Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session ZP07: Poster Session: Supplemental Posters (9:30am - 12:30pm)On Demand
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ZP07.00001: A Study on the Increase in Interest and Positive Perception of STEM Fields Through Student Engagement Jorge Carmona Reyes, Shanna Attai, Rob Altmann, John Davis, Judy York, Kerri Ranney, Emma Beaird, Truell Hyde Over the past two decades, workforce development within the U.S. Fusion program has been an ongoing issue. One of the long-term strategies for addressing this concern as stated in the final report titled `Fusion in the Era of Burning Plasma Studies: Workforce Planning for 2004 to 2014,' recommended implementation of outreach programs at all educational levels with the goal to attract a diverse group of students into pursuing a career in fusion science and engineering [Thomas et al, 2003]. Although multiple interventions have been created in an attempt to achieve this goal, they have yet to yield the desired outcome. The approach presented here is based on student engagement at the elementary school level. Because student engagement is dependent on both time and subject, proper measurement in which it changes through any intervention is challenging. This presentation will describe a new measuring tool developed by the authors that can quantify student engagement changes. The long-term goal of this study is to understand how such constructs change and how they depend on the STEM subject explored so that interventions can be more effective in order to increase college STEM classroom sizes. [Preview Abstract] |
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ZP07.00002: Inference of Experimental Impurity Transport and Impact of Charge Exchange Processes on Forward Modeling Francesco Sciortino, Nathan T. Howard, Earl S. Marmar, Tomáš Odstrčil, Jerry W. Hughes, Pablo Rodriguez-Fernandez, John E. Rice, Matthew L. Reinke We present a fully-Bayesian approach for the inference of radial profiles of experimental impurity transport coefficients [Sciortino et al. 2020, submitted] and examine the effect of charge exchange processes with background neutrals. Our forward model for laser blow-off injections of calcium (Z$=$20) is based on the pySTRAHL code, optimized for iterations in high-performance computing environments. Alcator C-Mod offers opportunities to examine high-performance cases where the only source of deuterium neutrals is due to wall recycling, thus avoiding complex modeling of neutral beams. Even in the C-Mod high-density, high neutral edge opacity conditions, charge exchange is demonstrated to be remarkably important in the outer confined regions. We present results from multiple operating regimes and compare to neoclassical, gyro-fluid and gyrokinetic models (both quasi-linear and non-linear) in each case, demonstrating quantitative agreement in diffusion profiles. Convection can be matched under certain assumptions, but is more weakly constrained; in particular, inferred pedestal profiles can be significantly modified by the inclusion of charge exchange in forward modeling. [Preview Abstract] |
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ZP07.00003: Laser-Ion Lens and Accelerator Tianhong Wang, Vladimir Khudik, Gennady Shvets Generation of highly collimated monoenergetic relativistic ion beams is one of the most challenging and promising areas in ultra-intense laser-matter interactions. We address this challenge by introducing the concept of laser-ion lensing and acceleration (LILA). Using a simple analogy with a gradient-index lens, we demonstrate that simultaneous focusing and acceleration of ions are accomplished by illuminating a shaped solid-density target by laser pulse at $10^{22}W/cm^2$ intensity and using the radiation pressure to deform/focus the target into a cubic micron spot. We show that the LILA process can be approximated using a simple deformable mirror model, and the analytical solution of the model will be provided and compared with 3D particle-in-cell simulations. Extensive scans of the laser and target parameters in 3D PIC simulations identify the stable propagation regime where the Rayleigh-Taylor (RT)-like instability is suppressed. Stable focusing is found at different laser powers (from few- to multi-petawatt), different laser formats (planar or gaussian), and different target compositions (from simple hydrogen target to two-ion-species target). Depending on those parameters, a wide range of ion kinetic energies – from 200MeV to 750MeV – can be obtained. [Preview Abstract] |
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ZP07.00004: Comparison of Edge Turbulence Characteristics Between DIII-D and C-Mod Simulations with XGC1 I Keramidas Charidakos, J.R. Myra, S. Ku, R.M. Churchill, R. Hager, C.S. Chang, S.E. Parker Processes taking place at the edge region of tokamaks govern the interaction of hot plasma with the vessel walls. Numerical modeling of the edge attempts to elucidate interactions between neoclassical drifts, turbulence and flows that control the SOL region. Here, we present post-processing analysis of simulations from the gyrokinetic code XGC1, comparing edge turbulence from a simulation of DIII-D against one of C-Mod. We find that the equilibrium $E \times B$ flux across the separatrix has a similar poloidal pattern in both discharges which can be explained by magnetic drifts and trapped ion excursions. Collisionality is noted to play a major role in that it prevents local charge accumulations from having global effects in C-Mod. In both cases, turbulent electron heat flux is higher than the ion one. We identify turbulent frequencies and growth rates of the dominant mode in both simulations. In C-Mod, these numbers point to the presence of a drift wave. In DIII-D, linear simulations with Gene reveal a trapped electron mode. Amplitude distributions of blobs are in agreement with experimental observations. Size distributions are consistent with the fact that most blobs are not connecting to the divertors and suggest that they are generated by the shearing of the turbulent modes. [Preview Abstract] |
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ZP07.00005: A Model for the Ion Velocity Distribution at a Target in a Grazing-Angle Magnetic Field Alessandro Geraldini Ions in the vicinity of a planar target are typically accelerated towards the target in a thin boundary layer, known as the Debye sheath, whose thickness is a few Debye lengths. Moreover, in fusion devices, where the magnetic field typically reaches divertor targets at grazing angles, the electric field distorts the approaching Larmor orbits at distances of a few ion sound gyro-radii from the target. If the Debye length is much smaller than the ion sound gyro-radius, the region where ion orbits are distorted is quasineutral and known as the magnetic presheath. The effect of the magnetic presheath on the velocity distribution of ions reaching the target is non-trivial, but crucial to calculate sputtering rates. A model for the ion distribution function reaching the target that includes the effect of gyro-orbit distortion is presented. Electrons are assumed to be adiabatic, with a negligible gyro-radius. The model ion distribution function is compared to numerical solutions of the magnetic presheath and Debye sheath, showing good agreement for large ion temperature. Important features such as the average angle of incidence and approximate shape of the energy-angle distribution are captured by the model also when the ion and electron temperatures are comparable. [Preview Abstract] |
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ZP07.00006: Design of a Permanent Magnet Stellarator Caoxiang Zhu, Kenneth Hammond, David Gates Non-planar coils are the most complicated and expensive part of a stellarator. Permanent magnets provide a novel method to produce optimized stellarator configurations using very simple coils. The new concept for generating 3D fields using permanent magnets has led to the world’s first permanent magnet stellarator, which has been funded by ARPA-E and FES and will be located at PPPL. The project will design and construct a half-period of the magnet structure for a possible stellarator concept that would use components from NCSX, including the toroidal field coils and vacuum vessel, together with an array of neodymium magnets. The magnets are designed by the state-of-the-art code FAMUS employing topology optimization techniques. Conceptual designs of the magnet including the physics properties of the planned equilibrium and support structures for permanent magnets will be presented. Numerical calculations show that permanent magnets can produce plasma shapes not readily accessible with physical coils, including configurations with improved thermal and fast-ion confinement. The methods used during and the results from the design effort will be described in detail and the status of the construction activity will be summarized. [Preview Abstract] |
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ZP07.00007: A 105 GHz ECH System and Initial Plasma Heating Experiments on the Proto-MPEX Facility. TS Bigelow, TM Biewer, JF Caneses, JB Caughman, RH Goulding, C Lau, J Rapp A 105 GHz gyrotron system has been utilized to make preliminary plasma heating experiments on the Prototype Materials Plasma Exposure eXperiment (Proto-MPEX) at ORNL. Proto-MPEX is a linear device that utilizes a 200 kW, 13.56 MHz helicon plasma generator and is intended for material sample exposure to plasmas. Additional plasma heating systems include a 25 kW 8 MHz ion cyclotron heating ICH system, and a 75 kW 28 GHz electron Bernstein Wave (EBW) system. Extensive experiments have been performed studying the plasma heating and coupling efficiency of the various heating systems. The higher frequency ECH is of interest for comparison to the 28 GHz EBW heating mode for higher density access and other heating regimes. An existing 140 GHz TE15,2 mode gyrotron was tuned to the TE10,2 operating mode and a waveguide and launching system were installed. Although the efficiency of the mode converter was not optimized and body current was high, short pulse power at 104.9 GHz was launched into Proto-MPEX of up to 40 kW and 40 ms pulse length. Some preliminary heating experiments were performed that showed some heating at one 2$^{\mathrm{nd}}$ harmonic resonance location but the desired core plasma heating has not yet been obtained. Other experiments in support of the MPEX design project are currently being performed. [Preview Abstract] |
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ZP07.00008: Closing the Equity Gap to Reach Our Scientific Goals Royce James, Arturo Dominguez, Carolyn Kuranz, Elizabeth Merritt, Nick Murphy, David Newman, Raspberry Simpson, Edward Thomas, Ellen Zweibel APS DPP stands poised to create a healthy climate of diversity, equity and inclusion critical to solving the challenges we face in our field. We acknowledge, as a community, that lack of an open and welcoming climate is a serious problem and inhibitor to achieving our collective goals. Established institutional practices, tropes, and policies have caused and propagated harm to marginalized members and potential members of our honored division. Modeled from best practices in Academia, Industry, Faith communities, and longstanding successful cultural collectives like Women in Physics, we devised a strategy to gather disaggregated data and perspectives across the division at last year's conference. Additionally, we caucused in a Climate {\&} Inclusion Town Hall to add context to the gathered survey data with participant experiences to kick off this initiative. Survey results have been disaggregated by demographics to determine equity gaps in discipline specific milestones such as Early Career Grants, Postdoc and Tenure Track Positions, and Invited Talks. These gaps will be used to identify external experts to assist in charting a diverse and equitable course forward to eradicate anti-Blackness, marginalization, and oppression in both our national community and home institutions.. Impacts from the Diversity, Equity, and Inclusion Organizing Collective Committee's efforts in these and other division-wide climate improvement strategies will be reported. [Preview Abstract] |
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ZP07.00009: Subcritical Magnetic Dynamos of Middle-aged Sun-like Stars Reconcile Solar-Stellar Activity Observation Bindesh Tripathi, Dibyendu Nandy, Soumitro Banerjee Long-term solar magnetic activity reconstructions indicate the solar dynamo operates in two distinct -- grand minimum and regular activity -- modes. By employing bifurcation analysis of a physically-motivated time delay dynamo model, we establish this to be a direct consequence of dynamo hysteresis. We reproduce the observed bimodal distribution of sunspots, but only for subcritical dynamos. We also demonstrate how the Sun can enter into the grand minima episodes and recover from it. A theoretical framework consistent with these findings explain confounding observations of an abrupt midlife transition in stellar activity, characterized by reduced angular momentum loss rates and breakdown of gyrochronology relations. Our study indicates that an evolving dynamo bridges a diversity of phenomena in Sun-like stars across their lifetime. (Ref: \underline {https://arxiv.org/abs/1812.05533}) [Preview Abstract] |
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ZP07.00010: MHD modeling of a MA-class dense plasma focus with a doped-deuterium fill Jeff Narkis, Eric Hahn, Daniel Lowe, David Housley, Fabio Conti, Farhat Beg It is well-known that the structure and evolution of the plasma current sheath in a deuterium-fill dense plasma focus (DPF) is affected by the presence of mid-to-high Z dopants. Here we present MHD simulations of a MA-class DPF with a hemispherical anode, a similar configuration to that used in recent experiments on the Gemini DPF at the Nevada National Security Site, in which noble-gas dopants are prescribed in varying fractions. A non-LTE, multi-group radiation diffusion model is used to quantify the increased radiative cooling expected by the addition of high-Z dopants. The effect of dopants on the development of instabilities is also studied by seeding the simulations with a density perturbation. Peak currents are varied from two to a few MA to investigate potential variations in sheath dynamics and neutron yield scaling with peak current due to the presence of dopant. It is worth noting that these simulations do not include kinetic effects, such as neutrons produced by beam-target fusion. [Preview Abstract] |
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ZP07.00011: Confinement Physics on Plasma Injector 3 Kelly Epp, R. Rablah, S. Howard, M. Laberge, M. Reynolds, R. Ivanov, P. Carle, W. Young, A. Froese, C. Gutjahr, K. Bell, S. Bolanos, A. Rohollahi, R. Corfu, A. Wong, C. Eyrich Achieving energy gain with Magnetized Target Fusion (MTF) requires the plasma to satisfy a set~of goals: particle inventory (10$^{\mathrm{21}}$ ions), magnetic~flux (0.3 Wb) to confine the plasma without MHD instability, and energy confinement time significantly~longer than the compression time.~To study the physics of reactor-scale plasmas, General Fusion (GF) has constructed Plasma Injector 3 (PI3).~The toroidal magnetic field in PI3 is produced by a~pulsed power supply that also provides a low-voltage pulse to compensate resistive losses on a timescale of 10-50 ms.~Once the toroidal field is established, PI3 uses a 50 microsecond pulse of coaxial helicity injection to produce a spherical tokamak plasma with total lifetime of 20 ms, within an aluminum flux conserver of radius 1 m, evap. coated with Li.~Diagnostics include Mirnov probes, visible imaging, interferometers, spectroscopy, Doppler thermometry,~Thomson scattering, AXUV, and FIR polarimetry. The goal is to determine the magnetic profile, stability, and the energy confinement time of the ST plasma during the first 7 ms to evaluate its suitability for compression to fusion conditions by an imploding liquid metal flux conserver. Comparing PI3 data to our SPECTOR devices (vessel radius $=$ 0.2 m) will inform the requirements of the next generation injector for GF's Fusion Demonstration Plant. PI3 is upgrading power supply from 3.5 MJ to 7 MJ by Fall of 2020. [Preview Abstract] |
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ZP07.00012: Viscosity of the strongly coupled strongly magnetized one component plasma Brett Scheiner, Scott Baalrud The viscosity tensor of the magnetized one-component plasma, consisting of five independent shear viscosity coefficients, a bulk viscosity coefficient, and a cross coefficient, is computed using equilibrium molecular dynamics simulations and the Green-Kubo relations. A broad range of Coulomb coupling and magnetization strength conditions are studied. Magnetization is found to strongly influence the shear viscosity coefficients when the gyrofrequency exceeds the Coulomb collision frequency. Three regimes are identified as the Coulomb coupling strength and magnetization strength are varied. The Green-Kubo relations are used to separate kinetic and potential energy contributions to each viscosity coefficient, showing how each contribution depends upon the magnetization strength. The shear viscosity coefficient associated with the component of the pressure tensor parallel to the magnetic field, and the two coefficients associated with the perpendicular component of the pressure tensor, are all found to merge to a common value at strong Coulomb coupling. [Preview Abstract] |
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ZP07.00013: Direct numerical simulation of Doppler laser cooling of ultra-cold ion plasmas in a Penning trap with a rotating wall Chen Tang, Dominic Meiser, John Bollinger, Scott Parker Ultra-cold ion crystals in Penning traps enable interesting research at the forefront of different areas of physics. Doppler laser cooling ions to a fraction of millikelvin allows the formation of a two-dimensional hexagonal structure. There are two major differences of Doppler cooling in a Penning trap when compared to neutral atom traps. The motion of ions is subject to the external trap electric and magnetic fields, as well as the Coulomb interactions between ions. We observe both exact crystal and non-equilibrium states can exist at extremely low temperature. The ion planar modes are separated into two branches, the higher frequency cyclotron and the lower frequency magnetron branch. The potential energy in the magnetron branch can be relatively large for non-equilibrium states even when the thermal kinetic energy is very low. A direct numerical simulation of many interacting ions in a Penning trap with a rotating wall is implemented to classically model the ions dynamics. Both axial and planar Doppler cooling are modelled using stochastic momentum impulses based on two-level atomic scattering rates. The numerical simulations help us characterize the ultra-cold ion crystal by observing the power spectrum density, mean square displacement and other detailed diagnostics. [Preview Abstract] |
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