Recent research on high-pressure hybrid radiofrequency/arc (RF/DC) generator of singlet oxygen for DOIL is presented.
A stable hybrid RF/DC discharge with a diffusive arc root near the anode side was demonstrated experimentally under
well defined conditions. A minimization of anode erosion and a non-equilibrium state of the arc plasma were achieved in
this way. The RF discharge is used for the ignition of the DC arc and its sustainment. The hybrid discharge can be
characterized as an RF sustained (i.e. non-self sustained in the pure DC mode) DC arc between a conventional glowing
tungsten cone cathode and a cooled aluminum cylindrical anode with a diffusive arc mode. The diffusive mode of the arc
is assisted by a plasma anode formed inside the aluminum anode channel due to the radiofrequency. The generation of
singlet oxygen was achieved by a laterally symmetric injection of neutral oxygen in a mixture of O<sub>2</sub>+He+NO into the
Ar+He plasma jet of the hybrid RF/DC plasmatron. An overview of basic characteristics and CFD modeling of some key
gas flow phenomena are presented. The research is directed to experimental investigation and theoretical modeling of the
hybrid plasma. In the case of its successful completion it will be used for pumping a discharge oxygen-iodine laser.
A scalable high pressure centrifugal spray generator of singlet oxygen for chemical oxygen-iodine laser (COIL) was
developed. This generator uses nitrogen as chlorine diluting gas. Different spray nozzles were tested which could be
assembled together and so enable a high chlorine flow rates for a high-power COIL. The designed generator can produce
singlet oxygen, O<sub>2</sub>(<sup>1</sup>Δg), with reasonable chlorine utilization and O<sub>2</sub>(<sup>1</sup>Δg) yield even at very high generator pressures,
which cannot be attained by other O<sub>2</sub>(<sup>1</sup>Δg) generators. This high-pressure operation is beneficial for a pressure recovery
system of the laser. Another advantage of this generator is a very high BHP utilization. The problem of heating of exit
gas was solved by introducing additional nitrogen between the separator rotor and stator.
The COIL operation using a new method of I<sub>2</sub> generation is demonstrated. The method is based on the gas-phase
chemical reaction between Cl<sub>2</sub> and HI in a separate reactor. This process is easily scalable and can simplify the COIL
operation by providing better control of I<sub>2</sub> flow rate. A yield of I<sub>2</sub> in the generation reaction up to 85% was achieved in a
reasonable volume of the reactor. A small-signal gain up to 0.75 %-cm<sup>-1</sup> at temperature of 150 K in the center of
supersonic cavity was measured. A comparison with the established evaporation way of I<sub>2</sub> delivery confirmed that the
chemical method has little or no impact on the COIL kinetics. The COIL output power measured with the chemical and
evaporation methods was nearly identical at comparable conditions.
Latest advances in development of a hybrid RF/DC plasma jet generator of O<sub>2</sub>(<sup>1</sup>Δ) for a discharge oxygen-iodine laser
are presented. This novel apparatus is based on a fast mixing of hybrid Ar+He plasma jet of DC electric arc sustained by
an RF discharge with an injected neutral O<sub>2</sub>+He+NO stream. Calculations of singlet oxygen yield have shown that only
non-equilibrium plasma with a high content of heated electrons (~3 eV) and a gas temperature of ~2500 K appears to be
promising for an achievable yield of singlet oxygen up to ~42 %. A stable high-pressure hybrid RF/DC plasmatron with
a diffusive arc mode near the anode side (assisted by a plasma anode) was demonstrated experimentally in the mixture
Ar:He = ~9.84:5 mmol/s at a power level of 610 W (RF power 490 W and DC arc power 120 W) and at a pressure of
165 Torr. The specific energy of the plasma jet was 41 J/mmol. A generation of singlet oxygen was performed by a
laterally symmetric injection of neutral mixture O<sub>2</sub>:He:NO = 1.5:2.44:0.22 mmol/s into the plasma jet of the hybrid
RF/DC plasmatron. The estimated yield of singlet oxygen O<sub>2</sub>(<sup>1</sup>Δ) was ~5 % at a pressure of 10.5 Torr.
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: CH<sub>3</sub>I, CF<sub>3</sub>I 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 CF<sub>3</sub>I, respectively. The atomic iodine number density in the supersonic flow attained 4.22 × 10<sup>14</sup> cm<sup>-3</sup>. The
dissociation efficiency was substantially better for HI than for studied organic iodides.
A chemical oxygen-iodine laser driven by the centrifugal spray generator of singlet oxygen was developed and
experimentally studied. Modeling and experimental studies showed that the designed generator can produce singlet
oxygen, O<sub>2</sub>(<sup>1</sup>Δg), with a high efficiency (chlorine utilization 0.68 - 0.87 and O<sub>2</sub>(<sup>1</sup>Δg) yield 0.35 - 0.7) even at very high
generator pressures (25 - 70 kPa), which cannot be attained by other O<sub>2</sub>(<sup>1</sup>Δg) generators. This high-pressure operation
should be beneficial for a pressure recovery system of the laser. Another specific feature of the generator is a very high
BHP utilization (0.24-0.6). The developed separator can effectively remove even small droplets (> 1 μm) from gas at the
generator exit. Preliminary experiments on the COIL driven the centrifugal spray generator provided the small signal
gain up to 0.5 % cm<sup>-1</sup>.
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 O<sub>2</sub>(<sup>1</sup>Δg). Low values of
small signal gain measured in the O<sub>2</sub>(<sup>1</sup>Δg) flow did not correspond to high efficiency of I generation. This was ascribed to
O<sub>2</sub>(<sup>1</sup>Δg) quenching by DO<sub>2</sub>· radical.
A new spray-type generator of singlet oxygen, O<sub>2</sub>(<sup>1</sup>Δ), 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.
A cw/pulsed radiofrequency discharge coupled by electrodes in coaxial arrangement was used to dissociate iodine atoms
from CH<sub>3</sub>I or CF<sub>3</sub>I 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 N<sub>2</sub> 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).
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 CH<sub>3</sub>I or CF<sub>3</sub>I. Some recent experimental results of this research are also
The alternative method of atomic iodine generation by chemical process from gaseous reactants for a chemical oxygen
iodine laser (COIL) was experimentally investigated. Research on efficiency of the atomic iodine generation, suitable
configuration of iodine atom injection into the laser cavity and small signal gain measurements was performed, and some
results were included in this contribution.
An advanced Chemical Oxygen-Iodine Laser (COIL) using the chemical generation of atomic iodine was studied. Atomic iodine is produced by the reaction of atomic chlorine with hydrogen iodide (HI) in two separated reactors tightly attached to the supersonic laser cavity. The iodine-contained mixture is injected to the flow of singlet oxygen by means of the supersonic orifices located 5 mm downstream the nozzle throat. The atomic iodine number density in the laser cavity up to 1.2 x 10<sup>15</sup> cm<sup>-3</sup> and a small-signal gain up to 0.35 %/cm were achieved. An rather high quenching of singlet oxygen by HI caused that the attained laser power was low. The results of small signal gain and the laser power are compared with the previous system including the mixing of reactants upstream the nozzle throat.
A spray type singlet oxygen generator (SOG) for chemical oxygen-iodine laser (COIL) was studied. Mathematical modeling has shown that a high O<sub>2</sub>(<sup>1</sup>&Dgr;) yield can be attained with BHP (basic hydrogen peroxide) spray in the Cl<sub>2</sub>-He atmosphere. It was found experimentally that O<sub>2</sub>(<sup>1</sup>&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 O<sub>2</sub>(<sup>1</sup>&Dgr;) flow.
An alternative method of atomic iodine production for a Chemical Oxygen-Iodine Laser (COIL) was studied. The proposed all-gas process include reaction of chlorine dioxide (C1O<sub>2</sub>) with nitrogen oxide (NO) followed by subsequent reaction of atomic chlorine with hydrogen iodide (HI). In difference to our previous experiments, atomic iodine was produced separately from the primary flow. The generated atomic iodine was injected through two rows of sonic orifices into the supersonic part of the converging-diverging nozzle, 2 mm downstream the nozzle throat. A penetration of atomic iodine to the primary flow was substantially improved by introducing additional nitrogen downstream the iodine injector. This led to an increasing I number density and static temperature. Inversed order of reactants injection (HI-NO instead of NO-HI) substantially increased the production efficiency. Some results were explained by 2-D modelling. Number density of atomic iodine up to 1.6 × 10<sup>15</sup> cm<sup>-3</sup> was attained in laser cavity with nearly 100% efficiency.
The chemical oxygen-iodine laser (COIL) with a chemical method of atomic iodine generation was studied. Two
methods of atomic iodine generation were proposed and developed. They are based on fast reactions of gaseous
hydrogen iodide with chemically produced chlorine or fluorine atoms. Atomic iodine formation via Cl atoms we studied
earlier by mixing of reaction gases directly in the primary O<sub>2</sub>(<sup>1</sup>Δg) flow in COIL. A revealed oxidation of HI by singlet
oxygen and the O<sub>2</sub>(<sup>1</sup>Δg) quenching by some reaction product, however, reduced the attainable laser gain. This problem
could be avoided by atomic iodine generation in separate reactors with following injection of atomic iodine into the
primary O<sub>2</sub>(<sup>1</sup>Δg) flow. Gain measurements using this arrangement are presented in this paper. New experimental results
on atomic iodine production via F atoms are also summarized. Using of reactive gases commercially available in
pressure cylinders is the main advantage of this method.
The generator of singlet oxygen (SOG) remains still a challenge for a chemical oxygen-iodine laser (COIL). Hitherto,
only chemical generators based on the gas-liquid reaction system (chlorine-basic hydrogen peroxide) can supply singlet
oxygen, O<sub>2</sub>(<sup>1</sup>Δ), in enough high yields and at pressures to maintain operation of the high power supersonic COIL
facilities. Employing conventional generators of jet-type or rotating disc-type makes often problems resulting mainly
from liquid droplets entrained by an O<sub>2</sub> (<sup>1</sup>Δ) stream into the laser cavity, and a limited scalability of these generators.
Advanced generator concepts investigated currently are based on two different approaches: (i)O<sub>2</sub>(<sup>1</sup>Δ) generation by the
electrical discharge in various configurations, eliminating thus a liquid chemistry, and (ii) O<sub>2</sub>(<sup>1</sup>Δ) generation by the
conventional chemistry in novel configurations offering the SOG efficiency increase and eliminating drawbacks of
existing devices. One of the advanced concepts of chemical generator - a spray SOG with centrifugal separation of gasliquid
phases - has been proposed and investigated in our laboratory. In this paper we present a description of the
generator principle, some essential results of theoretical estimations, and interim experimental results obtained with the
Recent experimental results on new all gas-phase chemical generation of atomic iodine via atomic fluorine for a Chemical Oxygen-Iodine Laser (COIL) are presented. Advantages of this method are emphasized in comparison with the conventional use of molecular iodine as a precursor of atomic iodine for lasing. Fluorine atoms are produced by fast reaction of molecular fluorine with nitrogen oxide and then react with hydrogen iodide to atomic iodine. Reaction conditions and the most convenient experimental arrangements were searched for their application in the supersonic COIL. An inevitable instrument used in this investigation was the optical Iodine Scan Diagnostics (ISD) of generated atomic iodine, based on the tunable diode probe laser. Concentration of atomic iodine was mapped by this method in the reactor at different experimental configurations, pressure and concentration of reactants. This research supported by mathematical modeling revealed that, the best arrangement would be generating atomic iodine in a separate reactor and injecting it into the singlet oxygen flow in the COIL.
New results of experimental investigation of the chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) are presented. Atomic fluorine was produced at first step by the reaction of molecular fluorine with nitrogen oxide. At second step atomic fluorine reacted with hydrogen iodide producing atomic iodine. It follows from obtained results that two experimental arrangements may be used in COIL. First, atomic F generated in a separate reactor may be injected into singlet oxygen stream with a subsequent HI injection. Second, atomic I may be produced in a separate reactor and then injected into a singlet oxygen stream. It was found that yield of the atomic iodine in the second arrangement may be higher, but a higher loss of I atoms at I atoms injection is anticipated due to wall recombination. The processes of I atoms and F atoms injection will be investigated in a near future.
Two alternative chemical methods of atomic iodine generation for a chemical oxygen-iodine laser (COIL) were studied. These methods are based on fast reactions of gaseous hydrogen iodide with chemically produced chlorine and fluorine atoms. Both processes were studied first in small-scale reactors. A yield of atomic iodine in the Cl system and nitrogen (non-reactive) atmosphere exceeded 80%, while in the F system it was only up to 27% related to F<sub>2</sub> or 50% related to HI. The process of atomic iodine generation via Cl atoms was employed in operation of the supersonic COIL. A laser power of 430 W at 40 mmol Cl<sub>2</sub>/s, and the small signal gain up to 0.4%/cm were attained. The proposed methods promise an increase in laser power, easier control of laser operation, and simpler iodine management in comparison with the conventional source of atomic iodine using I<sub>2</sub>. The experimental results obtained so far with this experimental arrangement did not proved yet increasing COIL chemical efficiency because some process quenching a part of singlet oxygen was indicated. Therefore a modified experimental set-up has been designed and prepared for further investigation.
Chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) was investigated experimentally. This all-gas process includes atomic fluorine as an intermediate species. In the two-step reaction mechanism, F atoms are produced in reaction of molecular fluorine with NO and react further with hydrogen iodide to iodine atoms. The efficiency of this process was studied in dependence on mixing conditions, flow rate of reacting gases and pressure in the reactor. The maximum concentration of atomic iodine was obtained at approximately equimolar ratio of reacting gases (F<sub>2</sub>, NO and HI), which agrees with the stoichiometry of the production reactions. A shortage of any of the reacting gases limits the rate of atomic iodine formation. A considerable excess of F<sub>2</sub> against NO at a simultaneous deficit of HI had a most detrimental effect on atomic iodine production. Sufficiently high concentrations of atomic iodine (5 to 8 x 10<sup>15</sup> cm<sup>-3</sup>) can be achieved by this method even at pressure 4 - 9 kPa that enable to inject the gas with iodine atoms into the singlet oxygen flow upstream the nozzle throat in the chemical oxygen-iodine laser.
Development of a Chemical Oxygen-Iodine Laser (COIL) with alternative ways of atomic iodine generation is aimed at power increase and simplified laser operation. Advantages of chemical generation of atomic iodine using gaseous reactants directly in the laser medium are confronted with disadvantages of using molecular iodine as a source of atomic iodine in conventional COIL devices. Some recent results on COIL operation with chemically generated atomic iodine supported with computational modeling are presented.
Results of experimental investigation of the chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) are presented. The work was focused on the reaction system with atomic fluorine as an intermediate species produced by the chemical way from gaseous reactants. At the first step, atomic fluorine is produced in reaction of molecular fluorine with nitrogen oxide. Then F atoms react with gaseous hydrogen iodide producing atomic iodine. The efficiency of this two-step process was studied thoroughly in dependence on mixing conditions, flow rate of reacting gases and pressure in the reactor. The results obtained on the small-scale device under experimental conditions simulating pressure and flow conditions in a COIL show that atomic iodine is generated by this alternative, advantageous method with rather high concentrations sufficient for operation of the supersonic COIL.
An alternative chemical way of atomic iodine generation for the chemical oxygen-iodine laser (COIL) was studied. This development was aimed at the laser power increase and simplification of the laser operation control. The method is based on the fast reaction of hydrogen iodide with chemically produced chlorine atoms. Kinetics of the process was studied in two types of the small-scale reactor and verified in the cavity of the supersonic COIL. The optimum yield of atomic iodine formation in the nitrogen atmosphere was very high (up to 100%) even in the COIL cavity and declined slightly with the distance from the supersonic nozzle throat. In the first experiments of atomic iodine generation in the flow of singlet oxygen in COIL, the gain of 0.18%.cm<sup>-1 </sup>was attained at rather low flow rate of atomic iodine (0.9 mmol.s<sup>-1</sup>). In earlier investigation of COIL in the conventional arrangement with molecular iodine, no gain was achieved at the corresponding I<sub>2</sub> flow rate (0.45 mmol.s<sup>-1</sup>). In the COIL with the new method of chemical generation of atomic iodine, a nearly constant gain along the flow axis was measured. It gives evidence that there is no strong quencher of excited atomic iodine in the reaction mixture. The published data represent the first results on gain measurement in the COIL with chemically generated atomic iodine. They promise an improvement of the COIL operation using the chemically generated atomic iodine.
Two-dimensional CFD model was applied for the study of mixing and reaction between gaseous chlorine dioxide and nitrogen monoxide diluted with nitrogen during atomic iodine generation. The influence of molecular diffusion on the production of atomic chlorine as a precursor of atomic iodine was predominantly studied. The results were compared with one-dimensional modeling of the system.
A study of recently proposed chemical method of atomic iodine production in the Chemical Oxygen-Iodine Laser (COIL) was performed. The process using gaseous reactants is based on the fast reaction of hydrogen iodide with chemically produced atomic chlorine. In the absence of singlet oxygen, the high yield of atomic iodine was attained (80 to 100 %). In the flow of singlet oxygen, the gain of 0.32 % cm-1 on 3-4 transition in iodine atom was achieved. It was found that both the rate of atomic iodine generation and gain depend substantially on mixing conditions of reacting gases. In laser experiments, effects of ratio of reactants, and their dilution by nitrogen on the laser output power were studied. The output power of 285 W was attained at chlorine flow rate of 27 mmol s<sup>-1</sup> corresponding to chemical efficiency of 11.7 %. It was the first time when gain and laser output power were achieved in the COIL with atomic iodine generated by the proposed method.
The results of theoretical and experimental investigation of gas phase chemical generation of atomic iodine, I(<SUP>2</SUP>P<SUB>3/2</SUB>), for stimulated emission in chemical oxygen-iodine laser (COIL) are presented. The method of I atoms generation employs a principal reaction X+HI implies I(<SUP>2</SUP>P<SUB>3/2</SUB>)+HX, where X equals F or Cl. A computational modeling was based on the 1D flow development exploring the chemical processes within the reaction systems, and was aimed at the theoretical understanding of the two complex reaction systems and finding out which is better applicable for conditions in COIL. The results of modeling were further used for a design of the device and conditions during the experimental investigation, and for an interpretation of the experimental results. The experimental work has been done, for the present, on the atomic iodine generation via Cl atoms. A high yield of atomic iodine of 70% to 100% (related to the initial HI flow rate) was attained in a flow of nitrogen. Gain was observed in preliminary experiments on the chemical generation of atomic iodine in a flow of singlet oxygen.
The mathematical modeling of reaction systems for chemical generation of atomic iodine is presented. This process can 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. The parametric study of the production of atomic fluorine and subsequently atomic iodine in dependence on the pressure and dilution with inert gas was made. The calculation of the interaction between produced atomic iodine and singlet oxygen was made with four different mixing/reacting schemes.
A method of the chemical production of atomic iodine aimed for application in COIL was studied experimentally. The method is based on chemical generation of chlorine atoms and their subsequent reaction with hydrogen iodide. Effects of initial ratio of reactants and the way of their mixing were investigated and interpreted by means of the developed model of the reaction system. In optimum conditions, the yield of iodine atoms, related to HI, attained 70 - 100 percent.
A chemical method of atomic iodine generation with a potential application in chemical oxygen-iodine laser (COIL) was investigated experimentally. The process consists in a fast reaction of gaseous hydrogen iodide with chlorine atoms produced in reaction of gaseous chlorine dioxide with nitrogen oxide. In conditions characteristic for a subsonic mixing region of COIL, atomic iodine was produced with a yield of 20-50 %. This is in a fair agreement with results ofmathematical modeling ofthis complex reaction system.