E. Bruins

Parametric study of small-signal gain in a slit nozzle, supersonic chemical oxygen-iodine laser operating without primary buffer gas

A detailed experimental study of the gain and temperature in the cavity of a supersonic chemical oxygen-iodine laser (COIL) is carried out to find optimal values of the flow parameters corresponding to the maximum gain. It is found that high gain (>0.7%/cm) can be obtained in a COIL operating without primary buffer gas and, hence, having a high gas temperature (>250 K) in the cavity. The measurements are performed for slit nozzles with different numbers and positions of iodine injection holes. Using a diode laser-based diagnostic, the gain is studied as a function of the molar flow rates of various reagents, with optical axis position along and across the flow, and Mach number in the cavity. Maximum gain of 0.73%/cm is obtained at chlorine and secondary nitrogen flow rates of 15 mmole/s and 7 mmole/s, respectively, for a slit nozzle with transonic injection of iodine. The gain is found to be strongly inhomogeneous across the flow. For a slit nozzle with iodine injection in the diverging part of the nozzle, the values of the maximum gain are smaller than for nozzles with transonic injection. Opening a leak downstream of the cavity in order to decrease the Mach number and increase the cavity pressure results in a decrease of the gain and dissociation fraction. The gain is a nonmonotonic function of the iodine flow rate, whereas the temperature increases with increasing iodine flow. An analytical model is developed for calculating in slit nozzles the iodine dissociation fraction F and the number N of O/sub 2/(/sup 1//spl Delta/) molecules lost in the region of iodine dissociation per I/sub 2/ molecule.

Spatial distribution of the gain and temperature across the flow in a slit-nozzle supersonic chemical oxygen-iodine laser with transonic and supersonic schemes of iodine injection

Spatial distributions of the gain and temperature across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit-nozzle supersonic chemical oxygen-iodine laser as a function of the iodine and secondary nitrogen flow rate, jet penetration parameter, and gas pumping rate. The mixing efficiency for supersonic injection of iodine (/spl sim/0.85) is much larger than for transonic injection (/spl sim/0.5), the maximum values of the gain being /spl sim/0.65%/cm for both injection schemes. Measurements of the gain distribution as a function of the iodine molar flow rate nI/sub 2/ were carried out. For transonic injection, the optimal value of nI/sub 2/ at the now centerline is smaller than that at off axis locations. The temperature is distributed homogeneously across the flow, increasing only in the narrow boundary layers near the walls. Opening a leak downstream of the cavity in order to decrease the Mach number results in a much larger mixing efficiency (/spl sim/0.8) than for a closed leak.

One-dimensional modeling of the gain and temperature in a supersonic chemical oxygen-iodine laser with transonic injection of iodine

A simple 1-D model is developed for the fluid dynamics and chemical kinetics in the chemical oxygen iodine laser (COIL). Two different I/sub 2/ dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two dissociation mechanisms chosen are the celebrated mechanism of Heidner (1983) and the newly suggested mechanism of Heaven (2001). The gain calculated using Heavens dissociation mechanism is much lower than the measured one. Employing Heidners mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of the flow parameters. Other predictions of the model (larger mixing efficiency and higher temperature with a leak opened downstream of the resonator and gain decrease along the flow) are also in agreement with the experimental observations.

Gain and Temperature in a Slit Nozzle Supersonic Chemical Oxygen-Iodine Laser with Transonic and Supersonic Injection of Iodine

Spatial distributions of the gain and temperament across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser as a function of the iodine and secondary nitrogen flow rate, jet penetration parameter and gas pumping rate. The mixing efficiency for supersonic injection of iodine is found to be much larger than for transonic injection, the maximum values of the gain being approximately 0.65 percent/cm for both injection schemes. Measurements of the gain distribution as a function of the iodine molar flow rate nI2 were carried out. For transonic injection the optimal value of nI2 at the flow centerline is smaller than that at the off axis location. The temperature is distributed homogeneously across the flow, increasing only in the narrow boundary layers near the walls. Opening a leak downstream of the cavity in order to decease the Mach number results in a decrease of the gain and increase of the temperature. The mixing efficiency in this case is much larger than for closed leak.

Mechanisms of COIL operation: experiment and modeling

Spatial distributions of the gain, temperature and I2 across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser (COIL) as a function of the iodine and secondary nitrogen flow rate and jet penetration parameter. The mixing efficiency for supersonic injection of iodine (~ 0.85) is found to be much larger than for transonic injection (~ 0.5), the maximum values of the gain being ~ 0.65%/cm for both injection schemes. Spatial distributions of the gain corresponding to the maximum power are found. A simple one-dimensional model is developed for the fluid dynamics and chemical kinetics in the COIL. Two different I2 dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two mechanisms chosen are the celebrated mechanism of Heidner and the newly suggested mechanism of Heaven. The gain calculated using Heaven’s dissociation mechanism is much lower than the measured one. Employing Heidner’s mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of flow parameters.

Supersonic COIL with iodine injection in transonic and supersonic sections of the nozzle

We report on a detailed experimental study of the gain and temperature in the cavity of a supersonic chemical oxygen-iodine laser operating without primary buffer gas and on preliminary power measurements in this laser. In particular, a study is carried out to find optimal values of the flow parameters corresponding to the maximum gain. The measurements are performed for slit nozzles with different numbers and positions of iodine injection holes. Using a diode laser based diagnostic, the gain and temperature in the cavity are studied. Maximum gain of 0.73%/cm is obtained at chlorine and secondary nitrogen flow rates of 15 mmole/s and 7 mmole/s, respectively, for a slit nozzle with transonic injection of iodine. Preliminary power measurements are performed. For slit nozzle with iodine injection in the diverging part ofthe nozzle output power of 287 W with chemical efficiency of 21% was measured at 15.1 mmole/s of Cl2 with no primary buffer gas. This is the highest reported chemical efficiency of a supersonic COIL operating without primary buffer gas.

Small-signal gain and iodine dissociation in a supersonic chemical oxygen–iodine laser with transonic injection of iodine

Measurements of the gain and temperature in the resonator of a supersonic chemical oxygen–iodine laser (COIL) with transonic injection of I2, using diode laser-based diagnostics, are reported. For conditions corresponding to the maximum chemical efficiency of this type of COIL (11.7 mmole/s of chlorine, no primary buffer gas, and 1.36 mmole/s of the secondary N2), the gain is a nonmonotonous function of the iodine flow rate. Maximum gain of 0.34%/cm is achieved for an iodine flow rate of 0.27 mmole/s. An analytical method is developed which enables the use of these dependencies for calculation of the iodine dissociation fraction F and the number N of O2(1Δ) molecules lost in the region of iodine dissociation per I2 molecule. It is found that F is a nonmonotonous function of the iodine flow rate, its maximum value being small (0.55).

Gain diagnostic in a supersonic COIL with transonic injection of iodine

Measurements of the gain and temperature in the resonator of a supemonic chemical oxygen-iodine laser (COIL) with transonic injection of 12, using diode laser based diagnostics, are reported. The measurements were carried out for a grid nozzle and two slit nozzles with ditSrent number and diameters of injection holes. Maximum gain of 0.54o/dcm was o&a&d for a slit nozzle with the same total cross section of the injection holes as for the grid n&e (for the later the maximum gain was only 0.34Ydcm). The gain is found to be ncmmonotonous function of the iodine flow rate, whereas the temperature increases with increasing iodine flow. The gain also incnxws with increasing oz(‘A) yield The measured temperatures in the resonator corresponding to the maximum gain are rather high (> 300 K).

Modeling of the Gain, Temperature, and Iodine Dissociation Fraction in a Supersonic Chemical Oxygen-Iodine Laser

We report on a simple one-dimensional model developed for the fluid dynamics and chemical kinetics in the chemical oxygen iodine laser (COIL). Two different I2 dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two dissociation mechanisms chosen are the celebrated mechanism of Heidner and the newly suggested mechanism of Heaven. The gain calculated using Heavens dissociation mechanism is much lower than the measured one. Employing Heidners mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of the flow parameters. Other predictions of the model (larger mixing efficiency and higher temperature with a leak opened downstream of the resonator and gain decrease along the flow) are also in agreement with the experimental observations.

Iodine dissociation in supersonic COILs with different schemes of iodine mixing

An analytical model is developed for calculating the iodine dissociation fraction F and the number N of O2(1AE)molecules lost in the region of iodine dissociation per I2 molecule in slit nozzles. The model is applied to results obtained for different mixing schemes.