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O2(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 UniversityAmes, IA 50011, USA
arakoni@iastate.edu natalie5@iastate.edumjk@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
Iowa State UniversityOptical and Discharge Physics
AGENDA
• Introduction to eCOIL
• Description of the model
• Oxygen-iodine kinetics mechanism
• NO/NO2 addition, I2 dissociation
• Concluding Remarks
GEC2006_Natalie_02
Iowa State UniversityOptical and Discharge Physics
ELECTRICALLY EXCITED OXYGEN-IODINE LASERS• In chemical oxygen-iodine lasers (COILs), oscillation at 1.315 µm
I(2P1/2)→ I(2P3/2) occurs by excitation transfer of O2(1∆) to I2 and I.
• Plasma production of O2(1∆) in electrical COILs (eCOILs) eliminates liquid phase generators.
• I2 injection and supersonic expansion (required to lower Tgas for inversion) occurs downstream of the plasma zone.
GEC2006_Natalie_03
• Ref: CU Aerospace
Iowa State UniversityOptical and Discharge Physics
NO AND NO2 INJECTION
• Excitation of O2(1∆) optimizes at Te = 1 eV whereas self sustaining discharges require Te = 2-3 eV.
• NO additive (lower ionization potential) to inlet flow may lower Te to a more optimum value.
• Significant electron impact dissociation of O2 produces large fluxes of O atoms which:
• Quench the upper laser level → Increases O2(1∆) for oscillation.• Dissociate I2 → Decreases O2(1∆) required to produce I atoms.
• NO2 injection may be used to control O atom inventory
NO2 + O → O2 + NO
GEC2006_Natalie_04
Iowa State UniversityOptical and Discharge Physics
GEOMETRY FOR CAPACITIVE EXCITATION
• Cylindrical flow tube 6 cm diameter
• Capacitive excitation (10s MHz) using ring electrodes.
• Ring injection nozzles
• Typical Conditions: He/O2=70/30, 3 Torr 10s to 100 W
• Outflow: O2(1∆)/O2 = 0.15 - 0.25
He/NO2Injection
He/I2InjectionPrimary inflow
He/O2/NO
NO2
GEC2006_Natalie_05
Outflow
• Electron impact [0.9 eV] and excitation of O2(1Σ) with quenching to O2(1∆) are the main channels of O2(1∆) production.
• O atom and O3 production result in quenching and I2-oxygen chemistry downstream. Iowa State University
Optical and Discharge Physics
O2(1∆) KINETICS IN He/O2 DISCHARGES
GEC2006_Natalie_06
• I2 is rapidly dissociated by atomic oxygen and O2(1∆, 1Σ).
• Population inversion by excitation transfer of O2(1∆) to I(2P3/2).
Iowa State UniversityOptical and Discharge Physics
OXYGEN-IODINE AND NOx KINETICS
GEC2006_Natalie_07
• NO/NO2 recycling chain scavenges O atoms.
Iowa State UniversityOptical and Discharge Physics
THE ROLE OF ADDITIVES
• The roles of additives (NO, NO2), their synergy with I2 injection and production of I(2P1/2) 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(2P1/2)?
GEC2006_Natalie_08
Iowa State UniversityOptical and Discharge Physics
• Poisson’s equation, continuity equations and surface charge are simultaneously solved using a Newton iteration technique.
• Electron energy equation:
∑ +=Φ∇⋅∇−j
sjjqN ρε
jjj StN
+⋅−∇=∂
∂φr
∑ Φ−∇⋅∇−+⋅∇−=∂∂
jjjj
s Sqt
))(()( σφρ r
( )e
ieiie
e qjTNnEjtn φλεϕκ∂ε∂ rrrr
=⎟⎠⎞
⎜⎝⎛ ∇−⋅∇−−⋅= ∑ ,25
DESCRIPTION OF 2d-MODEL: CHARGED PARTICLES, SOURCES
GEC2006_Natalie_09
Iowa State UniversityOptical and Discharge Physics
• Fluid averaged values of mass density, mass momentum and thermal energy density obtained using unsteady algorithms.
• Individual fluid species diffuse in the bulk fluid.
)pumps,inlets()v(t
+⋅−∇=rρ
∂ρ∂
( ) ( ) ( ) ∑+⋅∇−⋅∇−∇=i
iii ENqvvNkTtv vrrr
µρ∂ρ∂
( ) ( ) ∑ ∑ ⋅+−⋅∇++∇−−∇=i i
iiifipp EjHRvPTcvTtTc rrr ∆ρκ
∂ρ∂
( ) ( ) ( )SV
T
iTifii SS
NttNNDvtNttN ++⎟
⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛ +∇−⋅∇−=+
∆∆ r
DESCRIPTION OF 2d-MODEL: NEUTRAL PARTICLE TRANSPORT
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Iowa State UniversityOptical and Discharge Physics
GEC2006_Natalie_11
[NO] INLET ADDITIVE
• The effect of NO on electron density is small.
• O atoms are rapidly depleted by NO.
• Global model captures trends.
• He/O2/NO= 70/30/0-3
3 Torr, 40W, 25 MHz, 6000 sccm
• Global Model • 2d Model
Iowa State UniversityOptical and Discharge Physics
BASE CASE PARAMETERS
• Peak Te above that for optimum O2(1∆) production.
• Electron density localized due to rapid attachment.
• O2(1∆) yield is 15%.
• O atoms consumed primarily by O3production.
• He/O2=70/30, 3 Torr, 40W, 25MHz, 6000 sccm
GEC2006_Natalie_12MIN MAX
• He/O2=70/30, 6000 sccm 3 Torr, 40W, 25 MHz
He/O2
Iowa State UniversityOptical and Discharge Physics
0.2 sccm NO2 AND I2INJECTION
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• Injection: He/NO2=0.995/0.005, 36 sccm
• Injection: He/I2=0.995/0.005, 36 sccm
• Atomic O nominally depleted by NO2
• Excess atomic oxygen totally dissociates small amount of injected iodine.
He/O2 He/NO2 He/I2
MIN MAX
• He/O2=70/30, 6000 sccm 3 Torr, 40W, 25 MHz
He/NO2 He/I2He/O2
Iowa State UniversityOptical and Discharge Physics
GEC2006_Natalie_14
• Injection: He/NO2=0.9/0.1, 36 sccm
• Injection: He/I2=0.9/0.1, 36 sccm
MIN MAX
• Atomic oxygen is almost completely scavenged by NO2
• O2(1∆) is rapidly depleted by I2 in pumping reaction.
• Only fraction of injected I2is dissociated.
• I* peaks near inlet.
• He/O2=70/30, 6000 sccm 3 Torr, 40W, 25 MHz
3.6 sccm NO2 AND I2INJECTION
Iowa State UniversityOptical and Discharge Physics
EFFECT OF ADDITIVES ON GAS TEMPERATURE
MIN MAXGEC2006_Natalie_15
• He/NO2=0.995/0.005• He/I2=0.995/0.005
He/NO2 He/I2 or He/I (36 sccm)
• Gas temperature increases due to exothermicity of scavenging and dissociation reactions
NO2 + O → O2 + NO O + I2 → IO + I• Injection of I atoms reduces downstream Tgas.
• He/NO2=0.9/0.1• He/I2=0.9/0.1
• He/NO2=0.9/0.1• He/I=0.9/0.1
Predissociated iodine
• He/O2=70/30, 6000 sccm 3 Torr, 40W, 25 MHz
Iowa State UniversityOptical and Discharge Physics
GEC2006_Natalie_16
• Injection:•He/NO2=0.9/xxx, 36 sccm•He/I2=0.995/0.005, 36 sccm
• Injection:•He/NO2=0.9/xxx, 36 sccm•He/I2=0.9/0.1, 36 sccm
• NO2 injection has little effect on O2(1∆). • I2 and I quenching (laser pumping reactions) rapidly deplete O2(1∆).
O2(1∆) vs ADDITIVES
• He/O2=70/30, 6000 sccm 3 Torr, 40W, 25 MHz
Iowa State UniversityOptical and Discharge Physics
GEC2006_Natalie_17
ATOMIC OXYGEN vs ADDITIVES
• Injection:•He/NO2=0.9/xxx, 36 sccm•He/I2=0.995/0.005, 36 sccm
• Injection:•He/NO2=0.9/xxx, 36 sccm•He/I2=0.9/0.1, 36 sccm
• Optimum NO2 flow rate scavenges excess O atoms leaving enough atoms to dissociate injected I2.
• He/O2=70/30, 6000 sccm 3 Torr, 40W, 25 MHz
Iowa State UniversityOptical and Discharge Physics
GEC2006_Natalie_18
• Injection:•He/NO2=0.995/0.005, 36 sccm•He/I2=0.995/0.005, 36 sccm
• Injection:•He/NO2=0.9/0.1, 36 sccm•He/I2=0.9/0.1, 36 sccm
• Optimum NO2 injection will optimize density of I* for a given O2(1∆) production.
IODINE SPECIES vs ADDITIVES
• He/O2=70/30, 6000 sccm 3 Torr, 40W, 25 MHz
Iowa State UniversityOptical and Discharge Physics
OPTIMIZING I* PRODUCTION
GEC2006_Natalie_19
• Injection:•He/NO2=0.9/xxx, 36 sccm•He/I2=0.995/0.005, 36 sccm
• Injection:•He/NO2=0.9/xxx, 36 sccm•He/I2=0.9/0.1, 36 sccm
• Predissociation of I2 lessens the need to have a small O atom flow for dissociation of I2.
• Optimum NO2 completely scavenges O atoms.
Iowa State UniversityOptical and Discharge Physics
CONCLUDING REMARKS
GEC2006_Natalie_20
• Oxygen-iodine kinetics in flowing afterglows for electrically excited chemical-oxygen-iodine lasers has been computationally investigated.
• NO2 injection scavenges O atoms.
• Reduces amount of quenching of I*.
• Also reduces the amount of dissociation of I2.
• End result is delicate balance is required.
• Injection of pre-dissociated I2 eliminates competition between these two processes and more easily optimizes I*.
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