Why is the analysis of plasma generator probe parameters so complicated? How to optimize?

The probe analysis plasma generator plasma parameter measurement and diagnosis uses a simple plasma diagnosis method, but this method also has its complexity, why is it complicated? How to optimize in actual operation? In order to reduce the interference of the plasma generator probe to the plasma and facilitate the manufacture of the probe, it is usually necessary to select a thin wire with a radius of a<λDe. Therefore, to determine the current collected by the probe, it is necessary to know the movement path of the charged particles in the sheath, which makes the analysis of the probe quite complicated. As the probe voltage increases or decreases, the width of the sheath will increase, and the effective collection area will also increase.
In addition, dual probes and transmitting probes with more complex structures have also proven to be useful in many cases. The oscillation of the plasma potential in the high-frequency driven plasma generator also complicates the analysis. Since the probe generally uses a quasi-electrostatic method, in order to eliminate the influence of the mechanical potential oscillation on the probe measurement during the low-temperature plasma surface treatment, the probe bias is usually made to vibrate together with the plasma.
Therefore, how to optimize the analysis results of the plasma generator probe? The detection theory generally assumes that the electrons in the plasma have a Maxwell distribution. But in many cases, electrons will deviate from the Maxwell distribution. Therefore, in the case of general measurement of the electron energy distribution function, it can be directly used to calculate the plasma density of a low-temperature plasma generator.
By comparing the plasma density obtained with the probe ion saturation current and other measurement methods, it can be found that the plasma density measured by microwave is more accurate under discharge conditions, while the plasma density measured by the probe ion saturation current is more accurate. The bulk density is generally higher than the result obtained by microwave measurement. However, in many cases, the density measured by probe and microwave technology is very close. The key to the accuracy of measuring plasma density with ion saturation current is whether the electron distribution at the edge of the probe sheath is close to the Maxwell distribution, which determines the relationship between plasma density and plasma type.
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