Research On The Diagnostic System For Arc Plasma In Vaccum Switch

Plasma is widely used and there are many diagnostic methods.The diagnosis method of vacuum arc in academic circles mainly includes Langmuir probe method and spectroscopic method.The thesis designed a Langmuir probe for vacuum switch arc plasma diagnosis,completed the development of the overall diagnostic system,and conducted experimental research on the factors that affect the plasma parameters.Based on sufficient investigation,the thesis selected Langmuir probe method as the diagnosis method of the vacuum switch arc plasma.In the probe design,the radius of the front wire of the Langmuir probe should be much larger than the Debye length,which is related to the plasma electron temperature and electron density.In order to obtain the electron temperature and electron density in the k A level pulse vacuum arc concerned in this paper,the paper built a vacuum switch arc simulation model based on the FLUENT simulation platform and performed simulation calculations.Based on the classical fluid mechanics equations,the thesis deduced the magneto-fluid equations suitable for vacuum arcs,specified the boundary conditions,converted them into the standard form of FLUENT custom equations,and modified the built-in solver of FLUENT to complete secondary development.In the paper,we calculated the Debye length according to the electron density and electron temperature obtained by simulation,selected the appropriate wire radius of the probe tip,and completed the probe size design.Combined with the probe shape and material selection,the Langmuir probe suitable for vacuum switch arc plasma diagnosis was finally developed.The thesis has completed the development of the vacuum arc generator,which mainly includes the plate pole vacuum switch and the trigger source circuit.The dynamic scanning method was selected as the probe measurement method,and according to the requirements of this method for the scanning signal of the Langmuir probe,a bipolar scanning power supply with a stable output frequency of 0.8 MHz and a voltage range of-60 V to + 60 V was developed.According to the requirements of the gain-bandwidth product,the LTC6090 chip was selected as the main operational amplifier,and the power supply for the filter,amplifier unit and chip was designed accordingly,which includes RC filtering,Buck-Boost power loop,TL494 control part,output voltage sampling and auxiliary power supply.Corresponding hardware and software measures were taken for the electromagnetic interference that occurred in the system.The hardware mainly adopts methods such as additional filtering devices,ground potential isolation,and nearby grounding.The software is mainly to average the results of multiple measurements.The thesis used the developed vacuum switch arc plasma diagnostic system to test the flat pole vacuum switch.After measuring the I-V curve of the Langmuir probe,the parameters of the metal vapor plasma of vacuum switch arc were calculated.The test results were consistent with the parameter ranges of existing papers,and had similar distribution rules.Besides,the effect of the current amplitude on the parameters of the vacuum switch arc plasma was studied.We changed the peak value of the pulse current to 150 A,450A,and 1k A respectively.The experiment indicated that the electron temperature remained basically unchanged when the current was small,but the electron temperature rose when the current increased.Besides,the electron density increased with increasing current,but the growth rate gradually slowed down.In order to study the effect of electrode spacing on the parameters of vacuum switch arc plasma,this paper measured the parameter distribution of vacuum switch arc plasma with a peak current of 450 A when the electrode spacing was 8mm,10 mm,and12mm,and found that the electron temperature was concentrated between 1.17 e V and 1.67 e V.Besides,the electron density decreased with increasing electrode spacing,and the greater the electrode spacing,the faster the electron density decreased.