O 2 ( 1 ) PRODUCTION AND OXYGEN-IODINE KINETICS IN FLOWING - PowerPoint PPT Presentation

O 2 ( 1 ∆ ) PRODUCTION AND OXYGEN-IODINE KINETICS IN FLOWING AFTERGLOWS FOR ELECTRICALLY EXCITED CHEMICAL-OXYGEN-IODINE LASERS* Ramesh Arakoni, Natalia Y. Babaeva, and Mark J. Kushner Iowa State University Ames, IA 50011, USA arakoni@iastate.edu natalie5@iastate.edu mjk@iastate.edu http://uigelz.ece.iastate.edu October 2006 * Work supported by Air Force Office of Scientific Research and National Science Foundation. GEC2006_Natalie_01

AGENDA • Introduction to eCOIL • Description of the model • Oxygen-iodine kinetics mechanism • NO/NO 2 addition, I 2 dissociation • Concluding Remarks Iowa State University Optical and Discharge Physics GEC2006_Natalie_02

ELECTRICALLY EXCITED OXYGEN-IODINE LASERS • In chemical oxygen-iodine lasers (COILs), oscillation at 1.315 µm I( 2 P 1/2 ) → I( 2 P 3/2 ) occurs by excitation transfer of O 2 ( 1 ∆ ) to I 2 and I. • Plasma production of O 2 ( 1 ∆ ) in electrical COILs (eCOILs) eliminates liquid phase generators. • I 2 injection and supersonic expansion (required to lower T gas for inversion) occurs downstream of the plasma zone. • Ref: CU Aerospace Iowa State University Optical and Discharge Physics GEC2006_Natalie_03

NO AND NO 2 INJECTION • Excitation of O 2 ( 1 ∆ ) optimizes at T e = 1 eV whereas self sustaining discharges require T e = 2-3 eV. • NO additive (lower ionization potential) to inlet flow may lower T e to a more optimum value. • Significant electron impact dissociation of O 2 produces large fluxes of O atoms which: • Quench the upper laser level → Increases O 2 ( 1 ∆ ) for oscillation. • Dissociate I 2 → Decreases O 2 ( 1 ∆ ) required to produce I atoms. • NO 2 injection may be used to control O atom inventory NO 2 + O → O 2 + NO Iowa State University Optical and Discharge Physics GEC2006_Natalie_04

GEOMETRY FOR CAPACITIVE EXCITATION • Cylindrical flow tube 6 cm diameter • Capacitive excitation NO 2 (10s MHz) using ring electrodes. He/NO 2 He/I 2 Primary inflow Injection Injection He/O 2 /NO • Ring injection nozzles • Typical Conditions: Outflow He/O 2 =70/30, 3 Torr 10s to 100 W • Outflow: O 2 ( 1 ∆ )/O 2 = 0.15 - 0.25 Iowa State University Optical and Discharge Physics GEC2006_Natalie_05

O 2 ( 1 ∆ ) KINETICS IN He/O 2 DISCHARGES • Electron impact [0.9 eV] and excitation of O 2 ( 1 Σ ) with quenching to O 2 ( 1 ∆ ) are the main channels of O 2 ( 1 ∆ ) production. • O atom and O 3 production result in quenching and I 2 -oxygen chemistry downstream. Iowa State University Optical and Discharge Physics GEC2006_Natalie_06

OXYGEN-IODINE AND NO x KINETICS • NO/NO 2 recycling chain • I 2 is rapidly dissociated by atomic scavenges O atoms. oxygen and O 2 ( 1 ∆ , 1 Σ ). • Population inversion by excitation transfer of O 2 ( 1 ∆ ) to I( 2 P 3/2 ). Iowa State University Optical and Discharge Physics GEC2006_Natalie_07

THE ROLE OF ADDITIVES • The roles of additives (NO, NO 2 ), their synergy with I 2 injection and production of I( 2 P 1/2 ) in eCOILS were computationally investigated. • Global modeling: Basic kinetics and scaling • 2-d modeling: Hydrodynamics and injection strategies. • What are tradeoffs in using additives to optimize I( 2 P 1/2 )? Iowa State University Optical and Discharge Physics GEC2006_Natalie_08

DESCRIPTION OF 2d-MODEL: CHARGED PARTICLES, SOURCES • Poisson’s equation, continuity equations and surface charge are simultaneously solved using a Newton iteration technique. ∑ − ∇ ⋅ ε ∇ Φ = + ρ N j q j s j ∂ N r j = −∇ ⋅ φ + S j j ∂ t r ∂ ρ ∑ = − ∇ ⋅ φ + − ∇ ⋅ σ −∇ Φ s q ( S ) ( ( )) j j j ∂ t j • Electron energy equation: ( ) r r ∂ ε r r ⎛ ⎞ n 5 ∑ = ⋅ − κ − ∇ ⋅ εϕ − λ ∇ = φ ⎜ ⎟ e j E n N T , j q e i i e e ∂ t ⎝ 2 ⎠ i Iowa State University Optical and Discharge Physics GEC2006_Natalie_09

DESCRIPTION OF 2d-MODEL: NEUTRAL PARTICLE TRANSPORT • Fluid averaged values of mass density, mass momentum and thermal energy density obtained using unsteady algorithms. ∂ ρ r = −∇ ⋅ ρ + ( v ) ( inlets , pumps ) ∂ t r ( ) ∂ ρ v v r r ( ) ( ) ∑ = ∇ − ∇ ⋅ ρ − ∇ ⋅ µ + NkT v v q N E i i i ∂ t i ( ) ∂ ρ c T r ( ) r r ∑ ∑ p = −∇ − κ ∇ + ρ + ∇ ⋅ − ∆ + ⋅ T v c T P v R H j E p i f i i i ∂ t i i • Individual fluid species diffuse in the bulk fluid. ( ) ⎛ ⎞ ⎛ ⎞ + ∆ N t t r ( ) ( ) ⎜ ⎟ ⎜ ⎟ + ∆ = − ∇ ⋅ − ∇ + + N t t N t v D N i S S ⎜ ⎟ ⎜ ⎟ i i f i T V S N ⎝ ⎠ ⎝ ⎠ T Iowa State University Optical and Discharge Physics GEC2006_Natalie_10

[NO] INLET ADDITIVE • Global Model • 2d Model • The effect of NO on electron density is small. • O atoms are rapidly depleted by NO. • Global model captures trends. • He/O 2 /NO= 70/30/0-3 3 Torr, 40W, 25 MHz, 6000 sccm Iowa State University Optical and Discharge Physics GEC2006_Natalie_11

BASE CASE He/O 2 PARAMETERS • Peak T e above that for optimum O 2 ( 1 ∆ ) production. • Electron density localized due to rapid attachment. • O 2 ( 1 ∆ ) yield is 15%. • O atoms consumed primarily by O 3 production. • He/O 2 =70/30, 3 Torr, 40W, 25MHz, 6000 sccm • He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz Iowa State University MIN MAX Optical and Discharge Physics GEC2006_Natalie_12

0.2 sccm NO 2 AND I 2 He/O 2 He/NO 2 He/I 2 INJECTION • Atomic O nominally depleted by NO 2 • Excess atomic oxygen totally dissociates small amount of injected iodine. • Injection: He/NO 2 =0.995/0.005, 36 sccm • Injection: He/I 2 =0.995/0.005, 36 sccm • He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz Iowa State University Optical and Discharge Physics MIN MAX GEC2006_Natalie_13

3.6 sccm NO 2 AND I 2 He/O 2 He/NO 2 He/I 2 INJECTION • Atomic oxygen is almost completely scavenged by NO 2 • O 2 ( 1 ∆ ) is rapidly depleted by I 2 in pumping reaction. • Only fraction of injected I 2 is dissociated. • I* peaks near inlet. • Injection: He/NO 2 =0.9/0.1, 36 sccm • Injection: He/I 2 =0.9/0.1, 36 sccm • He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz Iowa State University Optical and Discharge Physics MIN MAX GEC2006_Natalie_14

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 • He/NO 2 =0.9/0.1 • He/I 2 =0.9/0.1 Predissociated iodine • He/NO 2 =0.9/0.1 • He/I=0.9/0.1 • Gas temperature increases due to exothermicity of scavenging and dissociation reactions NO 2 + O → O 2 + NO O + I 2 → IO + I • Injection of I atoms reduces downstream T gas . • He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz Iowa State University Optical and Discharge Physics MIN MAX GEC2006_Natalie_15

O 2 ( 1 ∆ ) vs ADDITIVES • Injection: • Injection: • He/NO 2 =0.9/xxx, 36 sccm • He/NO 2 =0.9/xxx, 36 sccm • He/I 2 =0.995/0.005, 36 sccm • He/I 2 =0.9/0.1, 36 sccm • NO 2 injection has little effect on O 2 ( 1 ∆ ). • I 2 and I quenching (laser pumping reactions) rapidly deplete O 2 ( 1 ∆ ). • He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz Iowa State University Optical and Discharge Physics GEC2006_Natalie_16

ATOMIC OXYGEN vs ADDITIVES • Injection: • Injection: • He/NO 2 =0.9/xxx, 36 sccm • He/NO 2 =0.9/xxx, 36 sccm • He/I 2 =0.995/0.005, 36 sccm • He/I 2 =0.9/0.1, 36 sccm • Optimum NO 2 flow rate scavenges excess O atoms leaving enough atoms to dissociate injected I 2 . • He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz Iowa State University Optical and Discharge Physics GEC2006_Natalie_17

IODINE SPECIES vs ADDITIVES • Injection: • Injection: • He/NO 2 =0.995/0.005, 36 sccm • He/NO 2 =0.9/0.1, 36 sccm • He/I 2 =0.995/0.005, 36 sccm • He/I 2 =0.9/0.1, 36 sccm • Optimum NO 2 injection will optimize density of I* for a given O 2 ( 1 ∆ ) production. • He/O 2 =70/30, 6000 sccm 3 Torr, 40W, 25 MHz Iowa State University Optical and Discharge Physics GEC2006_Natalie_18

OPTIMIZING I* PRODUCTION • Injection: • Injection: • He/NO 2 =0.9/xxx, 36 sccm • He/NO 2 =0.9/xxx, 36 sccm • He/I 2 =0.995/0.005, 36 sccm • He/I 2 =0.9/0.1, 36 sccm • Predissociation of I 2 lessens the need to have a small O atom flow for dissociation of I 2 . • Optimum NO 2 completely scavenges O atoms. Iowa State University Optical and Discharge Physics GEC2006_Natalie_19

CONCLUDING REMARKS • Oxygen-iodine kinetics in flowing afterglows for electrically excited chemical-oxygen-iodine lasers has been computationally investigated. • NO 2 injection scavenges O atoms. • Reduces amount of quenching of I*. • Also reduces the amount of dissociation of I 2 . • End result is delicate balance is required. • Injection of pre-dissociated I 2 eliminates competition between these two processes and more easily optimizes I*. Iowa State University Optical and Discharge Physics GEC2006_Natalie_20