High-Resolution Spectroscopic and
Electrical Diagnostics of Barrier Discharges
Tomáš Hoder
Department of Physical Electronics
Masaryk University, Brno, Czech Republic
hoder@physics.muni.cz
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Outline
v Barrier discharge and the streamer mechanism introduction
v The necessary resolution to catch the streamer discharge
phenomenon at its characteristic scales in air at atmospheric
pressure – the instantaneous electric field quantification
v Recent advances in electrical measurements on barrier
discharges
v Application on surface barrier discharge in contact with water
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Barrier discharge
Kogelschatz 2002 PSST
Wagner 2003 Vacuum
Černák et al. 2011 PPCF
Brandenburg 2017 PSST
- Presence of insulating barrier between the electrodes
- Typically AC or pulsed applied voltage waveform
- Different geometries for different uses: volume barrier discharges for ozone production,
plasma jets for use in medicine, water treatment, coplanar type for surface treatment…
surface barrier
discharges
plasma
jets
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Streamer discharge
Raizer Yu 1997 Gas discharge physics
Hodges et al. 1985 Phys. Rev. A
Ebert et al. 2006 PSST
Marode et al. 2009 PPCF
• Streamer is contracted fast moving ionizing wave.
• Streamer is characterized by a self-generated electric field enhancement et the head
of the growing discharge channel, leaving a filamentary plasma behind.
• Usually it results from the space charge left by electron avalanches.
• Streamers in barrier or corona streamer microdischarges in air at atmospheric pressure are,
however, challenging the standard technique resolutions – duration only few units of ns.
Electron avalanche(s) Streamer head propagation
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Resolution in time and space and what is possible today?
The nanosecond resolution of ICCD devices is a standard and a broad variety
of spectroscopic methods for basic plasma parameter determination is at disposal.
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Streamer discharges and picosecond signal recording
The barrier or corona streamer discharges in air are, however,
challenging the standard technique resolutions – duration only few units of ns.
→ need for resolution in picosecond timescales!
Using TC-SPC
(cross-correlation
technique)
Δt<0.1ns
Δx=100μm
Kozlov et al. 2001
J. Phys. D: Appl. Phys.
Hoder et al. 2012 Phys. Rev. E
Using TC-SPC
(cross-correlation
technique)
Δt≈10ps and Δx=10μm
Höft et al. 2013 J. Phys. D: Appl. Phys.
Using streak camera
coupled with far-field
microscope
Δt≈50ps and Δx=10μm
barrier discharge
pulsed barrier discharge
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Streamer discharge in atmospheric pressure air
Luque et al. 2008 J.Phys.D:Appl.Phys.
Hoder et al. 2010 J.Phys.D:Appl.Phys.
Different voltages 21kV, 14kV, 10.5kV Based on modelling - various phenomena
takes place during the few nanoseconds of
the streamer lifespan: streamer
accerrelation, its head is expanding, the
amount of the net charge in the head is
increasing, …
… if you are lucky however, you can catch
experimentally at least its 1D development
in time … 0.7mm/ns.
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Optical emission spectroscopy on streamers in air
- towards the electric field
Ø in barrier discharges, coronas, lightning or
transient luminous events (Red Sprites, Blue Jets)
in atmospheric air, the ratio of intensities of first
negative and second positive systems of
molecular nitrogen is strongly dependent on E/N
19eV
electrons
11eV
electrons Gallimberti et al. 1974 J.Phys.D:Appl.Phys.
Kozlov et al. 2001 J.Phys.D:Appl.Phys.
Hoder, Bonaventura et al. 2015 J.Appl.Phys.
Instantaneous development
from non-steady-state kinetic model.
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Optical emission spectroscopy on streamers in air
- detailed know-how
v relaxation of electron energy distribution function
v proper selection of quenching constants
v rotational temperature dependence of FNS/SPS
v need for tens of microns and picoseconds
spatiotemporal resolution
v optimized kinetic model etc.
Hoder, Loffhagen et al. 2016 Plasma Sources Sci. Technol.
Hoder, Šimek et al. 2016 Plasma Sources Sci. Technol.
Hoder, Bonaventura, Bourdon et al. 2015 J.Appl.Phys.
Ø in barrier discharges, coronas, lightning or
transient luminous events (Red Sprites, Blue Jets)
in atmospheric air, the ratio of intensities of first
negative and second positive systems of
molecular nitrogen is strongly dependent on E/N
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Naidis 2009 Phys. Rev. E
Hoder, Bonaventura et al. 2015 J.Appl.Phys.
Experimentally studied microphysics of the streamer
in barrier discharge – basis for E/N determination
Ø Experimentally obtained mutual delay between the peak of spectrally resolved
emissions and the electric field
Ø Dilatation/increase of this delay give us the measure of the streamer expansion –
confirmed by 1D and 2D streamer models
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Optical emission spectroscopy on streamers in air
- limitations and challenges
Obrusník, Bílek et al. 2018 submitted
Paris et al. 2005 J.Phys.D:Appl.Phys.
Ø Uncertainty quantification,
localisation of its main sources and
uncertainty limitation by using well
selected cross-sections and life-
times
Ø Usually used Paris’s formula slightly
underestimates the el. field value
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Hoder, Bonaventura et al. 2016 PSST
Hoder, Synek et al. 2017 PPCF
Stepanyan et al. 2014 J.Phys.D:Appl.Phys.
Obrusník, Bílek et al. 2018 submitted
Babaeva et al. 2016 PSST
Luque et al. 2008 J.Phys.D:Appl.Phys.
Experimentally studied microphysics of the streamer
in barrier discharge – basis for E/N determination
Based on the previous knowledge from the picosecond spectroscopy we can:
• Locate the streamer head with high precision
• Determine its electric field waveform shape with high resolution and
• Quantify its amplitude with quantified uncertainty
(knowing also where the uncertainty comes from)
We also obtained reliable values for the peak electric field in the streamer heads
for barrier discharges in different arrangements:
• Confirming the intervals of typical values given by fluid and hybrid models
• Around 500Td (approx. 120kV/cm) for volume streamers
• And around 1200Td (approx. 300kV/cm) for surface streamers
Important know-how for remote electric field
determination in microscopic discharges (where
accurate laser spectroscopy has insufficient
absorption path) or as a fundamental knowledge
for atmospheric electricity investigation.
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Höft et al. 2013 J.Phys.D:Appl.Phys.
Braun et al 1992 PSST
1
Experimental study of electric current
of the barrier discharge - typical cases
Ø Typical current pulse recorded by Rogowski-type current probes or on resistor shunts –
uncertainty in several milliamperes
Ø The fast rise (few nanoseconds), sharp peak and the exponential decay is known –
the finer structure of the current pulse known from models is hidden in the noise
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Synek et al. 2018 submitted
Černák et al. 1993 J.Appl.Phys.
Electrical current measured by
self-assembled current probe
• Resistors placed in coaxial arrangement
• Signal recorded through coaxial cable
• Measurement of the voltage drop on total
resistivity of input 50Ohm and internal
resistivity of the oscilloscope input :-O
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Synek et al. 2018 submitted
Electrical current measured by
self-assembled current probe
• Significantly higher bandwidth of the probe compared to Pearson 2877 or CT-1 probes,
pulse FWHM decreases from 10ns for Pearson to 2.8ns for self-assembled probe
• Increased signal-to-noise ratio, sensitivity in several units of microamperes!
CT-1
Pearson
2877
self-assembled current probe
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Estimated separation of electrical current
for electrons and ions
Synek et al. 2018 submitted
• Electron current is represented by intense short profile, while the ionic current is of
low amplitude (tens of microamperes) and much longer decay (approx. 200times)
• Complication of the unknown displacement current, for its solution an appropriate
computer model is necessary
Each current pulse is a summation of two
profiles, for electrons and for ions:
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Synek et al. 2018 submitted
Statistical analysis of the electrical current
for electrons and ions
• Electron current is comparable with the ionic current or several subsequent pulses
with small variation – as expected from charge equilibrium
• The amplitude is increasing and decay of ionic current shortening for subsequent
current pulses – increased conductivity due to the local heating or discharge
mechanism change/modification
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Synek et al. 2018 submitted
Evidence of repetitive micro-pulses,
described as sub-critical pulses
• Amplitude of few tens of microamperes, transferred charge of 0.5pC, i.e.
approximately 107 electrons, sub-critical with respect to the Raether-Meek threshold
and in comparison to the microdischarge bridging the gas gap
• The amplitude remains almost stable, the frequency is changing with the changing
local electric field – hypothetically due to the amount of drifted ionic charge and/or
the local electric field at the residual charge domains
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Based on the enhanced electrical current measurements we can:
• Estimation of the separated electronic and ionic current components
• Determine the current with almost microampere sensitivity
• Quantify the transferred charge to sub-picocoulomb amounts
(corresponding to sub-Raether-Meek amount of 107 electrons)
We also obtained new knowledge about the statistical behavior of the
current pulses in volume barrier discharge:
• Evidence of new phenomena responsible for change in ionic current
amplitude and decay
• Probably heating of the gas within one half-period or discharge
mechanism variation/modification
• Detection of repetitive micro-pulses – hypothesis of discharging of
residual surface charge micro-domains
Results of electrical current measured by
self-assembled current probe
Barrier discharge in air
at water interface
• Both electrodes are not in contact with
plasma.
• Plasma originates from triple-junction –
line where the liquid (de-ionized water),
solid (fused silica cuvette) and gas (air
with water vapor) meet
• 13 kV peak-to-peak voltage
• 15.4 kHz sine frequency
• Chamber rinsed with 1 slm of air
εair
εwater
εsilica
plasma
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Voráč et al. 2017 J. Phys. D: Appl. Phys.
Pavliňák et al. 2014 Appl. Phys. Lett.
Galmiz et al. 2017 Plas. Proc. Polym.
Galmiz et al. 2016 J. Phys. D: Appl. Phys.
air
§ water level is marked by horizontal grey line
§ triple-line marked by red line, is raised due to capillary effect
Negative streamer
discharges with cathode spots
Positive streamer
branched discharges
ICCD imaging – discharge morphology
water
anode
water
cathode
21
spot
§ Expected behavior from the surface barrier discharges with solid metallic electrodes
§ Variations of small pulses for negative discharges and large distinct pulses for positive
Negative streamer discharges Positive streamer discharges
Detailed comparison of current pulses
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§ Distinct structure for the charge transferred by positive streamers
§ Continuous transitions of transferred charge between subsequent pulses for
negative streamers
Statistical comparison of current pulses
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Positive streamer dischargesNegative streamer discharges
§ Electric field amplitude over 1000Td (240kV/cm)
§ Comparable to the electric fields in other surface barrier discharges
§ Necessity to improve the kinetic model – additional quenching processes
First results on electric field quantification
for discharge at the water interface
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Spectrally resolved recordings for
positive streamer discharges
pertimeinterval
• The progress in electric field quantification and its uncertainty
was presented for streamer based discharges in atmospheric air
• New technique for fast and sensitive electrical current
measurements was shown for barrier discharges
• Above mentioned approaches were applied onto the barrier
discharges in contact with water and preliminary results were
shown … to be finished.
Conclusion and Outlook
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Thank you for your attention!
And many thanks to my colleagues
Zdeněk Bonaventura, Petr Synek, Milan Šimek and others…
This research has been funded by the Czech Science Foundation project nr.16-19721Y
and also supported by the project CZ.1.05/2.1.00/03.0086 funded by European
Regional Development Fund and project LO1411 (NPU I) funded by Ministry of
Education Youth and Sports of the Czech Republic.
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Optical emission spectroscopy on streamers in air
- detailed know-how of streamer head spectrum
Hoder, Bonaventura, Bourdon et al. 2015 J.Appl.Phys.
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Corrected electrical current on the frequency
limitations of the current probe and cables
• Further increase of the bandwidth of
the probe >> pulse FWHM 2.0ns
• Reconstruction of the original current
signal entering the measuring system
Synek et al. 2018 submitted
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Corrected electrical current on the frequency
limitations of the current probe and cables
Synek et al. 2018 submitted
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Corrected electrical current on the frequency
limitations of the current probe and cables
Synek et al. 2018 submitted
Introduction – triple-junction surface discharges
The special position of triple-junction in discharge physics:
§ Typically interface of dielectrics, gas and electrode media (metal stripe or liquid)
§ Surface barrier discharge for flow control, plasma assisted combustion, polymer
treatment and ozone generation – exhibit presence of strong charge separation in
narrow sheath!
ε1
ε3ε2
êanode
Boeuf and Pitchford 2005 JAP Pavlinak et al. 2014 APL
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Recent results in surface barrier discharges in 30kPa air
30 kPa synthetic air
7.2 kVpp sine voltage at 11 kHz
Pipa et al. 2012 Rev. Sci. Instrum.
Hoder et al. 2017 Plasma Phys. Control. Fusion
access to the mean electric field
in the gap also from electrical measurement
first microdischarge is shown in green color,
the second one in red
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Recent results in surface barrier discharges in air
Hoder et al. 2017 Plasma Phys. Control. Fusion
Babaeva et al. 2016 Plasma Sources Sci. Technol.
Ø E/N development within two subsequent microdischarges mutually affected by surface charge
Ø Surface streamers of 1200Td (similar value as in recent hybrid models) and lower for propagation
on the contact-line with previously deposited charge
first microdischarge second microdischarge
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Nanosecond discharges and laser diagnostics
Laser diagnostics offers direct measurement of the basic plasma parameters or particle densities.
However, the distortion of the plasma using higher powers or unresolved spatial gradients due to
necessary long accumulation paths is still a challenge to solve.
§ Power loss in reactor chamber calculated from electrical measurements data is 1.45 W.
§ Rough estimate of power consumed in discharges is 0.8 W while the rest goes to
capacitive losses.
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Electric current and voltage characteristic
massiveOES is FREE software which allows batch processing of large data sets of
molecular spectra. Handles overlapping molecular spectra. Includes Boltzmann fit
feature and all essential functions (linearization, line broadening etc.)
Voráč J, Synek P et al. 2017 PSST
- processed over 5000 spectra of OH, N2, N2
+ and NH molecules
Voráč J, Synek P et al. 2017 JPD:AP
- state-by-state fitting procedure
Novel massiveOES free-software
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Detailed view of discharges
• Positive and negative streamer discharges
observed depending on voltage polarity.
• Average diameter in hundreds of microns.
• Cathode spot was observed for negative
streamer discharges at the triple-line
• Branching phenomena observed for
positive streamers
• In both cases discharge originates from
triple-junction and propagates along
cuvette towards live electrode
Positive
streamer
discharges
Negative
streamer
discharges
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