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 JT4: High-pressure Discharges and MicrodischargesLive
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Chair: Toshiro Kaneko, Tohoku University, Japan |
Tuesday, October 6, 2020 1:00PM - 1:30PM Live |
JT4.00001: Thomson scattering diagnostics of a streamer discharge in atmospheric-pressure air and laser-produced plasmas for light sources Invited Speaker: Tomita Kentaro Laser Thomson scattering (LTS) is well-known as a powerful technique to measure electron density (n$_{\mathrm{e}})$, electron temperature (T$_{\mathrm{e}})$, averaged ionic charge ($Z)$, and so on. LTS yields local values with high temporal resolutions. In this paper, collective and non-collective Thomson scattering measurements for two types of industrial plasmas are described. One is a streamer discharge in atmospheric-pressure air. The other one is laser-produced plasmas for extreme ultra-violet (EUV) lithography. Streamer discharge in atmosphere-pressure air has been studied for a long time and is used for various applications. To analyze the production mechanism of reactive species, information on electrons, especially for the electron velocity distribution function (EVDF) is crucial. The EVDF are provided by solving the electron Boltzmann equation. However, there has been no direct measurement of the EVDF in the air streamer. Then, LTS was performed to measure the EVDF of the air streamer. It was found that the measured EVDF clearly deviated from the Maxwellian distribution, as predicted by the Boltzmann equation. Extreme-ultraviolet (EUV) lithography is a promising technology for high-volume manufacturing of next-generation semiconductor devices. Laser-produced Sn plasma is known to show sharp and strong spectrum in the EUV regime (at $\lambda =$13.5 nm). However, the optimization of Sn plasma requires to measure and control Z and T$_{\mathrm{e}}$ in the region of larger ion density (n$_{\mathrm{i}})$ within the etendue limit. However, these parameters (Z, T$_{\mathrm{e}}$ and n$_{\mathrm{i}}=$n$_{\mathrm{e}}$/Z) have never been measured owing to the extremely small size (\textasciitilde 500 $\mu $m) and short lifetime (\textasciitilde 20 ns). We performed LTS measurement. Then, time-resolved and two-dimensional profiles of n$_{\mathrm{e}}$, T$_{\mathrm{e}}$, and Z of the EUV light sources were revealed. As the result, 1) a characteristic hollow-like density profile was observed, 2) significant amount of “useless” Sn ions should exist within the limited etendue, whose temperature was too low to contribute EUV emission. [Preview Abstract] |
Tuesday, October 6, 2020 1:30PM - 1:45PM Live |
JT4.00002: Comparison of Non-Resonant and Resonant Preionization for Dual-Pulse Laser Plasma Ignition in Air Azer Yalin, Carter Butte, Ciprian Dumitrache Laser ignition of fuel-air mixtures is of interest for a number of combustion applications. In particular, recent experimental and modeling studies have focused on preionization schemes, with dual pulses, owing to promising results relating to pulse energy requirements, extension of the lean limit and combustion efficiency when igniting fuel-air mixtures. In this submission we compare preionization via non-resonant 266 nm radiation versus resonant 287 nm radiation based on 2$+$1 resonance enhanced multi-photon ionization (REMPI) of molecular oxygen (with nanosecond duration pulses in both cases) using a combination of experimental and modeling approaches. Experimentally, we measure gas temperature and electron density via Rayleigh and Thomson scattering respectively, perform chemiluminescence imaging of the OH radical, and record pressure traces of combustion events. On the modeling side, we have developed a 2-D spatially resolved gas dynamic plasma model to capture the plasma kernel evolution. Using these tools we find that the REMPI approach can be attractive in terms of forming relatively high electron density plasmas (order 10$^{\mathrm{18}}$ cm$^{\mathrm{-3}})$ with lower total pulse energies by a factor of \textasciitilde 2.5 as compared to the non-resonant scheme. Differences in the plasma driven gas dynamics as well as ignition characteristics between the two schemes are also discussed. [Preview Abstract] |
Tuesday, October 6, 2020 1:45PM - 2:00PM Live |
JT4.00003: Student Excellence Award Finalist: The Ionization Mechanism of Thermal Sparks Nicolas Minesi, Pierre Mariotto, Gabi-Daniel Stancu, Christophe Laux Recent experimental studies demonstrated that nanosecond discharges can produce fully ionized plasmas via the so-called thermal spark. In room air, it was shown that the plasma can reach full ionization within a few nanoseconds, and that the gas temperature can increase above 40,000 K. In this work, experimental and numerical approaches are used to investigate this fast ionization. The electron number density is measured using the Stark broadening of the H$_{\mathrm{\alpha }}$ line. The lineshape fitting of the N$^{\mathrm{+}}$ and O$^{\mathrm{+}}$ lines between 480 and 520 nm provides (i) the electron temperature, assumed equal to the gas temperature, and (ii) a second measurement of the electron number density by Stark broadening. A third measurement of the electron number density is given by the continuum radiation of electrons. These measurements are compared to the output of a 0-D numerical simulation performed using ZDPlasKin and BOLSIG$+$. The originality of the kinetic model is to consider not only the excited electronic states of N$_{\mathrm{2}}$, but also the excited electronic states of O and N. We show that the experimental and numerical results agree only if the ionization of excited states of O and N are included in the simulations. [Preview Abstract] |
Tuesday, October 6, 2020 2:00PM - 2:15PM Live |
JT4.00004: Control of electron dynamics and plasma chemistry in atmospheric rf plasma jets via voltage waveform tailoring Ihor Korolov, David Steuer, Volker Schulz-von der Garthen, Zoltan Donko, Lena Bischoff, Gerrit Hubner, Peter Hartmann, Yue Liu, Thomas Mussenbrock, Julian Schulze Atmospheric pressure capacitively coupled radio frequency discharges operated in He/N2 and He/O2 mixtures and driven by tailored voltage waveforms are investigated using a COST microplasma reference jet as a function of the reactive gas admixture and the number of consecutive harmonics used to drive the discharge. We demonstrate that Voltage Waveform Tailoring (VWT) allows one to enhance the control of the dynamics of energetic electrons in distinct spatio-temporal regions of interest within the electrode gap and the RF period and, thus, to optimize and control the generation of helium metastables, atomic nitrogen or oxygen species. [Preview Abstract] |
Tuesday, October 6, 2020 2:15PM - 2:30PM Live |
JT4.00005: Dense, cold, nonequilibrium plasma states in nanosecond-scale pulsed laser microdischarges Taemin Yong, Mark Cappelli We describe studies of the generation of dense non-equilibrium plasma states in atmospheric pressure. Discharge plasmas are produced using a Nd:YAG laser (15 ns, 15 mJ, 532 nm) followed by second-stage electron heating using a relatively low energy picosecond laser (20 ps, 1.2 mJ, 532 nm). A third, continuous-wave HeNe laser (10 mW, 632.8 nm), is used to record time-resolved (but spatially averaged) inverse Bremsstrahlung absorption from which electron number density is inferred. The analysis of the data relies weakly on estimates of electron temperature obtained from the continuous background emission in the visible range of the spectrum. Comparisons are made to electron density inferred from Stark broadening the OI 777 nm line. We find that second-stage picosecond laser heating elevates the average electron density by approximately 20 {\%}, and present a model to understand the underlying kinetics. [Preview Abstract] |
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