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 JP14: Poster Session: Fundamental Plasmas: Diagnostics (2:00pm - 5:00pm)On Demand
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JP14.00001: Ion Heating in the PHAse Space MApping (PHASMA) Experiment Earl Scime The PHAse Space MeAsurements (PHASMA) experiment, features laser induced fluorescence diagnostics for ion measurements, Thomson scattering for electron velocity distribution function measurements, and a microwave scattering system for turbulence measurements. PHASMA is designed to enable the direct measurement of ion and electron vdfs in space-relevant plasma phenomena including reconnection, shocks, and turbulence. To create the conditions necessary for different experimental regimes, PHASMA employs a 2 kW, steady-state helicon source capable of generating variable-density background hydrogen, helium, and argon plasmas with controllable plasma pressure (relative to the magnetic pressure), collisionality, and azimuthal flow shear. A key feature of the helicon plasma source is the capability to create 1eV ions over a wide range of plasma conditions. Early experiments in PHASMA resulted in helicon source ion temperatures less than 0.2 eV. The very low ion temperatures appear to be result from poor coupling of the slow wave to the plasma due to changes in antenna design during construction of PHASMA. We report ion temperature measurements as a function of modifications of the antenna structure designed to restore the high ion temperatures typically observed in helicon sources. [Preview Abstract] |
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JP14.00002: Flow velocity measurements of a flux rope in PHASMA Prabhakar Srivastav, Peiyun Shi, Eric Reynolds, Cuyler Beatty, Earl Scime Current-driven instabilities play a critical role in the evolution of magnetic flux ropes -- in laboratory and astrophysical systems. A single flux rope is created with a pulsed plasma gun in the PHASMA (PHAse Space Mapping) experiment. The flux rope exhibits a kink instability. Axial and poloidal flows during the growth of the instability are measured with an array of Mach probes. The poloidal flow velocity is investigated in the context of the flux rope rotation for plasma gun currents below and at the kink threshold. We also present measurements of the magnetic field structure, the electron temperature, and the plasma density of the flux rope. [Preview Abstract] |
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JP14.00003: Microwave heterodyne interferometer measurements on pulsed plasmas in the PHASMA experiment Cuyler Beatty, Prabhakar Srivastav, Peiyun Shi, Earl Scime First line integrated density measurements of a pulsed helicon plasma using a none perturbative microwave heterodyne interferometer on the PHAse Space MApping (PHASMA) experiment are presented. The interferometer has two sources, one fixed at 31.700 GHz and the other set to 32.586 GHz, giving the desired frequency off-set for the mixers and demodulator. Line integrated density measurements of single flux rope experiments are also presented. These measurements were corroborated with Langmuir probe data taken at the same time. This work is supported by NSF Grants PHY-1827325 and PHY-1902111 [Preview Abstract] |
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JP14.00004: Incoherent Thomson Scattering System for Laboratory Space Plasma on PHASMA Device Peiyun Shi, Earl Scime, Prabhakar Srivastava, Ripudaman Singh Nirwan, Cuyler Beaty, Thomas Steinberger The PHASMA (PHAse Space Mapping) experiment is designed to simulate space plasma in laboratory, including magnetic reconnection through the merger of two flux ropes from two biased gun plasmas. A new incoherent Thomson scattering system will measure the evolution of electron velocity distribution functions perpendicular and parallel to the ambient magnetic field during the magnetic reconnection process. These will be some of the first measurements of bulk electron acceleration and heating in laboratory magnetic reconnection. The Thomson scattering system provides sub-millimeter spatial resolution; sufficient to diagnose the several millimeters sized magnetic reconnection electron diffusion region in PHASMA. Due to the relatively modest plasma density \textasciitilde 1019 m-3 and electron temperature \textasciitilde 10 eV, the challenge for the Thomson scattering system is suppressing stray light at the laser wavelength 532 nm while collecting enough scattered photons. To address this challenge, two Volume Bragg Gratings are used in series as a notch filter with spectral bandwidth \textless 0.1 nm and optical density OD7. An intensified CCD with Gen III intensifier of peak quantum efficiency \textgreater 47{\%} is also used as the detector in a 1.3 m spectrometer. Preliminary results of gun plasma electron temperature will be reported and compared with measurements obtained from a triple Langmuir probe. [Preview Abstract] |
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JP14.00005: Measuring magnetic fields using laser induced fluorescence of argon neutrals Tyler Gilbert, Katey Stevenson, Thomas Steinberger, Earl Scime Faraday rotation and Zeeman splitting have both been used to measure magnetic fields in laboratory and astrophysical plasmas. In reconnecting laboratory plasmas, arrays of probes have typically been used to measure the evolution of the magnetic field topology. An optical diagnostic capable of generating images of the magnetic field topology would provide a non-perturbative technique for measuring the evolution of the magnetic field during magnetic reconnection. Here we present proof-of-principal magnetic field measurements from a diode laser-based laser induced fluorescence diagnostic. The measured Zeeman splitting of $\sigma $ peaks in neutral argon is the basis of the measurement approach. The particular transition selected is very sensitive to the local magnetic field strength ..()()()..[\textit{Thompson et al}., 2018]. A Toptica single mode laser is fiber coupled to the PHAse Space MApping experiment (PHASMA) for Ar I measurements in helicon source generated plasmas. The target sensitivity for the diagnostic is magnetic field changes less than 10 Gauss across a sheet laser beam. 1. D.S. Thompson, T.E. Steinberger, A.M. Keesee, {\&} E.E. Scime, ``Laser induced fluorescence of Ar-I metastables in the presence of a magnetic field,'' \textit{Plasma Sources Science and Technology}, \textbf{27}, 065007 (2018) [Preview Abstract] |
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JP14.00006: Plasma Impedance Tomography for Imaging Plasma Dynamics Erik Tejero, Ami DuBois, George Gatling, Lon Enloe, David Blackwell, David Walker, Bill Amatucci Plasma impedance probes measuring the self-impedance of the antenna-plasma system have been shown to provide accurate measurements of electron plasma density for space and laboratory plasmas. Plasma impedance probes measuring the mutual impedance between two antennas and a plasma dielectric have been successfully flown on sounding rockets and satellites. At the US Naval Research Laboratory, we have recently developed a noninvasive method for generating real-time images of plasma density and magnetic field. The method consists of measurements of the complex mutual impedance between elements of an antenna array and an image reconstruction algorithm. The impedance spectra are collected after a short pulse has been applied to each element in sequence. These spectra provide path-independent information about the plasma dielectric that are used to reconstruct images of plasma density and magnetic field. The goal is to develop a system capable of providing tomographic reconstructions at a rate of a 0.1{\%} of the peak plasma frequency of the system. Recent numerical and experimental results will be presented. [Preview Abstract] |
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JP14.00007: Considerations in Comparing Experimental Results and Theory of Biased Impedance Probes David Blackwell, David Walker, Richard Fernsler, Erik Tejero, Ami DuBois, Carl Enloe, George Gatling, William Amatucci This presentation discusses two outstanding problems that have been present for a number of years in the Space Physics Simulation Chamber group's work on impedance probes. These are, (a) impedance curves indicative of a much higher energy absorption than can be accounted for using standard collision models given the plasma parameters, and (b) divergence at low frequency between predicted and measured impedance curves using our linear model. We compare numerical results of our different models to experimental data to determine under what conditions such models are valid and what areas are in need of improvement. It is our hope that defining and presenting these problems in a systematic method will help focus future theoretical and experimental efforts in impedance probe research. [Preview Abstract] |
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JP14.00008: Development of a High-Time/Spatial Resolution Self-Impedance Probe for Measurements in Laboratory and Space Plasmas Ami DuBois, Erik Tejero, George Gatling, William Amatucci Impedance probes are often used on satellites and sounding rockets to measure fundamental plasma parameters in the ionosphere. Conventional impedance probe methods generally involve sweeping the frequency and measuring the complex plasma impedance. However, plasma parameters drastically change in the time it takes to complete a measurement, which reduces the accuracy and spatial resolution of the measurement. Development of a fast impedance probe is ongoing at the U.S. Naval Research Laboratory (NRL) with the goal of increasing the spatial resolution of measurements. To achieve this, a short-time Gaussian monopulse with a center frequency of 40 MHz is utilized. Laboratory experiments performed in the Space Physics Simulation Chamber at NRL show that it is possible to make measurements of the full frequency spectrum in 10 \textmu s, equating to a spatial resolution on the order of 1 cm. Impedance probe results using the novel short-time pulsed method will be presented which demonstrate that plasma parameters such as electron density, sheath frequency, and electron-neutral collision frequency can be derived from the data, and results compare well with conventional methods and theoretical impedance models. [Preview Abstract] |
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JP14.00009: Ionospheric plasma characterization using the NRL SPADE plasma impedance probe* William Amatucci, Erik Tejero, George Gatling, Dave Blackwell, Dave Walker The Space PlasmA Diagnostic suitE (SPADE) instrument, developed by the U.S. Naval Research Laboratory (NRL), is a plasma impedance probe designed to monitor background space plasma conditions and provide early warning of the onset of hazardous levels of spacecraft charging. SPADE has been operating on the International Space Station (ISS) since May 2019 as part of the Department of Defense Space Test Program's STP-H6 mission. The SPADE experiment consists of two dipole antennas, one active antenna that is used to excite the local plasma and another passive dipole antenna that observes the excitation. The active probe is swept across a range of frequencies and DC voltage biases to determine the plasma impedance spectrum. The impedance measurements yield properties of the plasma, such as density, plasma potential, and electron temperature, while also providing data indicating the charging level of the ISS relative to the local plasma. SPADE responds to slight changes in the plasma sheath that forms around a charged object, providing a unique method for the early detection of charging. SPADE active dipole measurements demonstrating the characterization of ionospheric plasma conditions and ISS charging will be presented. *This work supported by the NRL Base Program. [Preview Abstract] |
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JP14.00010: PIN Diode and Amplifier Array for Imaging Transient X-ray Bursts From Suprathermal Particles Yi Zhou, Paul Bellan Transient 6 keV x-ray bursts having a duration of about one microsecond are detected in the Caltech jet experiment [1]. Since the plasma is both cold (2 eV) and highly collisional (mean free path about one micron in a plasma having a spatial scale of 10’s of cm), x-rays are caused by suprathermal particles with at least 6 keV energy. An 80-channel array of PIN diodes and amplifiers for a fast coded-aperture imaging system is being developed to aid imaging x-ray emissions from these energetic particles. The transient x-rays have been detected successfully by a prototype channel of the array with single 6 keV photon sensitivity. A 4-channel coded-aperture camera based on the prototype channel is currently being tested. [1] R. S. Marshall, M. J. Flynn and P. M. Bellan, Physics of Plasmas 25 (2018) Art. No. 112101 [Preview Abstract] |
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JP14.00011: Electron Velocity Distribution Functions from the Merger of Two Magnetic Flux Ropes in the Phase Space Mapping Experiment Ripudaman Singh Nirwan, Earl Scime, Peiyun Shi, Prabhakar Srivastava The Phase Space Mapping experiment is designed to observe the magnetic reconnection of two magnetic flux ropes generated by biased plasma guns. The resulting opportunity to study electron velocity distribution functions in the reconnection area is exploited by the use of incoherent Thomson scattering. The suppression of stray light at the input wavelength (532 nm) is achieved by the use of Volume Bragg Gratings with minimal bandwidth (\textless 0.1nm), allowing for more precise data to be compared with those obtained from a triple Langmuir probe. Measurements of the distribution functions obtained perpendicular and parallel to the ambient magnetic field, the first of such observations in a controlled setting, will be presented. [Preview Abstract] |
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JP14.00012: Characterization of a Silicon Photomultiplier Detector Array for Measurements of Neutron Yield and Spectrum Using Time-of-Flight Technique Jacquelynne Vaughan, Q. Looker, G. Chandler, J. L. Porter, M. Bailly-Grandvaux, F. N. Beg A short pulse high intensity generated neutron source has applications in fusion research, security, and industrial scanning. It is important to know the source neutron yield and spectrum for applications. This information could be obtained by fielding an array of neutron detectors operated in pulse-counting mode. This detection scheme was implemented at the LaNSA at the Nova Laser Fusion Facility in the 1990's with a detector 4 meters in diameter. The development of Silicon photomultipliers (SiPM) has now enabled the development of a miniature version of LaNSA. This new device was calibrated at the Ion Beam Laboratory at Sandia, using a 300 kV Cockroft-Walton generator that accelerated a D$+$ beam into an ErT$_{\mathrm{2}}$ target. Ensuing D-T fusion reactions produced 3.5 MeV alpha particles and 14 MeV neutrons. Neutron detectors characterized included an EJ232Q coupled to a single PMT, and an EJ228 coupled to a SiPM array. The data from these detectors were correlated using the associated particle method and analyzed to produce absolute yields and energy spectra. [Preview Abstract] |
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JP14.00013: Bayesian Inference Model for Neutron Classification Aria Johansen, Anton Stepanov, Uri Shumlak The shear-flow stabilized Z-pinch experiment FuZE produces quasi steady-state neutron emission lasting for 10 $\mu$s. These neutrons may be created by thermonuclear reactions indicating controlled fusion, or by pinch instabilities. Given the well characterized effects of scattering in plastic scintillators, detecting by photomultiplier tubes, and digitizing by ADCs, a neutron emission function can be estimated by using Bayesian inference in a statistical forward model. The model includes fusion events, scattering, and scintillating detector functions with their associated variance. This gives statistical bounds on what fractions of thermonuclear and beam target produced neutrons are possible with the device, without using neutron time of flight energy measurements. Discretization of the pinch into sectors and time of neutron emission into segments allows for spatiotemporal resolution of the neutron emitting region. This refines the line source model proposed by Mitrani et al, while introducing time dependence to the neutron yield. Using other diagnostic data, the neutron yield may further inform temperature and density profiles of the Z-pinch. [Preview Abstract] |
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JP14.00014: Gamma Reaction History on Sandia's Z Machine Kevin Yates, Yongho Kim, Hans Herrmann, Kevin Meaney, Justin Jorgenson, Gordon Chandler, Pat Lake, Michael Jones, John McKenney, Chris Ball, Decker Spencer, Morris Kaufman, James Corcoran, Kevin McGillivray, Ken Moy Reaction History diagnostics are being fielded on Sandia's Z machine to demonstrate the ability to measure gamma ray reaction history. Tritium introduction into the Z experiments provides necessary gammas for analysis of the reaction history. We will outline the proposed experiments which include mixtures of deuterium (99{\%}) and tritium (1{\%}) as well as deuterium (50{\%}) and helium 3 (50{\%}) with the ultimate goal of diagnosing the evolution of the fusion plasma on Z. D$^{\mathrm{3}}$He also has a steep dependence on ion temperature, making the reactivity ratio between DT and D$^{\mathrm{3}}$He a sensitive ion temperature indicator. D$^{\mathrm{3}}$He is also highly sensitive to non-thermal beam reactions and can provide an indication of the degree of thermalization of the fusion plasmas. [Preview Abstract] |
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JP14.00015: Tomography of ion flow and temperature measured by a coherence imaging spectroscopy using Gaussian processes Kenji UEDA, Masaki NISHIURA, Naoki KENMOCHI Coherence Imaging Spectroscopy (CIS) is a new type of doppler spectroscopy to obtain the velocity and temperature of ions and enable us to acquire two-dimensional spatial information through a fringe pattern analysis. Since an interferogram measured with a CIS camera system becomes a line-integrated quantity of line spectra, the tomographic technique containing spectra with a doppler shift and broadening is required to reconstruct the local profiles. In this research, a Gaussian process (GP) was applied to the tomographic method. A GP is a statistical model, which represents non-parametric functions with probabilistic behavior, and provides smooth solutions to inverse problems even with bad conditions. The method consists of two steps: a formulation of the transformation process from the local profiles to the original interferogram of the CIS, and an inverse transformation by the Bayesian inference based on GP. In this case, we determined the hyperparameters from a marginal likelihood optimization and imposed physical constraints. The proposed method demonstrated the reconstruction of the local ion flow velocity and temperature in the magnetospheric plasma of the RT-1 device. The substantial origin of drift forces is discussed to explain the toroidal ion flow. [Preview Abstract] |
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