The time-resolved E-field mapping in an atmospheric pressure plasma jet (review paper), as shown above, requires:
the right measurement setup,
the maps of radial & tangential E-field components,
the computation of time-resolved E-field lines mapping.
Whereas plasma jet for biomedical applications is growing exponentially due to the wide variety of E-field effects on cell functions (related paper), no simple-to-use tool was available to measure both E-field strength and direction with its temporal evolution in an atmospheric pressure plasma jet before 2013. Indeed, the first measurement has been carried out at San Francisco during the IEEE Pulse Power and Plasma Science Conference. Since then, it becomes more and more a routine technique.
However, coupled to a Cartesian robot, Kapteos E-field probes give a much better insight into the complex plasma jet dynamics.
How to obtain a time-resolved E-field mapping in an atmospheric pressure plasma jet?
1st step: Measurement setup
The measurement setup for Equivalent Time-Domain (ETD) E-field mapping of an atmospheric pressure plasma jet is composed of:
a High Voltage (HV) source generating a repetitive signal,
a plasma jet generator,
a Digital Sampling Oscilloscope (DSO),
a coupler to tap a small part of the signal generated by the HV source to trig the DSO,
a transverse E-field probe eoProbe™ ET1-air with its probe-related optoelectronic converter eoSense™ to get both radial and tangential E-field components Er and Ez in the plasma jet,
a Cartesian robot to move the E-field probe.
The key point is to trig the DSO with the HV source in order to get a common time reference for all measurements carried out with the E-field probe.
2nd step: Mapping of radial & tangential E-field components
This step consists in recording at least one period of the horizontal E-field component measured by the transverse probe for each position scanned by the Cartesian robot in the symmetry plane of the plasma jet. Then, by rotating the probe one quarter-turn, the same mapping of the vertical E-field component is carried out to get the spatial-temporal variations of the tangential E-field component Ez in the atmospheric pressure plasma jet. The interference induced by the probe on the E-field distribution being weak but not null (especially when probe is in the plasma jet), this experimental configuration with a single probe at sames positions for measuring both radial and tangential E-field components minimizes therefore potential artifacts and constitutes the best configuration.
3rd step: Computation of time-resolved E-field lines mapping
After dividing a signal period into N temporal sampling points, a map of either Er or Ez can be easily drawn from associated records. A post-treatment with Mathematica™ software is here used to get the electric field lines from both Er and Ez maps at each sampling point ti. From there it is straightforward to make a video of the temporal evolution of both E field strength and E-field lines in and around the plasma jet.
Key features of full dielectric probes for time-resolved E-field mapping in an atmospheric pressure plasma jet
Withstand E field: > 10 MV/m
non-perturbative optical technology with low permittivity E-field probe: εr ~ 3.6
ultra high orthogonal E field components rejection ratio: > 50 dB
ultra high spatial resolution: < 1 mm
high measurement reproducibility: 0.15 dB
ultra compact E-field probe: ∅ = 5.5 mm
Courtesy of IMEP-LAHC Lab. (Farah AlJammal)
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