Effect of filament supports on emissive probe measurements

We have constructed an emissive probe with a thin tungsten filament spot-welded across two nickel wires insulated with ceramic paint. We show that the ceramic supports covering the nickel wires have a large effect on the potential measurements in low-density plasmas. It is found that the potential m...

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Bibliographic Details
Published in:Review of scientific instruments 2013-01, Vol.84 (1), p.013506-013506
Main Authors: Wang, X., Howes, C. T., Horányi, M., Robertson, S.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CERAMICS
DEBYE LENGTH
Emissivity
FILAMENTS
LANGMUIR PROBE
NICKEL
PLASMA DENSITY
PLASMA POTENTIAL
Plasma potentials
PLASMA SHEATH
Plasmas
TUNGSTEN
Wire
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Summary:We have constructed an emissive probe with a thin tungsten filament spot-welded across two nickel wires insulated with ceramic paint. We show that the ceramic supports covering the nickel wires have a large effect on the potential measurements in low-density plasmas. It is found that the potential measured by the emissive probe is more negative than the potential derived from a Langmuir probe current-voltage (I-V) characteristic curve when the plasma density is so low that the emitting filament remains immersed in the sheaths of the ceramic supports. The length of the filament L needs to be larger than about 2 Debye lengths (L > 2λ De ) in order to avoid the influence of the ceramic supports and to achieve reliable plasma potential measurements using emissive probes.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.4776201