Thomson microwave scattering for electron number density diagnostics of miniature plasmas at low pressure

Wang, Xingxing; Ranjan, Apoorv; Shneider, Mikhail N.; Shashurin, Alexey

doi:10.2514/6.2019-3250

Cited by 4 publications

(1 citation statement)

References 12 publications

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“…Однако среди них очень мало работ по исследованию атмосферной низкотемпературной плазмы, которая может быть использована в медицине, а также для обработки термочувствительных материалов. Один из описанных в литературе методов исследования атмосферной плазмы, который также успешно использовался для исследования плазмы низкого давления, основан на регистрации рассеянного от исследуемой области плазмы СВЧ-сигнала частотой 10…11 ГГц [7,[17][18][19][20][21]. В этих работах исследуемая область плазмы с размерами меньше длины волны зондирующего сигнала размещалась между двух рупорных антенн на некотором удалении от них.…”

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Diagnostics of Atmospheric Plasma Jets of Helium and Argon Barrier Discharge in a Cylindrical Microwave Cavity Resonator

Astafiev

Altmark

Lesiv

et al. 2023

Izv. vysš. učebn. zaved. Ross., Radioèlektron.

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Introduction. Technologies related to the use of low-temperature atmospheric plasmas are developing at a rapid pace. Creation of new low-temperature plasma sources for specific applications requires monitoring of dynamic processes in such discharges with a high time resolution. Electron concentration is one the most important plasma characteristics, which can be very low for a low-temperature atmospheric pressure plasma. However, the methods currently available for diagnostics of gas-discharge plasmas are either characterized by insufficient sensitivity or unable to monitor dynamic processes in non-stationary discharges. In this regard, the development of new diagnostic approaches to low-temperature atmospheric plasma seems to be a relevant research direction.Aim. To develop a diagnostic method for an atmospheric plasma with a low gas temperature and a low electron concentration in a cylindrical microwave resonator.Materials and methods. The proposed diagnostic method is based on the well-known principle of measuring the frequency shift and the Q-factor of the eigenmodes of the microwave resonator, inside which the plasma under study is located.Results. Measurements of the atmospheric barrier discharge plasma jets in a helium and argon stream in a cylindrical microwave resonator were performed. The proposed geometry made it possible to significantly increase the sensitivity of measurements. It became possible to exclude the effect of polarization degeneracy in a round cylindrical resonator. The developed system was also tested on test objects with a known value of permittivity.Conclusion. A method for microwave diagnostics of stationary and non-stationary cold atmospheric plasma jets in a cylindrical resonator, inside which transmitting and receiving antennas are installed, as well as an orthogonal thin conductor preventing the excitation of undesirable modes, was developed.

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Diagnostics of Atmospheric Plasma Jets of Helium and Argon Barrier Discharge in a Cylindrical Microwave Cavity Resonator

Astafiev

Altmark

Lesiv

et al. 2023

Izv. vysš. učebn. zaved. Ross., Radioèlektron.

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Thomson and collisional regimes of in-phase coherent microwave scattering off gaseous microplasmas

Patel

Ranjan

Wang

et al. 2021

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The total number of electrons in a classical microplasma can be non-intrusively measured through elastic in-phase coherent microwave scattering (CMS). Here, we establish a theoretical basis for the CMS diagnostic technique with an emphasis on Thomson and collisional scattering in short, thin unmagnetized plasma media. Experimental validation of the diagnostic is subsequently performed via linearly polarized, variable frequency (10.5–12 GHz) microwave scattering off laser induced 1–760 Torr air-based microplasmas (287.5 nm O2 resonant photoionization by ~ 5 ns, < 3 mJ pulses) with diverse ionization and collisional features. Namely, conducted studies include a verification of short-dipole-like radiation behavior, plasma volume imaging via ICCD photography, and measurements of relative phases, total scattering cross-sections, and total number of electrons $$N_{e}$$ N e in the generated plasma filaments following absolute calibration using a dielectric scattering sample. Findings of the paper suggest an ideality of CMS in the Thomson “free-electron” regime—where a detailed knowledge of plasma and collisional properties (which are often difficult to accurately characterize due to the potential influence of inhomogeneities, local temperatures and densities, present species, and so on) is unnecessary to extract $$N_{e}$$ N e from the scattered signal. The Thomson scattering regime of microwaves is further experimentally verified via measurements of the relative phase between the incident electric field and electron displacement.

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Thomson microwave scattering for diagnostics of small plasma objects enclosed within glass tubes

Ranjan

Patel

Wang

et al. 2022

Review of Scientific Instruments

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In this work, coherent microwave scattering in the Thomson regime was demonstrated for small-scale plasmas enclosed within a glass tube and validated using a well-known hairpin resonator probe technique. The experiments were conducted in a DC discharge tube with a diameter of 1.5 cm and a length of 7 cm. Thomson microwave scattering (TMS) diagnostics yielded electron number densities of about 5.9 × 1010 cm−3, 2.8 × 1010 cm−3, and 1.8 × 1010 cm−3 for air pressures in the discharge tube of 0.2, 0.5, and 2.5 Torr, respectively. Measurements using the TMS technique were consistent across the tested microwave frequencies of 3–3.9 GHz within the margin of error associated with non-idealities of the IQ mixer utilized in the circuit. The corresponding densities measured with the hairpin resonator probe were 4.8 × 1010, 3.8 × 1010, and 2.6 × 1010 cm−3. Discrepancies between the two techniques were within 30% and can be attributed to inaccuracies in the sheath thickness estimation required for correct interpretation of the hairpin resonator probe results.

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Thomson microwave scattering for electron number density diagnostics of miniature plasmas at low pressure

Cited by 4 publications

References 12 publications

Diagnostics of Atmospheric Plasma Jets of Helium and Argon Barrier Discharge in a Cylindrical Microwave Cavity Resonator

Diagnostics of Atmospheric Plasma Jets of Helium and Argon Barrier Discharge in a Cylindrical Microwave Cavity Resonator

Thomson and collisional regimes of in-phase coherent microwave scattering off gaseous microplasmas

Thomson microwave scattering for diagnostics of small plasma objects enclosed within glass tubes

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