Plasma Physics 2 6. Dielectric barrier discharge Vylepsit … 1 Lecture series contents 1.Townsend breakdown theory, Paschen‘s law 2.Glow discharge 3.Electric arc at low and high pressures 4.Magnetized low-pressure plasmas and their role in material deposition methods. 5.Brief introduction to high-frequency discharges 6.Streamer breakdown theory, corona discharge, spark discharge 7.Barrier discharges 8.Leader discharge mechanism, ionization and discharges in planetary atmospherres 9.Discharges in liquids, complex and quantum plasmas 10.Thermonuclear fusion, Lawson criterion, magnetic confinement systems, plasma heating and intertial confinement fusion. Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 2 Where are we in the IV chart? •We have seen last time that the deformation of the E field in various real-life scenarios leads to a formation of non-uniform discharge structures (streamers, arcs, coronas). •Today, we are expanding further on those by analyzing DBDs which operate in Townsend/Glow part of the IV characteristic volt-ampérová charakteristika elektrických DC výbojů (vznik jednoho mikro-výboje bariérového výboje můžeme pro daný čas uvažovat jako DC) Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 3 Barrier discharge fundamentals •A barrier discharge is characterized by the fact that there is a dielectric between the electrodes, preventing the formation of a conductive channel – an electrical short cannot occur • •Some fundamental configs (Brandenburg 2017): • • • • • • • • • • • • • • •Often filamentary, here is a glow discharge at the atm. pressure: 4 mm Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 4 General barrier discharge mechanism •(Dielectric) barrier discharge occurs between electrodes, at least one of which is covered by a dielectric. • •An important driver for DBD formation is charge accumulation on the dielectric. • •When described by an equivalent circuit, it behaves like a capacitor. • •Due to the dielectric, it always has to be driven by an AC field • Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 5 Dielectric barrier discharge – ancient history •Ancient history - G.C.Lichtenberg (1777): dust Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic Screen Shot 2016-11-21 at 23.26.19.png 6 Brief history of the dielectric barrier discharge •Ozone generation, Lichtenberg figures, streak measurements. W. Siemens 1857 and Buss 1932, Klemenc 1937, Manley 1943, Samoilovich 1966, Gibalov 1981, Eliasson, Kogelschatz 1983, Heuser 1985, Okazaki 1993, Zhu, Hidaka 1996, Guikema 2000, Kozlov 2001, Wagner 2010 Screen Shot 2016-11-22 at 21.18.07.png Screen Shot 2017-02-22 at 22.13.59.png Screen Shot 2016-11-22 at 21.16.28.png Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 16 Initial observations of DBD discharges • •Optical and electrical studies historically performed in Aachen (Pietsch, Heuser, Gibalov) and in ABB (Hirth, Kogelschatz, Eliasson): • • Streak camera – pulsed barrier discharge Lichtenberg figures prouduvá měření Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 14 General forms of the DBD discharge •Basic modes of the DBD are filamentary and (Brandenburg 2004): • • • • • • • • • • • • • • • • • • •In the filamentary mode, the fialment diameter is sub-millimeter. Individual filaments také nanoseconds and the electric field is hundreds of Td owing to the streamer mechanism. • •In the diffuse mode, the discharge size is given by electrode width but the mode is not universaly stable. • •Penning ionization – one of phenomena contributing to the stability of the discharge • •Diffuseness is important for various applications of the discharge. Note that even the filaments can be distributed uniformly and the discharge is pseudo-diffuse. • filamentary diffuse Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 15 Diffusion barrier discharges (Massines) Diffusion barrier discharge in He Diffusion barrier discharge in N2 Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 17 General DBD mechanism – repetitive mode • •Even in early 2000s, the mechanism of DBD discharges was still being speculated on. • • Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic CURRENT IN DBD DISCHARGES • 7 Measuring electrical current in a DBD discharge •You can either measure current using induction-based probes or by measuring voltage on a parallel resistor. • •Equivalent circuit for a single-filamentary discharge in air. Pearson 2877, 300 Hz – 200 MHz Tektronix CT-1, 25 kHz – 1 GHz BNC sonda, 0 kHz – 2 GHz ICCD imaging: Synek et al. 2018 PSST Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 8 Electrical characterization of a DBD discharge •To measure the actual current is challenging, because the Maxwell translation current makes a major contribution. •the gap voltage determines the effective electric field between the dielectrics Eeff = Ugap/g •jR is the pure discharge current •q is the charge transferred by a discharge • •The following factor is not negligible: Merbahi 2004, Pipa 2012 Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 9 Analyzing electrical measurements •Single-filamentary volume barrier discharge in atmospheric pressure argon. • • Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 9b Analyzing electrical measurements •Single-filamentary volume barrier discharge in atmospheric pressure argon. • You cannot simply subtract the sine component to get the correct current Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 10 An alternative method for obtaining jR •Let‘s start with the equation for the total current Screen Shot 2017-01-19 at 14.17.57.png Screen Shot 2017-01-19 at 14.18.06.png Screen Shot 2017-01-18 at 17.58.26.png Screen Shot 2017-01-18 at 20.43.41.png Screen Shot 2017-01-18 at 17.58.47.png Screen Shot 2017-02-13 at 21.12.38.png Conduction current Translational current plate capacitor capacitance Measured current density From Kirchhoff’s laws Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 11 •If we take into account the deposited surface charge, then (Bonaventura 2020): An alternative method for obtaining jR surface charge deposition step condition on the boundary of a dielectric (Tirpák) Screen Shot 2017-02-13 at 21.12.38.png after a few modifications: the calculated current jR obtained from Kirchhoff laws is identical to conduction current jC Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 12 QV diagrams of the DBD discharge •Manley 1943 showed that the energy dissipated in a DBD can be obtained from Lissajouse figures, graphically. •Today, these plots are called more accurately – QV plots/diagrams Merbahi et al. 2004 JPDAP Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 13 QV diagrams of the DBD discharge •So how do the equivalent circuit and QV plots play together? • • • • • • • • • • • • • • • • • • • • •Power dissipated in the discharge can be obtained from current and voltage: • • •And for total dissipated energy, it has to hold that: Screen Shot 2017-01-19 at 14.17.57.png Screen Shot 2016-11-21 at 23.49.54.png Effective capacitances obtained directly from experiment Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic VOLUME DIAGNOSTICS OF DBD PLASMAS • 18 Applying cross-correlation spectroscopy to understand DBDs (Kozlov 2001) Symmetrical atm. pressure discharge Time-correlated photon counting technique Light emission during the discharge Light emission in the Townsend phase Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 19 Measuring the electric field in DBDs •Spectroscopic method based on nitrogen emission bends, developed by Kozlov in 2001 • • Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 20 Spatio-temporal evolution of DBDs •Applicable to different types of DBDs • • objemový bariérový výboj koplanární bariérový výboj povrchový bariérový výboj A screenshot of a computer Description automatically generated with medium confidence Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 21 Spatially resolved simulations of DBD discharges •Simulating a co-planar DBD discharge, Jánský 2022 Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic SURFACE CHARGE IN DBD DISCHARGES • 22 Surface charge in DBDs •Pockels effect has been used to measure surface charge (Zhu 1996), for a point-to-plane config Positive tip transitioning to negative polarity Negative tip transitioning to positive polarity Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 24 •There is a „surface streamer“ forming in point-to-plane DBDs (Kumada 2009) •The electric field exceeded an equivalent of 30kV/cm at higher pressure (experiments done at low pressure) Surface charge in DBDs Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 25 •srovnání množství deponovaného náboje určeného skrze elektrická měření a ekvivalentní obvod a skrze Pockelsův efekt (Bogaczyk 2012): • •objemový bariérový výboj za atmosférického tlaku v heliu: Screen Shot 2016-12-08 at 11.32.21.png Screen Shot 2017-02-14 at 21.24.11.png Povrchový náboj bariérového výboje Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic SELF ORGANIZATION OF FILAMENTARY DBD DISCHARGES • 26 přenos náboje skrze jednotlivé výboje střední vzdálenost filamentů Self organization of filamentary DBDs (Guikema 2000) Localized filaments – they „prefer“ to ignite in discrete places, rather than randomly. The decisive mechanism is the surface charge accumulation and the „dose“ of charge deposited by individual discharges. Text Description automatically generated with low confidence A picture containing text, clipart Description automatically generated Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 26b Samo-organizace filamentů bariérových výbojů (Stollenwerk 2004) Localized filaments – they „prefer“ to ignite in discrete places, rather than randomly. The decisive mechanism is the surface charge accumulation and the „dose“ of charge deposited by individual discharges. Text Description automatically generated with low confidence A picture containing text, clipart Description automatically generated Chart, histogram Description automatically generated Text Description automatically generated Logo Description automatically generated with medium confidence pozitivní náboj negativní náboj Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 27 Self organization of filamentary DBDs Microscopic view of the charge accuulation effect neúplné pokrytí nábojem reprodukce polohy skrze lokální elektrické pole Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic DBD APPLICATIONS • 28 Ozone generation (Eliasson 1987) •Possibly oldest application of DBD discharges •Motivated formulation of the first physical and chemical models. •1D model described the formation of a transient glow discharge at high pressure. •Actuall EEDF was calculated and from it, rate coefficients and transport properties were deduced. • The mechanism for ozone formation and potential ozone loss was identified as follows: Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 29 Ozone production – oxygen dissociation Text Description automatically generated Chart Description automatically generated Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 30 Ozone production – effect of admixtures In industrial production, gases that form metastable excited species are often added, further enhancing the dissociation rate of oxygen by plasma. Microdischarge in pure oxygen Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 31 Ozone production – an industrial setup A picture containing indoor, armor Description automatically generated A picture containing indoor Description automatically generated A picture containing text, clipart, vector graphics Description automatically generated Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 32 Surface processing pro reaktivní plyny a depozice (Massines 2012) změna kontaktního úhlu, PET povrch, DCSBD (Homola 2017) DCSBD – in-line opracování, no-pinholing, i tepelně citlivé povrchy/vzorky Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 33 Excimer light sources Very intense UV light sources •surface and water cleaning by UV •UV curing and photopolymerization •excimer lasers for semiconductor applications • Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic 34 Excimer light sources Very intense UV light sources •surface and water cleaning by UV •UV curing and photopolymerization •excimer lasers for semiconductor applications • Pozor je to pro verejnost … jednoduseji, schemata nazorna, ne moc analyz, jen par rovnic Takeaways •What is a DBD and what are its various arrangements • •Where is the voltage drop in DBDs, what are the methods for accurately measuring plasma power and voltage? • •What are some methods of DBD diagnostics. • •DBD applications