Miroslav Čenský

Chemical generation of atomic iodine for chemical oxygen–iodine laser. I. Modelling of reaction systems

Abstract The mathematical modelling of reaction systems for chemical generation of atomic iodine is presented. This process is aimed to be applied in the chemical oxygen–iodine laser (COIL), where it can save a substantial part of energy of singlet oxygen and so increase the laser output power. In the suggested method, gaseous reactants for I atoms generation are admixed into the COIL primary gas flow containing singlet oxygen. Two reaction systems were proposed, based on the reaction of hydrogen iodide with chemically generated atomic fluorine or chlorine. It was found that the reaction path via Cl atoms better matches the experimental conditions of COIL with a yield of atomic iodine of up to 67%. As a result of modelling, a suitable reaction system and design of experimental arrangement for the effective production of atomic iodine in laser conditions were found.

Production of iodine atoms by RF discharge decomposition of CF3I

Generation of atomic iodine by dissociation of CF3I in a RF discharge was studied experimentally in a configuration ready for direct use of the method in an oxygen?iodine laser. The discharge was ignited between coaxial electrodes with a radial distance of 3.5?mm in a flowing mixture of 0.1?0.9?mmol?s?1 of CF3I and 0.5?6?mmol?s?1 of buffer gas (Ar, He) at a pressure of 2?3?kPa. The discharge stability was improved by different approaches so that the discharge could be operated up to a RF source limit of 500?W without sparking. The gas leaving the discharge was injected into the subsonic or supersonic flow of N2 and the concentration of generated atomic iodine and gas temperature were measured downstream of the injection. An inhomogeneous distribution of the produced iodine atoms among the injector exit holes was observed, which was attributed to a different gas residence time corresponding to each hole. The dissociation fraction was better with pure argon as a diluting gas than in the mixture of Ar?He, although the variation in the Ar flow rate had no significant effect on CF3I dissociation. The dissociation fraction calculated from the atomic iodine concentration measured several centimetres downstream of the injection was in the range 7?30% when the absorbed electric energy ranged from 200 to 4000?J per 1?mmol of CF3I. The corresponding values of the fraction of power spent on the dissociation decreased from 8% to 2% and the energy cost for one iodine atom increased from 30 to 130?eV. Due to a possible high rate of the atomic iodine loss by recombination after leaving the discharge, these values were considered as lower limits of those achieved in the discharge.

Chemical generation of atomic iodine for the chemical oxygen-iodine laser. II. Experimental results

Abstract A new method for the chemical generation of atomic iodine intended for use in a chemical oxygen–iodine laser (COIL) was investigated experimentally. The method is based on the fast reaction of hydrogen iodide with chemically produced chlorine atoms. Effects of the initial ratio of reactants and their mixing in a flow of nitrogen were investigated experimentally and interpreted by means of a computational model for the reaction system. The yield of iodine atoms in the nitrogen flow reached 70–100% under optimum experimental conditions. Gain was observed in preliminary experiments on the chemical generation of atomic iodine in a flow of singlet oxygen.

RF discharge generation of I atoms in CH3I and CF3I for COIL/DOIL

A cw/pulsed radiofrequency discharge coupled by electrodes in coaxial arrangement was used to dissociate iodine atoms from CH3I or CF3I molecules diluted in a carrier gas (a mixture of Ar and He). The discharge chamber was arranged directly inside an iodine injector (made of aluminum) to minimize the recombination of generated atomic iodine and enabling an increased assistance of UV light for a photo-dissociation enhancement of I atoms production. The effluent of the discharge chamber/iodine injector was injected into the flow of N2 downstream the nozzle throat. Measurements of I atoms concentration distribution at different distances from the injection and in two directions across cavity were done by means of absorption measurements at the wavelength of 1315 nm. Dependences of atomic iodine concentration on main RF discharge parameters and flow mixing conditions were measured. This novel method could be an alternative to the chemical generation of atomic iodine and also an efficient alternative to other electric discharge methods of I atoms generation for chemical oxygen-iodine laser (COIL) and discharge oxygen-iodine laser (DOIL).

Advances in the RF atomic iodine generator for oxygen-iodine laser

Recent advances in the RF atomic iodine generator for oxygen-iodine lasers are presented. The generator is based on the RF discharge dissociation of a suitable iodine donor immediately before its injection to the flow of singlet oxygen. The discharge is ignited directly in the iodine injector, and the configuration is ready for the laser operation. The dissociation fraction was derived from the atomic iodine number density measured at a presupposed position of laser resonator. The dissociation fraction and the fraction of RF power spent on the dissociation (discharge dissociation efficiency) were measured for the following donors: CH3I, CF3I and HI. A significant improvement of the discharge stability was achieved by increasing the cross-sectional area of the exit injection holes and employing a tangential inlet of working gas into the discharge chamber. The flow rates 0.15 mmol/s and 0.19 mmol/s of produced atomic iodine were achieved using the HI and CF3I, respectively. The atomic iodine number density in the supersonic flow attained 4.22 × 1014 cm-3. The dissociation efficiency was substantially better for HI than for studied organic iodides.

Research on advanced chemical and discharge oxygen-iodine lasers

Generation of singlet oxygen and atomic iodine for operation of the chemical or discharge oxygen-iodine laser (COIL/DOIL) is described, employing novel methods and device configurations proposed in our laboratory. A centrifugal spray generator of singlet oxygen was developed, based on the conventional reaction between chlorine and basic hydrogen peroxide. Recent results of theoretical and experimental investigation of the generator parameters are presented. A new conception of the discharge generator of singlet oxygen was initiated, based on a combined DC arc jet and RF discharge techniques. Principle of the generator currently developed and constructed is described. A new device configuration was designed for the alternative method of atomic iodine generation using a radiofrequency discharge decomposition of iodine compounds like CH3I or CF3I. Some recent experimental results of this research are also presented.

Spray generator of singlet oxygen with a centrifugal separation of liquid

A new spray-type generator of singlet oxygen, O2(1Δ), with a following centrifugal separation of depleted liquid was studied. This generator was developed to fulfill following requirements suitable for an advanced Chemical Oxygen- Iodine Laser (COIL): (i) a high-pressure operation, (ii) a single pass of reaction liquid, (iii) an efficient disengagement of gas/liquid mixture, and (iv) a scalability for airborne and mobile application. The generator design takes advantage of very high g/l interfacial surface area of a fine spray produced by a two-phase nozzle and a very fast liquid separation by applying a high centrifugal force.

Study of COIL active medium with atomic iodine generated via fluorine atoms

A generation of atomic iodine via F atoms with their immediate injection to the supersonic COIL nozzle has been studied. Very high concentrations of I atoms were obtained in the laser cavity in the absence of O2(1Δg). Low values of small signal gain measured in the O2(1Δg) flow did not correspond to high efficiency of I generation. This was ascribed to O2(1Δg) quenching by DO2· radical.

Contribution to development of chemical and discharge oxygen-iodine lasers

A chemical centrifugal spray generator of singlet oxygen, chemical methods of atomic iodine generation, and discharge generation of atomic iodine for chemical and/or discharge oxygen iodine lasers (COIL and/or DOIL) are the topics investigated currently in the Institute of Physics AS in Prague. Some main results of this research are presented on a background of the general COIL technology.

Advanced spray generator of singlet oxygen

A spray type singlet oxygen generator (SOG) for chemical oxygen-iodine laser (COIL) was studied. Mathematical modeling has shown that a high O2(1&Dgr;) yield can be attained with BHP (basic hydrogen peroxide) spray in the Cl2-He atmosphere. It was found experimentally that O2(1&Dgr;) was produced with a ≥50% yield at a total pressure up to 50 kPa (375 Torr). A rotating separator was developed that can segregate even very small droplets (≥0.5 &mgr;m) from O2(1&Dgr;) flow.