Departures from local thermodynamic equilibrium in cutting arc plasmas derived from electron and gas density measurements using a two-wavelength quantitative schlieren technique

PREVOSTO, LEANDRO; ARTANA, GUILLERMO; KELLY, HÉCTOR; MANCINELLI ,BEATRIZ

JOURNAL OF APPLIED PHYSICS

AMER INST PHYSICS

Año: 2010

0021-8979

A two-wavelength quantitative Schlieren technique that allows inferring the electron and gasdensities of axisymmetric arc plasmas without imposing any assumption regarding statisticalequilibrium models is reported. This technique was applied to the study of local thermodynamicequilibrium (LTE) departures within the core of a 30 A high-energy density cutting arc. In order toderive the electron and heavy particle temperatures from the inferred density profiles, a generalizedtwo-temperature Saha equation together with the plasma equation of state and the quasineutralitycondition were employed. Factors such as arc fluctuations that influence the accuracy of themeasurements and the validity of the assumptions used to derive the plasma speciestemperature were considered. Significant deviations from chemical equilibrium as well as kineticequilibrium were found at elevated electron temperatures and gas densities toward the arc coreedge. An electron temperature profile nearly constant through the arc core with a value of about14 000–15 000 K, well decoupled from the heavy particle temperature of about 1500 K at the arc core edge, was inferred.