Electrostatic Probe Diagnostic Method For Low-frequency Discharge Plasma

In recent years, artificial discharge plasma has been widely applied in many fields of aerospace, radar countermeasure and material surface treatment etc. Electrostatic probe as the plasma diagnostic method with high spatial resolution, is one of the main ways to obtain various physical parameters and their distribution characteristics of current DC discharge and RF discharge plasma. However, in the diagnosis of low frequency discharge plasma, electrostatic probe will appear the serious deviation because of the plasma potential interference. In order to solve this problem, this paper makes the effective improvement of the traditional double probe, which mainly includes the following three aspects of the work:First of all, we analyze low frequency discharge plasma interference on the electrostatic probe diagnostic factors and mechanism. Double probe product of Impedance company is tested and analyzed. We establish the interference equivalent circuit model of low frequency plasma discharge device to the probe; get the low-frequency plasma space potential distribution of fluctuation and show the main reasons of influencing the precision of probe diagnostic;Second, we propose an anti-interference double probe diagnostic system which can be suitable for low frequency discharge plasma; according to influence factors, take a series of discharge plasma anti-interference measures on the low frequency plasma, including electrical isolation and balance the stray capacitance, series connection of low-frequency blocker, sliding integral algorithm; complete the hardware design of new probe system, probe structure design and PC software development work, form a complete set of low-frequency discharge immunity probe diagnostic system prototype.Finally, the probe diagnostic system is used in a typical 30KHz low-frequency discharge plasma device, and compared with the products of Impedance company and the microwave diagnostic method. The experimental results show that, the traditional double probe diagnostic results and microwave diagnostic results compared to errors of the order of 0.59, and the proposed probe system error within 0.2 orders of magnitude (inherent error is less than the microwave method); verified the theoretical analysis and effectiveness of the proposed modified method.The main results of this paper,on the one hand, theoretically clarify the mechanism of interference in low frequency discharge in the traditional double probe and response measures; on the other hand, provide effective equipment for the diagnosis of plasma parameters and the distribution of various types of low frequency plasma source, expanding the application of the double probe diagnostic method in the field of low frequency plasma discharge which can also apply to other types of spatial potential fluctuations in serious discharge plasma devices.