Deviation from Local Thermodynamic Equilibrium State in Thermal Plasma
Spectroscopic analysis of Ar–H<sub>2</sub> and Ar–N<sub>2</sub> plasmas revealed that the population density of the excited states of each species (Ar, H and N) followed a Boltzmann distribution, but each species had its own respective excitation temperature. The temperature of the argon was lower than that of the hydrogen in the plasma of Ar–H<sub>2</sub> mixture. The temperature of the nitrogen was close to that of the argon in the plasma of Ar–N<sub>2</sub> mixture under one atmospheric pressure. The estimation of the temperatures defined by the velocity distribution functions from the experimental conditions indicate that there are the possibilities to have higher temperatures for the hydrogen than that for the argon in the plasma. These results suggest that there is a deviation from local thermodynamic equilibrium (LTE) in these plasmas under one atmospheric pressure. The deviations from LTE in these plasmas are explained by the differences in the energy flow in the plasmas. The energy flows of these plasmas are considered as follows from the estimated relaxation times of energy distributions for each species. As for the Ar–H<sub>2</sub> plasma, the electric energy is transferred to the electrons and then the energy of electrons is transferred to the hydrogen atoms. The argon atoms are mainly heated by collisions with the hydrogen atoms. In the case of the Ar–N<sub>2</sub> plasma, both the argon atoms and the nitrogen atoms are heated by collisions with the electrons which obtain the electric energy. As a result, the temperature state of <I>T</I><sub>e</sub>≈<I>T</I><sub>H</sub>><I>T</I><sub>Ar</sub> and <I>T</I><sub>e</sub>><I>T</I><sub>Ar</sub>≈<I>T</I><sub>N</sub> could exist in the plasma.
- ISIJ international
ISIJ international 38(11), 1165-1169, 1998-11-15
The Iron and Steel Institute of Japan