Langmuir probe diagnostics of an atmospheric pressure, vortex–stabilized nitrogen plasma jet

Abstract

Langmuir probe measurements in an atmospheric pressure direct current (dc) plasma jet are reported. Sweeping probes were used. The experiment was carried out using a dc non-transferred arc torch with a rod-type cathode and an anode of 5 mm diameter. The torch was operated at a nominal power level of 15 kW with a nitrogen flow rate of 25 Nl min À1. A flat ion saturation region was found in the current-voltage curve of the probe. The ion saturation current to a cylindrical probe in a high-pressure non local thermal equilibrium (LTE) plasma was modeled. Thermal effects and ionization/recombination processes inside the probe perturbed region were taken into account. Averaged radial profiles of the electron and heavy particle temperatures as well as the electron density were obtained. An electron temperature around 11 000 K, a heavy particle temperature around 9500 K and an electron density of about 4 Â 10 22 m À3 , were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found throughout the plasma jet. The electron and heavy particle temperature profiles showed good agreement with those reported in the literature by using spectroscopic techniques. It was also found that the temperature radial profile based on LTE was very close to that of the electrons. The calculations have shown that this method is particularly useful for studying spraying-type plasma jets characterized by electron temperatures in the range 9000-14 000 K. V

On the use of the double floating probe method to infer the difference between the electron and the heavy particles temperatures in an atmospheric pressure, vortex-stabilized nitrogen plasma jet

“…7 and 8 shows that the present results are in good agreement with those reported by using a single probe method in the same dc plasma torch, where marked LTE departures were also found. 17 These results also support the validity of the hypothesis of the kinetic deviations with respect to LTE suggested in Ref. 27.…”

“…17 The factor 1.4 in Eq. (3) corresponds to an estimation of 1/ln|1 + d/R p | with d/R p ≈ 1 (S = 2 π R p L p is the probe collecting area, M is the ion mass, and T h∞ is the heavy particles temperature far from the probe).…”

“…2,3,5 The Langmuir (electrostatic) probes long ago became one of the most important tool in plasma diagnostics and a) Electronic mail: prevosto@waycom.com.ar they are extensively used to obtain spatially and timeresolved information on plasma parameters, mostly in lowpressure plasmas. [6][7][8] However these probes have been also successfully employed to study high-pressure highly-ionized plasma discharges, [9][10][11][12][13][14][15][16][17][18] which are typically found in atmospheric pressure, high-current arc torches. Double floating probe method 19 offers some advantages over (single) Langmuir probes.…”

“…17 To derive the electron and heavy particle temperatures, and the plasma composition, it was necessary to take a critical assumption regarding the kinetic deviations with respect to the local thermal equilibrium (LTE). 27 The work described here concerns the application of the double floating probe method to study such atmospheric pressure plasma jet.…”

Electron density measurements of atmospheric-pressure non-thermal N2 plasma jet by Stark broadening and irradiance intensity methods

“…Typical methods to measure the electron density include the Langmuir probe, laser heterodyne interferometry, and laser Thomson scattering, as well as optical emission spectroscopy (OES). [10][11][12][13][14][15][16][17][18] The probe method is not suitable for electron density measurement of non-thermal atmospheric-pressure plasmas because of the limited size of the discharge and strong collisional processes. The complicated and expensive laser system also limits the use of laser diagnostics in real applications.…”