Investigation of the relevant kinetic processes in the initial stage of a double-arcing instability in oxygen plasmas

B. MANCINELLI; L. PREVOSTO; J. C. CHAMORRO; F. O. MINOTTI; H. KELLY

PHYSICS OF PLASMAS

AMER INST PHYSICS

Lugar: New York; Año: 2018

1070-664X

A numerical investigation of the kinetic processes in the initial (nanosecond range) stage of the double-arcing instability was developed.The plasma-sheath boundary region of an oxygen-operated cutting torch was considered.The energy balance and chemistry processes in the discharge were described. It is shown that the double-arcing instability is a sudden transition from a diffuse (glow-like) discharge to a constricted (arc-like) discharge in the plasma-sheath boundary region arising from a field-emission instability. A critical electric field value of 10^7 volts/m was found at the cathodic part of the nozzle wall under the conditions considered. The field?emission instability drives in turn a fast electronic-to-translational energy relaxation mechanism, giving rise to avery fast gas heating rate of at least 10^9 K/s, mainly due to reactions of preliminary dissociation of oxygen molecules via the highly excited electronic state O2(B^3Sigmau-) populated by electron impact.It is expected that this fast oxygen heating rate further stimulates the discharge contraction through the thermal instability mechanism.