Investigation on the electron density and temperature in a nanosecond pulsed helium plasma jet with Thomson scattering

Abstract

AbstractDiagnostic of spatiotemporal distribution of the electron density and temperature of atmospheric pressure plasma jets is a difficult task, as Thomson scattering, which is the most used measurement, suffers from the stray light induced by Rayleigh scattering. In this paper, a new strategy is reported to restrain the stray light in Thomson scattering. With a physical mask placed at the output of a single spectrometer, the scattering signal is obtained with a relatively high ratio of signal to noise. The electron density in a pulsed kHz‐driven atmospheric plasma jet interacting with a dielectric target is measured by using this method. A donut‐shaped distribution of electron density is observed at an axial position 1 mm away from the nozzle. The radius of the ring structure decreases with the reduction of the gas flow rate. The electron density reaches a maximum of about 4.5 × 1020 m−3 at a delay time of 150 ns from the onset of the pulse. A similar time relationship between the electron density and plasma emission intensity is also identified. Higher applied voltage leads to a faster increasing and a higher peak value of the electron density. Pulse width shows little impact on the generation and decay of electrons.