Influence of released surface electrons on the pre-ionization of helium barrier discharges: laser photodesorption experiment and 1D fluid simulation

Abstract

The presented work highlights the role of residual weakly-bound surface electrons acting as an effective seed electron reservoir that favors the pre-ionization of diffuse barrier discharges (BDs). A glow-like BD was operated in helium at a pressure of 500 mbar in between two plane electrodes each covered with float glass at a distance of 3 mm. The change in discharge development due to laser photodesorption of surface electrons was studied by electrical measurements and optical emission spectroscopy. Moreover, a 1D numerical fluid model of the diffuse discharge allowed the simulation of the laser photodesorption experiment, the estimation of the released surface electrons, and the understanding of their impact on the reaction kinetics in the volume. The breakdown voltage is clearly reduced when the laser beam at photon energy of 2.33 eV hits the cathodic dielectric that is charged with residual electrons during the discharge pre-phase. According to the adapted simulation, the laser releases only a small amount of surface electrons in the order of 10 pC. Nevertheless, this significantly supports the pre-ionization. Using a lower photon energy of 1.17 eV, the transition from the glow mode to the Townsend mode is induced due to a much higher electron yield up to 1 nC. In this case, both experiment and simulation indicate a retarded stepwise release of surface electrons initiated by the low laser photon energy.

Role of excimer formation and induced photoemission on the Ar metastable kinetics in atmospheric pressure Ar–NH3 dielectric barrier discharges

“…The yield for such reaction, γph, is assumed comparable to the one of ions and Ar(1s) atoms (R17)) in Table 2. Note that, γph includes the contributions of both direct, VUV-induced electron emission and VUV-induced desorption of electrons bound to the plasma-exposed dielectrics by weak polarization interactions [70][71][72][73]. In addition, photons are described with an infinite speed: photoemission is therefore instantaneous after the spontaneous dissociation of Ar2*.…”

Influence of Oxygen on the Multiple-Current-Pulse Behavior in an Atmospheric Homogeneous Helium Dielectric Barrier Discharge With Air Impurities

“…Due to the stronger electronegativity of O 2 (compared to N 2 ), the attachment reactions are only available for O 2 , but not for N 2 [25]- [28]. Thus the attachment reaction is one of the important differences between the chemical reactions regarding O 2 and N 2 .…”

“…Then, a question arises whether, in the study of MCP behaviors, the oxygen in air impurities will remarkably affect the discharge characteristics and its ignorance will lead to quantitatively or qualitatively unacceptable results. As a matter of fact, the presence of O 2 in the helium discharges has been investigated by Nemschokmichal et al [25]- [28]. They proposed that due to the strong electronegativity of O 2 , anions are formed and the attachment of electrons would reduce the effective ionization, thereby influencing the ignition of the discharge and other discharge characteristics.…”

Electric Breakdown in Long Discharge Tubes at Low Pressure (Review)

“…In [105], illumination of a dielectric (BSO crystal) with a LED at a wavelength of 632 nm reduced the surface charge lifetime by a factor of 10 3 . In [106], the ignition voltage of barrier discharge in helium decreased significantly when a dielectric (glass) was irradiated with a neodymium laser at a wavelength of λ 532 nm, and radiation with λ 1064 nm caused a transition of a discharge from the glowing mode to Townsend. It is believed that it is the desorption of electrons upon illumination of a dielectric surface with discharge radiation that leads to the synchronization of breakdowns in the filament form of barrier discharge [101,102,104].…”