Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session NR1: Diagnostics I |
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Chair: Richard Miles, Princeton University Room: Ballroom I |
Thursday, October 3, 2013 10:00AM - 10:30AM |
NR1.00001: Temperature diagnostics of a non-thermal plasma jet at atmospheric pressure Invited Speaker: Jan Sch\"{a}fer The study reflects the concept of the temperature as a physical quantity resulting from the second thermodynamic law. The reliability of different approaches of the temperature diagnostics of open non-equilibrium systems is discussed using examples of low temperature atmospheric pressure discharges. The focus of this work is a miniaturized non-thermal atmospheric pressure plasma jet for local surface treatment at ambient atmosphere [1]. The micro-discharge is driven with a capacitively coupled radio frequency electric field at 27.12 MHz and fed with argon at rates of about 1 slm through the capillary with an inner diameter of 4 mm. The discharge consists of several contracted filaments with diameter around 300 $\mu$m which are rotating azimuthally in the capillary in a self-organized manner. While the measured temperatures of the filament core exceed 700 K, the heat impact on a target below the plasma jet remains limited leading to target temperatures below 400 K. Different kinds of temperatures and energy transport processes are proposed and experimentally investigated. Nevertheless, a reliable and detailed temperature diagnostics is a challenge. We report on a novel diagnostics approach for the spatially and temporally resolved measurement of the gas temperature based on the optical properties of the plasma [2]. Laser Schlieren Deflectometry is adapted to explore temperature profiles of filaments and their behaviour. In parallel, the method demonstrates a fundamental Fermat's principle of minimal energy. Information acquired with this method plays an important role for the optimization of local thin film deposition and surface functionalization by means of the atmospheric pressure plasma jet. \\[4pt] [1] Sch\"{a}fer et al., Eur. Phys. J. D 60, 531 (2010).\\[0pt] [2] Sch\"{a}fer et al., Rev. Sci. Instrum. 83, 103506 (2012). [Preview Abstract] |
Thursday, October 3, 2013 10:30AM - 10:45AM |
NR1.00002: Investigation of plasma densities in noble gas discharges by THz Time Domain Spectroscopy Steffen Marius Meier, Tsanko Vaskov Tsankov, Dirk Luggenh\"{o}lscher, Uwe Czarnetzki Terahertz Time Domain Spectroscopy (THz TDS) is a non-invasive diagnostic method using ultra-short ($\sim$ps) radiation pulses with a broad spectral width ($\sim$0.1-5 THz) in the far-infrared region of the electromagnetic spectrum. Here this novel technique is applied to the determination of electron densities in low-temperature plasmas. The technical requirements will be introduced and advantages and challenges will be discussed. A new analysis method allows dealing with an inherent artefact resulting from the experimental technique. Application is made to ICP discharges in noble gases. The measurements are performed in a magnetic multi-pole ICP discharge at a filling gas pressure of 20 Pa. Densities up to $\approx 1 \cdot 10^{14}$ cm$^{-3}$ are obtained and a non-linear dependence on the power is observed for all noble gases. By comparison with an analytical model electron pressure and gas heating effects are identified. Measurements and model show good agreement suggesting that neutral gas depletion due to a very high electron pressure (up to 80\% of the filling gas pressure) is the major reason for the observed trends. [Preview Abstract] |
Thursday, October 3, 2013 10:45AM - 11:00AM |
NR1.00003: Progresses on resonance hairpin probe Shantanu Karkari, Nishant Sirse, Gurusharan Singh Gogna, Miles Turner This paper briefly reviews the recent developments on resonance hairpin probe as a diagnostic tool for characterizing low temperature electro-negative and strongly magnetized plasmas. As well known the hairpin is capable of measuring absolute values of electron density provided the plasma surrounding the pins is homogeneous and free from adjoining dielectrics. However this is far from reality because of several factors that influence the actual resonance condition such as the proximity of the probes ceramic support and the presence of sheaths around the resonator pins all contributing to the effective permittivity observed by the hairpin. On the other hand dual resonance frequency has been observed in magnetized plasma. The hairpin probe was also applied in conjunction with pulsed laser photo-detachment for measuring time-resolve negative ion density in pulsed-dc magnetron discharge. Recently an independent method based on a pulsed hairpin probe is developed for quantifying electronegative plasma parameters. Using this method both negative ion density and its temperature has been estimated. The results are found to be in good qualitative agreement with those obtained from pulsed photo-detachment technique. [Preview Abstract] |
Thursday, October 3, 2013 11:00AM - 11:15AM |
NR1.00004: ABSTRACT WITHDRAWN |
Thursday, October 3, 2013 11:15AM - 11:30AM |
NR1.00005: Diode laser heterodyne interferometry for refractive index measurement of small-scale plasmas in high pressure gases Keiichiro Urabe, Hitoshi Muneoka, Sven Stauss, Kazuo Terashima The electron density is one of the most important plasma parameters; however, the behavior of the electron density in high-pressure small-scale plasmas (so-called microplasmas) is still not well understood. We have studied the electron density in direct-current microplasmas operated at atmospheric pressure by using laser heterodyne interferometry and reported some results using CO$_{2}$ laser as a light source. By measuring the temporal evolutions of the refractive index of the plasmas by the interferometer, the temporal changes of the electron and gas number densities can be derived. Because of its shorter wavelength, using near-infrared diode laser (890 nm) as a light source allows improving the spatial resolution of the measurement over that obtained using a CO$_{2}$ laser (10.6 $\mu $m). Furthermore, by replacing a lock-in amplifier used in our previous CO$_{2}$-laser interferometry by a custom-made phase detecting module, the response time and temporal resolution of the measurements could be improved. Finally, we discuss potentials of the diode laser interferometry for the measurement of electron and gas number densities with the measurement results of pulsed microplasmas operated in atmospheric and higher pressure gases. [Preview Abstract] |
Thursday, October 3, 2013 11:30AM - 11:45AM |
NR1.00006: Cavity Enhanced Thomson Scattering for Low Temperature Plasmas Azer Yalin, Adam Friss, Brian Lee, Isaiah Franka This contribution describes the design, simulation, and initial experimental development of a novel laser Thomson scattering (LTS) system for measurement of weakly-ionized low temperature plasmas. The LTS approach uses a high power intra-cavity beam of power $\sim$10-100 kW to provide increased scattered photon counts and sensitivity as compared to conventional LTS experiments that use light sources with orders of magnitude lower average power. The high power intra-cavity beam is generated by locking a narrow linewidth source laser to a high-finesse optical cavity via Pound-Drever-Hall locking. The plasma (to be studied) is housed with the high-finesse optical cavity. The high-power source is combined with a detection system comprised of a high-suppression triple monochromator and a low-noise photomultiplier tube used in photon counting mode. We present simulations of signal strengths and scattering spectra including elastic scatter background, detector dark counts, and random (counting) noise contributions. Expected experimental performance is assessed from fits to the simulated data. The number density and electron temperature of a 10$^{10}$ cm$^{-3}$ plasma should be accurately measurable with standard deviation of \textless 5{\%} in a measurement time of 5 minutes per wavelength channel. We also present experimental development including characterization of laser locking, and initial Rayleigh and Raman signals which will be used to calibrate the Thomson system. [Preview Abstract] |
Thursday, October 3, 2013 11:45AM - 12:00PM |
NR1.00007: Diagnostics of inductively-coupled plasmas in HBr: Bromine atom and electron densities Jean-Paul Booth, Nishant Sirse, Robert Soriano, Mickael Foucher, Pascal Chabert Inductively-coupled plasmas (ICP) containing hydrogen bromide are widely used gas for conductor-etch applications, often using mixtures with Cl$_{2}$ and O$_{2}$. However, very few scientific studies (whether theoretical, simulation or experimental) have been made of HBr plasmas. We have studied pure HBr plasmas in an industrial-scale ICP (diameter 550mm, height 100mm, excited at 13.56MHz by a 4-turn planar coil) adapted for advanced diagnostic techniques. We have developed a new detection scheme for Br atoms using two-photon laser-induced fluorescence (TALIF). The relative variation of Br atoms was determined as a function of HBr pressure (5-90 mTorr) and RF power (20-500W). The Br density increases with pressure over this range, although the dissociation fraction (Br density divided by the total gas pressure) decreases with pressure. The Br density also increases with RF power up to about 100W, but then progressively saturates. The Br decay rate was measured in the afterglow of a pulsed plasma. The electron density was determined using a microwave hairpin resonator, and was found to peak. at 10 mTorr HBr pressure at all RF powers. This behaviour is very similar to that observed in pure Cl$_{2}$, although the densities are about a factor 2 lower in HBr. [Preview Abstract] |
Thursday, October 3, 2013 12:00PM - 12:15PM |
NR1.00008: Measurement of Time-Dependent Ion Velocity Distribution Function by Laser Induced Fluorescence in a Cylindrical Hall Thruster with Driven Spoke Yuan Shi, Ahmed Diallo, Yevgeny Raitses, Stephane Mazouffre This paper reports, for the first time, effects of spoke on ion velocity distribution function measured by time-resolving laser induced fluorescence. To scan ion speed, the 5d$^{4}$F$_{5/2}$-6p$^{4}$D$_{5/2}$ transition of Xe$+$ is excited using tunable diode laser. Photons from 6p$^{4}$D$_{5/2}$-6s$^{4}$P$_{3/2}$ transition are collected by a photomultiplier tube and counted by a multichannel scaler. To subtract background, a mechanical chopper is used to generate laser pulses whose power is monitored by a photodiode. To achieve phase-locked accumulation of fluorescence photons, spoke is driven using successively phase-shifted square waves on anode segments and the driving signal is used to synchronize photon accumulation to spoke in data post processing. To resolve three ion velocity components, two laser beams are established, with one beam measuring axial velocity and the other beam measuring some linear combination of radial and azimuthal velocities, depending on the position of collection volume with respect to thruster plume. Measurements shows ion distribution function oscillates with spoke. Along the thruster axis, ion density is strongly modulated while axial ion velocities are not affected. Off-axis effects of spoke will also be discussed. [Preview Abstract] |
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