Showing papers on "Power density published in 1971"

Direct Determination of Optical Gain in Semiconductor Crystals

Abstract: We report a new technique for measuring the stimulated emission spectrum and optical gain of semiconductor materials. Amplified spontaneous emission is used to determine the gain factor by relating the measured variation in light output to variation in the length of the excitation beam. Results for CdS crystals at 2°K are presented that indicate net gains as high as 160 cm−1 at λ = 4907 A are possible with ∼ 12‐MW/cm2 optical pump power density from a nitrogen laser.

UNIFORM ELECTRICAL EXCITATION OF LARGE‐VOLUME HIGH‐PRESSURE NEAR‐SONIC CO2–N2–He FLOWSTREAM

Abstract: Aerodynamic techniques are described whereby continuous electric discharges may be produced uniformly over large volumes in near‐sonic CO2–N2–He flowstreams. Experiment shows that discharge input power scales with pressure for the range 30–150 Torr thereby maintaining a fixed specific power load of ≃ 270 kW/lb(mass)/sec, while diffuse discharges at 1‐atm pressure have been achieved at much lower specific power levels. Discharges occupying 4.5‐ and 43‐liter volumes with the corresponding flowrates 2700 and 28 000 cfm are each uniform over their entire volumes, indicating that volume‐flowrate scaling is not affected by wall diffusion. Using these discharge techniques, a closed cycle 28 000‐cfm 5.6 × 76 × 100‐cm3 CO2 laser amplifier channel has been designed to produce in excess of 20 kW laser power, continuous. In preliminary experiments small‐signal gains reaching 1.9%/cm have been measured transversely across both cold and hot extremities of this device.

Initiation criteria for diverging gaseous detonations

Abstract: Further experiments on the direct initiation of spherical detonation waves in oxy-acetylene mixtures in the pressure range 20–120 torr have been carried out with detailed monitoring of the time history of the energy deposition. The magnitude of the spark energy required for direct initiation is found to depend on the discharge time, increasing in magnitude as the discharge time increases. For a fixed discharge time, the dependence of the magnitude of the source energy is found to be inversely proportional to the mixture composition. On the basis of an average power density correlation [i.e., (total spark energy/(total discharge time) × (source volume)], the discrepancies in the magnitude of the critical initiation energy can be resolved. The order of magnitude of the critical power density required for direct initiation is found to be of comparable order of magnitude as the power density of a self-sustained detonation wave. The dependence of the critical power density on initial pressure is similar to that obtained previously based on source energy (i.e., increases with decreasing pressure or increasing induction delay). Since the power density itself cannot be a meaningful parameter as the source energy can be made vanishingly small with an appropriate reduction in the discharge time or source volume or both, it is proposed that the critical energy in the limit of infinite power density should be used as the universal parameter to correlate with the properties of the explosive mixture. In view of the good agreement between the ideal-point-blast theory and experiments on laser-generated blast waves, even at very early times after the termination of the laser pulse, we concluded that the experimental value of the critical energy using a laser spark should represent the limiting value at infinite power density. A phenomenological model is proposed to gain physical insight into the coupling mechanisms between chemical kinetics and hydrodynamics in a transient flow structure such as that of the spherical wave. The coupling mechanisms are modelled by a global function which leads to an effective energy release at the front which is independent of either the local shock strength or the shock radius. The model recovers the essential features of the three propagation regimes of the reacting blast corresponding to different magnitudes of the source energy. Particularly interesting is the theoretical prediction that unless the source energy is very large, the reacting blast first decays to sub-Chapman-Jouguet velocity and then approaches its final C-J conditions extremely slowly. This prediction finds experimental confirmation in the experimental work of Struck and Brossard. Using an experimentally determined induction-zone thickness of the order of magnitude of the recently defined hydrodynamic thickness, quantitative results on the critical energy as well as transverse wave spacings from the present model were found to agree unexpectedly well with experiments.

Electron emission system

Abstract: A storage system for the mass recording and readout of digital data with ultra high resolution An electron beam structure is provided for forming a beam of extremely small focused spot diameter, on the order of 01 microns, and high current density capability, on the order of 1,000 amperes per sq cm, which records data by scanning over defined areas of the storage medium surface and micromachining elemental portions of said medium as a function of beam modulation Readout may be subsequently accomplished by similarly scanning the beam at reduced power density and detecting electrons that have been transmitted by or reflected from the storage medium

Temperature in Gunn diodes with inhomogeneous power dissipation

Abstract: The output power of Gunn oscillators is limited by the increased temperature which affects the velocity-field curve and which may also permanently damage the diode or the metal contacts. The behavior of these oscillators indicates that the dissipation power density is more or less inhomogeneous, depending on the kind of oscillation mode. The present paper makes use of simple models of the dipole domain mode and the accumulation mode in an analysis of the inhomogeneous dissipation power density. The temperature increase caused by this dissipation power is then calculated. The temperature dependence on diode dimensions and mounting is also discussed. It is shown that the temperature is lower when the anode is turned towards the heat sink than when the cathode is turned the same way. This difference amounts to 150°K for an accumulation mode diode with 500°K maximum temperature in the former case.

Microwave survey meter

Abstract: A device to measure low level near field microwave power density, such as leakage from a microwave appliance. A radial array of semiconductor diodes functions both as an antenna and a detector. The dc current generated in the array by an electric field causes a voltage drop across a load resistance. The voltage drop is a function of electric field strength and is measured by a sensitive dc voltmeter calibrated in power density. A switching sequence in the device provides both an internal battery check and an operational test of the diode array before the device is utilized to measure a microwave field.

Erration storage system with collimated electron beam for minimal spherical ab

Abstract: A storage system for the mass recording and readout of digital data with ultra high resolution. An electron beam structure is provided for forming a beam of extremely small focused spot diameter, on the order of 0.1 microns, and high current density capability, on the order of 1,000 amperes per sq. cm., which records data by scanning over defined areas of the storage medium surface and micromachining elemental portions of said medium as a function of beam modulation. Readout may be subsequently accomplished by similarly scanning the beam at reduced power density and detecting electrons that have been transmitted by or reflected from the storage medium.

Method for the production of masks in the manufacture of semiconductor components

Abstract: IN A PROCESS FOR THE PRODUCTION OF MASKS IN THE MANUFACTURE OF SEMICONDUCTOR COMPONENTS, ONTO A COATED OR UNCOATED SEMICONDUCTOR SUBSTRATE IS SPUTTERED A COMPOSITION CONTAINING A SILICON OXIDE OR NITRIDE COMPOUND AT A POWER DENSITY NO GREATER THAN ABOUT 0.2 WATT PER CM.2 UNTIL A COATING THICKNESS OF AT LEAST 0.1 UM. IS ATTAINED AND THEN AT A POWER DENSITY NO GREATER THAN ABOUT 0.4 WATT PER CM.2 UNTIL THE COATING HAS ATTAINED A THICKNESS OF 0.3 TO 2.0 UM., THEN THE POWER DENSITY IS INCREASED TO 3 TO 5 WATTS PER CM2 TO PARTIALLY DECOMPOSE THE PHOTORESIST MASK AND TEAR OPEN THE COATING SUPERIMPOSED THEREON; THIS IS FOLLOWED BY SOLVENT AND ULTRASONIC TREATMENTS TO REMOVE THE REMAINING PHOTORESIST AND SUPERIMPOSED COATING.

Method for electron beam welding at high speeds

Abstract: The invention concerns a process of welding by an electron beam. The process is one of electron beam welding in which an electron beam is oscillated locally in a direction along a desired path on the work so as to determine a zone over which the beam is swept upon the work pieces which zone has a trailing edge at one end directed in the direction of the relative displacement of the parts with respect to the gun and a leading edge at its other end directed in the opposite direction to the relative displacement and where the power density of the beam is made to vary in a desired manner. For example, it may be reduced when it is abreast of the trailing edge of the swept zone with respect to the power density when the beam is abreast of the loading edge of the swept zone.

Interferometric studies of the interaction of focused Nd-laser-radiation with thin absorbing surface layers

Abstract: An interferometric method is used to study plasmas generated by the high energy and power density of Nd-laser radiation focused on a thin graphite deposit on the back side of 2–3 mm thick glass discs. The features considered here are the behaviour with time of the expansion of the plasmas from the back side of the slides in the direction of the propagating beam, under normal gas pressure and temperature conditions and the distribution of densities inside the volume determined by the shock wave.

Monitoring of power distribution in nuclear reactor cores

Abstract: One of the most characteristic features of modern reactor design is the steady growth of the overall capacity and specific power density of reactor cores; this requires operation of the individual fuel elements at close to their maximum permissible power and optimization of power distribution in the core for most economical and safe operation. This in turn demands accurate and reliable measurement of power fields in the core and continuous perfection of theoretical and practical monitoring techniques. Obviously, most accurate power distribution measurements require fitting of every single fuel assembly or fuel channel with a detector. However, such an approach is justified only if the detectors are placed outside the core as, for example, in thermal monitoring of channel-type nonboiling-water reactors. In most modern reactors the power distribution is measured with the aid of detectors located at discrete points inside the core. When using this technique one must take into account the fact that a large number of detectors, which are neutron absorbers and as a rule present an additional hydraulic resistance to coolant flow, is liable to deterioriate the reactor performance. In-core measurements meet with considerable difficulties as a result of the rigorous radiation, temperature, and other conditions under which in-core detectors must operate. This probably explains the relatively late appearance of reliable, in-core power-field measuring systems. The first systems for measuring neutron fluxes in reactor cores were based on periodic activation of indicators and subsequent counting of their induced activity outside the core with the aid of special semiautomatic devices [1-4]. Such periodic monitoring systems were later replaced by continuous monitoring systems with r~eutron or gamma detectors permanently left in the core (see Table I).

High efficiency injection laser cavities

Abstract: The specification describes injection lasers employing heterosemiconductor structures for obtaining an enlarged crosssectional area cavity defined by an optical waveguide terminated by the cleaved faces of the semi-conductor structure (usually known as mirrors). The enlarged area of the cavity allows higher power output from the laser for the same power density on the mirrors. The power density is limited by damage to the mirrors. The waveguide produces an output consisting of two plane wave lobes for each mode. Techniques for mode enhancement are described from which higher ultimate power for a single mode and higher efficiency can e predicted without exciting modes of other order. Separation between the thresholds of competing modes can be enhanced, for example, by placing a spherical reflector in the path of one output lobe to focus the energy back into the original cavity while at the same time aperturing the mirror to block modes of other order. This expedient is based upon the uniqueness of the lobe angle for a given mode. Also described is a technique for combining the dual lobe output characteristic of this laser structure by using a beam splitter in reverse.

Bremsstrahlung power density: long-range interactions.

Abstract: The power density of bremsstrahlung and the recombination rate are found for a fully ionized, nonrelativistic hydrogen plasma dominated by long-range collisions. The results show that the bremsstrahlung energy radiated per unit volume per second is greater than previously predicted.

Decrease in Power Density due to Finite Electrode Conductivity in Liquid Metal MHD Generator

Abstract: In the liquid metal MHD power generator, the electric conductivity of the working fluid is so large as to be comparable with that of the electrode. Under such circumstances the perfect conductor approximation no longer holds for the electrode, because the electric potential loses its constancy and acquires a certain pattern of distribution in the electrode as well as in the fluid. The extent of distortion in the electric equipotential lines and lines of force depends on the ratio of conductivity between electrode and fluid, and on the load connection. The power density becomes non-uniform, and furthermore the average power density becomes smaller than in the case of a generator with the perfect conductor electrode. The effect due to this finite conductivity of the electrode is contrary in trend to that due to end loss, as analyzed by Sutton with both aspect ratio and load factor as parameters. The results obtained in our present experiments with a mercury blow-down facility have agreed very well with the ...

Measurements of plasma parameters in a simulated thermionic converter.

Abstract: Cesium-filled thermionic energy converters are examined as candidate electrical energy sources in spacecraft requiring tens to hundreds of kilowatts of electric power. The high operating temperatures necessary for a large specific power and high efficiency inevitably impose stringent constraints on the converter fabrication to achieve the desired reliability of the power system. The converter physics for reducing operating temperatures and cesium plasma losses are studied to achieve high reliability without sacrificing the power performance of the converters. Various cesium parameters which affect the converter performance are: (1) electron temperatures, (2) plasma ion densities, and (3) electric potential profiles. These were investigated using a Langmuir probe in a simulated converter. The parameters were measured in different cesium discharge modes.