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 QR3: Plasma Diagnostics III |
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Chair: Brian Bentz, Sandia National Laboratories Room: Century III |
Thursday, October 31, 2019 1:45PM - 2:00PM |
QR3.00001: Addressing the Challenges of Using Pulse Induced Fluorescence to Obtain Accurate Surface Recombination Coefficients Kristopher Ford, Joel Brandon, Sang Ki Nam, Steven Shannon Pulse Induced Fluorescence is a fast and easily implemented technique for obtaining surface recombination coefficients from optical emission spectroscopy data. However, the traditionally implemented extraction of these coefficients from PIF data is reliant on an accurate fixed gas temperature. Here, the resulting temperature dependent uncertainty is discussed and addressed through rotational temperature measurement in conjunction with PIF measurements. In these experiments, a trace amount of nitrogen is introduced to estimate gas temperature from the second positive nitrogen band. The modified method has been demonstrated in an inductively coupled oxygen plasma over quartz, which is meant to be easily translatable to other dielectric/electronegative gas combinations similar to those found in semiconductor manufacturing equipment. [Preview Abstract] |
Thursday, October 31, 2019 2:00PM - 2:15PM |
QR3.00002: Radial distribution of air species diffusing into an RF Helium atmospheric pressure plasma jet Tam Nguyen, Peng Lin, Vincent Donnelly, Demetre Economou The effluent composition and properties of an atmospheric pressure plasma jet (APPJ) vary with the humidity of the ambient air. In order to achieve better control of the chemistry in the jet a coaxial shielding gas (N$_{\mathrm{2}})$ is employed that separates the plasma jet from the ambient. In this study, we use optical emission spectroscopy to measure the radial distribution of Ar (naturally occurring in air) diffusing into a 2 slm He plasma jet excited by a 13.7 MHz, 4.5 kV peak voltage. Ar 811.5 nm emission is magnified by a lens, fed into a spectrometer, then Abel inverted. Calibration is obtained by adding a known small amount of Ar to the He feed gas and recording a small increase in Ar emission, providing absolute Ar radial density profiles. At an axial distance of 5 mm from the nozzle, Ar mole fractions of 2.5x10$^{\mathrm{-5}}$ and 4x10$^{\mathrm{-5}}$ were obtained on axis with 4.5 slm and without nitrogen shielding gas, respectively. The Ar mole fraction was 3X higher at the radial edge of the plasma. At 1 mm from the nozzle, the Ar mole fraction on axis was 1x10$^{\mathrm{-6}}$ rising by 5X at the plasma edge. The effect of flow rate of the working and shielding gas will also be shown, along with comparisons with a 2D convective diffusion simulation of species concentration profiles. [Preview Abstract] |
Thursday, October 31, 2019 2:15PM - 2:30PM |
QR3.00003: Analysis of PROES and OES measurements of 100 Hz pulsed Ar Capacitively Coupled Plasma Keith Hernandez, Matthew Goeckner, Lawrence Overzet Findings are reported for Optical Emission Spectroscopic (OES) and Phase Resolved OES (PROES) measurements of a pulsed (100 Hz) capacitively coupled plasma (CCP) through Ar. OES spatiotemporal plots made from the Ar 750.4 nm spectral line and voltage measurements of the powered electrode were used to find three regions of interest (ROI) during the RF power on time. PROES measurements were made of these three ROI (plasma turn-on and approach to steady-state) and excitation rates were calculated using a kinetic model for the plasma environment. For the region of the steady-state the excitation rate is large for roughly 1/3 of the RF period, which is similar to that expected in continuous CCPs. The other two ROI (at the beginning of the power turn-on when the intensity is appreciable and at the time of maximum emission intensity) demonstrated excitation rates' profiles with additional heating contributions. These additions are consistent with the expected maximums in the electric field through the plasma which can be attributed to additional joule heating. [Preview Abstract] |
Thursday, October 31, 2019 2:30PM - 2:45PM |
QR3.00004: Rotational Temperature Evolution in Non-Self-Sustaining DC Discharge Plasma Source for Nitrogen Vibrational Excitation Yuki Kunishima, Keisuke Takashima, Toshiro Kaneko A Non-Self-Sustaining DC (NSS DC) discharge plasma source has been developed aiming for nitrogen fixation through nitrogen vibrational excitation. This plasma source is composed of two power sources; a nanosecond pulse plasma generator and a DC power supply. The apparent reduced electric field ($E/N)$ suitable for efficient nitrogen vibrational excitation is controlled by the applied DC voltage. It is found that the NSS DC discharge can turn into self-sustaining discharge when the nitrogen power loading is significantly high \textasciitilde sub kW. This leads to loss of the apparent $E/N$ control. Extension of the traveling distance of the ionization waves by the elongated nanosecond pulse width realize the NSS DC discharge at lower pulse repetition rates down to 3 kHz. This allows us to operate the NSS DC discharge at higher voltage without much increase in the discharge power loading and apparent $E/N$ of 3 Td is achieved. The temporal change of the nitrogen rotational temperature is estimated from a nitrogen second positive emission band. Observed relatively minor gas temperature rise due to the DC power loading may suggest that most of the DC discharge power loading is used for the nitrogen vibrational excitation. [Preview Abstract] |
Thursday, October 31, 2019 2:45PM - 3:00PM |
QR3.00005: Spatial Diagnostic Techniques of Striations in a DC Glow Discharge. Zachary White, Ryan Gott, Gabe Xu A common phenomenon observed in DC glow discharges and other plasma applications is the appearance of striations, alternating light and dark regions in the plasma. Although the occurrence of striations has been observed for many decades, the underlying nature of these instabilities has not been completely understood quite yet. The goal of the current work is to characterize the electron temperature and density of the standing striations in a DC plasma discharge. Measurements on the center of the striation, corner of the striation, and the dark space within the discharge were taken to obtain a general idea of how the characteristics of the striation changed over the striation length. The methods used to measure these properties in the plasma were by measuring the neutral lines of the plasma using optical emission spectroscopy and backing out the temperature and density by using a simplified Corona model and using Langmuir probes. To get a better understanding of the plasma, the gas pressure was ranged from 100 mTorr -- 1 Torr. The results of the current project were necessary to provide a comparison for the future diagnostic work that will be done using the Laser-Collisional Induced Fluorescence (LCIF) method. [Preview Abstract] |
Thursday, October 31, 2019 3:00PM - 3:15PM |
QR3.00006: Determining Metastable Density Through Afterglow Electron Density Measurements Steven Shannon, Kristopher Ford, Corey DeChant, Joel Brandon, David Peterson, Sang Ki Nam Metastable density is a key parameter for predicting plasma chemistry, particularly because it acts as a strong driver for plasma density through stepwise ionization. Most often, laser absorption is used to determine the metastable density in low pressure plasmas. However, it would be advantageous to measure both metastable and electron density simultaneously from a single diagnostic. This work proposes the use of a hairpin microwave probe in a power modulated plasma to determine both densities. Metastable pooling in the plasma afterglow generates a local maximum in the electron density trace, which can be used with simplified rate equations to determine metastable density. The method was first proposed by Greenberg and Hebner (J. Appl. Phys. 73, 1993), and is refined here for argon and helium plasmas. The results are compared with fluid simulations from the Multiphysics Object Oriented Simulation Environment, MOOSE. [Preview Abstract] |
Thursday, October 31, 2019 3:15PM - 3:30PM |
QR3.00007: Machine Learning for Low Temperature Plasma Diagnostics Bhaskar Chaudhury, Nirbhay Ram, Agam Shah, Himanshu Tyagi, Manas Bhuyan, Kaushal Pandya, Mainak Bandyopadhyay Langmuir Probe based measurements of the current (I) at various applied voltages (V) is probably the simplest way to diagnose low temperature plasmas. The standard (classical) approach requires analysis of different regions of the I-V curve for the determination of plasma parameters (electron density, temperature etc.). However, the classical approach can be error prone if there is a significant noise (due to collisions, RF noise, magnetic field etc.) in the Langmuir probe data resulting in inaccurate plasma characterization. To address this issue, we have developed a Machine Learning (ML) based algorithm to interpret the Langmuir probe based I-V data obtained from ROBIN (inductively coupled single RF driver based negative ion source) experiments, wherein we have explored Convolutional Neural Networks (CNNs) for determining the plasma parameters. Our analysis indicates that the classical approach is reasonably effective in measurement of plasma parameters, however this method is practically not accurate enough for experimental data with significant noise component and ML based method offers much better accuracy in such cases. The primary reason is that CNN based algorithm adaptively exploits the pattern in the I-V data unlike the classical model which uses fixed rules for the interpretation of the data. By performing extensive statistical analysis of the results, we have studied network's robustness, accuracy and computational demands compared with the classical approach. [Preview Abstract] |
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