What is the purpose of the displacement current in plasma jets ? How it can be calculated or measured. Is it possible to identify the plasma bullets from the discharge current?
I think you can measure it with Langmuir probe!
The probe tip simultaneously collects
electron current, ion current & displacement current.
The displacement current create by the time-varying electric field across the probe sheath.
I=Aε0(dE(t)/dt)
I= Displacement current
A= Outer area of the sheath surrounding the probe tip
ε0= Permittivity of free space
E= Electric field within the sheath
How it can be measured? or How electric field can be calculated? from Poisson's equation? My purpose is experimental method to measure displacement current.
some authors has reported that it is measured in plasma-off case, but what is its reason?
The required answers may hopefully be seen from
[1] A. Guthrie and R. K. Wakerling (eds), “The characteristics of electrical discharges in magnetic fields”, McGraw, 1949.
[2] L. C. Woods, “Theory of Tokamak Transport: New Aspects for Nuclear Fusion Reactor Design”, Wiley, 2006.
You can try to measure the displacement current (ID) in a way similar to what was done in [1]. In that work, the authors measured ID by placing a coil around a dielectric material that surrounds the plasma jet. I'm not entirely sure if that ID measurement is the 'real' ID, but I guess that it is a good approach to.
Ref. [2] may also help you.
[1] https://bib.irb.hr/datoteka/789754.AnalBioanalChem_2015_2.pdf (DOI: 10.1007/s00216-015-8969-7 )
[2] https://core.ac.uk/download/pdf/80776387.pdf (final version at: Article Measurement and control of the streamer head electric field ...
)
To measure the displacement current with the plasma off, as suggested above, one must put an electrode where the edge of the plasma would be. I have often done that when I worked in that field.Then the current to that electrode is the displacement current as no ion or electron current are following. The edge of the plasma is where the electron density is roughly the same as the ion density and is where the plasma light emission ends except for light caused by secondary electrons crossing the sheath.
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