Theoretical And Experimental Research On The Double Flush-mounted Probe Diagnostics

As the aircraft re-entering into the atmosphere,the over dense plasma sheath are formed around the surface of the aircraft due to the shock wave heating and ablation of chemical thermal protection materials.The communication signal is subsequently influenced and even stopped attributed to the reflection,scattering,and refraction of the electromagnetic wave by the plasma sheath.Therefore,solving the problem of blackout induced by the plasma sheath is crucial for national defense security.At present,limited to the detection techniques,the parameters and processes related with the plasma sheath are still extremely rare.Therefore,we designed a new double flush-mounted probe to detect the sheath plasmas.This probe can stablely work for a long time in the high temperature,ablative region similar with the reentry plasma sheath.At the same time,the of double electrodes' structure ensures that the probe can work without additional reference electrodes.Moreover,the diagnosis theory of Langmuir probe is not suitable for the new type probe's structure any more.Therefore,I have studied the double flush mounted probe diagnosis throughly in the past years,the design of structure,the theoretical model and experimental research on the diagnostic methods of double flush-mounted probe have been done.Combine the Langmuir probes' theory,the double flush-mounted probes' sheath expansion effect has been studied on the static plasma environment in the laboratory,and the theoretical model analysis has been developed.According to the effect of sheath collision on the ion current,the Bohm velocity has been corrected in the collision environment and calibration and test experiments have been performed both in laboratory plasma devices and wind tunnel environments.The double flush-mounted probe diagnosis overcome the difficulty in measuring the plasma of the high temperature ablation area of the aircraft,which give a strong theoretical model for the further diagnostic experiment of the plasma sheath in flight as well as the detection in adjacent space.The key points of this thesis are summarized as follows:1.A new type probe,double flush-mounted probe,has been designed and fabricated.This probe could achieve long time stable diagnose in the high temperature complex ablative plasma area.2.In the collisionless plasma,the sheath expansion of the double flush-mounted probe have been corrected,and the theoretical correction model with the different radius' parameters has been developed.Consequently,the effective diagnostic range of double flush-mounted probe could be expanded.3.In the medium pressure as well as the wind tunnel plasma environment,the double flush mounted probe and the calculation method have been tested in detail.The ablation rate is about one order of magnitude less than the traditional Langmuir probe.The measurement errors of the Bohm velocity in sheath are within the range of 25%.