Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session YO08: Measurement and Diagnostic Techniques for Low Temperature PlasmasLive Streamed
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Chair: Sophia Gershman, PPPL Room: 402 ABC |
Friday, October 21, 2022 9:30AM - 9:42AM |
YO08.00001: Coherent Thomson scattering: a four-wave mixing approach to plasma diagnostics Mikhail S Mokrov, Mikhail N Shneider, Alexandros Gerakis The proposed novel four-wave mixing technique of coherent Thomson scattering (CTS) makes use of induced optical lattices within a plasma, to scatter off a third beam from them, giving rise to the coherent CTS signal beam. The technique builds on an established and demonstrated single shot diagnostic method, termed coherent Rayleigh-Brillouin scattering (CRBS), which has already been successfully applied to neutral flows and neutral species in glow discharges. Owing to its four-wave mixing nature, CTS will enable higher spatial resolution and lower detectable number densities for the electrons than conventional Thomson scattering, as applied to low and high temperature plasmas. Towards this goal, the theoretical framework for CTS has been developed, as well as the specification of the appropriate operational experimental parameters for successful CTS implementation in e.g. a low temperature plasma. The one-dimensional nonstationary Boltzmann equation was solved for electrons in the BGK approximation with allowance for the ponderomotive force, together with the Poisson equation for the potential distribution. As an example, nonequilibrium weakly ionized Argon plasma was considered. Importantly, this has led to the simulation of the anticipated CTS spectra for the case when the wavelength of the induced optical lattices is much smaller than the Debye length. Ultimately, successful experimental demonstration of CTS can find application in a multitude of areas in plasma physics, since it will allow for detailed, non-perturbative measurements of electron density and temperature, hard to be attained by other measurement techniques. |
Friday, October 21, 2022 9:42AM - 9:54AM |
YO08.00002: Trapping and manipulating a single particle in dusty plasma using optical trapping Pubuduni AK Ekanayaka MEW, Chuji Wang, Saikat Chakraborty Thakur, Edward Thomas Most current studies on laser manipulation of particles in dusty plasma have been performed by suspending groups of particles within plasma sheath. This study reports on the trapping and manipulating a single particle in dusty plasma both inside and outside the plasma sheath using a recently developed universal optical trap (UOT) technique. Based on the results, it was demonstrated that the integrated UOT plasma system was able not only to trap particles in the dusty plasma, but also transport the trapped particles to a different location in the plasma. As a result of three balanced forces, optical force, Coulomb force, and gravitational force, individually introduced Single wall carbon nanotube particles are trapped by UOT in Argon or Argon/Air combination RF plasma, operating at pressures ranging of tens – hundreds of millitorr with input rf power 1-10W. A real-time imaging system was used to monitor the stability and motion dynamics of trapped particles. Additionally, we investigate how different optical configurations and plasma operating conditions are affecting particle trapping and manipulations. |
Friday, October 21, 2022 9:54AM - 10:06AM |
YO08.00003: Optimization of laser-induced breakdown spectroscopy for analyzing heterogeneous materials Shubho Mohajan, Nicholas F Beier, Sadee Lamothe, Ying Wan, Amina E Hussein Rapid, real-time elemental analysis of heterogeneous materials such as agricultural soils and oil sands tailings are globally demanded for environmental resource management and sustainable food production. Although laser-induced breakdown spectroscopy (LIBS) is ideally suited for rapid multi-element analysis, analyzing heterogeneous samples using LIBS is extremely difficult due to signal variability, matrix effects, difficulties in quantifying trace elements, and classifications of complex samples. Our research intends to improve LIBS measurement accuracy by optimizing the experimental setup and data analysis method. Recent experimental findings indicate a trade-off between enhancing the signal-to-noise ratio of emission lines and the contribution of continuum emission from free electrons via the inverse bremsstrahlung process when the laser energy is increased. The contribution of continuum emission can be decreased by collecting plasma emission at a more co-linear angle with the laser beam. For further minimization of the continuum emission contribution, the continuum emission is estimated using least-squares regression and performed continuum normalization and baseline correction. Through data-driven modeling employing machine learning algorithms and proper sample preparation, the LIBS signal variability caused by heterogeneity in the target can be greatly reduced. Our research shows that bitumen concentration can be determined in heterogeneous tailings samples using partial least squares regression (PLSR), and LIBS measurement is significantly improved for wet samples compared to dried tailings samples, confirming the capability of LIBS to perform multi-element analysis of heterogeneous samples in the field without sample preparation. |
Friday, October 21, 2022 10:06AM - 10:18AM |
YO08.00004: Trends and Uncertainty Quantification of Excited State Populations in Capacitively Coupled Argon Plasmas Ruairi O'Connor, Dan Fries, Philip L Varghese, Noel T Clemens, Laxminarayan L Raja A low-temperature capacitively-coupled plasma generator has been developed to study fundamental properties of argon plasmas. Such glow discharge systems are being used in plasma physics research and find use in the semiconductor manufacturing industry. The device consists of two cylindrical plate electrodes powered by a 13.56 MHz radio-frequency source. Our device operates at pressures from 0.1-10 Torr and up to 120 W input power, producing plasmas in which the electron temperature ranges from 0-3 electron-volts and the background gas temperature remains close to ambient at ~295 K. We perform simultaneous current and voltage measurements to determine the phase shift, the power deposited in the plasma and the DC bias. Absolute radiance calibrated Optical Emission Spectroscopy measurements in the visible and near infra-red are used to determine population densities of excited argon states. The emission lines observed correspond primarily to transitions from the 4p states to metastable argon states. We report on changes in the upper state population densities as a function of plasma pressure and power. A Monte-Carlo approach is implemented for uncertainty quantification (UQ). The UQ results are used to assess possible deviations from equilibrium population distributions. |
Friday, October 21, 2022 10:18AM - 10:30AM |
YO08.00005: Bayesian Inference for Plasma Temperature and Density from Emission Spectroscopy Todd A Oliver, Craig Michoski, Samuel J Langendorf In emission spectroscopy, it is common to infer plasma temperature and |
Friday, October 21, 2022 10:30AM - 10:42AM |
YO08.00006: Characterizing the Life-Cycle of Threshold Electrostatic Discharges Using Coupled Electrical and Optical Measurement Claudia A Schrama, Sarah Hinnegan, Jonathan Barolak, Daniel Adams, Alex Wilhelm, Charles G Durfee Electrostatic discharge (ESD) poses danger around electronics and sensitive materials. ESDs from tools or hands with limited stored charge are closer to threshold, so we are studying the energy transfer and plasma dynamics in these ESDs. We are making electrical and optical measurements to understand the nonlinear time dependent resistance along with the plasma and neutral density evolution to inform our ESD models. |
Friday, October 21, 2022 10:42AM - 10:54AM |
YO08.00007: The effect of sheath dielectric on the inferred plasma parameters of a DC biased hairpin resonator probe Pawandeep Singh, Swati Swati, Avnish K Pandey, Jay K Joshi, Yashshri Patil, Shantanu Karkari A hairpin resonator probe (HP) measures absolute electron density in a plasma. It is primarily based on the resonance principle of a parallel wire transmission line, where the quarter-wavelength of the characteristic resonance frequency equals the physical length of the HP [1]. However, owing to the finite sheath width formed around its pins, its accuracy is compromised. As a consequence, the resonance frequency is underestimated, and the electron density is inferred incorrectly. This limitation may be resolved by introducing sheath correction based on a capacitive model in which the series combination of sheath and plasma capacitances is compared to the effective capacitance of the area between the pins, with the sheath dielectric equal to the constant vacuum value. While the sheath width is calculated analytically by calculating the Poisson's equation, along with the continuity and momentum equations, under the assumption of an electron free sheath [2]. In this work, the impact of electron and ion sheath surrounding the cylindrical pins of the HP on the inferred plasma characteristics in a 13.56 MHz CCRF argon and oxygen discharge is studied using a DC biased HP. The capacitance model is addressed by applying a bias-dependent sheath dielectric value surrounding the probe pins [3]. It is found that the peak in the resonance frequency corresponds to a relatively higher value of the applied bias than the plasma potential. Furthermore, its impact on estimating the plasma parameters, including plasma potential, electron temperature, and electronegativity, is discussed with a plausible explanation. |
Friday, October 21, 2022 10:54AM - 11:06AM |
YO08.00008: Non-Invasive Laser Triggering for Investigation of Threshold Electrostatic Discharge Physics Sarah C Hinnegan, Claudia A Schrama, Patrick Hunt, Philip D Flammer, Charles G Durfee The study of the physics of naturally occurring electrostatic discharges (ESDs) at early times is challenged by the difficulty in overcoming pre-trigger requirements of laser probes. In this work, ultraviolet (UV) pulses from a diode-pumped solid-state, Q-switched laser system are used to trigger ESDs. We use an open-air spark gap with a gap voltage held near threshold. The laser intensity is in the microjoule range so that seed electrons are produced through the photoelectric effect on the cathode. In contrast to laser-triggered spark gaps, the resulting discharges are anticipated to be very similar to those produced by random seed electrons. |
Friday, October 21, 2022 11:06AM - 11:18AM |
YO08.00009: Novel methods for in situ high-density surface cleaning (scrubbing) of ultrahigh vacuum long narrow tubes to reduce secondary electron yield and outgassing Ady Hershcovitch, Art Custer, Mark Erickson, Joe Poole Electron clouds in existing accelerators limit machine performance through dynamical instabilities and associated vacuum pressure increases. Bare metal vacuum walls have shown to prevent electron cloud formation. Proper scrubbing of stainless steel, copper, or niobium vacuum walls can mitigate the problems of electron clouds and increase accelerator luminosity. Present scrubbing by ion beams and plasmas has resulted in unsatisfactory surface cleaning by not scrubbing all surfaces and poor debris pumping-out due to low-density plasma generation. Novel plasma discharge cleaning techniques and tools are being developed for in-situ scrubbing long, small diameter tubes by generating high-density plasmas to completely affect each exposed surface. One technique involves high plasma density magnetron mole, the other is based microwave plasma injection that generates high-density plasma. High-density plasma scrubbing in the viscous gas flow range can reach all surfaces and pump out all debris effectively. |
Friday, October 21, 2022 11:18AM - 11:30AM |
YO08.00010: Effects of pulsed photoemission in plasma breakdown Peng Zhang, Brian Z Bentz, Asif Iqbal, Yang Zhou, Kevin Youngman Photoemission of electrons by pulsed laser light offers opportunities to trigger and control plasmas and discharges. However, the underlying mechanisms are not sufficiently characterized to be fully utilized. Photoemission is highly nonlinear, achieved, for example, through multiphoton absorption, above threshold ionization, and photo-assisted tunneling, where the dominant process depends on the work function of the material, photon energy and associated fields, surface heating, and background fields. To characterize these effects, Townsend breakdown experiments were performed and interpreted using a quantum model of photoemission. In the low-current regime considered, it is found that laser-induced photoemission is sufficiently de-coupled from space charge effects to be observable. The effect of laser heating of the electrode and the dominant photoemission mechanisms are characterized for different reduced electric fields and laser intensities and photon energies. The quantum model of photoemission is incorporated into a simple global model to study the transient current-voltage behaviors of the plasmas measured in experiments. |
Friday, October 21, 2022 11:30AM - 11:42AM |
YO08.00011: Initial Results from The Plasma Antenna Test Setup David D Blackwell, Aaron E Cohen, Michael A Rupar, William E Amatucci This paper presents initial results from the operation of a laboratory prototype plasma antenna. The device consists of a plasma column with cold electrons (Te <= 4 eV) and density in the range 109-1011 cm-3. A coupling loop connects a low power (< 5 W) RF signal to the column. This signal is received by a dipole receiver in the near field of the antenna. A second coupling loop can be moved along the plasma column to measure the phase of surface waves excited along the length of the plasma. We measured the dispersion of the plasma surface waves and the near field azimuthal antenna pattern over a range of input ionization power and a frequency range from 5- 400 MHz covering the VHF and lower UHF. It was found that the plasma antenna operated similar to a thin wire metal antenna with respect to frequency resonances corresponding to the length of the plasma column, but had a somewhat altered spatial directionality which changed to some extent with changing plasma density. These initial measurements demonstrate 1) that the plasma column operates as an antenna and the operation overlaps with a conventional metal antenna, and 2) changing the characteristics of the plasma column changes that operation. |
Friday, October 21, 2022 11:42AM - 11:54AM |
YO08.00012: DC-driven streamer coronas in wind Benjamin C Martell, Lee R Strobel, Carmen Guerra-Garcia Recent numerical studies have reported on the influence of wind on streamer development, but experimental studies are lacking. The disparity between typical streamer speeds and realistic wind speeds means that wind has little influence at the timescales of streamer propagation, but it will impact the behavior of the discharge at the longer timescales of ion motion. This will impact the self-pulsating behavior of the discharge under DC conditions. In this contribution we present a wind tunnel study of DC-driven positive streamer coronas in a tip-to-plate configuration and exposed to lateral winds (relative to the needle orientation) of up to 30 m/s. The experimental data is presented in terms of statistical properties of the discharge, inferred from high resolution, large sample-size electrical waveforms and synchronized imaging. The measurements are interpreted from the viewpoint of enhanced charge transport in wind using an analytical model. The results from this work have implications in problems related to atmospheric electricity (e.g., lightning attachment to wind turbines, p-static wick efficiency, EMI) as well as plasma flow reactors. |
Friday, October 21, 2022 11:54AM - 12:06PM |
YO08.00013: Update on Sandia National Laboratories Plasma Research Facility Shane M Sickafoose, Brian Z Bentz, Jonathan H Frank, Nils Hansen, Matthew M Hopkins, Amanda M Lietz, Christopher J Kliewer, Dirk van den Bekerom This presentation will provide an update on the activities and structure of Sandia’s Low-Temperature Plasma Research Facility (PRF), funded by DOE Office of Science, Office of Fusion Energy Sciences, General Plasma Science. The PRF is a resource available to anyone in the international Low-Temperature Plasma (LTP) community to access the advanced resources available at Sandia (not restricted to the US collaborators). Capabilities are accessed through an annual proposal process which opens immediately following the GEC conference. Available resources include both experimental and modeling capabilities that represent many person-years and millions of dollars of development through DOE and other investments (some for decades). Examples of real-time diagnostics include Laser-Induced Fluorescence (LIF), Laser-Collision-Induced Fluorescence (LCIF), Photofragmentation LIF (PF-LIF), and Molecular Beam Mass Spectrometry (MBMS). Advanced modeling capabilities are also available, including state-of-the-art PIC-DSMC modeling tools along with access to Sandia’s high-performance computing (HPC) capabilities (many 10K’s of cores). |
Friday, October 21, 2022 12:06PM - 12:18PM |
YO08.00014: In situ detection of solvated oxygen atoms Brayden Myers, Arthur Dogariu, Benjamin Beeler, Katharina Stapelmann As a diradical and powerful oxidant, atomic oxygen plays an integral role in a wide range of low temperature plasma applications. However, it remains difficult to account for, especially in the aqueous phase. Current detection techniques require inherently problematic chemical probes, which, along with a lack of chemical reference data, preclude a full understanding of its effects. Here we present a novel technique to detect solvated O atoms directly by employing femtosecond two-photon absorption laser induced fluorescence (TALIF). The use of an ultrafast laser provides sufficient excitation, without heating the liquid, to allow for the detection of laser-excited O despite the aggressive quenching environment in water. Critically, an effort is made to absolutely calibrate the recorded signal for density with molecular dynamics simulations of solvated O atoms. From this, currently unknown quantities for solvated O atoms can be estimated and a value for the previously unreported Henry’s law constant is given. Uncertainties are examined and the possible extension of this method to other atomic species of interest discussed. These measurements serve as a proof of concept for a powerful experimental technique to quantify solvated O densities directly without chemical probes. |
Friday, October 21, 2022 12:18PM - 12:30PM |
YO08.00015: Novel plasma diagnostics for low-temperature plasma in contact with liquids: Brewster angle-cavity ringdown spectroscopy Rongrong Wu, Chuji Wang Application of low temperature plasma (LTP) emanates from interactions of the LTP agents such as reactive species (RS) with a targeted medium. The spatial profile and temporal dynamics of RS in situ are of vital importance for LTP diagnostics. Yet, it is one of the most challenging tasks, especially when LTP interacts with a wet medium, e.g., a medical solution, mainly because traditional spectroscopic techniques such as optical emission spectroscopy suffer from large optical losses. We report on the development of a Brewster angle-cavity ringdown spectroscopy (BA-CRDS) system for LTP diagnostics. The system can be used to measure various plasma species in solutions such as OH and HOO radicals. The detection limit, i.e., the minimum detectable absorbance, is 1.2×10-5, equivalent to 6 ppb OH radicals in water at 308 nm. The absorption cross section of HgBr2 in aqueous phase is measured to be (1.8±0.1)×10-18 cm2, close to the reported data in gas phase (1.4 ×10-18 cm2). The temporal behavior of distilled water, when interacting with a helium plasma jet, is characterized at different plasma power and gas flow rates. The temporal behaviors of other solutions, e.g., HgBr2, Methanol, etc., are also explored. Some reaction pathways leading to the removal of substances such as HgBr2 by OH radical and the formation of H2O2 in the solutions are proposed. These results demonstrate that the BA-CRDS system is a powerful tool for quantification of RS in aqueous phase with high detection sensitivity. |
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