A comparative study of transient characteristics of argon and hydrogenated-argon pulse-modulated induction thermal plasma

Solving a time-dependent two-dimensional local thermodynamic equilibrium (LTE) model simulation of Ar and Ar-H₂ atmospheric pressure, a high-power RF-induction thermal plasma was performed. The effects of shimmer current level (SCL) in pulse-modulated mode and hydrogen concentrations on different flow fields were predicted. The radiation intensities of Ar I (751 nm) for different SCL were calculated from the temperature fields. For the same operating conditions as simulation, plasma was successfully generated in pulse-modulated mode and spectroscopic measurements were carried out to investigate the effects of SCL upon temporal plasma properties. Response times (rising, falling, on-delay, and off-delay time) of temporal radiation intensity were crosschecked for both experimental and simulated ones. The rising time increased gradually with the decrease of SCL, though the falling time remained almost unchanged with SCL. For example, for Ar plasma at 86%, 79%, 72%, 65%, 50%, and 40% SCL the rising times were 2.7, 3.0, 3.4, 3.4, 3.6, and 3.8 ms, respectively. And for Ar-H₂ plasma (2.4% H₂), at 87%, 77%, 72%, 63%, 55%, and 45% SCL, rising times were 2.5, 3.0, 3.0, 3.4, 3.7, 3.9, and 4.0 ms, respectively. Hydrogen inclusion slowed down the plasma response during the off-to-on pulsing transition at lower SCL and constricted the plasma axially. Finally, part of the simulated results was compared with experimental determinations and acceptable agreements were found. The discrepancies, in few cases, explicated mainly that the LTE assumption did not prevail in pulse-modulated plasma, especially around the on-pulse transition