High-Spatial-Resolution Multichannel Thomson Scattering Measurements for Atmospheric Pressure Microdischarge

Abstract

High-spatial-resolution multichannel Thomson scattering measurement scheme is applied to the diagnostics of a microplasma produced between two knife-edge electrodes separated by a 100 µm microgap and driven by 2.45 GHz microwave. The method provides spatial profile of electron density, electron temperature, and gas temperature simultaneously in a single measurement, with a spatial resolution of ∼25 µm; the gas temperature is derived from the spectrum of rotational Raman scattering caused by molecules contained in the discharge gas. Measurements are carried out for discharges with air and He/N2(5%) mixture gas at atmospheric pressure and the differences in the basic plasma parameters are discussed.

Current status of microplasma research

“…As a first example, the Thomson scattering method has been applied to the measurements of n e and T e in a microwave (2.45 GHz) discharge in a micro-gap [30]. A typical result in air discharge gives n e ∼ = 2 × 10 15 cm −3 and T e ∼ = 1.2 eV at an input power of 100 W, while T g ∼ = 2500 K. This shows that microplasma can be in nonequilibrium state even under DC operation when the residence time τ d is kept small.…”

Measurement of Electron Density and Temperature Using Laser Thomson Scattering in PANTA

“…The predicted LTS signal per one laser shot is small. However, accurate LTS measurements are possible with signal accumulation methods as done in many previous studies [4,5,15,16]. the Nd:YAG laser (Continuum, Surelite III, laser energy 130 mJ at λ = 532 nm) was used as the light source.…”

“…1 (b). Because the basic configuration of the TGS has been already reported in many studies [4,5,17], only a brief explanation is presented here. The TGS mainly comprises six achromatic lenses ( f = 250 mm, diameter 46 mm), three diffraction gratings (2400 lines/mm), an entrance slit (width 0.2 mm), a physical notch filter (width 0.5 mm) at the first image plane, and an intermediate slit (width 0.2 mm) at the second image plane.…”

“…Laser Thomson scattering (LTS) is widely known as a reliable technique for the nonintrusive simultaneous measurement of electron density (n e ) and electron temperature (T e ) for various types of plasmas, such as magnetic confinement fusion plasmas [3], low-temperature plasmas for industrial applications [4][5][6], laser-produced plasmas [7][8][9], and others [10].…”

Heterodyne Interferometer for Measurement of Electron Density in High-Pressure Plasmas

“…This is because that electrons play a major role for carrying external energy to heavy particles inside the plasma, and all other excited species can be calculated theoretically from the plasma parameters of electron density, electron energy distribution, and gas composition. Diagnostics of electron density have in the APPs have been reported by many researchers using Langmuir probe methods (Chang, 1973;Chang & Laframboise, 1976), Stark broadening measurement (Laux et al, 2003), and laser Thomson scattering measurement (Kono & Iwamoto, 2004). However, these methods have limitations for the APP measurements due to their finite sensitivities, expected perturbations or interferences, spatiotemporal resolutions, etc.…”