Effects of secondary electron emission coefficients on Townsend's second ionization coefficient in argon dielectric barrier discharges

Abstract

One-dimensional fluid model simulations are performed to investigate how the secondary electron emission arising from ions (γ i ), metastable atoms (γ m ), and photons (γ p ) affect Townsend's second ionization coefficient (γ ) in argon dielectric barrier discharges. Since Townsend's breakdown criterion determines the value of γ , it is naturally affected by the discharge condition such as the reduced electric field (E /p) as well as the combination of γ i , γ m , and γ p . It also depends on the other contributions from the indirect ionization processes such as cumulative ionizations or metastable-metastable collision ionizations. When the nonionic electron-yielding processes such as the effects of γ m , γ p , and the indirect ionizations are considered, the calculated γ increases largely under the higher pd (pressure times distance) branch of the Paschen curve. Since the experimental characteristics of γ , which decreases with E /p, can hardly be explained without such nonionic processes, the contributions of those processes can be quite important in Townsend discharges especially under high pd conditions. These processes tend not to appear and γ tends to converge to γ i under the lower pd branch of the Paschen curve. The value of γ i can possibly be estimated by using γ under the lower pd condition.

Metastables as a probe for low-temperature plasma characteristics in argon

“…It is noted that the ejected electron with 0 has a chance to be back-scattered in the direction of the material surface on collision with surrounding neutral atoms in a low-temperature plasma. In fact, the secondary ionization coefficient by metastables γ m , generally used for the modeling of low-temperature plasmas, has a lower value [54], as compared with γ m measured and calculated in a vacuum in table 7.…”

Influence of surface parameters on dielectric-barrier discharges in argon at subatmospheric pressure

“…The experimental and numerical findings reported in [14][15][16][17][18][19][20] clearly illustrate the importance of the surface parameters of the dielectric material in DBDs. In the present paper, numerical modelling results for DBDs with a dielectric barrier on both electrodes in argon at subatmospheric pressure are presented and discussed.…”

“…Furthermore, a recent parameter study on the CO 2 dissociation in a geometrically symmetric DBD by means of timeand space-dependent fluid modelling showed that a markedly higher power density with raised CO 2 conversion frequency is obtained for dielectrics with larger ε r [18]. The effects of secondary electron emission coefficients on Townsend's second ionization coefficient in a narrow-gap argon DBDs was analysed by one-dimensional fluid model simulations in [19], demonstrating that the experimental characteristics of that ionization coefficient can hardly be explained without secondary electron emission due to ion impact. Akashi et al [20] also showed by means of two-dimensional fluid modelling of an atmospheric-pressure oxygen DBD that the decrease of the secondary electron emission results in a decrease of the number of filaments and an increase of the electron density.…”

Effects of relative permittivity on primary and secondary streamers in atmospheric pressure dielectric barrier discharge

“…where γ (referred to as the gamma coefficient) was set to 0.01 [29,30]. • All radial derivatives of densities were set to zero at open boundaries [31] The charge density Q accumulated on the dielectric surface was calculated as follows:…”