| Plasma is the fourth fundamental state of matter, it is a quasi-neutral ionized gas which contains a range of reactive species including electrons, ions and neutral particles and exhibits collective behavior. Because the plasma chemical reaction processes are very complex, thus it is challenging to investigate the plasma reaction mechanism. It is necessary to establish the plasma diagnosis system for the discrimination of different reactive species, at the same time, the inhomogeneous distribution of transient species requires diagnostic tools to be temporally and spatially resolved. The development of diagnostic technique which has the advantage of temporal and spatial resolved, in-situ, non-intrusive is key important for further study of plasma reaction mechanism. Based on this goal, the following works have been carried out in this dissertation:I. A highly-sensitive in-situ diagnosis approach for real-time monitoring of nitrogen dioxide (NO2) has been developed in dielectric barrier discharge (DBD) and ns-pulsed direct current discharge based on pulsed cavity ring-down spectroscopy (CRDS) with a\xs scale time resolution. The time evolutions of NO2 concentrations have been investigated. In DBD of NO2/Ar mixture at 900 V and 10 kHz, the NO2 sharply decreases at the beginning of the discharge, then slowly increases, and then becomes constant under the different initial NO2 concentrations (1.5×1013 cm-3?2.79×1014 cm-3); while if the initial NO2 number density is as low as 1.5×1013 cm-3, the final NO2 number density could larger than the initial one. In ns-pulsed direct current discharge of NO2/Ar mixture at-1300 V and 30 Hz, for the higher initial NO2 concentrations (3.05 x 1014 cm-3,8.88×1013 cm-3), the NO2 sharply decreases at the beginning of the discharge afterglow and then become almost constant, and the pace of decline increases with pulse duration; however, for the lower initial NO2 concentration of 1.69 ×1013 cm-3 the NO2 also decreases at the beginning of the discharge afterglow for 200 ns and 1 ?s pulse durations, while it slightly increases and then declines for 2 ?s pulse duration. Thus, in the case of lower NO2 concentrations, the removal of NO2 could not be promoted by a higher mean energy input. An oscillating decline phenomenon of NO2 concentration during the air ns-pulsed direct current discharge afterglow has been observed for the first time. There are a number of peaks and valleys within tens of microseconds. The oscillation trends are similar under the different discharge voltages (-1000 V,-1300 V) and discharge durations (1 ?s,2 ?s), while the time span between valleys tends to increase with the afterglow time.?. The combination of CRDS and optical emission spectroscopy (OES) provides a practical tool in the study of the effective inverse photon efficiency(PE-1). A common diagnostic for chemical erosion of carbon is OES of the CH radical which is based on the conversion of photon fluxes of the CH(A2??X2?) emission into particle fluxes of methane by means of inverse photon efficiency (D/XB) in tokamaks. For similar plasma parameters as the ITER detached divertor, the photon flux of CH(A2??X2?) obtained by OES has much less variance with electron temperature (Te) than the calculated by electron impact excitation of CH(X2?). It is suggested that CH(A2?) is dominantly created by dissociative recombination (DR) of CHx+ instead of the electron impact excitation of CH(X 2?), and CH radicals deviate from excitation equilibrium. The DR processes of CHx+ increase the photon flux of CH(A2??X2?) at lower electron temperature which weaken the change of photon flux with Te. Thus the value of PE-1 slightly changes with Te compared with D/XB. The probability that each particular DR reaction actually excites the CH(A2?) level is not given in the databases. The combination of OES and CRDS provides a method to determine it. The fractions of CH(A2?) produced in all the DR processes are in the range from 4% to 13% and increase with Te at Te< 1 eV. Our experimental results indicate that the chemical erosion measured by OES approach should be treated with more caution, and the role of DR processes in the photon fluxes of the molecular CH(A2??X2?) band emission should be valued in the regions of ITER divertor. |
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