O 2 ( 1 ) PRODUCTION AND OXYGEN-IODINE KINETICS IN FLOWING AFTERGLOWS FOR ELECTRICALLY EXCITED CHEMICAL-OXYGEN-IODINE LASERS*

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1 O 2 ( 1 ) PRODUCTION AND OXYGEN-IODINE KINETICS IN FLOWING AFTERGLOWS FOR ELECTRICALLY EXCITED CHEMICAL-OXYGEN-IODINE LASERS* Ramesh Arakon, Natala Y. Babaeva, and Mark J. Kushner Ames, IA 50011, USA arakon@astate.edu natale5@astate.edu mjk@astate.edu October 2006 * Work supported by Ar Force Offce of Scentfc Research and Natonal Scence Foundaton. GEC2006_Natale_01

2 AGENDA Introducton to ecoil Descrpton of the model Oxygen-odne knetcs mechansm NO/NO 2 addton, I 2 dssocaton Concludng Remarks GEC2006_Natale_02

3 ELECTRICALLY EXCITED OXYGEN-IODINE LASERS In chemcal oxygen-odne lasers (COILs), oscllaton at µm I( 2 P 1/2 ) I( 2 P 3/2 ) occurs by exctaton transfer of O 2 ( 1 ) to I 2 and I. Plasma producton of O 2 ( 1 ) n electrcal COILs (ecoils) elmnates lqud phase generators. I 2 njecton and supersonc expanson (requred to lower T gas for nverson) occurs downstream of the plasma zone. GEC2006_Natale_03 Ref: CU Aerospace

4 NO AND NO 2 INJECTION Exctaton of O 2 ( 1 ) optmzes at T e = 1 ev whereas self sustanng dscharges requre T e = 2-3 ev. NO addtve (lower onzaton potental) to nlet flow may lower T e to a more optmum value. Sgnfcant electron mpact dssocaton of O 2 produces large fluxes of O atoms whch: Quench the upper laser level Increases O 2 ( 1 ) for oscllaton. Dssocate I 2 Decreases O 2 ( 1 ) requred to produce I atoms. NO 2 njecton may be used to control O atom nventory NO 2 + O O 2 + NO GEC2006_Natale_04

5 GEOMETRY FOR CAPACITIVE EXCITATION Cylndrcal flow tube 6 cm dameter Prmary nflow He/O 2 /NO NO 2 He/NO 2 Injecton He/I 2 Injecton Capactve exctaton (10s MHz) usng rng electrodes. Rng njecton nozzles Outflow Typcal Condtons: He/O 2 =70/30, 3 Torr 10s to 100 W Outflow: O 2 ( 1 )/O 2 = GEC2006_Natale_05

6 O 2 ( 1 ) KINETICS IN He/O 2 DISCHARGES Electron mpact [0.9 ev] and exctaton of O 2 ( 1 Σ) wth quenchng to O 2 ( 1 ) are the man channels of O 2 ( 1 ) producton. O atom and O 3 producton result n quenchng and I 2 -oxygen chemstry downstream. GEC2006_Natale_06

7 OXYGEN-IODINE AND NO x KINETICS I 2 s rapdly dssocated by atomc oxygen and O 2 ( 1, 1 Σ). Populaton nverson by exctaton transfer of O 2 ( 1 ) to I( 2 P 3/2 ). GEC2006_Natale_07 NO/NO 2 recyclng chan scavenges O atoms.

8 THE ROLE OF ADDITIVES The roles of addtves (NO, NO 2 ), ther synergy wth I 2 njecton and producton of I( 2 P 1/2 ) n ecoils were computatonally nvestgated. Global modelng: Basc knetcs and scalng 2-d modelng: Hydrodynamcs and njecton strateges. What are tradeoffs n usng addtves to optmze I( 2 P 1/2 )? GEC2006_Natale_08

9 DESCRIPTION OF 2d-MODEL: CHARGED PARTICLES, SOURCES Posson s equaton, contnuty equatons and surface charge are smultaneously solved usng a Newton teraton technque. ε Φ = N jq j + ρs j N j = r φ j + S j t ρs t = j q j r ( φ + S ) ( σ ( Φ)) j j Electron energy equaton: ( n ε ) e t r r 5 = j E ne Nκ εϕ λ Te, 2 r j = r qφ e GEC2006_Natale_09

10 DESCRIPTION OF 2d-MODEL: NEUTRAL PARTICLE TRANSPORT Flud averaged values of mass densty, mass momentum and thermal energy densty obtaned usng unsteady algorthms. ρ r = ( ρv ) + ( nlets, pumps t r ( ρv ) rr = NkT ρvv µ + t ( ρc ) pt r = κ T + ρvc pt + P v f t ( ) ( ) ( ) R H + j Indvdual flud speces dffuse n the bulk flud. ( t + t) = N ( t) r ) N + q N ( t t) N v f D NT + SV + N T v E r r E S S GEC2006_Natale_10

11 Global Model 2d Model [NO] INLET ADDITIVE The effect of NO on electron densty s small. O atoms are rapdly depleted by NO. Global model captures trends. He/O 2 /NO= 70/30/0-3 3 Torr, 40W, 25 MHz, 6000 sccm GEC2006_Natale_11

12 He/O 2 BASE CASE PARAMETERS Peak T e above that for optmum O 2 ( 1 ) producton. Electron densty localzed due to rapd attachment. O 2 ( 1 ) yeld s 15%. O atoms consumed prmarly by O 3 producton. He/O 2 =70/30, 3 Torr, 40W, 25MHz, 6000 sccm He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz MIN MAX GEC2006_Natale_12

13 He/O 2 He/NO 2 He/I sccm NO 2 AND I 2 INJECTION Atomc O nomnally depleted by NO 2 Excess atomc oxygen totally dssocates small amount of njected odne. Injecton: He/NO 2 =0.995/0.005, 36 sccm Injecton: He/I 2 =0.995/0.005, 36 sccm He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz GEC2006_Natale_13 MIN MAX

14 He/O 2 He/NO 2 He/I sccm NO 2 AND I 2 INJECTION Atomc oxygen s almost completely scavenged by NO 2 O 2 ( 1 ) s rapdly depleted by I 2 n pumpng reacton. Only fracton of njected I 2 s dssocated. I* peaks near nlet. Injecton: He/NO 2 =0.9/0.1, 36 sccm Injecton: He/I 2 =0.9/0.1, 36 sccm He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz GEC2006_Natale_14 MIN MAX

15 EFFECT OF ADDITIVES ON GAS TEMPERATURE He/NO 2 He/I 2 or He/I (36 sccm) He/NO 2 =0.995/0.005 He/I 2 =0.995/0.005 Predssocated odne He/NO 2 =0.9/0.1 He/I 2 =0.9/0.1 He/NO 2 =0.9/0.1 He/I=0.9/0.1 Gas temperature ncreases due to exothermcty of scavengng and dssocaton reactons NO 2 + O O 2 + NO O + I 2 IO + I Injecton of I atoms reduces downstream T gas. He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz GEC2006_Natale_15 MIN MAX

16 O 2 ( 1 ) vs ADDITIVES Injecton: He/NO 2 =0.9/xxx, 36 sccm He/I 2 =0.995/0.005, 36 sccm Injecton: He/NO 2 =0.9/xxx, 36 sccm He/I 2 =0.9/0.1, 36 sccm NO 2 njecton has lttle effect on O 2 ( 1 ). I 2 and I quenchng (laser pumpng reactons) rapdly deplete O 2 ( 1 ). He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz GEC2006_Natale_16

17 ATOMIC OXYGEN vs ADDITIVES Injecton: He/NO 2 =0.9/xxx, 36 sccm He/I 2 =0.995/0.005, 36 sccm Injecton: He/NO 2 =0.9/xxx, 36 sccm He/I 2 =0.9/0.1, 36 sccm Optmum NO 2 flow rate scavenges excess O atoms leavng enough atoms to dssocate njected I 2. He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz GEC2006_Natale_17

18 IODINE SPECIES vs ADDITIVES Injecton: He/NO 2 =0.995/0.005, 36 sccm He/I 2 =0.995/0.005, 36 sccm Injecton: He/NO 2 =0.9/0.1, 36 sccm He/I 2 =0.9/0.1, 36 sccm Optmum NO 2 njecton wll optmze densty of I* for a gven O 2 ( 1 ) producton. He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz GEC2006_Natale_18

19 OPTIMIZING I* PRODUCTION Injecton: He/NO 2 =0.9/xxx, 36 sccm He/I 2 =0.995/0.005, 36 sccm Injecton: He/NO 2 =0.9/xxx, 36 sccm He/I 2 =0.9/0.1, 36 sccm Predssocaton of I 2 lessens the need to have a small O atom flow for dssocaton of I 2. Optmum NO 2 completely scavenges O atoms. GEC2006_Natale_19

20 CONCLUDING REMARKS Oxygen-odne knetcs n flowng afterglows for electrcally excted chemcal-oxygen-odne lasers has been computatonally nvestgated. NO 2 njecton scavenges O atoms. Reduces amount of quenchng of I*. Also reduces the amount of dssocaton of I 2. End result s delcate balance s requred. Injecton of pre-dssocated I 2 elmnates competton between these two processes and more easly optmzes I*. GEC2006_Natale_20