Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session UF21: Plasma Diagnostics: Spectroscopy II |
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Chair: Mark Johnston, Sandia National Laboratories Room: GEC platform |
Friday, October 8, 2021 10:15AM - 10:30AM |
UF21.00001: High-Speed Mass Spectrometer for Characterizing Multispecies Flash Desorbed Plasmas in Pulsed Power Applications Susan J Ossareh Sandia National Laboratories operates the world’s largest pulsed power facility, the Z-machine, used for research in fusion, energy, and national security. However, it is experiencing a power flow problem that could be partially attributed to gas desorption when a pulse runs through the inner magnetically insulated transmission lines (MITL). Due to the high currents the Z-machine creates, the MITL electrode heats up, causing flash desorption and forming a plasma which causes current loss This project will help develop an ultra-fast mass spectrometer, allowing direct measurements of the gasses from the electrodes heated to 4000°C in 50 nanoseconds. A mass spectrometer with this capability would allow more accurate predictive modeling of current loss for Next Generation Pulsed Power Drivers. The design for this spectrometer is based on an existing plasma diagnostic, the Energy and Velocity Analyzer for Distributions of Electric Rockets (EVADER) probe, which combines an electrostatic analyzer and Wien filter, yielding the ion-energy distribution function of species and their charge state. Recent work has aimed to increase measurement speed while maintaining low current resolution. Evaluation of the improvements to the diagnostic will be performed on a well-characterized ion source. |
Friday, October 8, 2021 10:30AM - 11:00AM |
UF21.00002: Absorption spectroscopy of reactive species generated by non-thermal process plasmas Invited Speaker: Keigo Takeda Atomic radicals in process plasmas are very important species to determine the process reactions. Absorption spectroscopy is one of optical methods for measuring the behaviors of atomic radicals. The atomic radicals have resonance lines in the vacuum ultraviolet (VUV) region. The absorption spectroscopy in the VUV region basically needs specialized VUV light source. Wavelength conversion methods in the VUV region are very powerful tools for obtaining VUV laser radiations although they need large tunable laser systems and special technique for frequency mixing in non-linear gas medium. In our group, micro-discharge hollow cathode lamp (MHCL) has been developed as a VUV light source [1], and the VUV absorption spectroscopy with the MHCL has been applied to measure the absolute densities of atomic radicals. From the results, the reaction mechanisms in low pressure plasma processes have been clarified in our group. Moreover, the behaviors of atomic species generated by atmospheric pressure plasma jets have been also investigated with VUV absorption spectroscopy [2-5]. Recently, new VUV light source with a self-absorbing effect has been successfully developed for the measurement of background absorption near the absorption line of target atomic radical caused by molecular species or particles in the process plasma. These can contribute to pushing the study of reaction mechanism due to atomic radicals in the plasma processes. [1] S. Takashima, M. Hori, T. Goto, A. Kono, M. Ito, K. Yoneda, Appl. Phys. Lett. 75 (1999) 3929. [2] M. Iwasaki, K. Takeda, M. Ito, T. Yara, T. Uehara, M. Hori, Jpn. J. Appl. Phys. 46 (2007) L540. [3] K. Takeda, M. Kato, F. Jia, K. Ishikawa, H. Kano, M. Sekine, M. Hori, J. Phys. D: Appl. Phys. 46 (2013) 464006. [4] K. Takeda, K. Ishikawa, H. Tanaka, M. Sekine, M. Hori, J. Phys. D: Appl. Phys. 50 (2017) 195202. [5] K. Takeda, T. Kumakura, K. Ishikawa, H. Tanaka, M. Sekine, M. Hori, Appl. Phys. Express 10 (2017) 036201. |
Friday, October 8, 2021 11:00AM - 11:15AM |
UF21.00003: Diagnostics of a pulsed microwave discharge used for nitrogen fixation by means of infrared absorption and emission spectroscopy Omid Samadi Bahnamiri, Abhyuday Chatterjeea, Rony Snyders, Nikolay Britun Nowadays, plasma-assisted nitrogen fixation processes have been demonstrated as a highly promising alternative to the environmentally impacting Haber-Bosch process [1]. The community develops abundant attempts to optimize these processes to attain a higher order of fixation at lower energy cost. One of the best potential candidates, low pressure pulsed microwave (MW) discharges those based on surface wave launchers [2,3], remain particularly unexplored for nitrogen fixation. |
Friday, October 8, 2021 11:15AM - 11:30AM |
UF21.00004: Surface charge diagnostics by multiple internal reflection Kristopher Rasek, Franz X Bronold, Holger Fehske We propose to measure the charge accumulating at a plasma-dielectric interface via infrared multiple internal reflection. The negative charge deposited into the plasma-facing dielectric, forming the negative part of an electric double layer (the positive part being the plasma sheath), leads to a change of the reflection coefficient, when the interface is subjected to infrared radiation. Based on the Boltzmann equations for the charge kinetics of the double layer [1] and nonlocal surface response functions to calculate the reflection coefficient, we show theoretically and numerically that a local, Drude-like expression is in fact sufficient to describe the optical response. It contains only the integrated surface charge, enabling thus a straightforward analysis of measured data. To amplify the charge-induced change in the reflectivity, we suggest an experimental setup utilizing the plasma-solid interface as a multi-internal reflection element. Numerical results indicate that in such a setup the magnitude of the wall charge can directly be determined from the change it causes in the transmitivity of the optical element. |
Friday, October 8, 2021 11:30AM - 11:45AM |
UF21.00005: Experimental investigation of the initial condition of laser-induced plasmas by collective Laser Thomson scattering Yiming Pan, Kentaro Tomita, Atsushi Sunahara, Katsunobu Nishihara Temporal evolutions of two-dimensional (2D) plasma profiles produced by a Nd:YAG laser ( 5.9×109 W/cm2, 9 ns FWHM) were investigated at 0–20 ns, during and after the laser peak at 0.13–0.5 mm from the initial target surface by measuring the electron density (ne), temperature (Te), and drift velocity (Vd), using collective laser Thomson scattering (CTS). The ne peak was close to the target surfuce. The profile of Te was nonuniform and showed a peak at 0.3 to 0.4 mm above the target surface, and such high-temperature region of the plasma moved outward at the same speed as that of the expansion of the plasma. This indicated that the isothermal expansion ceased immediately after the peak of the ablation pulse. Even during the ablation pulse, the laser produced plasmas had considerable Vd, which was measured from the Doppler shift of the spectrum of CTS. The 2D profiles of Vd and pressure also show the plasma anisotropically expanded, strongly perferred the direction perpendicular to the target surface during the ablation pulse. |
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