The plasma absorption probe (PAP) was invented as an economical and robust diagnostic device to determine the electron density distribution in technical plasmas. It consists of a small antenna enclosed by a dielectric tube which is immersed in the plasma. A network analyzer feeds a rf signal to the antenna and displays the frequency dependence of the power absorption. From the absorption spectrum the value of the electron density is calculated. The original evaluation formula was based on the dispersion relation of plasma surface waves propagating along an infinite dielectric cylinder. In this letter the authors present the analysis of a less idealized configuration. The calculated spectra are in good qualitative agreement with their experimental counterparts, but differ considerably from those predicted by the surface wave ansatz. An evaluation scheme which takes our findings into account will improve the performance of the PAP technique further.
The plasma absorption probe is a recently developed tool for efficient determination of electron densities of low temperature plasmas. The occurrence of multiple absorption signals was a serious drawback for interpretation of the probe data. To remedy this drawback, a spherically symmetric design of an absorption probe is proposed. A spherical probe is tested in experiment and simulation and the suppression of the multiple absorption signals is demonstrated. The proof of principle for the concept is given.
The plasma absorption probe has been developed to provide a fast and efficient diagnostic tool for the characterisation of discharges, especially of reactive plasmas. Unlike Langmuir probes, the plasma absorption probe measures electron densities in reactive plasmas undisturbed by coatings of the probe surface. It consists of a semirigid coaxial cable with protruding inner conductor as an antenna, covered by a dielectric tube. The measurement principle is based on active resonance spectroscopy. A network analyser feeds the coaxial cable with HF of variable frequency and the power reflection spectrum is detected. At resonant frequencies, characteristic for the discharge, absorption signals are observed. In this paper, we present measurements of the plasma absorption probe for various discharge conditions and we evaluate the probes' further potential for the analysis of reactive plasmas.
The plasma absorption probe (PAP) is a recently developed tool for the efficient determination of electron densities, especially in reactive plasmas. A dielectric cover protects this probe against the influences in reactive plasmas and it withstands conditions where Langmuir probes are easily damageable. The lack of adequate calibration constants and the occurrence of multiple absorption signals were two major drawbacks, which are successfully overcome in this work. Design variations are tested by numerical computation and the model‐based achievements are established in experiment. In this work, a redesigned PAP is presented, which is optimised for the easy determination of electron densities. The developed tool works fast and efficiently, in particular in discharges in reactive gases.
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