Using Optical Diagnostics with Sub-Nanosecond Time Resolution

Transcription

1 The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory Sudies of Fs Ionizion Wve Dischrge Plsms Using Opicl Dignosics wih Sub-Nnosecond Time Resoluion K. Tkshim, A. Monello, W.R. Lemper, ndi.v.admovich

2 Objecives Genering conrolled, reproducible nsec pulse durion dischrges in plne-o-plne nd xil Fs Ionizion Wve geomeries, in dischrge secion wih ccess for opicl dignosics Mesuremens of FIW speed in wide rnge of pressures P~- orr, nd volge wveforms pek volge, rise ime, pulse repeiion re Developmen nd esing of new, porble psec CARS dignosic sysem Time- nd spilly resolved mesuremens of rpidly vrying elecric field in nsec pulse dischrges plne-o-plne nd FIW by IR -field psec CARS Mesuremens of elecron densiy in nsec pulse dischrges by Thomson scering * * wih luck

3 Single pulse nnosecond dischrge in plne-o-plne p geomery: spilly uniform? The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory Volge, kv Air, P6 orr, ν4 khz Time, nsec Single pulse pulse verge Brodbnd ICCD cmer imges, ge μsec Air, P6 orr, pulse repeiion re Hz

4 Repeiive nnosecond pulse dischrge: effec of residul ionizion on spil uniformiy Volge, kv Cmer ge: µsec - chode Time, μsec node Single pulse ICCD cmer imges in ir from 4 msec burs P6 orr, ν4 khz, pulses in burs, μsec cmer ge Air plsm remins uniform during enire pulse burs P4- orr fer firs - pulses: effec of residul ionizion Sme resul for shor cmer ges down o 4 nsec: jusifies he use of qusi--d pproch

5 ffec of residul ionizion: uniform plsm on nnosecond ime scle The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory Air, P6 orr, ν4 khz, pulse # in he burs Sme resul for shorer cmer ges down o 4 nsec: jusifies he use of qusi--d pproch

6 Nnosecond pulse dischrge plsm / sheh model qusi--d drif-diffusion, ime-dependen quions for elecron nd ion number densiy Poisson equion for he elecric field Nirogen, plne-o-plne dischrge geomery Boh elecrodes covered wih qurz ples Volge pulse: Gussin fi o experimenl wveform chode L plsm sheh node V pek pek pp exp, Vpek kv, 5 nsec l τ L τ ε Townsend ionizion i coefficien i vs. /N: fi o experimenl d; locl kineics only Dielecric ple chrging / plsm shielding: l s l,εε dv pp d l dv gp εl d le ε ε L L [ Γ x, Γ x, ]dx e C d C s R C d Numericl or nlyic soluion: ime-dependen elecron densiy nd elecric field in he plsm nd in he sheh, coupled pulse energy

7 Nnosecond pulse dischrge plsm / sheh model: key processes nd ime scles pp - pplied elecric field Gussin fi o experimenl pulse shpe V pek pek pp exp, Vpek kv, 5 nsec l τ L τ ε ν i - elecron impc ionizion frequency ν c ν s - frequency of dielecric chrging / sheh formion ν RC - RC frequency of he lod fer brekdown plsm / chrged dielecrics / sheh ν i Bp Ap exp - brekdown field pp, τ, pek le μ en l se μ en ν c, ν s l ε L ε εl εl ν i τ 4ln γ / Bp * * - field in he plsm he momen when coupled power peks, ν RC ν i R C ln plsm lod ν i * / ν i 3Bp ν i, γ, exp,, c s ξ ξ ν ν ln * * / 3

8 Nnosecond pulse dischrge plsm / sheh model: key resuls * pp : elecric field in he plsm ey esu s,, exp * * p pp i pp p ξ ξ ν γ RC pp p ν, mx & [ ], exp * * > i pp ξ ξ ν ξ ξ ξ RC [ ], l l l L l l l L pp s s s s p pp pp s ε s : elecric field in he sheh ln n n l s is s s ν μ l s : sedy se sheh hickness s s ε ε n e : elecron densiy in he plsm n n n n n n p p ln ln, ln / / γ γ γ

9 Anlyic nd numericl soluions: lecric field in he plsm nd in he sheh, kv/cm 87 nsec 88 nsec 89 nsec. sheh x, cm plsm 9 nsec 9 nsec Rpid field drop in he plsm fer brekdown Dominn effec: plsm shielding by chrging dielecric ples, sheh formion Sedy-se elecron densiy fer shielding n e ~ cm -3 Sedy-se sheh hickness / plsm hickness << Uniform field in he plsm Anlyic nd numericl soluions: excellen greemen n e, cm nsec 88.5 nsec sheh plsm 9 nsec 88 nsec 86 nsec 8 nsec x, cm Plsm elecric field, kv/cm numericl model pplied volge nlyic soluion brekdown V pp /Ll/ε shielded plsm Time, nsec lecron densiy, cm brekdown shielded plsm numericl model nlyic soluion Time, nsec

10 Anlyic nd numericl soluions: lecron densiy in he plsm nd coupled power Power densiy, kw/cm 3 5. numericl model nlyic soluion. 4 3 brekdown V pp /Ll/ε shielded plsm 8 9 Time, nsec Coupled pulse energy, mj P * 6 orr, V pek kv Numericl, w/o sheh Numericl, wih sheh Anlyic soluion Iniil elecron densiy, cm -3 Q ol Qbrek Qfer Clod V pek V V pek ν RC π τ pulse Mos of he power coupled during brekdown pulse, Q / fer Q brek ~ ν RC τ pulse ~. Coupled pulse energy scles s he number densiy, cn be incresed by reducing τ pulse Pulse energies in N nd ir re lmos he sme: chmen insignificn shor pulse durions Anlyic nd numericl soluions: excellen greemen Good greemen wih pulse energy inferred from O om mesuremens by Two-Phoon LIF

11 Fs Ionizion Wve FIW dischrge Tes secion schemic The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory Air, P orr, U pek 6 kv ν khz, L cm

12 Wve propgion velociy ~ 4 cm/nsec mesured by cpciive probes x x cm Vol ge [kv] 5 5 4cm cm 8cm Time [ns]

13 Previous FIW dischrge experimens Moscow Insiue of Physics nd Technology A. Srikovskii, S. Srikovsky e l. Arrivl ime nd mpliude of fs ionizion wve in nirogen, P4 orr

14 Kineic modeling of FIW propgion qusi--d, long wvelengh pproximion The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory n e, cm -3 3 nsec Spce chrge, nc nsec 3.6 nsec 4 3 nsec nsec 3.6 nsec , kv/cm 5 5 nsec x, cm nsec 3.6 nsec x, cm x, cm y << x Nirogen, P orr, U pek 5 kv Chnnel heigh cm, elecrode gp cm Boh wve speed nd pek elecric field decrese long he lengh, u-4 cm/nsec Kineic model needs o incorpore full Bolzmnn equion, non-locl kineics effecs. Collborion wih modeling expers welcome!

15 IR -Field nsec CARS schemic nd mesuremen region The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory 473nm Dichroic Mirrors InSb IR LP Filer ωs ω P ωas ω P 476nm BP Filer Focusing Lens Bem Dump CF Lens IR Dichroic Mirror Δv CARS nergy Level Digrm Specromeer Cmer Dely Ph YAG Brodbnd Tunble Dye Lser 5mm CF Lens 5mm Lens 53 nm 67 nm Field Mesuremen Volume Volge CARS Genered Along ~ mm Line Segmen Deermined using scnning microscope slide nd NR bckground Non-Resonn CARS Signl vs Axil Locion Relive o Nominl Wis Posiion mm

16 Preliminry rw IR nsec CARS d elecric field mesured beween wo plne elecrodes in mospheric ir, no brekdown The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory verged over 3 pulses verged over 8 pulses

17 Overview of new psec CARS sysem The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory Dely Ph kspl Nd:YAG lser Hz, ~5 psec pulses 5 mj per pulse 53 nm From Specromeer Modeless Psec Dye Lser Brodbnd 67 nm ~ 6% conversion efficiency

18 Schemic of psec dye lser The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory Thin Film Polrizer reflec ~9% λ/ Pump λ/ Reflecing bem ou Bem splier prism Bem splier ~5:5 ~8: HR HR Bem dumps 4 mm sphericl lens AR HR 3 Cylindricl lens ~ mm AR Cylindricl lens ~5 mm AR RA prism Sokes bem ou oscillor cell iris pre-mp cell mplifier cell 6 mm lens

19 Porble, brodbnd psec CARS dignosic sysem The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory

20 Firs sensiiviy es of psec CARS: Deecing N nd CO in n opicl bsorpion cell The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory N v N v N ouside COv COv Mos of CARS signl comes from inside he cell -3 sho signl ccumulion Blue: 8 orr CO, 74 orr N Red: 9 orr CO, orr Ar Cpble of deecing O Δ genered in elecric dischrges pril pressure ~ orr Nex sensiiviy es: king CARS specr of N -CO mixure vibrionlly pumped by c.w. CO lser

21 Here is wh we expec o see nd more: Sponneous Rmn Specr in CO/N 4/96, P4 orr. Relive populion N.- CO, experimen T v 35 K N, experimen T v K CO, clculion T v 53 K N, clculion T v 7 K v39.- CO Wvelengh, nm Vibrionl qunum number Lser power: 5 W, T 5 K 5 vibrionl levels of N, 4 vibrionl levels of CO signl verging over few hundred pulses

22 Work in Progress / Technicl Issues The Ohio Se Universiy Nonequilibrium Thermodynmics Lborory New FIW dischrge secion sill in glss shop Need n IR deecor / -D deecor rry wih shor response ime ~ nsec Need o deermine sensiiviy limi low pressures nd elecric field Need o synchronize high volge nsec pulses nd CARS lser pulses nd conrol pulse jier ffec of MI noise from he pulser on CARS sysem elecronics ye o be deermined