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Study of Post-Discharge Processes
Soural, Ivo ; Hrachová, Věra (referee) ; Brablec, Antonín (referee) ; Krčma, František (advisor)
The decaying plasma was studied by the optical emission spectroscopy. DC discharge created at 45 – 200 mA in Pyrex and Quartz tubes in flowing regime was used. The emission of three nitrogen spectral systems (1st and 2nd positive and 1st negative) were studied in time evolution for pressures of 500 – 5 000 Pa at two wall temperatures – ambient and liquid nitrogen (150 K inside the decaying plasma). Results showed that all three nitrogen systems (respectively N2(B, v), N2(C, v) and N2+(B, v) states as their origins) had their population maxima called pink-afterglow in the afterglow part. These maxima decreased with the increase of pressure for all systems, and moved to the later decay time. Maxima increased with discharge current (respectively power) and moved to shorter time. Populations at temperature of 150 K were measured due to the experimental arrangement from 17 ms, only, and thus pink aftergow maximum wasn’t observed (only at 5 000 Pa some maximum was recognized). Populations were smaller at 150 K that populations measured at laboratory temperature at the middle decay time (50-100 ms). At the late time, the populations were higher at lower temperature at lower pressure. Higher shifts (in intensity and decaytime) of pink afterglow maxima were observed in Quartz tube in comparison with their values in Pyrex tube. Besides the populations, rotational temperatures of selected bands of three observed spetral systems (for 1st negative 0-0 band, 1st positive 2-0 band and for 2nd positive 0-2 band) were measured. Rotational temperatures were monitored from presumption that this kind of temperature is equal to temperature of neutral gas (at local thermodynamic equilibrium). Results from 1st negative and 1st positive system showed strong decreasing of rotational temperatures up to about 10 ms at post-discharge begin, then temperatures were constant up to 20 ms of decay time and after that they grew up. Temperatures increased with the increase of current. The part with decreased temperature correlated with pink-afterglow part of post-discharge. Unfortunately, rotational temperatures of 2nd positive system had bad reproducibility and the time profile shape was opposite. Experimental results were compared with numerical kinetic model created by group of prof. Vasco Guerra at Instituto Supetior Técnico in Portugal. Several sets of conditions for simulation at 500 and 1 000 K in active discharge were applicable for the calculation corresponding to the experiment. Comparison of numerical simulation and experimental data done for N2(B) state demonstrated that maxima populations in pink afterglow are depended on the temperature difference between active discharge and post discharge. Maxima populations were supposed in pink afterglow disappeared if the same temperatures in active and post discharges were supposed. Temperature in active discharge is higher at higher apllied power, as it was showed from rotational temperatures observation. The results clearly showed that real temperature profile must be included into the kinetic model.
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Study of Post-Discharge Processes
Soural, Ivo ; Hrachová, Věra (referee) ; Brablec, Antonín (referee) ; Krčma, František (advisor)
The decaying plasma was studied by the optical emission spectroscopy. DC discharge created at 45 – 200 mA in Pyrex and Quartz tubes in flowing regime was used. The emission of three nitrogen spectral systems (1st and 2nd positive and 1st negative) were studied in time evolution for pressures of 500 – 5 000 Pa at two wall temperatures – ambient and liquid nitrogen (150 K inside the decaying plasma). Results showed that all three nitrogen systems (respectively N2(B, v), N2(C, v) and N2+(B, v) states as their origins) had their population maxima called pink-afterglow in the afterglow part. These maxima decreased with the increase of pressure for all systems, and moved to the later decay time. Maxima increased with discharge current (respectively power) and moved to shorter time. Populations at temperature of 150 K were measured due to the experimental arrangement from 17 ms, only, and thus pink aftergow maximum wasn’t observed (only at 5 000 Pa some maximum was recognized). Populations were smaller at 150 K that populations measured at laboratory temperature at the middle decay time (50-100 ms). At the late time, the populations were higher at lower temperature at lower pressure. Higher shifts (in intensity and decaytime) of pink afterglow maxima were observed in Quartz tube in comparison with their values in Pyrex tube. Besides the populations, rotational temperatures of selected bands of three observed spetral systems (for 1st negative 0-0 band, 1st positive 2-0 band and for 2nd positive 0-2 band) were measured. Rotational temperatures were monitored from presumption that this kind of temperature is equal to temperature of neutral gas (at local thermodynamic equilibrium). Results from 1st negative and 1st positive system showed strong decreasing of rotational temperatures up to about 10 ms at post-discharge begin, then temperatures were constant up to 20 ms of decay time and after that they grew up. Temperatures increased with the increase of current. The part with decreased temperature correlated with pink-afterglow part of post-discharge. Unfortunately, rotational temperatures of 2nd positive system had bad reproducibility and the time profile shape was opposite. Experimental results were compared with numerical kinetic model created by group of prof. Vasco Guerra at Instituto Supetior Técnico in Portugal. Several sets of conditions for simulation at 500 and 1 000 K in active discharge were applicable for the calculation corresponding to the experiment. Comparison of numerical simulation and experimental data done for N2(B) state demonstrated that maxima populations in pink afterglow are depended on the temperature difference between active discharge and post discharge. Maxima populations were supposed in pink afterglow disappeared if the same temperatures in active and post discharges were supposed. Temperature in active discharge is higher at higher apllied power, as it was showed from rotational temperatures observation. The results clearly showed that real temperature profile must be included into the kinetic model.
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