No abstract

Summary: Materials exposure to a flowing post discharge jet can induce a significant rise of materials temperature. This increase is related to the recombination of the atomic species produced in the discharge at the surface of the exposed materials, which is a highly exothermic process. At pressures below 10 Torr, this process is the main loss term for the atoms far away from the discharge. Nevertheless, a very small number of reliable data concerning atomic recombination probabilities, γ, is available in the literature. In this work, such data are obtained for the recombination of the nitrogen atoms on five materials (copper, aluminium, alumina, brass and Nylon) by the adjustment between measured surface temperatures and calculated values obtained by a 3D modelling of the post discharge reactor, which includes the enthalpy deposition at the walls. Results show a general decrease of the γ‐values with increasing pressure, as already mentioned by other authors. The sensitivity of the method is also studied.Evolution with pressure of the N‐atom recombination probability γN for aluminium, copper, brass, alumina and Nylon.imageEvolution with pressure of the N‐atom recombination probability γN for aluminium, copper, brass, alumina and Nylon.

The density of neutral nitrogen atoms in a glass reactor was measured by two absolute methods: two-photon absorption laser induced fluorescence (TALIF) and catalytic probes. The source of N atoms was nitrogen plasma created in a quartz tube by surfatron microwave generator operating at 2.45 GHz and adjustable output power up to 300 W. The TALIF measurements were performed using a dye laser which was pumped by a YAG laser. At the exit of the dye laser, the beam frequency was doubled through a KDP crystal and then mixed in a BBO crystal. The wavelength of the output laser beam was chosen at 206.65 nm so two-photon absorption was suitable to excite nitrogen atoms from the ground state to the 5d 2D state. Absolute N density was determined by using calibration with krypton. Simultaneously, the N atom density was measured with a fiber optics catalytic probe (FOCP) with a well-activated iron catalytic tip. Measurements were performed by both methods at nitrogen flows between 0.2 and 2 l min−1, and discharge powers between 60 and 300 W. At rather high nitrogen flows, the N atom density increased monotonically with increasing discharge power, while at lower flow saturation was observed. TALIF showed somewhat higher values than FOCP which was attributed to the accuracy of both methods. The main advantage of TALIF is a broader detection range, while FOCP is an extremely simple and inexpensive technique.