Mixing of post-discharge O 2 /He flow with NO 2 /He flow: 3D modeling of experimental data

Abstract

Flow mixing and chemical kinetics in the afterglow of an electro-discharge source of singlet oxygen O 2 (a 1 ∆ g ) are studied theoretically using both a simple analytical approach and an advanced three-dimensional (3D) simulation with the FLUENT code. Calculated results are compared with titration measurements of atomic oxygen flow in the discharge oxygen-iodine laser (DOIL) system in which the first positive gain and continuous-wave laser oscillation were demonstrated [1,2]. It was shown [1] that atomic oxygen atoms in rf post-discharge O 2 /He mixtures effectively deplete O 2 (a 1 ∆ g ) molecules through quenching of the excited iodine atoms. Thus, the precise technique for O atom flow measurements and methods of removing O atoms are of importance for DOIL operation. One technique is through the admixing of NO 2 to the post-discharge flow which allows control of the O atom flow. Theoretical predictions of NO 2 * production (and equivalently the emission), using both an analytical solution of a simplified system of equations and thorough 3D modeling of the reactive mixing flows, are compared with experimental measurements of NO 2 * emission. Analysis of 3D calculated distributions of species concentrations and flow velocities shows how titration measurements should be calibrated correctly and validates the use of a simple analytical approach for the interpretation of titration measurements. It is recommended that NO 2 titrations for the flow conditions near to those examined use the value obtained from fully extinguishing the NO 2 * emission.

Multi-Disciplinary Research for High Energy Chemical Lasers, Closed-Cycle ElectricOIL Technology

“…Here, w/ is the flow velocity and the subscript "0" indicates the concentration of the various species at the plane of iodine injection (with the assumption that the molecular iodine is dissociated immediately by the O atoms) with spatial variation of 02(a) and I* being exp(-z/Z,) in agreement with Fig. 2 (2)(3)(4)(5)(6) which is higher than the upper bound of 2 x 10" cm /molecule-s given by Han et al . The simple exponential deactivation of 02(a) and I* suggests a simple process as expressed by reaction (2)(3)(4).…”

“…The program was initiated in July 2002. Work under this grant resulted in several major breakthroughs by the MRI team: (1) the first measurement of laser gain in a discharge driven oxygen-iodine supersonic cavity was demonstrated in 2004 at UIUC (2) the first measurement of positive gain in a discharge driven oxygen-iodine system was also demonstrated in a subsonic flow tube; at PS1 (3) the first continuous wave (cw) discharge driven oxysen-iodine laser was produced and power was increased by almost two orders of magnitude to over 5 watts during the period; (4) key measurements were made related to ElectricOlL specific kinetics; (5) Experiments with low power pulse-sustainer discharges support the intriguing results from the modeling; (6) Additional understanding of the electrodynamic phenomena in a pulse-sustainer type of discharge was attained using a detailed plasma discharge model; 7A new high pressure Transverse RF discharge unit was successfully operated at pressures up to 100 torr; and (8) atomic oxygen was found to play a crucial role in the chemistry of the system in the presence of iodine; (9) Laser performance with atomic iodine look promising. It was deemed necessary to scavenge a portion of the excess O atoms to achieve positive gain.…”

“…For li the purposes of this study Ojia A) yield is defined as the ratio of the 02(a A) state to all states of the O2 molecule. (1)(2)(3)(4)(5)(6) Yields foM…”

“…To zeroth order, we can approximate the 02(a) production as [02(a)] . k exc [e-][02]x , (2)(3)(4)(5)(6)(7)(8)(9) where t denotes the gas residence time in the discharge. The 02(a) yield is then simply ~kexc[e" ]T, and is thus highly dependent on the electron energy distribution via E/N and O2 fraction.…”

“…indicate a complex quenching effect which calls into question the equilibrium description of excitation given by (2)(3)(4)(5)(6) and (2)(3)(4)(5)(6)(7). Example traces of the scanning laser absorption/gain measurement are shown in Figure 2-47, for cases with and without the addition of h at 1.5 torr, 5% O2 in Ar, 70 W power, 350 K. Prior to the injection of I2, the 02(a) yield measured from the near-infrared emission was 0.25 ([02(a)] = 5.2 x 10 molecules/cm ), and the upper curve was observed, corresponding to zero gas-phase absorption.…”