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Influence of electron excited singlet delta oxygen (SDO) molecules produced in direct current (DC) glow discharged plasma on the induction length decrease in the H2-O2 mixture has been studied via ...

The kinetic processes occurring in an electric-discharge oxygen-iodine laser are analyzed with the help of a 2D (r, z) gasdynamic model taking into account transport of excited oxygen, singlet oxygen, and radicals from the electric discharge and their mixing with the iodine-containing gas. The main processes affecting the dynamics of the gas temperature and gain are revealed. The simulation results obtained using the 2D model agree well with the experimental data on the mixture gain. A subsonic oxygen-iodine laser in which singlet oxygen is generated by a 350 W transverse RF discharge excited in an oxygen flow at a pressure P = 10 Torr and the discharge tube wall is covered with mercury oxide is simulated. The simulated mixing system is optimized in terms of the flow rate and the degree of preliminary dissociation of the iodine flow. The optimal regime of continuous operation of a subsonic electric-discharge oxygen-iodine laser is found.

This work is devoted to the study of the possibility of obtaining the highest O2(a 1 � g) yield in ED SOG at the high absolute O2(a 1 � g) concentration needed for developing a powerful oxygen–iodine laser pumped by electric discharge. A singlet oxygen was produced in a transversal rf discharge in the pressure range 10–30 Torr of pure oxygen in the small-diameter (7 mm) quartz tube with HgO coating of the inner walls for removing atomic oxygen to eliminate fast O2(a 1 � g) quenching. It is shown that pd scaling (p—pressure, d—tube diameter) of the rf discharge actually allows an increase of the absolute O2(a 1 � g) density. The increase in the rf frequency from 13.56 to 81 MHz results in the essential increase of the O2(a 1 � g) yield (beyond 15% at such a high oxygen pressure as 15 Torr), but the subsequent transfer to the higher rf frequency of 160 MHz only slightly influences the maximally obtained O2(a 1 � g) yield. The effect of the NO admixture on the O2(a 1 � g) production has been also studied. The rate constant of O2(a 1 � g) quenching by NO k NO = (8.5 ± 1.5) × 10 −17 cm 3 s −1 was directly measured. The NO admixture (up to 20%) resulted in the noticeable increase in the O2(a 1 � g) yield mainly at low energy inputs. But this gain in the O2(a 1 � g) concentration drops with increasing energy input. Nevertheless it is shown that by combining the O2 + NO mixture with the HgO coating of the discharge tube walls one can provide the O2(a 1 � g) yield on the level of ∼21% at 10 Torr, ∼17% at 20 Torr and ∼13% at 30 Torr of O2 with the efficiency of ∼4–6%. The analysis of the NO admixture influence on the discharge structure and O2(a 1 � g) production has been carried out by using the 2D model. It was found that at the low energy input the NO admixture acts as an easily ionized species that enlarges the region occupied by plasma. Thus, in the O2 + NO discharge the normal current density is lower than in the pure oxygen discharge. As a result a higher energetic efficiency of O2(a 1 � g) production is also observed in the case of the O2 + NO mixture and the low energy input. In order to provide the optimal conditions for O2(a 1 � g) production (with regard to the yield and efficiency) in the continuous wave transversal VHF discharge at such high oxygen pressures as of 10–30 Torr it is necessary to find out the range of energy inputs where the VHF discharge operates in the regime of normal current density on the boundary with the abnormal regime and to remove atomic oxygen produced in the discharge by some volume or surface processes.

A 2D self-consistent simulation of an rf discharge in a gas flow in pure oxygen over a wide range of discharge parameters was carried out. The simulation was made at the experimental conditions of Part I of this paper for the discharge tube with an HgO coating where the most effective production of O2(a?1?g) was experimentally observed. The simulation goal is to study the features of transversal rf discharge self-organization at different rf frequencies, 13.56 and 81?MHz, to reveal the most optimal conditions for both the O2(a?1?g) yield and its energy efficiency. It was shown that the energy part absorbed by electrons increases with the frequency. The spatial discharge structure was studied at both frequencies. It was revealed that at the higher rf of 81?MHz the discharge operates in a mode of the normal current density even at high input powers. The kinetic processes which determined both O2(a?1?g) loss and production at experimental conditions were studied and discussed. The increase in rf frequency from 13.56 to 81?MHz reveals an increase in the SO yield and efficiency. It also connects with the decreasing of input energy losses in the sheaths.

The scaling on pressure for a discharge singlet oxygen generator based on the rf discharge excitation of O2 flow is studied in the context of the problem of oxygen?iodine laser pumping. With this aim, the evolution of O2(a?1??g) and molecules as well as O(3P) atoms in 13.56 and 81?MHz discharges at pressures up to 15?Torr has been investigated in detail. It is shown that fast quenching of O2(a1?g) by atomic oxygen with increasing pressure and energy input causes rapid saturation of the O2(a1?g) density in the discharge and limits the O2(a?1??g) yield on a rather low level of a few per cent. Covering of the discharge tube walls with mercury oxide for fast catalytic removal of oxygen atoms allows us to greatly increase the O2(a?1??g) yield as well as to avoid fast quenching of O2(a?1??g) in the early afterglow. It enables us to succeed in obtaining the rather high O2(a?1??g) yields at such high pressure as 10?15?Torr. So the singlet oxygen yield is ~10?12% at ~10?Torr. The transition to the higher frequency of 81?MHz even increases greatly the O2(a?1??g) yield up to ~16%.

The effect of the nonlocal nature of the electron distribution function on the dissociation rate of oxygen molecules in a dc glow discharge is studied. The concentration of oxygen atoms and the probability of their loss at the discharge tube wall are measured as functions of the discharge parameters by means of the timeresolved actinometric method involving argon atoms. An analysis of the measurement data in terms of both a discharge model in which the effect of the nonlocal nature of the electron energy spectrum is taken into account and a model in which this effect is ignored makes it possible to thoroughly investigate the balance of oxygen atoms in the discharge. The production rate of O(3 P) atoms and their concentration in the plasma are calculated with allowance for the nonlocal nature of the electron energy distribution function. The calculated values agree well with the experimental data and differ substantially from those obtained using a spatially homogeneous distribution function.

A self-consistent hybrid model of discharge in a plasma display cell is proposed, which provides an adequate description of a nonlocal electron distribution in nonstationary cases. A comparative analysis of the results of calculations based on the hybrid (nonlocal) and local models reveals considerable differences both in the discharge structure and in the emission dynamics.

This work is devoted to the experimental and theoretical study of rf frequency influence on the discharge structure and the O 2 (a 1 D g ) yield in a rf discharge in the tubes with HgO coating for removing atomic oxygen to avoid fast O 2 (a 1 D g ) quenching. Two series of experiments were carried in two discharge sets up: 1 - tube of large diameter of 14 mm, electrode length of 30 cm; 2 - tube of small diameter of 7 mm, electrode length of 10 cm. In the first series, the increase of rf frequency from 13.56 MHz to 81 MHz resulted in the singlet oxygen (SO) yield Y >15% at such high oxygen pressure as 10 Torr. 2D self-consistent model was developed to simulate the rf discharges in gas flow in a wide rage of discharge parameters both with and without HgO coating. Results of the simulation agreed very well with the experimental data. It is shown that at the high rf frequency the discharge operates in a mode of the normal current density so that the energy absorbed by electrons from the rf field increases with the frequency. In the second series we scaled up the rf discharge on the pd parameter ( p -pressure, d -tube diameter) to increase the oxygen pressure. The pd discharge scaling at the high rf frequency allowed to reach the O 2 (a 1 D g ) yield Y > 15% at oxygen pressure up to ~17 Torr. The effect of NO admixture on the O 2 (a 1 D g ) production has been studied in series 2 at rf frequency of 160 MHz. NO admixture (5÷20%) results in the noticeable increase in the O 2 (a 1 D g ) yield in comparison with the discharge tube without HgO coating. It is shown that combination of O 2 + NO mixture with HgO coating of the discharge tube walls provides the most optimal O 2 (a 1 D g ) production with the efficiency up to 7-10 % and allows to reach the threshold yield in 15 % at oxygen pressure even above ~20 Torr.

Quasi two-dimensional (r,z) model of large bore copper vapor laser (CVL) was developed. Full set of heat and species (charged and neutral) transfer equations, Maxwell equations and electron energy balance equation were solved for different pulse repetition rate in a temporally self- consistent manner, with the long term evolution of plasma kinetics followed over multiple excitation/afterglow cycles. Electron rate constants were for the first time taken from the realistic EEDF, which was the result of solving Boltzmann equation in two-term approximation with charged particle collisions taken into account. Laser radiation power was calculated together with external circuits (several magnetic switches are included) self-consistently. Our model includes the plasma-chemical and neutral kinetic processes in Cu/Ne/H 2 /HCl mixtures. Two-dimensional thermal radiation transfer was taken into account for the first time. The influence of skin-effect and H 2 /HCl additives on CVL characteristics was studied. Detailed hydrogen rotational and vibrational kinetics taken into account in a CVL model allows us to explain experimental results: radial redistribution of laser power, wall temperature increase, prepulse electron temperature and concentration decrease with hydrogen. The model was used for designing new laser system. After that this laser was constructed and gives first results lately. The laser shows good agreement with predictions, in already realized pure Cu mode (without any admixtures) it gives 105 W, whereas the prediction was 117 W.

A comparable analysis of continuous wave (CW) and pulse-periodic (PP) operation modes of an electro-discharge singlet oxygen generator (ED SOG) utilizing an 81?MHz discharge in the O2/NO mixture at elevated pressure (more than 10?Torr of O2) has been carried out. The discharge in both modes operates in the regime of the normal current density and therefore occupies only a part of the electrode's area depending on the inputted rf power. Due to the fact that the rf power in PP mode (during the pulse) is higher at the same energy input, the PP discharge can occupy a greater area compared with the CW discharge and is found closer to the boundary with the abnormal regime that is most effective for O2(a?1?g) production. Thereby it provides a higher O2(a?1?g) yield and efficiency with increasing pressure. The O2(a?1?g) yield of ~12% in PP mode of the O2/NO discharge has been realized with an efficiency of 12?18% against only ~9% and an efficiency of 8?12% in CW mode. This fact and the possibility to control additionally the duty cycle and pulsed rf power in PP discharge can be a prospective and useful means of optimizing the ED SOG in technological applications of an oxygen?iodine laser with electro-discharge pumping.