Bulletin of the American Physical Society
72nd Annual Gaseous Electronics Conference
Volume 64, Number 10
Monday–Friday, October 28–November 1 2019; College Station, Texas
Session CT3: Plasma Diagnostics I |
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Chair: Marien Simeni, University of Minnesota Room: Century III |
Tuesday, October 29, 2019 8:00AM - 8:15AM |
CT3.00001: Vacuum ultraviolet absorption spectroscopy using self-absorption effect in light source Sho Shimizu Vacuum ultraviolet absorption spectroscopy (VUVAS) using a plasma light source is useful for measuring the absolute density of atomic radicals in plasmas. For the VUVAS, background absorption due to molecules is serious issue. In this study, the possibility for the measurement of background absorption using a self-absorption has been investigated. A mixture of H$_{\mathrm{2}}$ and He was introduced into the micro-discharge hollow cathode lamp (MHCL) to obtain an emission of H atoms at Lyman $\alpha $ line, and then the light was introduced into a H$_{\mathrm{2}}$ inductively coupled plasma (ICP). The absorption intensities of the light due to H atom in the H$_{\mathrm{2}}$ ICP were measured as a function of H$_{\mathrm{2}}$ partial pressure in the MHCL. With the increase in the H$_{\mathrm{2}}$ partial pressure, the absorption intensity decreased from 17 to 6 percent. This is probably due to the effect of self-absorption by H atoms inside the MHCL. With the increase in the self-absorption, the peak intensity of H atom spectrum emitted from the MHCL decreases, while light in the spectrum edge region, which is less absorbed by H atoms, remains virtually unchanged. Using this light as a probe light, the background absorption in the target plasma could be estimated. [Preview Abstract] |
Tuesday, October 29, 2019 8:15AM - 8:30AM |
CT3.00002: Measurements of N$_{\mathrm{2}}$(A$^{\mathrm{3}}\Sigma _{\mathrm{u}}^{\mathrm{+}}$,v$=$0) Populations in a Nonequilibrium Supersonic Flow Wind Tunnel Elijah Jans, Ilya Gulko, Terry Miller, Igor Adamovich Absolute time-resolved population of N$_{\mathrm{2}}$(A$^{\mathrm{3}}\Sigma _{\mathrm{u}}^{\mathrm{+}}$,v$=$0) electronic state has been measured in the plenum of a Mach 5 blowdown wind tunnel by Tunable Diode Laser Spectroscopy (TDLAS). N$_{\mathrm{2}}$(A) is generated in the plenum of the wind tunnel using a ns pulse generator (30 kV, FWHM 10 ns), operated at a pulse repetition rate from 4 to 100 kHz. The wind tunnel is operated at the plenum pressure of P$_{\mathrm{0}}=$227 Torr, with the flow expanding to a static pressure of P$=$1.15 Torr in the test section, corresponding to the Mach number of 4.2. During the run, the laser wavelength is tuned to the peak absorption of the overlapping transitions Q$_{\mathrm{1}}$(18) and Q$_{\mathrm{3}}$(8) in the N$_{\mathrm{2}}$(B,v$=$2รพรพ$\leftarrow $A,v$=$0) band, at 771.417 nm, and the absorption signal is measured during the discharge burst and in the afterglow. At 4 kHz pulse repetition rate, N$_{\mathrm{2}}$(A,v$=$0) population peaks at 1.6x10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$ after each discharge pulse, , and decays between the pulses almost completely. At 100 kHz pulse repetition rate, N$_{\mathrm{2}}$(A,v$=$0) population increases during the first 5 pulses, peaking at 4x10$^{\mathrm{13}}$ cm$^{\mathrm{-3}}$, and then begins to decay before leveling off after 100 pulses. Comparison with kinetic modeling is expected to provide insight into the mechanism of N$_{\mathrm{2}}$(A) excitation and decay at these conditions. [Preview Abstract] |
Tuesday, October 29, 2019 8:30AM - 8:45AM |
CT3.00003: Simultaneous Measurement of Local Densities of Atomic Oxygen and Ozone in Pure 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 the difficulty in measuring their local densities. The ozone density is usually 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 dissociation by incident UV light, disturbs the measurement. Therefore the compensation of ozone interference is important in atomic oxygen measurement. In this study, we achieved the separation of ozone interference from discharge-originated atomic oxygen, by focusing on the laser intensity dependence of TALIF signals on them. By varying the laser intensity in the TALIF measurement, the atomic oxygen density is separated from the ozone interference signals. Under short-gapped pulsed barrier discharge, the measured atomic oxygen decay rate agreed with the ozone production rate. It means the atomic oxygen decay is dominated by ozone production reaction, not by the recombination of atomic oxygen. This compensation method can be applied to the absolute density calibration of atomic oxygen by ozone density. [Preview Abstract] |
Tuesday, October 29, 2019 8:45AM - 9:00AM |
CT3.00004: Oxygen atom and negative ion densities and kinetics by cavity ringdown spectroscopy Jean-Paul Booth, Abhyuday Chatterjee, Olivier Guaitella, Sergey Zyryanov, Dmitry Lopaev, Tatyana Rakhimova, Grant Ritchie Accurate absolute density and kinetic measurements of oxygen atoms and negative ions are necessary for rigorous testing of oxygen plasma models. We have developed cavity ringdown spectroscopy of the forbidden $^1$D-$^3$P transition at 630nm using an external cavity tuneable diode laser, and used it to measure oxygen atom densities and translational temperatures (from the Doppler profile) in DC positive column discharges as a function of O$_{2}$ pressure (0.5-7 Torr) and current (10-40 mA). We also developed time-resolved CRDS in (partial and full) modulated discharges, allowing the loss kinetics to be investigated and showing dramatic differences in the loss mechanisms between the discharge and the afterglow. We were also able to observe the weak photodetachment continuum absorption of O$^{-}$ negative ions, The negative ion density is minimal when the O atom mole fraction is highest, confirming that associative detachment is the dominant loss mechanism. [Preview Abstract] |
Tuesday, October 29, 2019 9:00AM - 9:30AM |
CT3.00005: Multi-diagnostic approach in homogeneous discharges to constrain effectively CO2 plasmas kinetic models Invited Speaker: Olivier Guaitella CO2 plasmas are a good example of the difficulty of creating predictive models when too many basic data are very poorly known. We have chosen to study simple plasma discharges, but with the help of numerous and complementary diagnostics in order to establish sufficiently complete data sets to effectively constraint kinetic models of pure (or in gas mixtures) CO2 plasma. We used DC and RF discharges at a few mbar, in continuous, pulsed or modulated mode. The vibration temperatures of CO and CO2 were measured by time-resolved infrared absorption, but also by Raman scattering. The absolute densities and loss frequencies of the oxygen atoms were obtained by TALIF and actinometry but also with a new CRDS technique using the transition O(3P) -\textgreater O(1D) at 630 nm. Gas temperature, electric field and spatial density profiles were also measured. All these measurements made it possible, step by step, to isolate and determine essential parameters and to develop excellent and reliable comparisons with the models. As an example, by working in a closed reactor without gas flow, it has been possible to determine the direct electron impact dissociation cross-section of CO2 for which values with orders of magnitude of discrepancy exist in the literature. Different surfaces such as glass fibers with CeO2 are now being studied in contact with the plasma to promote conversion efficiency. Surface reactivity was studied by isotopic exchange monitored with infrared absorption, and with IR transmission measurements through solid pellets. All this work provides access to a detailed description of CO2 plasma, but a similar approach can be applied to other gases to move towards a systematic method of kinetic scheme validation. [Preview Abstract] |
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