Interferometric measurement of particle densities in cascaded arcs at atmospheric pressure

Three plasma diagnostic methods, tunable infrared diode laser absorption spectroscopy, optical emission spectroscopy and microwave interferometry have been used to monitor concentrations of transient and stable molecules, CH 3 , CH 4 , C 2 H 2 , C 2 H 6 , and of electrons in capacitively coupled CH 4 -H 2 -Ar radiofrequency (RF) plasmas (f RF = 13.56 MHz, p = 100 Pa, φ total = 66 sccm) for various discharge power values (P = 10-100 W) and gas mixtures. The degree of dissociation of the methane precursor varied between 3% and 60%. The methyl radical concentration was found to be in the order of 10 12 molecules cm −3 and the electron concentration in the order of 10 10 cm −3 . The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons, C 2 H 2 and C 2 H 6 , produced in the plasma, increased with discharge power. The fragmentation rates of the methane precursor and conversion rates to the measured C-2 hydrocarbons were estimated in dependence on discharge power. Radial distributions of the electron and methyl radical concentrations, and of the gas temperature were measured for the first time simultaneously in the plasma region between the discharge electrodes. The measurements allow us to draw qualitative conclusions on the main chemical processes and the plasma chemical reaction paths.

Section: Abel Inversionmentioning

confidence: 99%

Diagnostic studies of species concentrations in a capacitively coupled RF plasma containing CH₄-H₂-Ar

Gathen

Röpcke

Gans

et al. 2001

“…The determination of radially resolved quantities in the case of rotationally symmetric plasmas from side-on distributions of line-of-sight integrated measurements is a well established method in the case of emission spectroscopy. The extension to interferometric diagnostics is also well known [3]. There are several new contributions related to the Abel inversion technique [4,5].…”

Section: Abel Inversionmentioning

confidence: 98%

“…The question may arise whether at this wavelength the influence of the neutral gas background on the refractive index is still negligible. A simple estimate on the basis of the data given in [3] shows, however, that for λ = 1 mm and the electron densities mentioned the neutral gas background has no significant influence.…”

Section: Introductionmentioning

confidence: 95%

Spatially resolved electron density distribution in an RF excited parallel plate plasma reactor by 1 mm microwave interferometry

Lukas

Müller

Gathen

et al. 1999

The electron distribution in the argon plasma of a capacitively coupled parallel plate reactor (13.56 MHz) is measured with spatial resolution. The line-of-sight integrated electron density is obtained with a quasi-optical heterodyne interferometer operating at the wavelength λ = 1 mm. The electron density distribution is measured in a sequence of planes between the electrodes whereby the radial distribution is determined in each plane by Abel inversion. This allows us to generate an (r, z) mapping of the electron density. The lateral resolution is 6.5 mm in the focal region; the phase resolution amounts to 7 × 10 −5 of a period so that a line density of 2 × 10 14 m −2 represents the lower limit of applicability.The spatial distributions are compared with electron density measurements at similar discharges by other groups and with probe measurements in the midplane of our discharge.

“…This approach exploits different wavelength dependencies of the TS and RS cross sections and was originally proposed by Miles and Limbach [37] and is named two-color laser scattering (2CLS). This method resembles two-color interferometry [38][39][40] where the refractive index includes contributions from neutrals (which increases with wavelength) and electrons (which decreases with wavelength). However, unlike 2CLS, two-color interferometry lacks temporal and spatial resolution and does not yield information on particle temperatures.…”

Section: Introductionmentioning

confidence: 99%

Two-color laser scattering for diagnostics of hydrogen plasma

Sobczuk

Dzierżęga

Zawadzki

et al. 2022

Two-color laser scattering (2CLS) method is proposed to measure electron and neutral densities, as well as electron and ion temperatures in hydrogen plasma. 2CLS uses two probe wavelengths to identify the Rayleigh scattering and Thomson scattering contributions coming from neutrals and electrons, respectively. Laser scattering signals were simulated for various conditions of a hydrogen plasma at thermodynamic equilibrium applying the available and calculated cross-sections for Rayleigh scattering by ground-sate and excited hydrogen atoms at probe wavelengths of 355 nm and 532 nm. The developed 2CLS method was eventually applied to study the laser-induced plasma in hydrogen at near atmospheric pressure. Temporally and spatially resolved electron and ion temperatures and densities of electrons and hydrogen atoms (ground-state and excited) were determined.