flow region of the Z-Machine at Sandia National Laboratories. High current densities (MA/cm\textasciicircum 2) during a 100nsec pulse, rapidly heat electrode surfaces, desorbing contaminants and entrained gases. These species form a dense (10\textasciicircum 19 cm\textasciicircum -3) surface plasma layer composed of neutrals and low charge state ions. Ions that get outside of this layer are subject to MV/cm electric fields, can cross the A- K vacuum gap, and carry current away from the load. Steaked visible spectroscopy using multifiber arrays allow for time and space resolved measurements of the plasma boundary region. The addition of surface dopants such as magnesium and lithium provide a means of measuring localized electric and magnetic fields near the boundary based on Zeeman and Stark affected lineshapes [1]. Data is analyzed using detailed, time-dependent, collisional-radiative and radiation transport modeling. [1] S. Biswas, M.D. Johnston, \textit{et. al}., ``Shielding of the Azimuthal Magnetic Field by the Anode Plasma in a Relativistic Self-Magnetic-Pinch Diode,'' Phys. of Plasmas, 25, 113102 (2018). [Preview Abstract] |
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YP10.00061: Initial results from shattered pellet injection disruption mitigation research on JET L.R. Baylor A Shattered Pellet Injector system has been installed on JET as a collaboration between the DOE, ITER Organization, and Euratom. The system has become operational in the present JET C38 campaign and is being used to investigate mitigation of disruption thermal and EM loads, radiation asymmetry during thermal mitigation, and runaway electron (RE) formation and dissipation. The system has capabilities to inject pellets of D2 and neon mixtures or argon. Scans of pellet neon content show possible saturation of radiated power above 50{\%} and peak power levels above 4 GW. The dissipation of RE current has been observed with Ar and Ne injection. Highlights of results will be presented. *See the author list of~E. Joffrin \textit{et al} 2019 \textit{Nucl. Fusion} 59 112021. Work supported by the US DOE under contract DE-AC05-00OR22725 and by the ITER Organization (TA C18TD38FU) and carried out within the framework of the EUROfusion Consortium, receiving funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. [Preview Abstract] |
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YP10.00062: Statistical Description of Merging Magnetic Islands David Wu, Muni Zhou, Nuno Loureiro, Dmitri Uzdensky The physical picture of interacting magnetic islands provide a useful paradigm for certain plasma dynamics in a variety of physical environments, such as the solar corona, heliosheath and the Earth’s magnetosphere. The dynamics of magnetic islands has been treated with a statistical approach by previous works, where the evolution of the island distribution function in the phase space of islands characteristic properties is governed by an integrodifferential equation. In this work, we take a similar approach to study the inverse energy transfer through the coalescence of magnetic islands in 2D, enabled by magnetic reconnection. An island kinetic equation is derived with a special collisional integral to incorporate the physics of merging behavior. The numerical solution of our island kinetic equation provides the evolution of the island distribution functions. The time evolution of important quantities such as the magnetic energy, energy integral scale and number of islands agrees with our simplified analytical prediction. Properties of the distribution function and the magnetic energy spectrum are also studied. [Preview Abstract] |
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YP10.00063: Measurement of sub-micron density gradient plasma scale length and collisionality evolution: Toward plasma optic performance optimization Graeme Scott A renewed interest in the plasma mirror (PM) is evident from the wealth of recent investigations published in the literature and as the PM's repertoire of applications evolves, the matter of their efficiency becomes increasingly important, and in our recent work we demonstrated how the traditionally lossy optical component can be optimized to be 96 {\%} reflective by introducing a finite density scale length to its surface. A recently developed technique will be presented where we simultaneously measure the sub-micron density scale length evolution as well as the collisionality and temperature of the plasma, and correlate this with the PM optical performance. This is a generally useful experimental technique in itself, since these parameters are challenging to experimentally measure in the vicinity of the critical surface. Tracking the evolution of the parameters over tens of picoseconds leads us to novel conclusions on the plasma composition and gives insight into the kinematic plasma expansion physics. This provides avenues for investigation of further plasma optic optimization techniques relevant to multipicosecond lasers, which is of particular interest in the context of multi-kiloJoule relativistic laser plasma interactions, as many such systems come online across the world. [Preview Abstract] |
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YP10.00064: Effect of RMPs on neutral fueling and exhaust in MAST Kurt Flesch, James Harrison, Andrew Kirk, Oliver Schmitz, Ian Waters The application of resonant magnetic perturbations (RMPs) at MAST has been shown to cause density pump-out during discharges that have a particular MHD response. This occurs in L-mode as well as H-mode discharges, which also show edge localized mode (ELM) mitigation. An analysis of the changes in fueling and exhaust show that RMPs cause an increase in total fueling to the plasma, from D-alpha emission measurements, but also a significant drop in particle confinement time, from a 0-D single reservoir particle balance of the main ion species, such that there is a net particle pump-out. In order to more accurately calculate this change in recycling, a more detailed analysis of the measured D-alpha emission was done. Synthetic diagnostics were created using EMC3-EIRENE modeling results of these discharges as a plasma source for the ray tracing code CHERAB. The generated synthetic images were compared to the corresponding absolutely calibrated images from experiment to better constrain the experimental measurements. Results still show an increase in recycling flux during RMPs, but with a lessened effect, causing the calculated confinement time to be even lower. [Preview Abstract] |
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YP10.00065: New methods for suppressing numerical Cherenkov instabilities in relativistic particle-in-cell simulations Yingchao Lu, Patrick Kilian, Chengkun Huang, Fan Guo, Hui Li, Edison Liang We present two novel methods for suppressing numerical Cherenkov instabilities in relativistic particle-in-cell simulations The WT scheme, a piecewise polynomial force interpolation scheme with time-step dependency, is proposed to remove the lowest order numerical Cherenkov instability (NCI) growth rate for arbitrary time steps allowed by the Courant condition. While NCI from higher order resonances is still present, the numerical tests show that for smaller time steps, the numerical instability grows much slower than using the optimal time step found in previous studies. \textunderscore A semi-implicit Maxwell solver derived from finite element method with O(N) computing cost is developed to improve the numerical dispersion properties [Preview Abstract] |
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YP10.00066: \textunderscore Fermi-type particle acceleration from magnetic reconnection at the termination shock of relativistic striped wind Yingchao Lu, Fan Guo, Hui Li, Edison Liang \textunderscore The termination shock of relativistic striped wind of obliquely rotating pulsars compresses the Poynting-flux-dominated flow and drives magnetic reconnection. Magnetic reconnection at the termination shock is highly efficient at converting magnetic energy into thermal energy and accelerating particles to high energies. By carrying out particle-in-cell simulations, we find that fermi-type mechanisms dominate the particle acceleration and power law formation. The maximum energy for electrons and positrons can reach hundreds of TeV if the wind has a Lorentz factor approximately 10\textasciicircum 6. [Preview Abstract] |
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YP10.00067: Plasmas in supercritical fluid with densely populated clusters Gunsu Yun, Seungtaek Lee, Juho Lee, Seok-yong Jeong, Young-uk Kim, Jeong-Young Ji In supercritical fluid (SCF) with dense population of stable clusters ($\sim 1000 \mbox{ mm}^{-3}$; mean size $\sim$ 200 nm)$^a$, elongated plasmas are produced along the optical axis of laser pulse (532 nm, 6 ns, 400 mJ, peak intensity $\sim 1$ TW/cm$^2$). The plasma has a strong afterglow with the lifetime up to 1 $\mu$s, increasing with the number density of clusters. For argon SCF plasmas, the electron temperature and density estimated from continuum emission spectra are $\sim 1$ eV and $\sim 10^{21} \mbox{cm}^{-3}$, respectively, corresponding to a high Coulomb coupling constant of the order of unity. The radial diffusion is weak, smaller than the diffusion length predicted by the one-component plasma theory for moderate to strong Coulomb coupling$^b$. These observations suggest that the presence of clusters strongly affects the particle and energy transport processes. $^a$S.T. Lee et al., APS Gaseous Electronics Conf.(2019). $^b$Daligault, Phys. Rev. Lett. 108 (2012). [Preview Abstract] |
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YP10.00068: Generation of Long Plasma Waveguides by Optical Field Ionization with High Order Bessel Beams Linus Feder, Bo Miao, Jaron Shrock, Mike Tomlinson, Harry Corin, Howard Milchberg Plasma waveguides will likely be an integral part of any future GeV-TeV laser-driven accelerators. In past work, plasma waveguides have been generated by laser-heated plasma hydrodynamic expansion [1] or capillary discharges [2]. In the former case, laser plasma heating has been produced either by inverse bremsstrahlung [1] or by excess electron kinetic energy from tunneling ionization [3,4]. We present recent experimental results demonstrating guiding over at least 10 cm in laser-generated plasma waveguides that do not mainly depend on hydrodynamic expansion for their formation. We show how a two-pulse Bessel beam scheme which uses an ultrashort J$_{\mathrm{0}}$ pulse followed by a higher order J$_{\mathrm{n}}$ pulse can generate a hydrogen plasma waveguide with an optimal refractive index structure. In addition to guiding results, we present femtosecond interferometry measurements of the waveguide generation and evolution and longitudinal measurements of the Bessel beam-hydrogen target interaction. [1] C. G. Durfee III, et al, Development of a plasma waveguide for high intensity laser pulses, Physical Review E 51,2368 (1995) [2] Y Erlich,et al,Guiding of High Intensity Laser Pulses in Straight and Curved Plasma Channel Experiments,Phys. Rev. Lett.~77, 4186 [3] Lemos,et al. Guiding of laser pulses in plasma waveguides created by linearly-polarized femtosecond laser pulses. Scientific Reports. 8. 10.1038 [4] R. J. Shalloo, et al, Low-density hydrodynamic optical-field-ionized plasma channels generated with an axicon lens, Phys. Rev. Accel. Beams~22, 041302 [Preview Abstract] |
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YP10.00069: Anisotropic diffusion of 2D superparamagnetic dusty plasma liquids. Fang Yang, Songfen Liu, Wei Kong The diffusion of two-dimensional (2D) superparamagnetic dust grains interacting via both Yukawa and dipole interactions is investigated based on the Langevin dynamics simulation. The magnetic dipole moment, induced by the external magnetic field, is tilted with respect to the 2D layer. It is demonstrated that there exist anisotropic diffusions in the liquid-like state, and the anisotropic diffusions are determined to be the normal type. The anisotropy degree depends on the system temperature and tilt angle of the magnetic dipole, particularly for the latter. Relevance between anisotropic diffusion and pairwise interaction potential energy are examined. The anisotropic oscillations of the system are presented as well. [Preview Abstract] |
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YP10.00070: Simulation on parametric decay instability excited by oscillating pump near lower hybrid frequency. Wei Kong, Xueyi Wang, Yu Lin, Liu Chen Decay instability of lower hybrid waves is important in plasma heating. Simulation of the instability must include both electron and ion kinetics with real mass ratio. In this work, the gyrokinetic electron and fully kinetic ion (GeFi) particle simulation model is used to study the parametric instabilities in uniform magnetized plasmas. The pump electric field near the lower hybrid frequency is treated in the dipole approximation. Three types of parametric decay processes, including the purely growing modulational instability, the non-resonant decay instability, and the resonant decay instability are obtained. Dependences of the parametric growth rates on wavenumber, pump strength and pump frequency are systematically investigated. The simulation results are compared with the predictions of existing linear theories. Effects of electron-to-ion temperature ratio on the non-resonant and resonant decays are also discussed. [Preview Abstract] |
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YP10.00071: Heating of the Compact X-ray Corona in Seyfert Galaxies Yajie Yuan, Anatoly Spitkovsky, Roger Blandford, Dan Wilkins There is observational evidence that the X-ray continuum source that creates the broad fluorescent emission lines in some Seyfert Galaxies may be compact and located at a few gravitational radii above the black hole. We consider the possibility that the compact X-ray emitting source may be powered by small scale flux tubes near the black hole that are attached to the orbiting accretion disk. Using three dimensional, time dependent force-free simulations, we find that the field linking the black hole and the disk can get twisted up by the differential rotation to try to form a magnetic tower. When the confinement provided by the field from the outer disk is strong, the forming magnetic tower can quickly become kink unstable, which leads to continuous reconnection and dissipates most of the extracted rotational energy relatively close to the black hole. Such a process may be able to heat up the plasma and produce strong X-ray emission. We estimate the energy dissipation rate and discuss its astrophysical implications. [Preview Abstract] |
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