Showing papers on "Power density published in 1977"

Behavioral and thermal effects of microwave radiation at resonant and nonresonant wavelengths

Abstract: Behavioral and thermal effects of radiating an animal with differing wavelengths of microwave energy at the same power density were investigated in the first of two studies. Five Long-Evans rats were trained to perform a lever-pressing task and were rewarded with food on a variable interval schedule of reinforcement. Rats were individually exposed in random order to 400-, 500-, 600-, and 700-MHz CW radiation at a power density of 20 mW/cm2 with the long axis of the rat's body parallel to the vector of the electric field. Radiation at all wavelengths produced rises of body temperature and stoppage of lever pressing. The averaged rise in body temperature was greatest and work stoppage was most rapid during exposures at 600 MHz. In the second study, six rats were exposed in random order to 600-MHz CW radiation at power densities of 5, 7.5, 10, and 20 mW/cm2 while performing the same behavioral task. Exposures at 10 and 20 mW/cm2 resulted in work stoppage, while exposures at 5 and 7.5 mW/cm2 did not. In addition, three of the rats were subsequently exposed while responding to 600-MHz pulsed radiation (1000 pps, 3- or 30-μs pulse durations at a peak power density of 170 mW/cm2 (averaged 0.51 and 5.1 mWcm2). No work stoppage occurred to pulsed radiation. Taken in sum, the data show that the mature Long-Evans rat is resonant at a frequency near 600 MHz while work stoppage during short-term exposures to 600-MHz radiation occurs at a power density between 7.5 and 10 mW/cm2.

MHD power generation with fully ionized seed

Abstract: Recovery of power density in the regime of fully ionized seed has been demonstrated experimentally using an MHD disk generator with the effective Hall parameter up to 5.0 when the seed was fully ionized. The experiments were conducted with a shock-heated and potassium-seeded argon plasma under the following conditions: stagnation gas pressure = 0.92 atm, stagnation gas temperature = 2750 K, flow Mach number = 2.5, and seed fraction = 1.4x 10 ~ 5. Measurements of electron-numb er density and spectroscopic observations of both potassium and argon lines confirmed that the recovery of power output was due to the reduction of ionization instability. This fact indicates that the successful operation of a disk generator utilizing nonequlibrium ionization seems to be possible and that the suppression of ionization instability can also provide higher adiabatic efficiency. Furthermore, the lower seed fraction offers technological advantages related to seed problems.

CANDU Fuel-Power Ramp Performance Criteria

Abstract: Extensive fuel performance data obtained from Canadian Deuterium Uranium (CANDU) power reactors and experimental reactors are analyzed. Various modes of power ramping that cause fuel defects are identified, and fuel defect criteria are derived. The probability of a defect occurring in a power ramp is found to depend on the magnitude of the ramped power, the power increase, the fuel burnup, and the time fuel dwells at the ramped power. Physical interpretations are offered in terms of mechanisms believed to account for power ramp defects. The dominant mechanism is considered to be stress corrosion cracking of the Zircaloy clad, induced by the release of such fission products as iodine from the fuel.

Performance of a large, CW, preexcited CO supersonic laser

Abstract: The performance of a CO laser having electrical excitation by a continuously operating, self-sustained glow discharge in a high-pressure gas mixture followed by a supersonic expansion to the cavity region has been studied. A threshold for lasing was found which corresponded to 0.035 eV of input energy per CO molecule. Beyond this, nearly 15 percent of the additional energy was extracted by the resonator. The total power reached 940 W with a maximum electrooptical efficiency of 13.7 percent and a specific power of 17 kJ/lb. The vibrational population distribution of the CO in the cavity, with and without lasing, was determined from the overtone emission spectrum. The data indicated a significant loss of vibrational energy during expansion.

Threshold power density measurements for electron-beam sustained discharge excitation of XeF and KrF

Abstract: Threshold power densities for electron‐beam‐stabilized discharge excitation of XeF and KrF lasers are reported for Ar+Kr+F2 and Ar+Xe+NF3 gas mixtures at 1 atm. Stable discharges were obtained with these gas mixtures for times greater than 0.5 μsec with lasing pulse width as long as 0.5 μsec. An analysis of data for several different pump power densities is presented which indicates that the threshold pump power density varies inversely with the cavity buildup time.

Diode-pumped miniature solid-state laser: design considerations

Abstract: The LED-direct pumped laser was considered theoretically as a way to miniaturize solid state lasers. The pumping efficiency of the system was calculated numerically by 3-D ray tracing. For LiNdP4O12, an efficient Nd stoichiometric material, the threshold power density and the pump power density necessary to obtain a 5-mW output power under optimum output coupling conditions were calculated to be 20 W/cm2 and 60 W/cm2, respectively, assuming a crystal size of 50 μm × 50 μm × 5 mm.

Parametric conversion of infrared radiation in an AgGaS2 crystal

Abstract: A computer calculation is reported of the main characteristics of a parametric converter of middle-infrared radiation in a silver thiogallate crystal pumped with ruby laser radiation. A description is given of experimental conversion of CO2 laser radiation to the visible range in an AgGaS2 crystal, confirming the results of calculations. The conversion efficiency is found to be 10% for Q-switched pump-laser radiation of 2.2×105 W/cm2 power density in a crystal 3.3 mm long.

Discharge‐related limitations of CO2 optical gain in TE channel waveguides

Abstract: Investigation of TE discharges in a 1.6‐mm square channel has revealed reasons for the inefficient operation of such devices as CO2 oscillators. At high repetition rates the pulsed glow discharges are not wall confined above 100 Torr. Thus wall cooling and complete volumetric excitation are reduced. Energy deposited into the cathode fall region creates considerable problems. At low pressures this energy is a large fraction of the total discharge energy, whereas for higher pressures the power and power density deposited in this region is very high. The resultant localized gas heating dissociates molecules, creates turbulence, and limits gain.

Investigation of a plasma mirror of an electron-beam-controlled CO2 laser with heating radiation power densities of 1011–1012 W/cm2

Abstract: It is shown that when an electron-beam-controlled CO2 laser operates in a simple single-stage scheme with a plasma mirror, the laser radiation is absorbed efficiently in the plasma. For a heating radiation power of several tens of gigawatts and a power density at the target q~1011–1012 W/cm2, the electron temperature and density in the plasma mirror were Te~200 eV and Ne~1019 cm–3. Helium-like Mg XI ions were obtained.

Fluid treatment by electron emission

Abstract: Improved efficiencies in the treatment of a fluid such as oxygen or an oxygen containing gas by electron emission so as to produce a product such as ozone may be achieved by regulating the manner in which energy is used within a fluid treatment cell and the circuit used to power such a cell. Such a cell normally consists of two electrodes separated from one another by a dielectric layer and an air gap. The apparatus used to power such a cell preferably includes a power supply, a timing generator, transistors for releasing power from the power supply to a transformer at periodic intervals, diodes for permitting power to be reconveyed from the transformer to the power supply, an inductance either built into or associated with the secondary of the transformer, this secondary being connected across the terminals of the cell. With this circuit energy is stored in the cell and in both of the inductances as power is supplied. Such energy is used on the reversal of the polarity of the cell before power is released to the cell. This promotes efficiency in terms of the amount of power consumed per unit of power produced.

Investigations to the Increase of the Specific Energy of a Gasdynamic CO-Laser

Abstract: The input power density and hence the output power of electrically excited gasdynamic lasers is limited by instabilities of the glow discharge. The application of theoretical results, which have been obtained with respect of convection or flow lasers, to the discharge region of an electrically excited gasdynamic CO-laser shows, that especially thermal instabilities cause this glow collapse. An increased convection of local heat concentrations in front of the anode surface results in an improved stability behaviour. Input power densities of up to 100 W/cm3 are now accessible to operate the glow discharge and hence specific laser output powers of 57 kJ/kg are obtained.

Apparatus for investigating stimulated emission from explosively formed metal vapors

Abstract: Apparatus was developed for investigating stimulated emission from metal vapors formed as a result of electric explosions of metal wires. The excitation was provided by a transverse discharge. A specific power output of 32 kW/cm3 and a specific energy output of 0.64 mJ/cm3 were obtained from the copper vapor. The dependences of the output power on the delay between the wire explosion and the excitation and on the interelectrode gap were determined.

A Multiple-Animal Array for Equal Power Density Microwave Irradiation (Short Papers)

Abstract: The introduction of multiple subjects into a microwave field invariably results in perturbations and interference patterns which make it difficult to accurately determine power densities at any specified location. To overcome this problem, investigators have restricted the number of subjects, which is inefficient, or used techniques to illuminate large volumes, which still results in large variations in power density due to curvature of the microwave field. An exposure array has been devised that negates these disadvantages and enables simultaneous irradiations of multiple animals at uniform average power density (/spl plusmn/5 percent). The array consists of microwave transparent cages positioned in accordance with the natural characteristics of the microwave field and separated sufficiently to insure minimum interaction between animals due to microwave reflection. The results of testing the array in an anechoic chamber at a freqnency of 2450 MHz using an isotropic field probe are presented.

Estimates of Optimal Operating Conditions for Hydrogen-Oxygen Cesium-Seeded Magnetohydrodynamic Power Generator

Abstract: The value of percent seed, oxygen to fuel ratio, combustion pressure, Mach number, and magnetic field strength which maximize either the electrical conductivity or power density at the entrance of an MHD power generator was obtained. The working fluid is the combustion product of H2 and O2 seeded with CsOH. The ideal theoretical segmented Faraday generator along with an empirical form found from correlating the data of many experimenters working with generators of different sizes, electrode configurations, and working fluids, are investigated. The conductivity and power densities optimize at a seed fraction of 3.5 mole percent and an oxygen to hydrogen weight ratio of 7.5. The optimum values of combustion pressure and Mach number depend on the operating magnetic field strength.

The jet pulse power supply system

Abstract: The power and energy requirements of the Joint European Torus (JET) are described. The problems involved in supplying such a load from the H. V. lines adjacent to the proposed JET sites are discussed and a cost comparison is made between the two possible components of the power supply, i. e. flywheel. generator-convertors and transformer-controlled-convertors. The proposed JET power supply system is described, together with an outline of the power supply control and its relationship with the overall JET control system. REVUE DE PHYSIQUE APPLIQUÉE TOME 12, DÉCEMBRE 1977, PAGE Classification Physics Abstracts 28.50 R 52.75

Numerical study of a CO(2) laser beam focused on a theta-pinch plasma in the axial direction.

Abstract: Using two different empirical density profiles for the end region of a theta-pinch plasma, one with a maximum density on the axis (radiation-dispersing profile) the other with a pronounced axial minimum (radiation-trapping profile), the trajectory of the CO2 laser beam (10.6 μm) focused axially on such a plasma was studied numerically. This calculation is used to evaluate the optical influence of the plasma, since the maximum power density in the focal plane can be reduced by several orders of magnitude owing to the presence of the plasma. This influence can be substantial even for very subcritical electron densities (ne ≪ 1019 cm−3). In cases of large dispersion, the characteristics of a multifocal lens capable of producing perfect focusing are found, and it is shown that the solution is not unique. The radial distribution of the laser beam power density is also calculated and shows numerous irregularities and discontinuities due to the nonuniform beam dispersion.

Comparison of the power distribution in uranium and plutonium fuel elements in the KWO core

Abstract: The introduction of plutonium-charged fuel elements was investigated with regard to a change in the axial power density distribution. An attempt was made to gather information regarding the influence of coolant temperature change on the local power production. The state of the reactor during the investigations was supposed to correspond to realistic operating conditions. During stretch-out operation, as a result of the reduction of the mean coolant temperature and the reactor power, the fall in coolant outlet temperature is greater than the rise in inlet temperature. Hence, the greatest coolant density change occurs at the coolant outlet. In this manner, the relative power density distribution is displaced toward the upper core half. In a special experiment, the influence of turbine load changes on the axial power density distribution in a noncontrolled reactor was investigated. A power reduction at the turbine causes a rise in the mean coolant temperature of the reactor. Owing to local coolant temperature differences, the power density was found to displace toward the upper core half in a noncontrolled reactor, this being more so the case for plutonium fuel elements. The investigations cited in this report and the good agreement between the theoretical predictions and the experimentsmore » permitted the recycling of the self-bred plutonium at KWO without restrictions on the operation of the reactor.« less

High-temperature, high-power-density thermionic energy conversion for space

Abstract: Theoretic converter outputs and efficiencies indicate the need to consider thermionic energy conversion (TEC) with greater power densities and higher temperatures within reasonable limits for space missions. Converter-output power density, voltage, and efficiency as functions of current density were determined for 1400-to-2000 K emitters with 725-to-1000 K collectors. The results encourage utilization of TEC with hotter-than-1650 K emitters and greater-than-6W sq cm outputs to attain better efficiencies, greater voltages, and higher waste-heat-rejection temperatures for multihundred-kilowatt space-power applications. For example, 1800 K, 30 A sq cm TEC operation for NEP compared with the 1650 K, 5 A/sq cm case should allow much lower radiation weights, substantially fewer and/or smaller emitter heat pipes, significantly reduced reactor and shield-related weights, many fewer converters and associated current-collecting bus bars, less power conditioning, and lower transmission losses. Integration of these effects should yield considerably reduced NEP specific weights.

Determination of the electron density profile of a laser plasma from the Stark broadening of spectral lines in vacuum ultraviolet

Abstract: Measurements were made of the Stark broadening of the Hα(182.17 A) and Hβ(134.95 A) lines of the C VI ions at various distances from a target in a plasma formed as a result of focusing of radiation on this target. The target was a planar slab of carbon and the laser radiation was focused into a spot 800 μ in diameter where the average power density was q~8×1011 W/cm2. The electron density Ne profile was determined over distances of 0–250 μ from the target. A plasma with a low Ne, gradient could form in a confined space. The refraction of far vacuum ultraviolet radiation was considered allowing only for the electron component of the plasma.

Verification of fuel centerline thermocouple readings through response to linear power decreases

Abstract: A method is presented whereby the true value and 95 percent confidence limits for fuel centerline temperatures are estimated from fuel thermocouple response to a linear decrease in rod power. Furthermore, it is shown that for moderate power decreases, these estimates are independent of uncertainties in the fuel rod thermal properties (including its gap conductance). The estimates are also independent of the absolute values of the initial thermocouple reading and power level. Data is presented from power decreases on the U.S. Nuclear Regulatory Commission, Battelle Pacific Northwest Laboratories assembly IFA-431 in the Halden reactor. The reactor power was linearly decreased approximately 20 percent in 30 seconds on several different occasions. The one-sided 95 percent confidence limits on centerline temperature from analysis of these runs varied from 67 to 292/sup 0/C, depending on the run, the rod, and the power level. However, in 33 of the 40 cases examined, thermocouples agreed with the estimated true value centerline temperature within 80/sup 0/C. Future work is recommended which could narrow the confidence limits and provide an independent measure of the fuel-to-cladding gap conductance.

Silent Discharge CO2 Laser

Abstract: Experiments on silent discharge CO2 laser are described. The discharge power density of 50 wcm-3 was achieved at a frequency of 100 kHz, and small signal gain and its spacial distribution were measured. Small signal gain of more than 0. 1%cm-1 could be easily obtained under the total pres-sure of 100-300 Torr. The efficicncy of laser excitation by silent discharge was found to be nearly the same as that by D. C. glow discharge.After the gain measurements, an optical resonator was arranged and output power up to280 mW was obtained. This is the first success to use silent discharge for cw CO2 laser.

Sodium-Sulfur Battery Research

Abstract: High energy density batteries are required for peaking and load leveling systems by the electric utilities and for electrical vehicle propulsion. The battery design depends upon the intended use since the energy density has to be optimized for the first application and the power density for the second application. The sodium-sulfur cell (1) is one of several electrochemical systems under development for the said applications.

Self-reflection of intense electromagnetic waves in plasmas

Abstract: A uniform electromagnetic wave of high power density, propagating in a collisional plasma gives rise to a modification in temperature-dependent collision frequency and in turn induces a gradient in the complex refractive index of the medium. A WKB solution of the problem predicts a backward propagating wave on account of the self-induced inhomogeneity. The amplitude of the backward (i.e. reflected) wave increases with increasing power density of the wave. This is a volume nonlinear effect and is appreciable for usually employed power densities.

Field and Power Density Distributions of the Dipolar Modes in a Partially Filled Cylindrical Plasma Waveguide (Short Papers)

Abstract: The field and power density distributions for the dipolar modes in a partially filled plasma waveguide have been studied at operating points in the vicinity of the plasma, the surface wave, and the gyro resonant frequencies. Results of both the quasi-static and exact analyses are presented. From the field distributions, the behavior of electrons at each resonance is clearly explained.