Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session PR3: Diagnostics I (Optical) |
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Chair: Richard B. Miles, Princeton University Room: Oregon Convention Center A106 |
Thursday, November 8, 2018 9:30AM - 9:45AM |
PR3.00001: Reactive species distribution and quenching coefficients in the effluent of an atmospheric pressure plasma jet using picosecond TALIF Sandra Schroeter, J. Bredin, A. West, J. Dedrick, K. Niemi, E. Wagenaars, T. Gans, D. O'Connell Atmospheric pressure plasmas (APPs) can be used as sources for reactive oxygen and nitrogen species (RONS), which are believed to play a key role in different plasma applications, such as industrial processing or biomedical applications. To investigate the effects of APP jets on treated media, it is necessary to quantify RONS and determine their spatial distribution in the plasma effluent region. Here, we present measurements of absolute atomic species densities of O, N, and H, in the effluent of a radio-frequency capacitively coupled plasma jet in helium with admixtures of N$_{\mathrm{2}}$, O$_{\mathrm{2}}$, and H$_{\mathrm{2}}$O, using picosecond two-photon absorption laser-induced fluorescence (ps-TALIF). The fast decay of the laser-excited states is typically a limiting factor of conventional nanosecond TALIF systems when investigating APPs due to the fast quenching rates of the laser-excited states, which have to be calculated from literature quenching coefficients, and an estimate of the gas composition. Using ps-TALIF, we are able to measure lifetimes of laser-excited states, and can also determine quenching coefficients with background gases. O, N, and H densities decay with different rates in the plasma effluent with increasing axial distance from the nozzle. Therefore, ratios of reactive species densities change with distance, which could be useful for tailoring species densities for applications. By investigating the reaction kinetics, we have identified important consumption pathways for these species. [Preview Abstract] |
Thursday, November 8, 2018 9:45AM - 10:00AM |
PR3.00002: Spatially Resolved Oxygen Recombination Coefficients from Pulse Induced Fluorescence Kristopher Ford, Joel Brandon, Sang Ki Nam, Steven Shannon Surface recombination coefficients remain a key parameter for plasma chemistry models, particularly for reactive radical species that play important roles in surface processing. Pulse induced fluorescence, or PIF, is an affordable and easily implemented method for this measurement. Here, a fast-gated iCCD array is used to take radial images of a low pressure inductive plasma. The active surface is quartz, and wavelength filters select the 844 nm line of atomic oxygen and the 750 nm line of argon for actinometry analysis. The decay constant from PIF intensity data provides an apparent surface recombination coefficient as a function of radial position. Double decay constant behavior is observed, which compares well to previous work in microwave oxygen plasma over silica. The surface loss probability profile and trends resulting from gas flow/pressure changes will be presented. The associated implications for gas dynamics and modeling will also be discussed. [Preview Abstract] |
Thursday, November 8, 2018 10:00AM - 10:15AM |
PR3.00003: Novel Plasma Diagnostic Method Using Spectroscopy for Hall Thruster Optimization Ariel Sandberg, Rebecca Martin, Julia Nistel, Brooke Brozek, Timothy Smith We present preliminary tests in a parallel-plate argon discharge plasma of an optical diagnostic that provides non-invasive, time-resolved qualitative measurements of relative neutral and ionic species densities. The technique uses retroreflected intrinsic line emission as a source for absorption \footnote{M.A. Cappelli et al., ``Vacuum ultraviolet absorption measurements of ground state xenon in the near field of a low power Hall thruster,'' AIAA-2003-5007, AIAA Joint Propulsion Conference, Huntsville, AL, 20-23 Jul 2003.}, with a ratio of reflected-and-absorbed emission strength to direct emission strength that decreases monotonically with absorbing species density. Time histories of this ratio clearly show low-frequency (100 mHz) oscillations driven in a $pd = 1.5$ cm-Torr argon discharge (at a plasma density of $2.5 \times 10^{13}$/cm$^3$ and electron temperature of 3.66 eV). Future experiments will add a parallel retroflected line emission beam, interference-filtered photomultipliers, and high-speed beam chopping to provide a two-point plasma wave dispersion diagnostic for hollow cathode ion acoustic turbulence \footnote{M.P. Georgin et al., ``Passive high-speed imaging of ion acoustic turbulence in a hollow cathode,'' AIAA-2017-4973, Jul 2017.} [Preview Abstract] |
Thursday, November 8, 2018 10:15AM - 10:30AM |
PR3.00004: Student Excellence Award Finalist: Coupling induced changes of complex samples to the experienced electric field during a plasma-surface interaction using Mueller polarimetry Elmar Slikboer, Ana Sobota, Enric Garcia-Caurel, Olivier Guaitella Mueller polarimetry is applied to characterize how complex samples (e.g. biomedical / organic layers) change during a plasma exposure while simultaneously measuring the electric field to which they are exposed to. Recently, new advances have been made by using imaging Mueller polarimetry on electro-optic crystals following different approaches allowing the imaging of all the individual electric field components separately (axial and radial), together with the temperature pattern formed inside the target. Now imaging Mueller polarimetry is used as an optical diagnostic technique for the first time to examine the Mueller matrix of a combined sample consisting of a complex material on top of an electro-optic crystal. The combined sample is exposed to guided ionization waves generated by a non-thermal atmospheric pressure plasma jet. The analysis of the measured Mueller matrices separates depolarization caused by surface properties of the complex sample from the retardance which is caused by the electric field going through it. This unique diagnostic allows to couple directly the spatial dependent changes of a sample under exposure of a plasma jet to the inhomogeneous electric field it experiences. [Preview Abstract] |
Thursday, November 8, 2018 10:30AM - 10:45AM |
PR3.00005: Non-uniform electric field diagnostics in an atmospheric pressure radio frequency helium plasma Lei Wang, Gheorghe Dinescu, Christophe Leys, Anton Nikiforov Electric fields in the sheath region of an atmospheric pressure radio frequency (RF) helium plasma are studied through Stark polarization spectroscopy. Helium lines around 492 nm including the forbidden line and field-free line are observed and analyzed in order to investigate the Stark effect under electric field. A fitting method based on one field-free line and two forbidden line profiles is proposed to study the non-uniform electric field (high/ low field region) in the sheath. Time resolved electric field measurements are conducted for the sheath region at the grounded electrode. The high field region exhibits a peak and valley value around 33 kV/cm and 12kV/cm. The low field region is characterized by a maximum and minimum value about 10 kV/cm and 6 kV/cm. The electric field and emission intensity approximately follow the current waveform in RF cycles. This work intends to contribute to the insight of electric field dynamics in the sheath of atmospheric pressure RF plasmas. [Preview Abstract] |
Thursday, November 8, 2018 10:45AM - 11:00AM |
PR3.00006: Student Excellence Award Finalist: Extending Stark Broadening Measurements to Low Electron Densities Using Active Spectroscopy in Helium Abdullah Zafar, Elijah Martin, Steve Shannon Passive spectroscopic measurements of Stark broadening have been reliably used to diagnose electron density for decades. Due to Doppler and instrument broadening, these passive techniques are limited to $n_e$ measurements of $\geq10^{14}$ cm$^{-3}$ for most atomic transitions. At Oak Ridge National Laboratory, a diagnostic approach has been implemented that leverages active spectroscopy to overcome this limitation. The diagnostic technique is based on measuring the spectral line profile of the $2^1$P$\rightarrow6^1$D He transition using Doppler-free saturation spectroscopy (DFSS), a laser-based absorption technique that significantly diminishes Doppler broadening and eliminates instrument broadening. The spectrum is then fit to quasi-static Stark broadening model to extract the electron density. Using this approach, $n_e$ has been successfully diagnosed via Stark Broadening measurements in a low density ($10^9-10^{12}$ cm$^{-3}$), low temperature (5-10 eV), magnetized (500-900 G), He plasma in the mTorr pressure range. Experimental results will be presented for $\pi$ and $\sigma$-polarizations and compared to Langmuir probe measurements. Crossover resonances (an artifact of the diagnostic) and collisional effects are also addressed along with their impact on the measurements [Preview Abstract] |
Thursday, November 8, 2018 11:00AM - 11:15AM |
PR3.00007: Abstract Withdrawn
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Thursday, November 8, 2018 11:15AM - 11:30AM |
PR3.00008: Tomography-based real-time spatial uniformity diagnostics for meter-sized plasmas Wonho Choe, Juhyeok Jang, Sanghoo Park, Joo Young Park In this presentation, we show optical emission spectral tomography diagnostics developed to measure spatial uniformity of meter-sized large-area plasmas for display manufacturing. The lines of sight and detector location were selected based on tomographic reconstruction tests using synthetic phantom images. The developed collection optics system is rather simple, consisting of slits, plano-convex lenses, optical bandpass filters, and array detectors. Using the collection optics, the line-integrated emission was acquired from meter-sized rectangular radio-frequency plasma, which was developed for display manufacturing. From the measured emission, two-dimensional (2D) spatial distributions of argon atomic emissions were obtained through tomographic reconstruction based on the Phillips--Tikhonov algorithm. The 2D argon plasma emission profiles matches well with the shape of the electrode and etch profile. In addition, 2D profiles of the excitation temperature were obtained from the measured argon emissions. [Preview Abstract] |
Thursday, November 8, 2018 11:30AM - 11:45AM |
PR3.00009: Development of a collective Thomson scattering system for laser-produced high-Z plasmas produced for soft X-ray light sources Yuta Sato, Raimu Fukada, Fumitaka Ito, Kentaro Tomita, Kiichiro Uchino We have developed a collective laser Thomson scattering system, which has been adapted to detect the ion feature spectra from EUV light source plasmas, and revealed spatial profiles of plasma parameters such as electron density (ne), electron temperature (Te), and averaged ionic charge (Z). [1], [2] However, this system is not sufficient to diagnose plasmas produced for soft X-ray light sources, with which less than 10 nm wavelength emission are required. This is because there is no information on the shape of ion feature due to a high number of averaged ionic charge. To solve this problem, we have been developing a new collective Thomson scattering system, which can detect both the ion feature and the electron feature, simultaneously. Using this system, ne can be fixed by the ion feature, and Te can be specified by the ne and electron feature. Then, Z can be determined from the ion feature even when Z is larger than 15, which is predicted for the water-window light (2.3- 4.4 nm) sources. In this research, the purpose is to achieve simultaneous measurement of the laser produced tin plasmas, whose Z is larger than 10. We have already succeeded to measure ion feature, however, S/N ratio of electron feature and self-emission of the plasmas is not sufficient. Therefore, we are trying to improve S/N ration by using Stimulated Brillouin Scattering system to compress probing laser pulse width . [1] Y. Sato et al. Jpn. J. Appl. Phys. 56, 036201 (2017) [2] K. Tomita et al. Sci. Rep. 7, 12328 (2017) [Preview Abstract] |
Thursday, November 8, 2018 11:45AM - 12:00PM |
PR3.00010: Development of a Virtually Imaged Phased Array (VIPA) Spectrometer for Electron and Ion Temperature Measurement Christopher Limbach Laser Thomson scattering is a well-known non-intrusive diagnostic technique for characterization of plasmas with high spatial and temporal resolution. Depending on the ratio of the scattering length to the Debye length, the scattering process may occur in the coherent, incoherent or transitional regime and the scattered light spectrum may span from picometers to nanometers around the excitation wavelength. \\ In this work, we report on the development and application of a high resolution and high bandwidth spectrometer based on a virtually imaged phased array (VIPA) optical element. Coupled with a grating for cross-dispersion, the device permits characterization of the Thomson line shape (form factor) across all scattering regimes. Operating with a maximum resolution of 0.24 GHz and a bandwidth of several nanometers, we demonstrate simultaneous point measurements of the Thomson electron and ion features in a laser-induced atmospheric pressure plasma. The resulting time-resolved dataset of ion and electron temperature and electron density is discussed in the context of the transition from local thermal equilibrium to non-equilibrium during the plasma recombination process with applications to Laser-Induced Breakdown Spectroscopy (LIBS) [Preview Abstract] |
Thursday, November 8, 2018 12:00PM - 12:15PM |
PR3.00011: Single shot gas and weakly ionized plasma flow measurements with coherent Rayleigh-Brillouin scattering Alexandros Gerakis, Mikhail Shneider We suggest the use of single shot coherent Rayleigh-Brillouin scattering (CRBS) as a gas or weakly-ionized plasma flow and translational temperature measuring technique, applicable to both atomic and molecular gases, as well as gas mixtures. 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 gas or gas mixture, in a single laser shot [1]. Preliminary estimates show that CRBS could detect gas flow velocities down to 10-20 ms-1 in a single laser shot, rendering it an ideal remote and non-intrusive diagnostic for aerospace applications, among other uses. We are currently working towards the application of single shot CRBS as a gas flow measurement technique and its use in neutral or weakly ionized gas flow environments. [1] A. Gerakis, M. N. Shneider, and P. F. Barker, "Single-shot coherent Rayleigh--Brillouin scattering using a chirped optical lattice," Opt. Lett. 38, 4449-4452 (2013) [Preview Abstract] |
Thursday, November 8, 2018 12:15PM - 12:30PM |
PR3.00012: Anisotropy in Microwave Scattering by a Small Plasma in a Magnetic Field Christopher Galea, Mikhail Shneider, Richard Miles Microwave scattering by a small plasma has been modeled in the literature, resulting in microwave scattering diagnostics such as radar resonance-enhanced multi-photon ionization (Radar REMPI) and the Rayleigh microwave scattering (RMS) technique. However, it has not yet been considered what the effect of an external magnetic field would be on the aforementioned diagnostics. A model based on the transport properties of plasma in a magnetic field has been developed to capture the effects of an external magnetic field on the microwave scattering by a small plasma. In the presence of an external magnetic field, the electron mobility becomes a tensor due to the differing transport properties of electrons along and perpendicular to the magnetic field, which in turn affects the microwave scattering signal both in magnitude and in polarization. The dependences of the scattered microwave signal magnitudes for the various polarizations on both the Hall parameter and the relative magnetic field orientation are derived, showing potential for remote measurements of magnetic field strength and topology. Potential limitations of the proposed measurement techniques will also be discussed. [Preview Abstract] |
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