E-beam Sustained Discharge Research Articles

Absorption Dynamics of Nitric Oxide in Gas Mixtures Excited by Pulsed Discharge

Vibrational relaxation of NO molecules excited by a pulsed e-beam sustained discharge (EBSD) with the use of CO laser probing was studied. We developed numerical model of vibrational kinetics in ensemble of NO molecules due to comparing the experimental and calculated data on absorption dynamics of vibrational excited NO molecules.

Influence of nitrogen oxides NO and NO2 on singlet delta oxygen production in pulsed discharge

The influence of nitrogen oxides NO and NO2 on the specific input energy (SIE) and the time behaviour of singlet delta oxygen (SDO) luminescence excited by a pulsed e-beam sustained discharge in oxygen were experimentally and theoretically studied. NO and NO2 addition into oxygen results in a small increase and decrease in the SIE, respectively, the latter being connected with a large energy of electron affinity to NO2. The addition of 0.1–0.3% nitrogen oxides was experimentally and theoretically demonstrated to result in a notable enhancement of the SDO lifetime, which is related to a decrease in the atomic oxygen concentration in afterglow. It was experimentally demonstrated that to get a high SDO concentration at the gas pressure 30–60 Torr for a time interval of less than ∼0.5 s one needs to add not less than 0.2% nitrogen oxides into oxygen. The temperature dependence of the relaxation constant for SDO quenching by unexcited oxygen was estimated by using experimental data on the time behaviour of SDO luminescence.

A pulsed overtone CO laser with efficiency of 16%

It is shown that the efficiency of a pulsed e-beam sustained discharge overtone CO laser in the multiline regime achieves 16% and in the single-line regime its efficiency is 0.75%. The theoretical and experimental data are in good agreement taking into account the local specific energy input.

Electric generators of singlet delta oxygen for an oxygen-iodine laser

Experimental and theoretical research into electric generators of singlet delta oxygen (SDO) for an oxygen-iodine laser made at the Lebedev Physics Institute and TRINITI is discussed. Breakdown and current-voltage characteristics of self-sustained electric discharge in SDO were studied both experimentally and theoretically, indicating that SDO and pure oxygen have quite different electric features. The electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures were experimentally studied. A comprehensive numerical model describing SDO kinetics in different kinds of discharge was developed. The pulsed EBSD in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amounts of carbon monoxide or hydrogen, the electric stability of the EBSD increases, the specific input energy (SIE) per molecular component being more than order of magnitude higher and coming to 6.5 kJ/(l atm(O2 + CO)) for the gas mixture O2: Ar: CO = 1: 1: 0.1. Theoretical calculations demonstrated that, for an SIE of 6.5 kJ/(l atm), the SDO yield may reach ∼20%, exceeding its threshold value needed for oxygen-iodine laser operation at room temperature. The calibration of the optical scheme for measuring the SDO absolute concentration and yield using the detection of luminescence of the SDO going from a chemical SDO generator was performed. The measurement of the SDO yield demonstrated that it was ∼10.5% for an SIE of ∼3.0 kJ/(l atm(O2 + CO)), which is about 1.5 times less than the results of theoretical calculations for such an SIE. SDO production in RF slab discharge ignited in oxygen gas mixtures was experimentally studied, experimental SDO yield being about 10%. The choice of electrode material was demonstrated to be very important.

Gain dynamics in the active medium of a pulsed e-beam sustained discharge CO laser: theory and experiment

The small-signal gain (SSG) dynamics is studied experimentally and theoretically in the active medium of a pulsed e-beam sustained discharge CO laser in a broad range of vibrational transitions, various compositions and densities of the active medium, as well as various positions of a small-aperture probe laser beam in the gas-discharge region. The results of measurements are compared with theoretical calculations based on a spatially homogeneous CO laser model taking into account the multiquantum VV exchange processes. The sensitivity of the SSG dynamics to variations in the active medium and pump parameters is studied. Good agreement is demonstrated between theoretical and experimental data on the SSG dynamics obtained by using corrected values of local energy input in the calculations.

Plasma parameter bi-stability in e-beam sustained discharge in Xe

The phenomenon of plasma parameter bi-stability in an e-beam sustained discharge in Xe has been theoretically studied using a numerical solution of an appropriate Boltzmann equation (BE) for the electron energy distribution function (EEDF) by taking into account electron–electron collisions. The EEDF and electron concentration are calculated self-consistently depending on the production rate of secondary electrons (q) and reduced electric field strength (E/N). Calculations show that ranges of q and E/N exist, where the BE has two different stable solutions. Relevant plasma parameters (effective electron temperature, electron drift velocity, electron current density) are also calculated under bi-stability conditions.

Chemical effects of 100 keV primary electrons in an e-beam sustained carbon dioxide laser discharge

The dissociation of carbon dioxide and the reaction of carbon monoxide with oxygen caused by a high-energy (approx. 100 keV) electron beam in a typical carbon dioxide laser gas mixture has been observed. The variation of reaction rates with electron energy and current, interelectrode spacing, and gas composition has been studied. The rates of both processes suggest that the reactions are caused by unthermalized secondary electrons. The conditions were investigated under which the carbon monoxide oxidation reaction could be used to offset dissociation in a laser and thus prolong its sealed life. For a secondary to primary current ratio of one hundred this condition should be satisfied for any practical device. A sealed run was carried out which demonstrated that dissociation by secondary electrons could be offset by the oxidation of carbon monoxide by the primary electrons.

Efficient near-infrared electro-ionization lasers

High power near-infrared radiation (1–3 μm) can be generated with electro-ionization lasers using rare gases at multi-atmosphere pressure. The best performance is obtained in a so-called e-beam sustained discharge where the e-beam is used to ionize the medium and to maintain the stability of the discharge. An intrinsic efficiency of 8% is feasible. The output power saturates with current due to electron collision mixing. A maximum of 8 kW cm 3 has been observed.

Effects of helium addition to Ar-Xe mixtures in high-pressure atomic-transition xenon lasers

The output energy and spectral distribution of the atomic-transition xenon laser have been investigated with ternary mixtures based on Ar-Xe to explore kinetic issues and to enhance particular lines of the xenon laser pumped by an e-beam and e-beam sustained discharge. Addition of helium into the Ar-Xe mixtures increased the 2.03 mu m line energy by a factor of 3-5 while suppressing the 1.73- mu m line even during single-line oscillation. The maximum output energy obtained at 2.03 mu m was 1.2 J/L and the intrinsic efficiency was approximately 1%. Effects of neon or krypton addition have also been studied with e-beam sustained discharge pumping.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discharge instabilities initiated by nonuniform laser extraction in electron-beam sustained discharge KrF lasers

The photon energy of KrF lasers (λ=248 nm) is sufficiently large to photodetach electrons from the halogen negative ion (F−) and to photoionize excited states of krypton. In electron-beam (e-beam) sustained discharge KrF lasers, the contribution of photogenerated electrons to the total rate of ionization can be large enough to significantly perturb the conductivity of the plasma. If laser oscillation is spatially nonuniform, the photoelectron contribution to the conductivity deforms the local electric field. This condition can ultimately lead to a local discharge ionization instability and an arclike termination of the discharge. In this paper, the effect of nonuniform optical extraction on the discharge stability of an e-beam sustained discharge KrF laser will be studied with results from a two-dimensional time-dependent discharge kinetics and laser extraction model. Examples of stable and unstable configurations will be presented. The time at which the arclike ionization instability terminates the discharge correlates with the time that multistep ionization becomes an appreciable fraction of the total rate of ionization . A criterion for discharge stability is proposed; gradients in conductivity caused by photogenerated electrons must be either perpendicular or parallel to the bulk electric field.

Future Developments and Applications of KrF Laser-Fusion Systems

Two different types of KrF lasers currently being analyzed as potential laser-fusion drivers: large electron-beam (e-beam)- pumped amplifiers using pure optical multiplexing for pulse compression and small e-beam sustained discharge lasers using a hybrid pulse compression technique. Both types of KrF lasers appear able to satisfy all of the requirements for commercial-applications ICF drivers, including cost, efficiency, pulse shaping, energy scaling, repetition rate, reliability, and target coupling. The KrF driver can effectively operate at efficiencies > 10% and can contribute < 10 mill/kWh to the cost of electric power production, with the total estimated cost of electricity from either KrF laser system being comparable (25 to 50 mill/kWh, 1985 dollars) with the cost from other methods of electric power production. The Aurora facility is described.

Conceptual Design of a Large E-Beam-Pumped KrF Laser for ICF Commercial Applications

Two types of KrF lasers appear attractive as a driver for an ICF electric power plant. The original concept uses large electron-beam-pumped amplifiers and pure angular multiplexing to deliver short, shaped pulses to the target. A recently conceived alternate concept uses many small, long-pulse e-beam sustained discharge lasers which transfer their energy through the forward Raman process to a multiplexed set of beams to deliver the energy to target. Preliminary comparisons of the two systems indicate that the original concept has both a lower cost and a lower system efficiency, and both concepts appear to be nearly equally attractive as an ICF driver for an electric power plant. This paper examines a 4.8 MJ, 5 Hz KrF laser system designed using the original concept. The laser uses 24 main amplifiers arranged in eight sets of three amplifiers each. This layout optimizes both the optical system and the gas flow system, and uses a simple target illumination scheme that provides neutron shielding to allow hands-on maintenance in the laser hall.

Electron-beam sustained discharge XeCl laser

In this work the construction characteristics and performances of a laser system operating with an e-beam sustained discharge are described. Operating with XeCl, the laser pulse energy is over 4 J. Details of the measurements on the system are also reported.

Performance Predictions for Electron-Beam Controlled On/Off Switches

An electron beam (e-beam) controlled switch makes use of the low-energy secondary electrons in a diffuse e-beam sustained discharge as the conducting medium which carries the switched current. The conductivity of the gas in the switch is negligible before the e-beam is turned on because the circuit parameters are chosen so that the open circuit voltage which appears across the switch electrodes is well below the static breakdown voltage of the gas in the switch gap. The e-beam switch can interrupt direct current because the density of the electrons in the switch decays by recombination and attachment when the e-beam is turned off and the switch conductivity decreases. In typical circuits, this decay in conductivity causes the switch voltage to rise and the switch current to fall, i.e., the switch turns off. This paper presents the results of a series of theoretical calculations which were performed in order to: 1) identify the electron transport and other gas properties which optimize the performance of e-beam switches, 2) evaluate the performance of several real gases for use in e-beam switches, and 3) determine the laws which predict the scaling properties of e-beam switches. Results are presented for N2, Ar, a N2:Ar = 1:9 mixture, and CH4. These results show that CH4 provides the best e-beam switch performance. Comparison of experimental results and theoretical predictions for CH4 supports both the theory and the predicted good e-beam switch performance for CH4.

Acoustic Suppression in a Pulsed Laser System

The paper describes experimental and theoretical studies aimed at achieving acoustic suppression in a high- energy pulsed electric discharge laser system. Small-scale experiments were conducted for an open-cycle system having a sonic orifice plate upstream of the cavity and an acoustic horn and sidewall muffler downstream. The theoretical studies address the performance of the attenuators used for the experiments in both the linear and nonlinear acoustic response regimes. The linear regime is investigated by developing analytical solutions; whereas for the nonlinear regime, a ''floating shock-fitting technique is applied. Comparisons of the theoretical predictions with the experimental results are presented. LOWING gas laser systems were a necessary step toward generating high average output power from a single cavity with good beam quality. In this paper we will be discussing a pulsed CO2 gas laser configuration in which laser initiation energy is added in a short duration e-beam sustained electric discharge. In practice, there could be a large number of pulses spaced a fraction of a second apart in a pulse train. During the intrapulse time, waste-heated gas must be removed from the cavity and acoustic disturbances, caused by waste-heat deposition during the initiation process, must be damped to a low level in order to assure the medium will produce a high quality output beam at the succeeding pulse. For a CO2 laser system operating at room conditions and with a 1 m path length between mirrors, a typical density homogeneity requirement is (<Wp) rms < 1 x 10 ~ 3. This paper summarizes an experimental and theoretical study of an attenuator configuration meant to achieve the desired performance. There are two basic categories of pulsed laser systems, depending on the system optimization criterion. Maximizing the average output power per unit mass in a pulse train is appropriate for open-cycle or blowdown facilities in which lasing mixture is stored at high pressure in tanks and one wants to get as much power from that fixed gas supply as possible. It typically involves low base flow Mach numbers (e.g., M, —0.1). More recently, interest has focused on closed- cycle systems in which maximizing average output power in a pulse train is the appropriate goal. This paper is concerned only with open-cycle systems. The generic elements in an open-cycle configuration are shown in Fig. 1. Taking advantage of the high pressure at which the gas will typically be stored, a sonic orifice plate with highly underexpanded jets is used to define the upstream boundary of the flow channel. The mass flow through the channel is controlled by fixing the plenum pressure and temperature just upstream of the orifice plate. The pressure drop across the orifice plate is chosen to insure that no ob- jectionable acoustic disturbances are transmitted into the plenum. Downstream of the laser cavity, there will be an

Laser transition with predissociation lower state in the no molecule

Vibrational relaxation of NO molecules excited by a pulsed e-beam sustained discharge (EBSD) with the use of CO laser probing was studied. We developed numerical model of vibrational kinetics in ensemble of NO molecules due to comparing the experimental and calculated data on absorption dynamics of vibrational excited NO molecules.