On the gas heating mechanism for the fast anode arc reattachment in a non-transferred arc plasma torch operating with nitrogen gas in the restrike mode

PREVOSTO, LEANDRO; KELLY, HÉCTOR; MANCINELLI ,BEATRIZ; CHAMORRO, JUAN CARLOS

PLASMA CHEMISTRY AND PLASMA PROCESSING

SPRINGER

Lugar: Berlin; Año: 2015 vol. 35 p. 1057 - 1070

0272-4324

The present work provides a detailed kinetic analysis of the time-resolveddynamics of the gas heating during the arc reattachment in nitrogen gas in order tounderstand the main processes leading to such a fast reattachment. The model includes gasheating due to the relaxation of the energy stored in the vibrational as well as the electronicmodes of the molecules. The results show that the anode arc reattachment is essentiality athreshold process, corresponding to a reduced electric field value of E/N*40 Td for theplasma discharge conditions considered in this work. The arc reattachment is triggered by avibrational instability whose development requires a time of the order of 100ls. ForE/N80?100 Td, most of the electron energy is transferred to gas heating through themechanism of vibrational?translational relaxation. For larger values ofE/Nthe electronic?translational energy relaxation mechanism produces a further intensification of the gasheating. The sharp increase of the gas heating rate during the last fewls of the vibrationalinstability give rises to a sudden transition from a diffuse (glow-like) discharge to aconstricted arc with a high current density (*107A/m2). This sudden increase in thecurrent density gives rise to a new anode attachment closer to the cathode (where thevoltage drop between the original arc and the anode is the largest) thus causing the decayof the old arc spot.