Study Of Time-resolved Plasma Probe Diagnosis Technique

Research on time resolution diagnostic technique of plasma based on the Langmuir probe are done to tackle the diagnostic problems of plasma parameters under periodic discharge circumstances including the pulse discharge. Diagnosis on time resolution of periodic discharge plasma is made by using a Lab VIEW program which controls the triggered data acquisition of Langmuir probe and undergoes the data processing automatically. In the present work, I-t curves are recorded for every scanning probe bias, and the Ⅰ-Ⅴ relations are obtained by transposing the data matrix. A much higher time resolution is achieved as compared with using the fast scanning method; however, the discharging has to be highly periodic. The method adopted in this work is of practical meaning given the wide application of periodic discharge plasma.To achieve better time resolution, the equivalent sampling method is studied and is integrated to the probe system. At first, a count delay trigger circuit, which improves the time resolution from4μs to0.5μs, is designed and produced. A new equivalent sampling method is proposed to further improve the time resolution by using a programmable data acquisition (DAQ) card in the present work. The method, in principle of ordinal sampling, is realized by programmingly operating the DAQ card instead of the conventional hardware means. By stepping down the real time sampling rate of the DAQ card with a certain rule, much higher time resolution than the highest time resolution of real time sampling may be achieved, due to the small difference between the adjacent sampling rates. Observations of100kHz sine and square wave signals show a correct construction of waveform, a high signal noise ratio, signals without distortion and clear rising and falling edges of square-wave. The minimum time resolution is12.5ns. It thus demonstrates that programmable DAQ card is preferable to improve the time resolution of equivalent sampling.In addition, both timing delay triggered circuit and programmable DAQ card techniques are used to record sine, square and triangle wave signals with a frequency of50kHz and100kHz. The latter method triumphs in reconstructing the wave signals.Hence, the equivalent sampling method with a programmable DAQ card is applied to the electrostatic probe system. Plasma parameters, such as the time dependent variation of the electron temperature and density, and their changes at the rising and falling edges of pulse signals are determined from the diagnosis on pulse modulated radio frequency inductive plasma, negative high voltage pulse radio frequency inductive plasma, respectively.