COIL activities in Japan: industrial COIL development

We have constructed a laser welding system, which enabled high-power laser welding by combining three laser beams of 1 mm wavelength. Its wavelength enables optical silica fibers transmission and the flexible system. The heart of this system consists of a 4 kW and a 6 kW Nd:YAG lasers and a 10 kW Chemical Oxygen-Iodine Laser (COIL). The average power of the combined beam is up to over 20 kW. The effects of various welding parameters were investigated, such as the laser power, pulse modulation, and so on. The 10 kW COIL has a very good beam quality which is 64 mm.mrad. The beam spot diameter is 0.48 mm at the focal point. On the contrary the beam quality of Nd:YAG laser is worse, but it has the function of pulse modulation which the COIL dose not have. As a result of the welding test with the 6 kW Nd:YAG laser, it was clarified that the pulse wave (PW) has good efficiency of deeper penetration at low welding speed. When the combined beam with CW COIL and PW Nd:YAG laser was used, 20 mm penetration on the stainless steel could be achieved at a welding speed of 1 m/min.

Simulation of chemical lasers such as the chemical oxygen-iodine laser (COIL) is of timely interest due to the recent acceleration of the airborne laser military development program and ongoing commercial development programs. As a contribution to these efforts, a 3-D COIL simulation model was developed based on the Computational Fluid Dynamics (CFD) code GASP which solves the conservative, finite-volume formulation of the full Navier-Stokes equations coupled to a new finite-rate, non-equilibrium chemistry model and a conservative, multicomponent molecular diffusion model. A 3-D simulation of the COIL flowfield was performed and compared to detailed species distributions measurements from experiment for the purpose of validation using a unique averaging technique developed to mimic the actual physics of the experimental gain measurement. These detailed comparisons demonstrate that the simulation model accurately predicts the experimentally measured distributions, a significant result in 3-D simulation of reacting flows. Additional results from the validated simulation include: development of new finite-rate COIL chemistry mechanism, evidence indicating the presence of H2O condensation in the COIL mixing nozzle, and evidence suggesting that the physical processes in the flow from the O2('A) generator are not completely understood.

Great success has been obtained in the R&D of a chemical oxygen-iodine laser (COIL) operating on the electronic transition of the iodine atom, which gets an excitation from the energy donor -singlet delta oxygen (SDO). The latter is normally produced in a chemical SDO generator using very toxic and dangerous chemicals, which puts a limit for civilian applications of COIL that is still a very unique apparatus. Totally new non-chemical SDO generator is needed to allow oxygen-iodine laser to achieve its full potential as a non-hazardous efficient source of high-power laser radiation. There was interest in producing SDO in electric discharge plasma since the 50's long before COIL appearing. The idea of using SDO as a donor for iodine laser was formulated in the 70's. However, the injection of iodine molecules into a low- pressure self-sustained discharge did not result in iodine lasing. One of the main factors that could prevent from lasing in many experiments is a rather high threshold yield approximately 15 percent at 300K, which is needed for obtaining an inversion population. An analysis of different attempts of producing SDO in different kinds of electric discharge plasma has been done which demonstrates that high yield at gas pressure of practical interest for modern COIL technology can be obtained only in non-self sustained electric discharge plasma. The reason is that the value of relatively low reduced electrical field strength E/N approximately 1E-16 V.cm 2 , which is an order of magnitude less than that for the self-sustained discharge, is extremely important for the efficient SDO production. Although different kinds of non-self sustained discharges can be used for SDO production, we got started experiments with e-beam sustained discharge in gas mixtures containing oxygen. High specific input energy up to approximately 3 - 5 kJ/ has been experimentally obtained. Theoretical calculations have been done for different experimental conditions indicating a feasibility of reasonable SDO yield. Experimental and theoretical research of self-sustained electric discharge in SDO produced in a chemical generator, which is very important for getting plasma-chemical kinetic data needed for an estimation of SDO yield, is also discussed.

Chemical oxygen-iodine laser (COIL) has a great potential for applications such as decommissioning and dismantlement (D&D) of nuclear reactor, rock destruction and removal and extraction of a natural resource (Methane hydrate) because of the unique characteristics such as power scalability, high optical beam quality and optical fiber beam. Five-kilowatt Chemical oxygen-iodine laser (COIL) test facility has been developed. The chemical efficiency of 27% has been demonstrated with a moderate beam quality for optical fiber coupling. Our research program contains conventional/ejector-COIL scheme, Jet-SOG/Mist-SOG optimization, fiber delivery and long-term operation.

A heuristic methodology is described that was developed to evaluate the chemical efficiency of high-power chemical oxygen iodine laser (COIL) devices and its application to the specific evaluation of the U.S. Air Force Phillips Laboratory's RotoCOIL laser. A heuristic equation that forms the basis of this methodology and describes the COIL energy flow, energy losses, and power extraction using measured data, code results, and empirical relations is presented. Using this equation and bounding values for some of its terms, it is shown that for the RotoCOIL performance data the experimentally measured average O 2 ( 1 Δ) yield of 0.40 is nearly 38% below that which would be consistent with the measured extraction power. By relating terms of the heuristic equation to performance of individual components of the COIL system, it is concluded that nearly 50% of the efficiency loss for the RotoCOIL laser derives from oxygen generator and delivery losses, whereas 15% is from nozzle inefficiencies and 11% from resonator losses.

Laser-based methods are known to be more efficient than traditional approaches for a range of tasks that include dismantling obsolete nuclear reactors, maintaining railroad tracks in good working condition, stimulating chemical reactions, and separating isotopes. Among the attractions of lasers are fewer byproducts, increased reactor cutting speed, enhanced lifetime and capacity of the railway, and the ability to deal with toxic agents without igniting them. Moreover, laser techniques are more effective than other methods in processing radioactive waste. Realizing these capabilities takes a high-power laser with superior optical quality. Acceptable cost and efficiency are additional requirements. High-power CO2 lasers are commercially available; however, they are expensive and inefficient, and suffer from deteriorating optical quality as power increases. Alternatives include so-called chemical oxygen-iodine lasers (COILs) and CO lasers. But the COIL, too, is expensive, and there is as yet no industrial prototype. And although NUPEC Corporation, in Tokyo, Japan, has impressively demonstrated a 20kW CO laser for cutting large arrays of steel pipes and plates,1 the system lacks an optical cable of transferring CO radiation. Furthermore, the laser requires cryogenic components, which adds to its cost. We propose a CO laser2 that dispenses with the need for an optical cable by installing the laser head on the manipulator. Our concept is based on the discharge of stable homogeneous radio frequency (RF) in a supersonic stream and the demonstration of laser generation in a small-scale experimental installation.3 We also devised a computational model for scaling the CO laser with RF discharge. Supersonic expansion makes it possible to obtain the required cryogenic temperatures, and the RF discharge enables us to get optimal parameters for vibrational excitation of CO molecules without an electronic gun. The reduced ratio of the electric field to gas density (E/N) in a column of gas is stated in the literature.4, 5 With our model, we can calculate the power parameters of the CO laser and optimize them to obtain high values of output power and efficiency. The cost of the laser is kept low through use of standard elements, for example, compressor, RF generator, and power station. Owing to the high density of the gas in front of the supersonic nozzle of the laser head and behind the supersonic diffuser, the closed contour serves as a pipeline that enables flexible positioning of the laser head, for example, on the manipulator. Consequently, no optical cable is needed to transfer laser radiation. A standard compressor can be used because values such as pressure and Mach number can be maintained in a stream that makes it possible to restore pressure upon an input in the compressor up to 1atm. Themodel consists of calculations of RF discharge parameters, vibrational kinetic equations, and dynamic gas equations that describe a supersonic stream in the RF discharge zone. We have considered low-current RF discharge with electron photoemission from the electrode surface and injection of electrons from electrode sheaths in a positive column. A low-current RF discharge is realized when the ratio of the time required for the ions to drift through the sheath and reach the electrode to the period of the RF field is much larger than unity.6, 7 Thus, the electrode sheaths have no time to break up and exist simultaneously at both electrodes. Plausible applications for the CO laser include dismantling obsolete nuclear reactors and hardening of the surfaces of railway rails. Our next step will be to test the laser in applications involving toxic agents, in processing radioactive waste by extracting ruthenium, and separating isotopes of heavy hydrogen and uranium. These applications can be extended substantially only once the laser is commercially available.

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.

The spectroscopically measured lineshape of an atomic transition provides a wealth of useful information relative to diagnosing the state of a gas. The center of the lineshape is specific to a particular transition of a specific atom. The width of the lineshape indicates the amount of broadening of the transition, due to the effects of both collisions with other particles in the gas and Doppler shift due to the movement of the atom. Since the Doppler shift is proportional to velocity, the width of the transition can be used to estimate the degree of random molecular motion in the gas, expressed macroscopically as temperature. A Doppler shift to the frequencies in the transition can also occur through the bulk motion of the gas, and this can be used to examine the velocity field of the gas. The astronomy community was the first to recognize the utility of these concepts in practical applications, stemming to the early 1930s.1,2 In 1934 Stuve and Elvey3 showed that by including a bulk gas velocity Doppler broadening term in the Voigt equation for the transition lineshape in addition to the random thermal motion term, it was possible to estimate whether a stellar atmosphere was ‘turbulent’ or not based upon the fit of the Voigt equation to the measured transition lineshapes for that atmosphere. Taking the theory a step further, using estimated optical paths or length scales for the stellar atmospheres that they were measuring, they were able to estimate median gas velocities and correlate increasing velocity magnitude with increasing temperature of the stellar atmosphere. More recently, continuously tunable diode lasers have been applied to lineshape measurement of transitions within species in the chemical oxygen-iodine laser (COIL) flowfield as a means to determine number density and laser gain on the I 2P1/2→2P3/2 transition. Davis and Allen et al4,5,6,7 applied lineshape measurement and Voigt fitting methods to various COIL species as a mechanism to determine concentration and translational temperature in the COIL flowfield as an experiment diagnostic. While the effect of the bulk gas velocity was not taken into account in these investigations, the diagnostics developed by these investigations provided the means to do so. Nikolaev et al,8 applied the same type of continuously tunable diode laser to the I 2P1/2→2P3/2 transition to investigate the influence of mean gas velocity through a COIL device upon the laser gain. They showed that by varying the angle at which the diode laser beam passes through the COIL flowfield, the line center gain can be varied through bulk velocity induced Doppler broadening. Using this mechanism, they were able to determine the mean flow velocity for the COIL and convert the laser gain

This paper describes results of the first phase of a Gas Research Institute (GRI) funded research program. The overall purpose of this research is to advance a fundamental change in the method currently used to drill and complete natural gas wells applying the U.S. Defense Department's StarWars laser technology. Results of tests conducted at the U.S. Air Force and the U.S. Army's high power laser research facilities are presented. Initial testing on reservoir rocks conducted with the Mid Infrared Advanced Chemical Laser (MIRACL) at the U.S. Army's High Energy Laser Systems Test Facility at White Sands, New Mexico, showed the potential for laser drilling. The laser beam drilled at a speed that indicates penetration could be increased by more than 100 times current rates. Planned testing for the next phase of this research is to use the Chemical Oxygen-Iodine Laser (COIL) high powered laser invented in 1977 by the U.S. Air Force Research Laboratory in Albuquerque, New Mexico, for air-to-air defense. COIL has gained notoriety as an airborne laser tactical weapon capable of tracking and destroying missiles. An annotated bibliography was developed for the GRI that comprehensively reviews published laser-rock interaction, current drilling research, and technical data related to laser applications in non-reservoir rocks.1 Developing commercial applications of StarWars laser technologies has commenced not only in the U.S., but also in Russia and the former Soviet Union.

Three dimensional transient analysis of bubble dynamics in centrifugal bubble singlet oxygen generator for scalable COIL

The recent demonstration of gain and continuous wave power extraction on the electronic P1/2 to P3/2 transition of the I atom using NCl(a1∆) as the pumping species proving the viability of the all gas-phase iodine laser (AGIL), has brought with it the need for an increased theoretical understanding of this complex system. Multiple gas phase chemical processes occur in this system: the generation of Cl atoms with F atoms, the generation of I atoms with Cl atoms, the production of NCl(a1∆) with Cl atoms and HN3, and the pumping of I to the I(P1/2) state with NCl(a1∆). Each of these processes may be composed of multiple individual chemical reactions describing production and loss processes. And finally, this set of processes occurs within a flowing gas, with the exoand endothermicity of the reactions complicating the coupling of the chemical reactions to the fluid dynamics and vice-versa. The goal of this paper is to provide an overview of the current theoretical understanding of this complex system with respect to the numerous measured finite-rate chemical processes and the coupled fluid dynamic-diffusional mixing processes. 1-D explorations of the AGIL finite-rate chemistry mechanism including sensitivity studies are shown. 3-D NavierStokes simulation studies of reactant mixing are examined, and predictions made for conditions to improve mixing and reaction in AGIL device hardware. Confirmation of these predictions in results from recent AGIL power extraction experiments is shown. * Member AIAA. Introduction The development of chemical lasers begins with the demonstration of the first iodine laser by Casper and Pimentel who in 1964 demonstrated lasing on the electronic P1/2 to P3/2 transition of atomic iodine at 1.315μm by photodissociating alkyl iodide compounds. The high energy and high atmospheric transmission of this wavelength developed considerable interest in the chemical generation of the I(P1/2) state. With no known chemical reactions directly producing high concentrations of I(P1/2), interest shifted to the use of energy transfer reactions to generate this state. Derwent, Kearns, and Thrush postulated the use of the first electronic excited state of oxygen, O2(a 1∆), as the transfer agent. O2(a∆) being both metastable and near-resonant with I(P1/2) would provide a logical energy transfer species. McDermott et al provided proof of concept for this hypothesis, demonstrating a laser based on the O2(a 1∆) to I(P3/2) energy transfer and producing the first chemical oxygen-iodine laser (COIL). With the advent of COIL also came the realization of one of its’ primary drawbacks, namely the 2 phase chemistry required to produce O2(a 1∆). The basic hydrogen peroxide solution used during O2(a 1∆) generation constitutes a large fraction of the overall weight of the system and adds water vapor, a relatively strong deactivator of I(P1/2). In order to circumvent the deleterious effects of the 2 phase COIL chemistry, energy donors for I were sought that could be generated in the gas phase at high number densities. The nitrene metastables were recognized as possible replacements for O2(a 1∆) as energy donors, primarily due to their visibility from investigations into their use as agents for generating short wavelength chemical lasers. The isovalent electronic structures of NCl(a1∆) and NF(a1∆) with respect to O2(a 1∆), long lifetimes, and the ability to generate large number densities in the gas phase made NCl(a1∆) and NF(a1∆) likely candidates for iodine energy donors. Yang et al were the first to investigate NCl(a1∆) as an iodine energy donor, measuring the transfer rate and key deactivation rates subsequently followed by a measurement of gain on the I(P1/2) to I( P3/2) transition. Similarly, Ray and Coombe measured the transfer rate followed by a pulsed laser demonstration via pulsed photolysis of ClN3 and CH2I2. With the early work of Yang et al, and Ray and Coombe establishing the viability of an NCl(a1∆) based transfer laser, significant effort was spent on measurement of the key rates constituting the complex chemistry of supporting these experiments. Henshaw measured the temperature dependence of NCl(a1∆) quenching by I(P3/2), as well as rates for chemical generation of NCl(a1∆).20 Setser with co-workers 34th AIAA Plasmadynamics and Lasers Conference 23-26 June 2003, Orlando, Florida AIAA 2003-4310 This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

The design of an optimized resonator for a supersonic chemical oxygen iodine laser (COIL) requires detailed information of the saturated gain distribution. By using diaphragms with slit apertures of various sizes at different positions in a stable resonator configuration it was possible to work out detailed information on the coupling characteristics and the influence of iodine repumping and deactivation processes. The measurements were performed at the DLR Lampoldshausen 10 kW supersonic COIL. A high Fresnel number stable resonator is coupled to the active medium and extends about 40 mm downstream from the exit plane of the expansion nozzle array. Apertures with slit widths ranging from 14% to 100% of the full resonator width were introduced into the cavity directly in front of the outcoupling mirror at a fixed z-position of 17 mm downstream of the nozzle exit. The center of another aperture with a fixed slit width of 10 mm could be positioned in flow direction from near the nozzle exit plane to about 29 mm downstream. The optical alignment was controlled with respect to the laser beam size and power density distribution at the outcoupling mirror. As a function of slit aperture the laser output power saturates well before the aperture of the resonator is fully opened. The experimental results are compared with calculations based on the theoretical model of Hager et al. Measured pressure values along the flow direction from the nozzle exit plane to well beyond the laser cavity show a strong dependence on position and width of the diaphragm, resulting from deactivation of unexploited singlet delta oxygen. After taking these pressure effects into account good agreement is found between theory and experiment. The data highlight the significance of deactivation processes for the achievable output power.

The key results gathered in the COIL Laboratory of the Institute of Physics AS in the Czech Republic since 1985 to date on the experimental and theoretical investigation of Chemical Oxygen-Iodine Laser (COIL), and related problems are reviewed in a certain context of historical perspectives of the COIL research and development.

A simple one-dimensional (1D) computational fluid dynamics (CFD) model of the chemical oxygen iodine laser (COIL) with supersonic mixing is compared with three-dimensional (3D) CFD models and with experimental measurements of the COIL parameters. Dependence of the gain, iodine dissociation fraction and temperature at the resonator optical axis and of the output lasing power on the iodine flow rate predicted by the 1D model is in good agreement with that found using 3D models and experimental results. Hence the 1D model can be used instead of much more complicated 3D models for estimates of the working parameters of supersonic COILs.

The US Air Force Research Laboratory has actively pursued the development of the Chemical Oxygen-Iodine Laser (COIL) since its invention in 19771. The power scaling potential of the COIL was verified in the late 1980's on the RotoCOlL device, which was later decommissioned. A smaller COIL teststand (ReCOIL) was then upgraded with a rotating-disk oxygen generator and a variable-height slit nozzle to become the principal testbed for continued COIL development. The modified device was named the Research assessment evice Iodine chemical Laser (RADICL). RADICL has supported several major test campaigns during the past 9 years, many of which have been published. These include 2-D gain maps2, iodine dissociation studies3, magnetic gainswitching demonstrations4, mode-locking5, metal cutting/fiber delivery demonstrations, and more recently measurements of water concentration and oxygen yield . Areview of the major results of these test programs and previously unpublished data are presented.