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M.Capitelli

M.Capitelli. Dipartimento di Chimica, Università di Bari, Italy IMIP-CNR, Bari, Italy. COLLABORATORS. Semiclassical Impact Parameter Method. MOLECULAR DYNAMICS. Quasiclassical Trajectory Method. Semiclassical Collisional Model. ELECTRON-IMPACT induced PROCESSES

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M.Capitelli

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  1. M.Capitelli Dipartimento di Chimica, Università di Bari, Italy IMIP-CNR, Bari, Italy

  2. COLLABORATORS

  3. Semiclassical Impact Parameter Method MOLECULAR DYNAMICS Quasiclassical Trajectory Method Semiclassical Collisional Model ELECTRON-IMPACT induced PROCESSES (inelastic+reactive) • COLLISION INTEGRALS • ground state • excited states HEAVY PARTICLE COLLISIONS (inelastic+reactive) GAS-SURFACE INTERACTION Boltzmann Equation for electrons (PIC-MCC) Chapman-Enskog Maxwell Distribution (DSMC) TRANSPORT PROPERTIES RATE COEFFICIENTS PARALLEL PLATE (PIC-MCC) KINETICS FLUIDYNAMICS LASER-PLASMA Interaction • MULTICUSP • (Magnetic Plasmas) • Filament • RF AEROSPACE RF TORCHES Microelectronics MICROWAVE DISCHARGES (Maxwell Equations) DIVERTOR Plasmas Reentry Problems Metallurgy Waste Discharges H-/D- Production Diamond Film Production QUANTUM CHEMISTRY

  4. - Open problems (1985-1995) in Multipole Magnetic Plasmas a) Validation of Bari code with FOM experiments b) Extension to D2 plasmas c) Pulsed discharges d) Rydberg states e) Wall effects - Cross Section Improvements (1995-2005) a) Electron-molecule cross sections b) Heavy particle collision cross sections c) Gas surface interaction - Kinetic models Improvements(1995-2005) a) New multipole zerodimensional code b) Parallel-plate 1D code c) RF and MW quasi 1D code - Air Plasmas a) N2 and O2 State-to-State Cross Sections OUTLINE

  5. - Open problems (1985-1995) in Multipole Magnetic Plasmas a) Validation of Bari code with FOM experiments b) Extension to D2 plasmas c) Pulsed discharges d) Rydberg states e) Wall effects - Cross Section Improvements (1995-2005) a) Electron-molecule cross sections b) Heavy particle collision cross sections c) Gas surface interaction - Kinetic models Improvements(1995-2005) a) New multipole zerodimensional code b) Parallel-plate 1D code c) RF and MW quasi 1D code - Air Plasmas a) N2 and O2 State-to-State Cross Sections OUTLINE

  6. Electron source term: Term due to inelastic collisions Flux of electrons along energy axis due to elastic collisions Term due to ionization collisions Flux of electrons along energy axis due to electron-electron collisions Term due to superelastic collisions Electron loss term VIBRATIONAL EXCITATION and NEGATIVE ION KINETICS MULTIPOLE MAGNETIC PLASMAS: !! Self-consistent non equilibrium vibrational kinetics coupled to the Boltzmann equation for the electron energy distribution function!! Time Evolution (heavy species)

  7. VALIDATION of BARI CODE with the FOM EXPERIMENTS (GORSE ET AL. 1992) comparison between experimental (a) and theoretical (b) vdfs at several pressures comparison between experimental (a) and theoretical (b) vdfs at several discharge currents Id

  8. !!PROBLEMS!! • calculations overestimate by a factor 10 the high lying vibrational levels giving satisfactory agreement with negative ion concentrations • FOM experimental vibrational distributions limited to v=5 • !!New: experimental determination by Mosbach and Dobele up to v=13!! vibrational distribution Nv measured in a H2 multicusp source (p = 11.25 mtorr, Id = 0.5 A, Vd = 100 V)

  9. EXTENSION to D2 PLASMAS theoretical EEDF (a) and Nv (b) in H2 and D2 sources (p = 4.5 mtorr, Id = 10 A, Vd = 115 V, plasma potential Vp = 2.9 V) dissociative attachment rates versus vibrational quantum number for H2 and D2 molecules

  10. (a) behavior of electron density ne (b) electron temperature Te (c) atomic concentration [H]/[D] (d) negative ion concentration [H-]/[D-] for H2 and D2 systems versus pressure p (Id = 10 A, Vd = 115 V)

  11. (a) behavior of electron density ne (b) electron temperature Te (c) atomic concentration [H]/[D] (d) negative ion concentration [H-]/[D-] for H2 and D2 systems versus current Id (p = 7.5 mtorr, Vd = 115 V)

  12. DISSOCIATIVE ATTACHMENT: H2 (X 1g,) + e  H2- H- + H E= 4.5 eV

  13. RESONANT VIBRATIONAL EXCITATION: H2 (X 1g, i) + e  H2- H2 (X 1g, f) + e E= 5 eV

  14. PULSED DISCHARGES: MODEL Relaxation of several quantities in the D2 post-discharge regime (a) EEDF, (b) e-da rate coefficient, (c) Nv, (d) D- density

  15. PULSED DISCHARGES: EXPERIMENT extracted H- current in a pulsed hydrogen discharge with a 2.7 ms pulse length and a 87 Hz repetition rate (p = 2.4 mtorr, Id = 15 A)

  16. Pinnaduwage et al. [Phys. Rev. Lett. 70, 754 (1993)] e + H2* H + H- Kda(Ryd)=10-6 cm3/sec Garscadden and Nagpal[Plasma Sources Sci. Technol. 4, 268 (1995)] Simplified model: (lumped excitation cross section on Rydberg states + lifetime of Rydberg states of 10-6sec + Kda(Ryd)=10-6 cm3/sec) Result: Contribution from Rydberg states 10 times the one from vibrationally excited states Gorse et al. [AIP Conf. Proc. 380, 109 (1995)] Model: Insertion of Garscadden model in the self-consistent kinetics in multipole magnetic plasmas Result: enhancement by a factor 2 Hiskes[Appl. Phys. Lett. 69, 755 (1996)] Model: collisional radiative model for H2* Rydberg states + Kda(Ryd)=10-6 cm3/sec Result: lifetime of Rydberg states of the order of 10-8sec Consequence: contribution of Rydberg states 1% RYDBERG STATES: HYSTORICAL SCENARIO/1

  17. Pinnaduwage et al. [Phys. Rev. A 55, 4131 (1997)] e + H2* = H + H- Kda(Ryd) = 510-5 cm3/sec Hassouni et al.[Chem. Phys. Lett. 290, 502 (1998)] Model: collisional radiative model for H2* Rydberg states + Kda(Ryd)=5 10-5 cm3/sec Result: enhancement by factor 2.7 Problem: Rydberg state from n>3 Pinnaduwage etal.[J.Appl.Phys. 85, 7064 (1999)] scaling law for Rydberg states which corresponds to n=12 An estimation For a plateau between 1010-1012cm-3 Rydberg concentrations of the order of 1/6 107 to 1/6 109 cm-3 can be of the same importance as the dissociative attachment from vibrationally excited molecules RYDBERG STATES: HYSTORICAL SCENARIO/2

  18. FUTURE IMPROVEMENTS COLLISIONAL RADIATIVE MODEL FOR RYDBERG STATES SCALING LAW FOR THE EXCITATION OF RYDBERG STATES LIFETIMES OF RYDBERG STATES SCALING LAW FOR DISSOCIATIVE ATTACHMENT FROM RYDBERG STATES

  19. Hiskes & Karo Model: trajectory calculations Results: strong deactivation of vibrationally excited molecules on iron surfaces - widely used in multicusp modelling Billing & Cacciatore Model: semiclassical/classical for describing atoms and molecules reaching the surface; quantum description of the interaction of the molecule/atom with the phononic and electronic structure of the metal Results : small deactivation of vibrationally excited molecules on copper surfaces WALL EFFECTS: HYSTORICAL SCENARIO

  20. Dissociation Probabilities and Energy Accommodation for H2(v,j) Colliding with a Cu(100) Surface as a Function of Vibrational and Rotational Angular Momenta v and j and Initial Kinetic Energy a) Dissociation probability b) Averaged values for reflected trajectories c) Energy transferred to surface phonons

  21. FORMATION OF VIBRATIONALLY EXCITED STATES from HETEROGENEOUS ATOM RECOMBINATION H(gas) + Hads H2() DIRECT ELEY RIDEAL (E-R) MECHANISM H(gas)  H (trapped) H(trapped) + Hads  H2() HOT ATOM (HA) MECHANISM Hads + Hads H2() HINSHELWOOD-LANGMUIR (H-L) MECHANISM !!Different energetics depending on the nature of the adsorbed atom e.g. physi-adsorbed; chemi-adsorbed!! PHYSI-ADSORBED: practically all the recombination energy can go into vibrational excitation of desorbed molecules in both E-R and H-L mechanisms CHEMI-ADSORBED: only the difference between the dissociation energy of the diatom and the adsorption energy of atom(s) can go into vibrational energy of the desorbed molecules

  22. semiclassical collisional method Hads equilibrium distance of 1.5 Å in thermal equilibrium with the surface Hgas (;) Ekin TS ELEY-RIDEL MECHANISM MD energetic fluxes surface temperature effect recombination probabilities H2 vibrational distribution reaction probabilities for different reaction products

  23. VIBRATIONAL DISTRIBUTIONS from PHYSIADSORBED H and D ATOMS on COPPER (E-R mechanism, BILLING&CACCIATORE)

  24. VIBRATIONAL DISTRIBUTIONS from CHEMIADSORBED H ATOMS on COPPER (HA-SHALASHILIN et al.) for the REACTION Hgas + Dads HD() P () vibrational quantum number

  25. VIBRATIONAL DISTRIBUTIONS from PHYSIADSORBED H ATOMS on GRAPHITE (E-R mechanism, H-L mechanism, SIDIS&MORISSET) SCHEME OF THE REACTION PATH (v, j) distribution of the H2 product

  26. VIBRATIONAL DISTRIBUTIONS from PHYSIADSORBED H ATOMS on GRAPHITE (E-R mechanism, BILLING&CACCIATORE) 0.50 0.40 0.30 0.20 0.10 0.00 0 2 4 6 8 10 12 VIBRATIONAL QUANTUM NUMBER TS = 500K

  27. - Open problems (1985-1995) in Multipole Magnetic Plasmas a) Validation of Bari code with FOM experiments b) Extension to D2 plasmas c) Pulsed discharges d) Rydberg states e) Wall effects - Cross Section Improvements (1995-2005) a) Electron-molecule cross sections b) Heavy particle collision cross sections c) Gas surface interaction - Kinetic models Improvements(1995-2005) a) New multipole zerodimensional code b) Parallel-plate 1D code c) RF and MW quasi 1D code - Air Plasmas a) N2 and O2 State-to-State Cross Sections OUTLINE

  28. CROSS SECTIONS IMPROVEMENTS ELECTRONIC EXCITATION to the lowest SINGLETS X 1g (i)  B 1 u X 1 g (i)  C 1u

  29. IMPACT PARAMETER (BORN cross section) TRANSITION DIPOLE MOMENT THEORETICAL APPROACH IMPACT PARAMETER METHOD • SEMICLASSICAL Method (quantal target - classical projectile) • ALLOWED Transitions (selection rules) • degenerate rotational levels TOTAL CROSS SECTION VIBRONIC EXCITATION DISSOCIATIVE EXCITATION STRUCTURAL FACTOR DYNAMICAL FACTOR

  30. CROSS SECTIONS for H2 ISOTOPIC VARIANTS E= 40 eV X 1g (i)  B 1 u

  31. RESONANT VIBRATIONAL EXCITATION H2 (X 1g, ni) + e  H2- H2 (X 1g, nf) + e E= 5 eV

  32. EXCITATION of low-lying RYDBERG STATES X 1g (i)  B’ 1 u X 1 g (i)  D 1u X 1g (i)  B” 1 u X 1 g (i)  D’ 1u

  33. s  n-4

  34. DISSOCIATION DIRECT DISSOCIATION through EXCITED STATES excited bound state ’ DISSOCIATION  B 1 u and C 1 u + low-lying RYDBERG STATES B’, B” 1 u , D, D’ 1 u DISSOCIATION pure repulsive state i

  35. theoretical approach in atom-molecule collisions: QCT Method atomic motion is considered classical on the potential energy surface (PES) initial and final states are approximated with pseudoquantization rules COMPUTATIONAL LOAD RELIABILITY of METHOD good months on fast processor

  36. RATE COEFFICIENTS for the PROCESS: H+H2(,Trot)  3H Trot=500 K H2 D2

  37. HYDROGEN VIBRATIONAL EXCITATION RATE COEFFICIENTS as a FUNCTION of FINAL VIBRATIONAL QUANTUM NUMBER

  38. HYDROGEN VIBRATIONAL DEACTIVATION RATE COEFFICIENTS as a FUNCTION of FINAL VIBRATIONAL QUANTUM NUMBER

  39. HYDROGEN VIBRATIONAL MONOQUANTUM DEACTIVATION RATE COEFFICIENTS

  40. HYDROGEN RECOMBINATION RATE COEFFICIENTS as a FUNCTION of FINAL VIBRATIONAL QUANTUM NUMBER !! normalized to total recombination, at different temperatures !!

  41. - Open problems (1985-1995) in Multipole Magnetic Plasmas a) Validation of Bari code with FOM experiments b) Extension to D2 plasmas c) Pulsed discharges d) Rydberg states e) Wall effects - Cross Section Improvements (1995-2005) a) Electron-molecule cross sections b) Heavy particle collision cross sections c) Gas surface interaction - Kinetic models Improvements(1995-2005) a) New multipole zerodimensional code b) Parallel-plate 1D code c) RF and MW quasi 1D code - Air Plasmas a) N2 and O2 State-to-State Cross Sections OUTLINE

  42. MULTIPOLE H2 DISCHARGES !! Time dependent electron kinetics and vibrational kinetics treated at the same level!! for i KINETIC MODELS IMPROVEMENTS ELECTRON ENERGY DISCRETIZATION each electron energy sub-interval a “different electron” characterized by a representative energy i (sub-interval mean energy) ELECTRONS STATE-TO-STATE KINETICS (electrons with different energies as molecular energy levels) discretized electron rate coefficients:

  43. VDF and EEDF as a function of PRESSURE TG =500 K DISCHARGE CURRENT=10 A DISCHARGE VOLTAGE=100 V

  44. VDF and EEDF as a function of CURRENT TG =500 K PRESSURE=7.5 mtorr DISCHARGE VOLTAGE=100 V

  45. BOUNDARY CONDITIONS  (WALL) POISSON EQUATION ELECTRIC FIELD SPACE CHARGE SURFACE REACTIONS ABSORPTION, SEC.EMISSION CHARGED PARTICLE KINETICS REACTION/DIFFUSION EQUATIONS EEDF ELECTR./ION DENSITY GAS COMPOSITION RF DISCHARGES: PARALLEL PLATES 1D(r)2D(v) self-consistent particle/continuum model • PIC/MCC • applied to ELECTRONS and IONIC SPECIES • GRID-DISCRETIZED RELAXATION technique • for REACTION-DIFFUSION part Cs: Boltzmann collision integral for charged/neutral collisions

  46. p = 10 mtorr d = 36 cm Vrf = 300 V mean kinetic energy(eV) number density (m-3) position (m) position (m) EEDF (eV-3/2) VDF (m-3) energy (eV) vibrational quantum number

  47. FUTURE STEPS CONSTRUCTION OF A DATA BASE OF CROSS SECTIONS FOR H2 AND ISOTOPES RYDBERG KINETICS AND GAS-SURFACE INTERACTIONS INSERTION OF THE COMPLETE DATA BASE IN 1D-2D CODES EXTENSION TO SURFACE SOURCES  VALIDATION OF THE PREDICTIVE CODE WITH DEDICATED EXPERIMENTS AGREEMENT PROTOCOL WITH ITER PROGRAMME

  48.  HARPOON REACTION INVOLVING CESIUM ATOM AND HYDROGEN MOLECULE Asymptotic Approach

  49. - Open problems (1985-1995) in Multipole Magnetic Plasmas a) Validation of Bari code with FOM experiments b) Extension to D2 plasmas c) Pulsed discharges d) Rydberg states e) Wall effects - Cross Section Improvements (1995-2005) a) Electron-molecule cross sections b) Heavy particle collision cross sections c) Gas surface interaction - Kinetic models Improvements(1995-2005) a) New multipole zerodimensional code b) Parallel-plate 1D code c) RF and MW quasi 1D code - Air Plasmas a) N2 and O2 State-to-State Cross Sections OUTLINE

  50. ELECTRON IMPACT induced PROCESSES in HOMONUCLEAR DIATOMIC MOLECULES ATOM-DIATOM COLLISION PROCESSES NON-DISSOCIATIVE IONIZATION of N2 DISSOCIATION/RECOMBINATION of O2 andN2 VIBRONIC EXCITATION and (PRE)DISSOCIATION of O2 andN2 ENERGY EXCHANGE (VT Processes) of O2 andN2 AIR PLASMAS

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