Showing papers on "Power density published in 1988"

Nuclear driven flashlamps

Abstract: Due to the low power density of pumping schemes for nuclear-pumped lasers prior to 1978, a method of utilizing the efficient production of narrow band fluorescence from excimers was developed. This method has since been referred to as a nuclear driven flashlamp. It is possible to achieve sufficient power densities, when combining the flashlamp with novel techniques of reactor/laser interfaces, to drive efficient, high power lasers directly with products from nuclear reactions.

Laser Breakdown Acoustic Effect of Ultrafine Particle in Liquids and Its Application to Particle Counting

Abstract: The mechanism of acoustic signal generation from an ultrafine particle in liquids by laser irradiation was found to shift from the photoacoustic effect to optical breakdown of the particle as the power density of the excitation beam increased. The acoustic signal generated from a 0.085 µm polystyrene ultrafine particle in water increased discontinuously at the beam power density of 7.0 ×1010 W/cm2, corresponding to its dielectric breakdown threshold. Then, a novel method in which ultrafine particles were counted individually by counting the breakdown acoustic pulses was proposed, and its counting principle was verified using the polystyrene ultrafine particles.

A double-heterojunction doped-channel pseudomorphic power HEMT with a power density of 0.85 W/mm at 55 GHz

Abstract: The authors report the DC characteristics and RF performances of a 50*0.2- mu m/sup 2/ AlGaAs/InGaAs/GaAs pseudomorphic HEMT with a doped InGaAs channel. A transconductance as high as 760 mS/mm and a maximum current density of 800 mA/mm leads to a power density of 0.85 W/mm with 3.3-dB gain and 22.1% power-added efficiency at 55 GHz. >

Millimeter Wave Monolithic GaAs Power FET Amplifiers

Abstract: Millimeter-wave monolithic GaAs power FETs with total gate widths of up to 400 pm and output powers up to 200 mW have been developed. These amplifiers were fabricated using sub-half-micrometer gate length FETs on MBE-grown epitaxial layers with n+ contact layers. A source overlay structure with via groundings has been used for the FET design. Power densities of 0.53 W/mm, 0.45 W/mm, and 0.25 W/mm were obtained at 34 GHz, 41 GHz, 54 GHz, respectively. Power-added efficiency of 33% was obtained at 35 GHz with 0.53 W/mm power density.

Physicochemical properties in tungsten films deposited by radio‐frequency magnetron sputtering

Abstract: The microstructure, reflectivity, resistivity, and oxygen contamination of thin tungsten films (<250 nm) deposited by rf magnetron sputtering on silicon substrates are reported. Three structural stages, depending on the operating conditions, are found to occur during the deposition: (i) In the range of the rf applied power density studied (<6 W cm−2), an amorphous structure is always observed when the film thickness does not exceed ∼80 nm. The resistivity remains at a fairly high level (≂1.3 μΩ m). (ii) Upon further deposition and if the power density is <0.6 W cm−2, the β‐W phase is detected. (iii) A thermally activated transformation of the β‐W phase into pure α–W occurs for a critical temperature ∼150 °C during depositions carried out at higher powers(≥1 W cm−2). The resulting β‐W or α‐W films consist of small grains (5–20 nm) which present a low dislocation density. Resistivity and reflectivity are mainly related to the oxygen content of the films. When the rf deposition power density is low (≤0.6 W c...

Infrared alkali halide fibers

Abstract: Polycrystalline alkali halide fibers were fabricated using a hot extrusion technique. Core-clad fibers of KBr/KCl had losses as low as 0.1 dB/m at 10.6 microm, but the average loss for 8OO/100O-microm fiber was 0.69 dB/m. The salt fibers were coated with Teflon to minimize surface fracture from microcleavage cracks and to protect the fiber from contamination. The maximum output power we have obtained from the fiber is 67 W of cw CO(2) laser power. This corresponds to a power density of 13.3 kW/cm(2). The 100O-microm salt fiber has been bent into a 12-cm diam circle with a 5% reduction in transmission.

Method and apparatus for measuring and regulating the flow rate of powder in a powder spraying device

Abstract: An apparatus and method for accurately determining the quantity of powder flowing in a spraying device includes a power density measuring element for measuring the powder density of the powder/gas mixture flowing in the spraying device and a device for measuring the flow rate of the pure gas prior to its mixing with the powder. Signals representative of the powder density and gas flow rate are generated and transmitted to an electronic evaluation device which calculates from these measurements the absolute flow rate of the powder per unit time.

Millimeter-wave GaAs power FET with a pulse-doped InGaAs channel

Abstract: Performance of a GaAs power MESFET has been improved significantly by incorporating a pulse-doped InGaAs layer in the GaAs n-channel. InGaAs provides electron transport properties superior to those of GaAs. The doping level of the GaAs layer can be very high, making it a very-high-transconductance device. Moreover, the conduction-band discontinuity at the heterointerface acts as a potential barrier for electron confinement; therefore, the power gain of the FET is significantly improved. The resulting device delivered a power density of 0.6 W/mm with 14% power-added efficiency and 3.5-dB gain at 60 GHz. At a gain of 5.1 dB, power density was 0.4 W/mm. >

AlGaAs/InGaAs/GaAs quantum-well power MISFET at millimeter-wave frequencies

Abstract: An AlGaAs/InGaAs/GaAs quantum-well MISFET developed for power operation at millimeter-wave frequencies is described. The InGaAs channel is heavily doped to increase the sheet carrier density, resulting in a maximum current density of 700 mA/mm with a transconductance of 480 mS/mm. The 0.25- mu m*50- mu m device delivers a power density of 0.76 W/mm with 3.6-dB gain and 19% power-added efficiency at 60 GHz. At 5.2 dB gain, the power density is 0.55 W/mm. A similar device built on an undoped InGaAs channel had much poorer power performance and no speed advantage. >

GaAs power MESFET with 41-percent power-added efficiency at 35 GHz

Abstract: A GaAs power MESFET has been optimized for Ka-Band operation. The device has an n/sup +/ ledge channel structure with a 0.25- mu m gate on MBE-grown material. An output power density of 0.71 W/mm was achieved with 5.2-dB gain and 34% power-added efficiency. When tuned for maximum efficiency, a power-added efficiency of 41% was obtained with a power density of 0.61 W/mm and a gain of 5.6 dB. >

Time average neutralized migma: A colliding beam/plasma hybrid physical state as aneutronic energy source — A review

Abstract: A D+ beam of kinetic energy Ti = 0.7 MeV was stored in a “simple mirror” magnetic field as self-colliding orbits or migma and neutralized by ambient, oscillating electrons whose bounce frequencies were externally controlled. Space charge density was exceeded by an order of magnitude without instabilities. Three nondestructive diagnostic methods allowed measurements of ion orbit distribution, ion storage times, ion energy distribution, nuclear reaction rate, and reaction product spectrum. Migma formed a disc 20 cm in diameter and 0.5 cm thick. Its ion density was sharply peaked in the center; the ion-to-electron temperature ratio was TiTe ∼ 103; ion-electron temperature equilibrium was never reached. The volume average and central D+ density were n = 3.2 × 109 cm−3 and nc = 3 × 1010 cm−3 respectively, compared to the space charge limit density nsc = 4 × 108 cm−3. The energy confinement time was τc = 20–30 s, limited by the change exchange reactions with the residual gas in the vacuum (5 × 10−9 Torr). The ion energy loss rate was 1.4 keV/s. None of the instabilities that were observed in mirrors at several orders of magnitude lower density occurred. The proton energy spectrum for dd + d → T + p + 4 MeV shows that dd collided at an average crossing angle of 160°. Evidence for exponential density buildup has also been observed. Relative to Migma III results and measured in terms of the product of ion energy E, density n, and confinement time τ, device performance was improved by a factor of 500. Using the central fast ion density, we obtained the triple product: Tnτ ≅ 4 × 1014 keV s cm−3, which is greater than that of the best fusion devices. The luminosity (collision rate per unit cross section) was ∼ 1029 cm−2s−1, with o.7 A ion current through the migma center. The stabilizing features of migma are: (1) large Larmor radius; (2) small canonical angular momentum; (3) short axial length z (disc shape); (4) nonadiabatic motions in r and z; (5) precession and enegy spread; (6) ambipolar potential; (7) radial density gradient;(8) large ion-to-electron temperature ratio; (9) metal walls in z; (10) suitability for external stabilization techniques (small volume, recurrent surfacing of ions); and particularly (11) diamagnetic well. Extrapolition of the results to reactor densities led to a D + 3He reactor “basic migma disc” 0.5 m in diameter and 0.25 m thick, suspended in a 10 T field, generating 1.5 MW(th). A 2-MW(e) power plant would consist of 3 such discs in a common volume. referred to as a triplet migmacell. Its specific power is projected to be 1 MW(e)/ton. A large power plant of any size would consist of a large number of migma discs in a common volume. The advantages f such modular systems are: (1) economy of mass production: capital cost per kW will be 25% that of fission and 10% that of DT fusion; (2) plants will be economical for all sizes above 10 kW(e); (3) minimal heat pollution, thanks to direct conversion of the changed ion kinetic energy into electricity; (4) no proliferative potential; and (5) large power-to-weight ratio due to absence of shielding. Anticipated physics problems in density increase are discussed.

Millimeter-wave AlGaAs/InGaAs/GaAs quantum well power MISFET

Abstract: State-of-the-art millimeter-wave power transistors using quantum-well MISFET structures have been developed. Single- and double-quantum-well devices have been built, with maximum currents of 700 mA/mm for the single-well and 900 mA/mm for the double-well devices. The single-well devices delivered a power density of 0.76 W/mm with 3.6-dB gain and 19% efficiency at 60 GHz. The double well MISFETs had a power density of 0.96 W/mm with 3-dB gain and 24% power-added efficiency at 55 GHz. The highest power-added efficiency was 31% with 0.68 W/mm power density and 4-dB gain. The power performance of the double-well device was better than that of the single-well device. >

Light‐activated silicon diode switches

Abstract: An experimental study of the fundamental limits to current density, power, and speed of light‐activated semiconductor switches (LASS) is described. The LASS investigated are high‐voltage silicon junction devices illuminated with 1.06‐μm laser light. A novel optical delay line is designed in sampling the laser pulses. Experimental results to date demonstrated a switch power of 6.7 MW, a peak electrical pulse power of 4.8 kW, a current density of 150 kA/cm2, a power density of 5.3 GW/cm3, and an electrical pulse rise time of 100 ps. The results of theoretical analysis indicate that the circuit configuration is the main limitation to the pulse rise time.

Earth-To-Satellite Microwave Beams: Innovative Approach To Space Power

Abstract: A new space power concept incorporating earth-to-satellite microwave power beams coupled to onboard regenerative electrochemical energy storage is proposed for energizing defensive satellite constellations. The system addresses housekeeping, orbital maneuvering and burst mode power requirements, and offers an attractive alternative to the nuclear and solar space power systems currently envisioned for this application. This energy-conversion system incorporates six steps: (1) generate primary DC power at surface stations along the satellite ground-track, (2) convert to microwave (RF) frequencies, (3) transmit in a narrow beam to spacecraft using phased-array antennas which track and lock-on to satellite receivers as they pass in range during a fraction of their orbit, (4) receive the energy and convert to DC in space using lightweight and inexpensive rectennas; (5) store the energy onboard as chemical energy by electrolysis of water to oxygen and hydrogen and (6) recover free energy onboard the spacecraft during the balance of the orbit continuously or on demand as pulsed power with a high power-density fuel cell. Component and overall systems considerations of this scheme are discussed in comparison with alternatives, outstanding research problems are defined and preliminary analyses are described. These include orbital mechanics and ground tracks of satellites, accessibility of orbiters to microwave beams, transmission efficiencies, electronic and mechanical designs of the transmitter and rectenna, regenerative fuel cell energy storage, power conditioning and thermal management. The development of readily space-deployable rectennae, their supporting structures, and high specific power solid oxide monolithic fuels cells are the main pacing technologies leading to a wholly non-nuclear space power system capable of supporting all defensive satellite power requirements.© (1988) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High-power, high-efficiency 770 nm 2D laser diode array

Abstract: A 2D laser diode array is described which operates at a power density of 2kw/cm/sup 2/, with an overall efficiency of 35% and a slope efficiency of 56%. The wavelength of operation is 770 nm. 6 refs., 4 figs.

Monolithic Two-dimensional Surface-emitting Arrays Of GaAs/AlGaAs Diode Lasers

Abstract: Monolithic two-dimensional arrays with light emission normal to the surface were obtained by fabricating edge-emitting quantum well GaAs/AlGaAs lasers with deflecting mirrors adjacent to both laser facets. The facets and mirrors were formed by ion-beam-assisted etching. Proton bombardment between adjoining lasers was used to prevent lasing in the transverse direction. At the highest pulsed current used in these experiments, 10.5 A, the power output of a 22-element array was 1.6 W, which corresponds to a power density of 160 W/sq.cm. At this level, the power output was still linear with current.

Harmonic power implications on free electron laser mirror design

Abstract: Calculations of the coherent-spontaneous radiation at the harmonic frequencies of a 1 μm free electron laser employing a tapered wiggler with a prebuncher have been performed utilizing a transverse-averaged cavity-mode code. The relative harmonic power adsorbed per unit area has been calculated for three possible metal mirror candidates and shown to be a small fraction of the total power density absorbed by the mirror.

Determination of proton stopping power in hot plasma at kalif

Abstract: First stopping power experiments with proton beam from a pinch reflex diode at the Karlsruhe Light Ion Facility KALIF have been performed and compared with the results of theoretical predictions. The maximum proton energy in these experiments is 1.5 MeV. The peak power density on the target is between. 0.15 to 0.3 TW/sq.cm. An enhancement of proton stopping power up to a factor of 2.6 is observed. These results are analysed with the target code KATACO. There is a good agreement between theoretical prediction and experimental results. The analysis shows that plasma temperatures of about 25 eV are achieved at KALIF.

Crystal protection mechanism of variable wavelength laser device

Abstract: PURPOSE:To prevent damage or breakdown of nonlinear optical crystal due to excessive power density of incident laser beam to nonlinear optical crystal by providing a particular half-mirror, a power density detector, a comparator and a light shielding mechanism. CONSTITUTION:A variable-wavelength laser device 11 which changes wavelength of laser beam 13a emitted therefrom by changing a relative incident angle for crystal surface of laser beam 13 incident to nonlinear optical crystal 16 is provided with a half-mirror 21 for branching the laser beam 13 incident to the nonlinear optical crystal 15, a power density detector 31 for detecting power density of branched laser beam 13, a comparator 33 for comparing a detected value of power density detector 31 with the present value and a light shielding mechanism 20 for shielding the laser beam 13 incident to the nonlinear optical crystal 16 based on an output of the comparator 33. The light shielding mechanism 20 is structured, for example, a shutter 26 adjacent to the optical axis of laser beam 13, a solenoid 30 to drive the shutter and a solenoid drive circuit 23 to drive the solenoid 30 based on an output of comparator 33.

Fuel igniting device

Abstract: PURPOSE:To ignite even a fuel with low conbustibility reliably and quickly by focusing a laser beam from a laser beam generating unit on a heat conducting plate in a combustion chamber by a focusing lens and igniting fuel with the heat energy. CONSTITUTION:Fuel is filled into a combustion chamber 9 by a fuel feeding unit 5. A laser beam from a laser beam generating unit 1 is focused on a heat conducting plate 4 (metal material with high heat conductivity such as steel iron) stuck to a light window 3 (heat-resistant glass) by a focusing lens 2. Since this laser beam has a high power density, the temperature of the heat conducting plate 4 rises very quickly to ignite the fuel. The temperature rise of the heat conducting plate 4 can be easily controlled in response to the combustibility (igniting temperature) of fuel by changing the radiation time of the laser beam. Accordingly, the nonignition of fuel can be prevented by the duration of the laser beam radiation time. In addition, the laser beam can be efficiently transmitted without being affected by the soot or the like in the combustion chamber until the laser beam reaches the heat conducting plate 4.

Permanent magnet generators for aerospace applications

Abstract: The primary design consideration for electrical generators used in aerospace applications is the maximisation of the power to weight ratio (power density). Since the gross power available from a generator is directly proportional to its operating speed and the generated frequency is unconstrained in an isolated system, it is natural to operate at high speeds. This high speed operation makes the use of a DC rotor field impractical due to brush wear, and therefore the field excitation is obtained from permanent magnets (PM). Many magnetic circuit configurations have been proposed by various researchers on PM machines, but there have been few attempts at quantitative comparisons. The author aims to provide such comparisons for popular configurations, in the power range 0.25-10 kW and the speed range 10000-100000 RPM suitable for unmanned aircraft and spacecraft. The general approach is to produce approximate designs for each configuration over the power and speed ranges, using formal optimisation methods, and then to compare the power density figures.

Multiplex power source system

Abstract: PURPOSE: To balance a load between power source equipments through simplified wiring without requiring adjusting work by calculating power consumption in each power source equipment digitally and transferring the data between the power source equipments CONSTITUTION: At first, voltages at points (a), (b), (c), (d) in each secondary circuit are read out and stored in a RAM 42 Then a microcomputer 40 calculates power consumption in its power source equipment 400 and stores the calculated power consumption in the RAM 42 Then an average power consumption is calculated based on that data and data representing power consumption of load being transferred from other power source equipments 400, and the calculated average power consumption is stored in the RAM 42 Thereafter, the power consumption of load stored in its power source equipment 400 is compared with the average power consumption and next pulse ON times of power transistors 23a, 23b are controlled based on the comparison result and the current voltage levels at points (a), (b), (c), (d) stored in the RAM 24 thus averaging power supply from each power source equipment 400 to the load COPYRIGHT: (C)1990,JPO&Japio

High Power Diode Laser Research In Mitsubishi Electric

Abstract: In practical uses, life time is an important parameter for high power diode lasers. In general, one can find out two components in degradation mode of the A1GaAs/GaAs lasers, that is, gradual and sudden increases of operation current to keep the output power constant. The gradual degradation might be due to increase of non-radiative recombination centers in an active region, or to some kinds of facet oxidation which results in slow reduction of reflec-tivity. In order to avoid or eliminate the gradual degradation, it has been required to reduce the mechanical stress and temperature rising and to passivate the facets. The sudden increase of operation current could be understood in terms of facet degradation, which is mainly caused by high optical power density. The most radical case is the so-called COD(catastrophic optical damage). The COD is one of thermal effects coming from local temperature rising attributed to self-absorption of light at the facet region where the population inversion is lost by fast surface recombination velocity. The COD level is increased by passivation of dielectric film such as Si 3 N 4 or Al 2 0 3 to 1.5-2.0 times higher than the bare facet. As absorption intensity at the facet is determined by not output power but inner power at the facet, the inner power is an essential parameter for high power diode lasers. Output power is varied by changing the facet reflectivity, even though the inner power is controlled to be same level. It is generally known that inner power density at passivated facet corresponds to approximately 2-3MW/cm 2 . The relationship between output power Po and inner power Pi is expressed as

Properties Of Alkali Halide Optical Fibers

Abstract: Polycrystalline alkali halide fibers were fabricated using a hot extrusion technique. Core/clad fibers of KBr/KC1 had losses as low as 0.1 dB/m at 10.6 μm, but the average loss for 800/1000 μm fiber was 0.69 ± .32 dB/m. The salt fibers were coated with teflon to mini-mize surface fracture from microcleavage cracks and to protect the fiber from contamination. The maximum output power we have obtained from the fiber is 67 watts of cw CO2 laser power. This corresponds to a power density of 13.3 kW/cm2. The 1000 μsalt fiber has been bent into a 12 cm diameter circle with a 5% reduction in transmission.

Properties of alloy MA21 after laser treatment

Abstract: 1. For the practical application of the alloy MA21 it is most favorable if it has a fine-grained quasieutectic structure obtained in continuous laser treatment. 2. Between the power density of the radiation, the geometry of the laser track, the corrosion rate, and the volume fraction of α-phase in the alloy MA21 there exist empirical correlations. 3. The permissible temperature interval to which the alloy MA21 may be heated in irradiation is ΔTp=60–70°C. 4. To eliminate the effect of nonsteady fluxes on the process of eutectic crystallization in CLHT in air, the wall thickness of parts must not be less than 30 mm. 5. A method of engineering calculation of the critical mass of the irradiated part was worked out: with it the parameters of the technological process of CLHT in air can be evaluated.

Nitrogen laser excited by microwave pulses

Abstract: The first results are reported of an experimental investigation of the energy parameters of a nitrogen laser (λ = 337.1 nm) excited by high-power nanosecond microwave pulses. The measurements were carried out for a specific pump power of 0.4–1.6 MW/cm3 at a gas pressure of 3–30 Torr when the length of the active medium was 20–100 cm. The lasing efficiency was determined as a function of the specific power deposited in the microwave discharge and of the length of the active medium. The maximum efficiency did not exceed 0.06% and the peak radiation power was 12.5 kW.

An innovative demonstration of high power density in a compact MHD generator

Abstract: : Magnetohydrodynamic (MHD) energy conversion is a candidate technology for satisfying the pulse power requirements for advanced weapon and discrimination systems for the Strategic Defense Initiative. However, to be competitive with alternative pulse power concepts utilizing nuclear or stored energy schemes the characteristic power per unit weight and volume of the MHD system requires improvement in performance well beyond the levels demonstrated in the past. In this regard, there are two primary performance parameters of concern: the power density and the specific energy. The power density is the ratio of the electrical energy output to the internal volume of the generator channel. The MHD process is a volumetric process and the power density is therefore a direct measure of the compactness of the system. As such, it controls the size and weight of a MHD power generating system for a given power output. The greater the characteristic power density, the smaller and lighter the channel, magnet, combustor and flow train will be. The second parameter, the specific energy, is the ratio of the electrical energy output to consumable energy used for its production. In the case of a chemically driven MHD system, the specific energy is a direct measure of the conversion efficiency from the latent chemical energy to electrical energy. In pulse power MHD systems with short operating durations the specific energy is the controlling parameter for the weight and volume of the stored reactants used to power the system. The two parameters are conceptually interrelated, and for a given mission scenario maximization of both, in general, are required for optimization of the system. However, for short operating durations the power density is the dominant parameter; whereas, for long durations, the specific energy is the dominant parameter.

Estimation of power-energy plots for secondary batteries

Abstract: A fast convenient method for estimating power plots for galvanic cells is discussed Comparisons between various electrochemical couples can be made with this method, along with the evaluation of different cell designs, and parameters, such as sustained peak power, can be estimated