Measurement Error Caused By Probe Placement In Plasma Internal Electromagnetic Field Measurement System

When a high-speed aircraft enters the atmosphere,due to the violent collision between the surface of the aircraft and the gas molecules,its kinetic energy continues to be converted into thermal energy,and the gas molecules are ionized during this process and wrapped on the surface of the aircraft,forming a plasma sheath with electromagnetic shielding effect.That is the "blackout" effect.The plasma sheath will cause serious interference to the flight control and communication of high-speed aircraft.Therefore,the analysis and research around the influence of plasma on the propagation characteristics of electromagnetic waves is the key to whether the "black barrier" effect can be solved.In order to comprehensively analyze and study the propagation of electromagnetic waves in a high-speed space target plasma,and to reveal the mechanism of action between plasma and electromagnetic waves,it is necessary to carry out plasma internal electromagnetic measurement experiments.In the plasma internal electromagnetic measurement experiment,it is necessary to irradiate the plasma flow field with a plane wave of 10 to 60 GHz,and use electromagnetic probes to receive and measure the electromagnetic wave in the plasma flow field to obtain the electromagnetic field strength distribution in the plasma.When conducting the plasma internal electromagnetic measurement experiment,the electromagnetic probe needs to be placed inside the plasma flow field.Due to the introduction of the probe,the plasma electron density and plasma collision frequency around the probe change,resulting in the plasma dielectric constant It also changes,which in turn affects the propagation of electromagnetic waves in the plasma.Eventually lead to errors in plasma internal experiments.In order to study the experimental error brought by the probe.First,this article uses ANSYS fluent simulation software to establish a plasma flow field model without probe placement,simulates and analyzes the results of the plasma flow field without probe placement,such as the velocity,temperature,pressure,and electron density,and calculates the temperature and pressure.Plasma collision frequency.Use the results of this model as the raw data for experimental analysis.Secondly,in order to reduce the experimental error caused by the placement of the probe,the shape of the probe needs to be analyzed.In this paper,four types of probes are used for research,which are round head rectangle,20° split tip probe,40° split tip probe and 60° split tip probe.Through simulation,the electron density and plasma collision frequency of the four probes are obtained.Comparing the four models with the plasma parameters without probe placement,it is found that the plasma parameters of the 60° split-tip probe model are closest to those without probe placement.Finally,this paper uses the plasma parameters in the 60° split-tip probe model and the plasma parameters without probe placement to model in CST to study the electromagnetic measurement error brought by the probe introduction.Through simulation calculations,the field strength distribution of the 10~60GHz electromagnetic wave between the probe and the plane wave emission end in the two models,and the electromagnetic field strength comparison of the probe in front,side and rear of the probe in the two models are found.When the needle is far away,the field strength does not change much,but at three positions of the probe,the field strength changes more obviously.The 60° split-point probe model at the three positions has less field strength and no attenuation when the probe is placed.Big.Finally,a table lookup method is used to compare and summarize the changes in field strength.The results are used as reference for the compensation of electromagnetic experiment errors in plasma.