1. (Bio)Plasma Chemistry Wouter Van Gaens, Annemie Bogaerts PLASMANT University of Antwerp, Belgium Plasma to Plasma! Workshop, Jan 2013

2. Plasma medicine applications  Microdischarge  Non-LTE plasma at atmospheric pressure  Large interest in plasma jets  Usually noble gas mixing with ambient air  Both physically and chemically complicated processes 1. Introduction NOBLE GAS PLASMA MIXING ZONE

3. Aim of this work  Insight in chemical phenomena (generally valid ?!?)  Simple model = low computational load  Mainly qualitative study  Implement humid air chemistry set with argon coupling  Reduced chemistry set (can be used in higher level models ?!?) 1. Introduction NOBLE GAS PLASMA MIXING ZONE

4. Other important/relevant humid air reaction chemistry modelling, i.a.:  Kogelschatz et al (1988) & Kossyi et al (1992) : Dry air  NIST Standard reference data (‘90-’00): Humid air  Combustion and atmospheric chemistry community (Herron, Atkinson, Tsang et al)  Gentille and Kushner (1995): Humid air  Plasma remediation of N x O y  Liu, Bruggeman, Iza and Kong (2010): He/H 2 O  General biomedical applications, hydrogen peroxide generation  Iza et al (‘10): He/O 2 /H 2 O  Plasma medicine, RF discharges  Sakiyama et al (2012): Humid air  Plasma medicine, surface micro discharge  Babaeva and Kushner (2013): Humid air  Plasma medicine, DBD filaments and fluxes towards wounded skin 1. Introduction

5. Recent review: X Lu et al, Plasma Sources Sci. Technol. 21 (2012) 03400) 2. Typical plasmajet configurations

6. Recent review: X Lu et al, Plasma Sources Sci. Technol. 21 (2012) 03400) 2. Typical plasmajet configurations

7. Device of our choice: Prof. P. Bruggeman, Eindhoven Univ. of Technology Needle electrode (Ø ± 0.5 mm) Coaxially inserted in dielectric tube (inner Ø ± 1.8 mm) Needle tip 1.9 mm from nozzle exit 2. Typical plasma jet configurations 10 mm 3 mm

8. Operating conditions: 6.5 Watt dissipated power RF discharge Ar gas feed 2 slm Possibility of oxygen admixture 2. Typical plasma jet configurations 9 mm 3 mm

9. 0D model ‘GlobalKin' Prof. M. J. Kushner, University of Michigan, US 3. Model Species kinetics Boltzmann solver(*) Electron energy equation (*) can be called very frequently with changing background gas composition!!!!!!!

10. 0D fluid model ‘GlobalKin' Prof. M. J. Kushner, University of Michigan, US 3. Model Species kinetics Boltzmann solver(*) Electron energy equation (*) can be called frequently, for example with changing background gas composition Power input!

11. 3. Model Assumptions to obtain ‘semi-empirical’ model 1) Pseudo-1D simulation (to give idea of “distance to nozzle”)  Volume averaged element moving along the plasmajet stream > imaginary cylinder  Moving speed ̴ flow velocity & Ø cylinder (1cm ≈ 1msec)  No radial transport (high flow speed) / no axial drift & diffusion flux

12. 3. Model Assumptions to obtain ‘semi-empirical’ model 2) Humid air diffusion  Ar replaced by N 2 /O 2 /H 2 O  Mixing speed fitted to literature values and 2D fluid simulation calculation Ellerweg et al (2012) Reuter et al (2012) 2D Fluid flow model

13. 3. Model Assumptions to obtain ‘semi-empirical’ model 3) T gas evolution  Fitted to measurements TU/e (Tg, radially averaged)  Self consistent Tgas calculations by model only accurate in first few mm!

14. Why ‘device specific’ plasma chemistry study (≠ more general approach)? P deposition as function of plasma jet position unknown > plasma properties matched to experiment T gas evolution device specific: crucial for chemistry (eg. NO x and O 3 ) Broad parameter study: more general chemical info 3. Model

15. 4. Reaction chemistry set Extended Ar/N 2 /O 2 /H 2 O chemistry set  85 implemented species!  Some advantages & differences compared to other models: 1.complex waterclusters 2.Argon implementation (less expensive) 3.Rot/Vib excited states (partially) included Ground StateExcitedCharged ArAr( 4 S), Ar( 4 P), Ar 2 * (a 3 Σ + u )e -, Ar +, Ar 2 +, ArH + N 2, NN 2,rot, N 2,vib, N 2 (A 3 Σ + u ), N 2 (a' 1 Σ - u ), N( 2 D)N 2 +, N 3 +, N 4 +, N + O 2, O 3, OO 2,rot, O 2,vib, O 2 (a 1 Δ g ), O 2 (b 1 Σ + g ), O( 1 D)O 2 +, O 4 +, O +, O -, O 2 -, O 3 - NO, NO 2, N 2 O, NO 3, N 2 O 3, N 2 O 4, N 2 O 5 N 2 O vib NO +, NO 2 +, NO 2 -, NO 3 - NH, HNO, HNO 2, HNO 3, HNO 4 H +, H 2 +, H 3 +, H2, H, H 2 O, H 2 O 2, HO 2, OHH*, H 2,rot, H 2,vib, H 2 *, OH (A)H 2 O +, H 3 O +, H 2 O 2 -, OH +, H -,OH - Waterclusters H 5 O 2 +, H 7 O 3 +, H 9 O 4 +, H 11 O 5 +, H 13 O 6 +, H 15 O 7 +, H 2 NO 2 +, H 4 NO 3 +, H 6 NO 4 +

16. 4. Reaction chemistry set Extended Ar/N 2 /O 2 /H 2 O chemistry set  1885 reactions! (can be reduced to ± 400 reactions) 278 electron impact & 1596 heavy particle reactions (692 dry air)

17. 5. Validation Calc. [O 3 ] vs. experim. [O 3 ] by TU/e (2% O 2 admixture)  Relatively good qualitative agreement  Detailed discussion in upcoming paper! Agreement for [O], [NO] and [OH] (literature) for similar devices.

18. 6. Output reaction chemistry model Similar conditions as for TU/e plasmajet device, except no O 2 admixture  Very rapid chem/phys quenching of energetic Ar states by air  Fast charge exchange by Ar ions  Strong [e - ] drop due to efficient dissociative electron attachment of air

19. 6. Output reaction chemistry model Biomedically active species  O 2 (a), O 3, NO, N 2 O, H 2 O 2, HNO 3 predicted to be very long living species  1-1000 ppm  N < H < O in lifetime and density, but ‘distance of treatment’ is crucial!  O into O 3 if T gas low/ into NO x if T gas high  Plasma becomes electronegative due to electron attachment in the far effluent

20. 6. Output reaction chemistry model Water cluster formation  Complex mechanism by implementing reaction rates (≠ Arrhenius form) by Sieck et al (2000)  Dominant positive charge carrier  Water cluster size gradually increasing in time  NO + clusters less abundant

21. 6. Output reaction chemistry model Example of parameter variation: 300K  Large changes in densities (up to order of magnitude)  Changes in chemical pathways less drastic!  Less NO, much more O 3 in far effluent  Faster recombination of radicals like O, H into OH, HO 2  Favors HNO 3 formation! (though net less NO x )  Chemical pathway changes taken into account in reduced chemistry set! Rel. ∆[X] vs. [X] with fitted T g profile cfr. experiment

22. 8. Conclusions & Outlook Large amount of chemical data studied Argon implementation Semi-empirical model (validation) More detailed chemical pathway analysis will be given in upcoming paper Idem ditto for effect of power, air humidity & flow speed on chemistry Reduced chemistry set Acknowledgments:  Prof. Dr. M. J. Kushner  Flemish Agency for Innovation by Science and Technology  Computer facility CalcUA  Prof. P. Bruggeman of Eindhoven University of Technology for providing experimental data

23. Thank you for your attention! Questions?