Characterization of a surface barrier discharge in helium

Abstract

A surface barrier discharge (SBD) operated with helium is investigated in a pressure range from 50 mbar to 1 bar and a gas flow of up to 400 sccm. A sinusoidal or pulsed excitation signal with a voltage amplitude of up to 1 kV and frequency in the range of 4 to 8 kHz is applied. Time resolved and time averaged ICCD pictures of the discharge are analysed. The temporally and spatially resolved concentrations of metastable excited species are determined using diode laser atomic absorption spectroscopy. The transition 2 3 S → 3 3 P • , absorbing the light of wavelength 388.975 nm, is used for the He(2 3 S) diagnostics. The absorption of the transition from the resonant level (2 1 P • → 3 1 D) at 667.999 nm is shown for comparison. Parallel to the absorption, the total light emission and the electrode voltage and current are traced. The role of the metastable excited species in sustaining a SBD in helium is discussed.

Effect of electron energy probability function on plasma CVD/modification in a 13.56 MHz hollow cathode discharge

“…To explain the variations of the electron density, we refer to the energy diagram of the Ar and He atomic system (figure 7) and the EEPFs of the pure argon plasma (figure 4) which the He atoms encounter when helium is introduced in the remote region. The required energy (24.5 eV) for He ionization is much greater than the ionization energy (11.7 eV) of Ar; in addition, the rate coefficient for direct electron impact ionization for He (∼10 −22 m 3 s −1 [39]) is much smaller than that for Ar (∼10 −17 m 3 s −1 [30]); therefore, direct electron impact ionization of He atoms could not be expected for all argon pressures. The energies of the metastable levels for argon (Ar m ) and helium (He m ) are 11.5-11.8 eV and 19.8-20.6 eV, respectively, and the rate coefficient for electron impact excitation in He (∼10 −14 m 3 s −1 [39]) is greater than that for Ar (∼10 −16 m 3 s −1 [30]).…”

“…The required energy (24.5 eV) for He ionization is much greater than the ionization energy (11.7 eV) of Ar; in addition, the rate coefficient for direct electron impact ionization for He (∼10 −22 m 3 s −1 [39]) is much smaller than that for Ar (∼10 −17 m 3 s −1 [30]); therefore, direct electron impact ionization of He atoms could not be expected for all argon pressures. The energies of the metastable levels for argon (Ar m ) and helium (He m ) are 11.5-11.8 eV and 19.8-20.6 eV, respectively, and the rate coefficient for electron impact excitation in He (∼10 −14 m 3 s −1 [39]) is greater than that for Ar (∼10 −16 m 3 s −1 [30]). The clear impact of He injection in the discharge was found at lower helium fractions, that is, for argon pressures of 10 and 30 Pa, where the electron density increases; we attribute this increase in the electron density to the contribution of He metastables in the direct ionization of Ar atoms in the ground state and/or to the ionization of He atoms from their metastable levels.…”

Piezoelectric Direct Discharge: Devices and Applications

“…In principle, all plasma diagnostics methods used for APP [56,57], especially for APPJ [58][59][60][61] can be applied for the characterization of the PDD. Additionally, some techniques used for characterization of RTP operation [62] can also be useful.…”

“…To the first category belong the single gas gap DBD with one or two dielectric barriers and the double gas gap DBD with micro-discharges ignited on both sides of the dielectric barrier. To the second category belong the surface DBD (SDBD) [56,91] and the coplanar surface DBD (CSDBD) [152].…”

Control of diffuse and filamentary modes in an RF asymmetric surface barrier discharge in atmospheric-pressure argon

“…However, the transition from a diffuse mode to a discharge driven by streamers, which is often less useful for applications requiring homogeneous treatment, is very sensitive to the driving voltage, feed-gas mixture and the properties of the dielectric barrier [8,9]. This is also true for asymmetric surface DBDs, or ASDBDs, which are typically reported to operate exclusively in non-diffuse modes in both atomic and molecular gases such as air [10][11][12], helium [13] and argon [14].…”