Bulletin of the American Physical Society
73rd Annual Gaseous Electronics Virtual Conference
Volume 65, Number 10
Monday–Friday, October 5–9, 2020; Time Zone: Central Daylight Time, USA.
Session JT3: Diagnostics I: Laser DiagnosticsLive
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Chair: Chris Kliewer, Sandia National Laboratories CA |
Tuesday, October 6, 2020 1:00PM - 1:30PM Live |
JT3.00001: Measurement of velocity distribution functions of heavy species in weakly ionized plasma flows via single shot coherent Rayleigh-Brillouin scattering. Invited Speaker: Alexandros Gerakis We experimentally demonstrate the use of single shot coherent Rayleigh-Brillouin scattering (CRBS) for the measurement of the velocity distribution function (VDF) of neutral flows, from which macroscopic quantities, such as the flow velocity, density and translational temperature can be extracted. We suggest the use of CRBS for the measurement of the VDF of heavy species in a weakly ionized plasma and report the progress towards that goal. In CRBS, a four-wave mixing technique, a high energy optical lattice of precisely tailored chirped frequency interacts with the medium, such as neutral or ionized gas. The variation of the CRBS signal intensity at different optical lattice phase velocities allows for the restoration of the VDF and the resulting CRBS lineshape is a direct mapping of the medium's VDF. CRBS has already been demonstrated to be the coherent analogue of spontaneous Rayleigh-Brillouin scattering in measuring the temperature, pressure, bulk and shear viscosity, speed of sound and polarizability of a stagnant gas or gas mixture, in a single laser shot [1]. Nanoparticles produced in an arc discharge at atmospheric pressure have also been measured in situ using CRBS [2]. We will discuss the recent progress of single shot CRBS as a gas flow measurement technique and its use in a weakly ionized plasma flow. 1. Gerakis, A., Shneider, M.N. and Barker, P.F., ``Single-shot coherent Rayleigh--Brillouin scattering using a chirped optical lattice'', Optics Letters, 38(21), pp.4449-4452, (2013). 2. Gerakis, A., Yeh, Y.W., Shneider, M.N., Mitrani, J.M., Stratton, B.C. and Raitses, Y., ``Four-wave-mixing approach to in situ detection of nanoparticles'', Physical Review Applied, 9(1), p.014031, (2018). [Preview Abstract] |
Tuesday, October 6, 2020 1:30PM - 1:45PM Live |
JT3.00002: A dual-color, frequency-agile, single-shot CRBS laser system for the measurement of neutral species velocity distribution function in weakly ionized plasmas Junhwi Bak, Robert Randolph, Alexandros Gerakis Resolving the velocity distribution function (VDF) of neutral species in weakly ionized plasmas can expand our understanding of physical interactions between charged and neutral particles. Towards this goal, we present a custom built, dual-color, frequency-agile, single-shot coherent Rayleigh-Brillouin scattering (CRBS) laser system, which is designed specifically to obtain remote, direct measurements of the VDF of neutral particles [1]. CRBS is a four-wave mixing technique in which the interference of two pump beams in a medium generates a moving optical lattice. A third probe beam is Bragg-scattered from the lattice, generating a fourth CRBS signal beam. By scanning the velocity of the lattice within a single laser pulse [2], single-shot CRBS can restore the VDF of neutral particles from the variation of the signal intensity per velocity component. The system is designed to maximize signal-to-noise level in a low-pressure plasma environment, being capable of measuring the VDF at pressures as low as 0.1 Torr. To achieve this, we adopt a three dimensional and two-color phase-matching scheme, details of which and of laser system will be presented in this work. [1] Gerakis, A., Bak, J., and Randolph, R., ``A frequency agile, high intensity, two color laser system for single-shot coherent Rayleigh-Brillouin scattering,''Manuscript in Preparation,2020. [2] Gerakis, A., Shneider, M. N., and Barker, P. F., ``Single-shot coherent Rayleigh-Brillouin scattering using a chirped optical lattice,''Opt. Lett., Vol. 38, No. 21, Nov 2013, pp. 4449--4452. [Preview Abstract] |
Tuesday, October 6, 2020 1:45PM - 2:00PM Live |
JT3.00003: Spatially-resolved time-evolution of rotation-vibration non-equilibrium and CH$_{\mathrm{4}}$ concentration measured by fs/ps CARS in a nanosecond-pulsed pin-to-pin discharge Timothy Chen, Benjamin Goldberg, Christopher Kliewer, Egemen Kolemen, Yiguang Ju To develop quantitative understanding of non-equilibrium plasmas for methane reforming, temporally and spatially resolved measurements of reactant concentration and rotation-vibration non-equilibrium are necessary. In this study, a recently developed rotational fs/ps CARS method was used to simultaneously measure rotational and vibrational temperatures of a pin-to-pin CH$_{\mathrm{4}}$/N$_{\mathrm{2}}$ nanosecond-pulsed discharge at 60 Torr. The CH$_{\mathrm{4}}$ concentration was measured separately using vibrational CARS in the same experimental setup. These measurements were conducted across a 2 mm length along the electrode axis within 150 $\mu $m of the cathode and from delays of 50 ns from the voltage pulse up to 800 $\mu $s. Significant gradients in N$_{\mathrm{2}}$ rotational and vibrational temperature and CH$_{\mathrm{4}}$ number density were observed across the measurement length. Peak vibrational temperature exceeding 6000K was observed, 0.8 mm from the cathode and 100 $\mu $s after the voltage pulse. Majority of the CH$_{\mathrm{4}}$ consumption occurred during the voltage pulse, but additional decrease was observed within the first 5 $\mu $s of the afterglow. [Preview Abstract] |
Tuesday, October 6, 2020 2:00PM - 2:15PM Live |
JT3.00004: Spatio-temporal distribution of atomic oxygen and ozone under pin-to-sphere oxygen discharge Yusuke Nakagawa, Takuya Kawakita, Satoshi Uchida, Fumiyoshi Tochikubo Pure oxygen discharge is preferable for production of atomic oxygen and ozone, while there is a difficulty in measuring their local densities. The ozone density is typically measured by UV absorption, but its resolution is insufficient to measure the local ozone density in filamentary discharges. The atomic oxygen density can be measured by TALIF, but the ozone interference, which is the in-situ atomic oxygen production due to the ozone photo-dissociation, disturbs the measurement. In this study, we achieved simultaneous measurement of densities of atomic oxygen and ozone, by focusing on the laser intensity dependence of TALIF signals on them. Under pure oxygen needle-to-sphere pulsed barrier discharges, the atomic oxygen density near the needle anode was approximately 3 times larger than that near the spherical cathode with dielectric barrier. There appeared the decay of ozone after the rapid ozone production near the anode, whereas the ozone density near the cathode reached constant without decay. The results indicate that high atomic-oxygen-production efficiency can be obtained near the anode, whereas eventual ozone production near the cathode is superior to that near the anode. The difference in the ozone behavior is supposed to arise from thermal decomposition of ozone. [Preview Abstract] |
Tuesday, October 6, 2020 2:15PM - 2:30PM |
JT3.00005: Time-resolved TALIF measurements of temperature and CO number density in an NRP discharge Jean Maillard, Erwan Pannier, Christophe Laux Time-resolved measurements of temperature and CO density are performed in the afterglow of Nanosecond Repetitively Pulsed (NRP) discharges in pure CO2 at atmospheric pressure and room temperature. We use Two-photon Absorption Laser-Induced Fluorescence (TALIF) in the first ten microseconds after the pulse. CO is excited with a 230 nm laser beam. An excitation spectrum is recorded with a camera and fitted to yield the rotational temperature and the CO density in the discharge. Preliminary measurements at 1-10 $\mu $s after the pulse have been carried out. Additional measurements within the first microsecond following the pulse are on-going. For these measurements, a second camera is triggered just before the laser pulse to measure the plasma emission. This new set-up allows a better subtraction of the plasma emission. It also enables to monitor the perturbations induced by the laser. A temperature of 1700 K is measured at the center of the discharge, which is consistent with the 2000 K measured in a previous study by infrared emission spectroscopy in the same discharge. At t $=$ 1 $\mu $s after the pulse, we report 16{\%} CO2 dissociation. [Preview Abstract] |
Tuesday, October 6, 2020 2:30PM - 2:45PM |
JT3.00006: Preliminary Data of a Laser-Induced Fluorescence Diagnostic of Electric Field Christopher Durot, Jenny Smith, John Foster The local electric field is a key parameter in gas chemistry modeling but is not always well known or simple to calculate. Measurements of the electric field generated under conditions of interest could help to inform and validate plasma chemistry models. The University of Michigan is developing a laser-induced fluorescence dip (LIF-dip) spectroscopy system in support of NRL gas chemistry studies. The LIF-dip technique uses Rydberg states as part of the level scheme to sensitively detect electric field magnitude. We present preliminary LIF measurements to confirm that our custom plasma source produces the excited metastable population necessary for the energy level scheme and explore relevant energy level lifetime and collisional quenching. [Preview Abstract] |
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