Vacuum ultraviolet radiation in and from an atmospheric pressure plasma source

This work presents a computational study of the atmospheric pressure plasma of the COST jet source in He + 0.1% N-2 buffer gas, incorporating the treatment of the VUV resonant radiation from He atoms at a wavelength of 58.4 nm. The plasma is driven by single- and multi-frequency waveforms at various peak-to-peak voltages between 400 V and 685 V. The simulations, which include the photoemission of electrons from the electrodes as well as the photoionization of the N-2 molecules indicate that these processes, induced by the VUV radiation, have relatively little influence on the discharge characteristics due to other more efficient charged particle production mechanisms, e.g., Penning ionization. While the plasma characteristics are computed along one spatial dimension perpendicular to the electrodes, the tracing of the VUV photons is executed in the real 3D geometry of the plasma source to allow the computation of the VUV photon flux leaving the device through the orifice. Photon fluxes up to approximate to 5 x 1015 <i cm(-2) s(-1), corresponding to an energy flux of approximate to 18 mW cm(-2) are found at multi-frequency operation.