Electron densities and energies of a guided argon streamer in argon and air environments

Abstract

In this study we report the temporally and spatially resolved electron densities and mean energies of a guided argon streamer in ambient argon and air obtained by Thomson laser scattering. The plasma is driven by a positive monopolar 3.5 kV pulse, with a pulse width of 500 ns and a frequency of 5 kHz which is synchronized with the high repetition rate laser system. This configuration enables us to use the spatial and temporal stability of the guided streamer to accumulate a multitude of laser/plasma shots by a triple grating spectrometer equipped with an ICCD camera and to determine the electron parameters. We found a strong initial n e -overshoot with a maximum of 7 × 10 19 m −3 and a mean electron energy of 4.5 eV. This maximum is followed by a fast decay toward the streamer channel. Moreover, a 2D distribution of the electron density is obtained which exhibits a peculiar mushroom-like shape of the streamer head with a diameter significantly larger than that of the emission profile. A correlation of the width of the streamer head with the expected pre-ionization channel is found.

Electric field measurement in the dielectric tube of helium atmospheric pressure plasma jet

“…The detection limits are mostly determined by the laser stray light and are in the order n e > 10 12 cm -3 . 52 The electron densities estimated in this work are well below 10 12 cm À3 just before the exit of the tube. In order to make better comparison with the measurements of the electron density by Thomson scattering and the estimation presented in this article, we calculated electron densities in the tube and the effluent of the plasma jet operating with gas flow of 1000 SCCM.…”

Electron characterization in weakly ionized collisional plasmas: from principles to techniques

“…Hübner et al [77] reported that the time-resolved n e varied in the range of (0.1-2.0) × 10 13 cm −3 and the T e ranged from 0.2-1.6 eV in a 250 ns-pulsed helium plasma jet driven at 20 kHz. A strong initial n e overshoot with a maximum of 7 × 10-13 cm −3 and a mean electron energy of 0.1-3.0 eV were observed in an argon plasma jet driven by a 3.5 kV positive dc pulse with a pulse width of 500 ns and a repetition frequency of 5 kHz [78]. Using a similar setup, Park et al [84] reported that the time-averaged n e was 1 × 10 9 cm −3 and T e was (1.0-2.5) eV via a comparison of the absolute intensity of continuum emission spectrum with the theoretically calculated neutral bremsstrahlung emissivity.…”

“…For further insights, the electrons in plasma jets has also been characterized using various electron diagnostic techniques, such as laser Thomson scattering [76][77][78], laser interferometry [79], Stark broadening of hydrogen atomic lines [80][81][82], and continuum radiation [84]. The line broadening method has been widely used for most electron studies in atmospheric-pressure plasmas, particularly in microwave-and radio-frequency-excited plasmas because of their high n e .…”

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.…”