Research on plasma electron density distribution based on microwave diffraction

Abstract

Abstract In this paper, a noncontact plasma microwave diffraction measurement method is proposed, which can obtain the electron density at different diameters of the cylindrical plasma. There is a lot of diffraction when a non-focused antenna is used to transmit plasma. As is well known, when the frequency of the incident microwave is lower than the characteristic frequency of the plasma, the microwave cannot be transmitted through the plasma, so this interface can be regarded as a metal. According to the microwave diffraction of the plasma, the size of the plasma corresponding to the characteristic frequency can be obtained. Furthermore, by sweeping the incident electromagnetic wave, the size of plasma with different characteristic frequencies can be obtained, and the distribution of electron density can be obtained. To verify the method, a cylindrical plasma was measured by microwave diffraction, in which the electron density of the plasma column gradually decreased along with the increase in radius. According to the diffraction of the plasma column at different frequencies, the distribution of the electron density along the diameter is obtained. In order to verify the distribution results, a Langmuir probe was used for diagnosis in a similar propagation path. The two diagnosis methods have a diagnosis deviation of less than 60%. Finally, the accuracy of diffraction diagnosis is given, and the next step to improve the accuracy of the diagnosis is given. In extremely high temperature, regular shape, nonuniformly distributed plasma, microwave diffraction diagnosis has a wider range of applications.