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Showing papers on "Power density published in 1975"


Journal ArticleDOI
TL;DR: In this article, a one-dimensional model for power transistor cooling is described and the theoretical predictions of the model are shown to be in good agreement for practical applications with three-dimensional computer simulations and experimental results.
Abstract: Differences between the measured thermal impedance of power transistors when determined by the pulsed heating curve and cooling curve techniques are discussed. These differences are shown to result primarily because the power density distributions of these devices change as devicesheat; as a result of these changes the heating curve and the cooling curve are not conjugate. It is shown that the cooling curve technique, when the cooling curve is initiated from the most non-uniform steady-state thermal, distribution, (maximum voltage, maximum power) will indicate a larger value for the thermal impedance than will the pulsed heating curve technique, even for pulses in excess of the dc power level. A one-dimensional model for power transistor cooling is described. The theoretical predictions of the model are shown to be in good agreement for practical applications with three-dimensional computer simulations and experimental results. Using this model, it is possible to estimate an average junction temperature and the area of power generation at steady-state. Both TO-66 and TO-3 encased devices of mesa and planar structures were included in this study.

95 citations


Journal ArticleDOI
TL;DR: In this article, an experimental 1/2−in.−diam cell was operated in air mass 1.4 sunlight with an output power density of 4.52 W/cm2 at an effective concentration of 312 suns with a power conversion efficiency of 17.5%.
Abstract: For terrestrial applications, the figure of merit for photovoltaic solar energy conversion devices is watts output per dollar of cost. AlGaAs/GaAs heterojunction cells have a very favorable watts per dollar figure of merit when used at high values of sunlight concentration. An experimental 1/2−in.−diam cell was operated in air mass 1.4 sunlight with an output power density of 4.52 W/cm2 at an effective concentration of 312 suns with a power conversion efficiency of 17.5%. The same cell was operated at 200 °C with an output power density of 3.45 W/cm2 at a 14% efficiency. The efficiency of the cell was 23% with a fill factor of 0.85 at a lower concentration ratio which is obtainable using simple concentrator schemes.

82 citations



15 May 1975
TL;DR: In this article, the authors measured and calculated results from determining the operating efficiencies of a laboratory version of a system for transporting electric power from one point to another via a wireless free space radiated microwave beam.
Abstract: The measured and calculated results from determining the operating efficiencies of a laboratory version of a system for transporting electric power from one point to another via a wireless free space radiated microwave beam are reported. The system's overall end-to-end efficiency as well as intermediated conversion efficiencies were measured. The maximum achieved end-to-end dc-to-ac system efficiency was 54.18% with a probable error of + or - 0.94%. The dc-to-RF conversion efficiency was measured to be 68.87% + or - 1.0% and the RF-to-dc conversion efficiency was 78.67 + or - 1.1%. Under these conditions a dc power of 495.62 + or - 3.57 W was received with a free space transmitter antenna receiver antenna separation of 170.2 cm (67 in).

55 citations


Journal ArticleDOI
TL;DR: Rats spent more time in the halves of shuttle boxes that were shielded from illumination by 1.2 GHz microwave energy than in the unshielded, and avoided the pulsed energy, but not the continuous energy.
Abstract: Rats spent more time in the halves of shuttle boxes that were shielded from illumination by 1.2 GHz microwave energy than in the unshielded. In Experiment 1, rats avoided the energy when it was presented as 30-musec pulses with a pulse repetition rate of 100 pulses per second (pps). The average power density was about .6 mW/cm2, and the peak power density was about 200 mW/cm2. In Experiment 2, the energy was presented both continuously and in pulse-modulated form, i.e., .5-msec exponentially decaying pulses at a rate of 1,000 pps. The average power density of the continuous energy was 2.4 mW/cm2, and the average power density of the pulse-modulated energy was .2 mW/cm2. The peak power density of the modulated energy was 2.1 mW/cm2. The rats avoided the pulsed energy, but not the continuous energy.

50 citations


Proceedings ArticleDOI
09 Jun 1975
TL;DR: In this paper, a method for resonant switching applicable to dc-to-dc power conversion is presented, which avoids solid state power device second breakdown stresses encountered with high voltage switching in conventional circuitry.
Abstract: A method for resonant switching applicable to dc to dc power conversion is presented. Zero current switching together with resonant control of current waveforms avoids solid state power device second breakdown stresses encountered with high voltage switching in conventional circuitry. General theory of circuit operation and design is described. Circuitry and performance are outlined for an operational 1500 watt dc to dc converter designed for nominal input voltage of 270 Vdc, with regulated output voltage in the 90 Vdc range. Operational performance and projected power densities (watts per pound) are found to be attractively competitive with the existing state-of-the-art. Further development work is being done at Martin Marietta Aerospace using resonant switching frequencies in the 200 KHz range for space flight hardware. Projected power density in this application is 140 watts per pound, under high performance and reliability requirements.

48 citations


Journal ArticleDOI
TL;DR: In this article, a cubic dispersion relation is obtained from linearization of the coupled hydrodynamic and Ohmic equations in which the electrical conductivity is dependent on the neutral density.
Abstract: The thermal and acoustic instabilities that could possibly cause arcing in high−power pulsed and cw gas lasers have been investigated A cubic dispersion relation is obtained from linearization of the coupled hydrodynamic and Ohmic equations in which the electrical conductivity is dependent on the neutral density We find that when the thermal wave is unstable the acoustic waves are damped, and vice versa The growth rate of the instability is proportional to the power density for low input powers while it goes as the cube root of the power density for high input powers

43 citations


Journal ArticleDOI
TL;DR: In this paper, a coaxial-pumped xenon laser employing a single intra-cavity prism was used to achieve high efficiency spectral narrowing to 0.13 nm and frequency tuning from 169 nm to 176 nm.

29 citations



Journal ArticleDOI
TL;DR: In this paper, a copper vapor laser operating at a wavelength of 5106 A and a pulse repetition rate up to 30,000 pulses/sec has been constructed and investigated, and the best results obtained to date are as follows: energy and power density of 35 μJ/cm−3 and 1.7 kW cm−3; pulsewidth 20 nsec; average density 0.7 W
Abstract: A copper vapor laser operating at a wavelength of 5106 A and a pulse repetition rate up to 30 000 pulses/sec has been constructed and investigated. The best results obtained to date are as follows: energy and power density of 35 μJ cm−3 and 1.7 kW cm−3; pulsewidth 20 nsec; average density 0.7 W cm−3; laser efficiency 1%.

24 citations


Journal ArticleDOI
TL;DR: In this paper, a continuously tunable cw dye laser was used to measure the absolute spectral response of a silicon photodiode and narrow band−pass filter by comparison with an electrically calibrated pyroelectric detector.
Abstract: A new approach to radiant power measurements is described. A continuously tunable cw dye laser was used to measure the absolute spectral response of a silicon photodiode and narrow band−pass filter by comparison with an electrically calibrated pyroelectric detector. The filtered photodetector was then used to measure the spectral power density from a standard lamp that had been calibrated by the classical technique. The agreement of better than 1% between the two measurements is well within the uncertainties identified with each measurement individually, of the order of 1%. A number of advantages in the new technique are identified.

Journal ArticleDOI
TL;DR: Using an incoherent AlxGa1−xAs light-emitting diode (LED) as a pump source, pulsed laser oscillation was observed in a 300μm-thick LiNdP4O12 crystal cooled to −35 C as discussed by the authors.
Abstract: Using an incoherent AlxGa1−xAs light‐emitting diode (LED) as a pump source, pulsed laser oscillation was observed in a 300‐μm‐thick LiNdP4O12 crystal cooled to −35 °C. The oscillation threshold power density is 8.2 W/cm2 for the LED pump, and is compared with that for an Ar laser pump and theoretical values. The temperature dependence of oscillation threshold and optical round‐trip loss are discussed.

Journal ArticleDOI
TL;DR: In this article, atomic and ionic species evaporation by a CO2 laser pulse at power density up to 107 W/cm2 from surfaces have been studied by time-resolved spectroscopy.
Abstract: Atomic and ionic species evaporated by a CO2 laser pulse at power density up to 107 W/cm2 from surfaces have been studied by time‐resolved spectroscopy. The time‐of‐flight results for three emitting species from surfaces at different temperatures are consistent with a thermal model for evaporation.

Journal ArticleDOI
01 Jan 1975
TL;DR: In this paper, a linear spark is used as the energy source and the complete time history of the energy deposition is determined by monitoring the current and voltage across the spark gap, where the duration and the energy of the spark are controlled via the R-L-C of the circuit.
Abstract: The present paper describes the current results of our continuing study of the direct initiation of unconfined detonations in a gaseous explosive mixture. A linear spark is used as the energy source and the complete time history of the energy deposition is determined by monitoring the current and voltage across the spark gap. The duration and the energy of the spark are controlled via the R-L-C of the circuit. Both oscillatory as well as single pulse discharges are used. In obtaining a single pulse discharge, a long exploding wire is used to block all but the first peak of an otherwise oscillatory discharge. The explosive mixture used throughout is stoichiometric oxy-acetylene at a representative initial pressure of 100 torr, although one case with p o =50 Torr is included for comparison. The flow structure generated by the discharge is monitored via single frame laser interferometry and multiframe and streak schlieren photography with a TRW image converter camera. The results indicate that for stoichiometric C 2 H 2 -O 2 at p o =100 Torr, the critical energy for direct initiation ranges from 0.3 to 8 joules/cm corresponding to an average power from 0.24 to 0.06 megawatt/cm, respectively. It is found that the critical energy depends on the average power density of the source in that it decreases with increasing power density. These appears to be a limiting critical energy of about 0.3 joules/cm as the power density approaches infinity. The maximum power of the ignition source in all cases is of the order of 10 6 watts/cm corresponding to peak Mach numbers M s > 7.0. This suggests that a sufficient though not a necessary condition for direct initiation might be that the source must be sufficiently powerful to generate a shock wave of the order of the Chapman-Jouguet Mach number of the explosive. The early-time hydrodynamic flow structure generated by the discharge is found to depart from that of the ideal blast wave theory. The energy-time profile, at least for the initial stages, is found to be given by a power law E=Bt α . Modelling the current sheet as a piston it is found that the shock trajectory determined from the energy-time profile agrees fairly well with that from actual measurements from the schlieren records.

Journal ArticleDOI
TL;DR: In this article, the second harmonic of the ruby laser radiation was used as the pump wave and the laser action was achieved when the longitudinal pump power density was 80 MW/cm2.
Abstract: Some parameters of a POPOP vapor laser were determined. Second harmonic of the ruby laser radiation was used as the pump wave. The laser action was achieved when the longitudinal pump power density was 80 MW/cm2. The vapor temperature was varied from 265 to 310°C.

Journal ArticleDOI
TL;DR: In this article, an experimental investigation was made of the interaction of λ = 10.6 μ laser pulses with graphite and Duralumin, the power density of the laser pulses was 1-5 MW/cm2 and the air pressure during irradiation was 0.5-760 mm Hg.
Abstract: An experimental investigation was made of the interaction of λ = 10.6 μ laser pulses with graphite and Duralumin. The power density of the laser pulses was 1–5 MW/cm2 and the air pressure during irradiation was 0.5–760 mm Hg. The duration of the laser pulses was ~3.3 μsec and the diameter of the irradiated spot was 15 mm. Throughout the investigated range of power densities and air pressures, the emission spectra of plasma jets resulting from the interaction between laser pulses and the investigated targets were quite similar to the spectrum of laser sparks in air. The brightness temperature of the plasma jets was independent (to within the limits of experimental error) of the target material and was governed by the laser density. The measured values of the velocity of propagation of the luminous jet front at atmospheric pressure were in satisfactory agreement with those calculated from the theory of optical detonation but the rise of the front velocity with decreasing pressure was slower than predicted by this theory.

Journal ArticleDOI
TL;DR: In this article, the authors describe the technique used to monolithically interconnect TRAPATT diodes in an array, resulting in a diode having low inductance interconnection and integrated heat capacitance which is necessary for long pulsewidths.
Abstract: This short paper is a description of the technique used to monolithically interconnect TRAPATT diodes in an array--resulting in a diode having low inductance interconnection and integrated heat capacitance which is necessary for long pulsewidths. For given power dissipation density and pulse length, the transient temperature rise in the diode decreases with the diameter. The reduction in diode diameter, however, leads to reduced power output. To take advantage of the reduction in temperature rise of small-size diodes while maintaining a large power output, a multiple-diode structure, monolithically interconnected, was fabricated. Pulsewidth operation of 50 mu s has been achieved at a dissipation power density as high as 200 kW/cm/sup 2/, whereas the dissipation density must be reduced to 100 kW/cm/sup 2/ for the same total-area single-disk diode to operate reliably at 50 mu s.

Journal ArticleDOI
TL;DR: In this paper, an electric discharge CO mixing laser is described in which N2 is vibrationally excited in a discharge and then mixed with cold CO providing laser action between 5.0 and 5.8 μ in a low-pressure high-Mach number channel.
Abstract: An electric‐discharge CO mixing laser is described in which N2 is vibrationally excited in a discharge and then mixed with cold CO providing laser action between 5.0 and 5.8 μ in a low‐pressure high‐Mach‐number channel. Results of experiments with a 21‐cm‐wide 1.3‐cm‐high channel are described. Maximum laser power obtained is 720 W corresponding to an efficiency of 7% and a specific power of about 21 kW (kg/s)−1.


Journal ArticleDOI
TL;DR: In this paper, an electron gun and associated electron optics were developed to provide the capability for electron-beam machining of high-density patterns in metal surfaces for information storage, and two companion papers by A.B. El-Kareh and Lynwood Swanson were presented.
Abstract: This paper describes an electron gun and associated electron optics developed to provide the capability for electron‐beam machining of high‐density patterns in metal surfaces for information storage. It is presented with two companion papers by A.B. El‐Kareh1 from the University of Houston and Lynwood Swanson2 from the Oregon Graduate Center. We omit certain aspects of the memory system such as analysis of the recording process and the readout considerations. Very briefly, to machine evaporatively at densities of 1010 bits/cm2 and at rates of 107 bits/sec requires a power density greater than 107 W/cm2 at voltages of 5000 V or less with careful selection of target material. Low voltage reduces the scattering range of electrons and high power density produces the high temperatures required for machining in the face of high rates of heat flow encountered with very small heated volumes.The electron gun employs a heated field‐emission cathode capable of good angular confinement of emission and low energy spre...

Journal ArticleDOI
TL;DR: In this article, an investigation of the conversion of infrared into visible radiation in an LiNbO3 crystal was made by mixing infrared radiation with that produced by a pulse ruby laser.
Abstract: An investigation was made of the conversion of infrared into visible radiation in an LiNbO3 crystal. This was done by mixing infrared radiation with that produced by a pulse ruby laser. Infrared radiation of wavelengths 1.6-3 μ was converted by the ooe interaction using different phase-matching angles. A quantitative dependence of the converted-radiation power on the laser pump power was obtained. The converted-radiation power reached saturation for a pump power density of 5 MW/cm2 when the phase-matching angle was 90° and the conversion took place in a 2-cm long crystal.

Journal ArticleDOI
01 Nov 1975
TL;DR: In this article, Ni-Cr resistors on glazed alumina substrates, hermetically sealed in a dry nitrogen atmosphere, survive and remain stable when subjected to power densities greater than 2000 W/in2.
Abstract: Untrimmed Ni-Cr resistors on glazed alumina substrates, hermetically sealed in a dry nitrogen atmosphere, survive and remain stable when subjected to power densities greater 2000 W/in2. Large (>7 × 10−4in 2 ) resistors with standard top-hat trimming fail at less than 1000 W/in2 due to hot spots, however, a change in trim line configuration results in stable resistors at greater than 1200 W/in2. Resistance-time characteristics depend on mean resistor temperature, which increases (at a given power density) as the square root of resistor area. Results predict, e.g., that all resistors in a 3/8 × 3/8 × 0.080 inch (0.5W) package can be powered at 2000 W/in2 for several years before a 1 percent resistance change is experienced. The resistor area for such a configuration, 2.5 × 10−4in2, is 50 times less than that required with the present power density design value of 40 W/in2. Resistors deposited on unglazed alumina are even more stable than those deposited on glazed alumina because of their lower operating temperature.


Book ChapterDOI
01 Jan 1975
TL;DR: In this article, a mechanism to adjust the cross-section of the arc column of a cold cathode P.I.G. ion source has been developed, which can adjust the electron flux density over a wide range with a fixed ion source power.
Abstract: A mechanism to adjust the cross-section of the arc column of a cold cathode P.I.G. ion source has been developed. The cross-section of the plasma column, and therefore the electron flux density can be adjusted over a wide range with a fixed ion source power. We have achieved in producing an arc column with power density up to about 370 kW/cm2 and about 140 kW/cm3. With this ultra-high power density, a great improvement on ion production has been obtained. The peak beam currents of the doubly charged He-3 and He-4 have been increased, from 150 μA to 750 μA and from 50 μA to 400 μA respectively, using our compact cyclotron. **



Journal ArticleDOI
TL;DR: In this paper, a tunable (λ=720-970 nm) laser system utilizing organic dye solutions was built and investigated, which consisted of an oscillator with a dispersive resonator (diffraction grating) a prism telescope, and a single-pass power amplifier using the same dye solutions.
Abstract: A tunable (λ=720–970 nm) laser system utilizing organic dye solutions was built and investigated. The system comprised an oscillator with a dispersive resonator (diffraction grating) a prism telescope, and a single-pass power amplifier using the same dye solutions. The system was excited with a Q-switched ruby laser. When the excitation power was divided in the ratio 1:4 between the oscillator and amplifier, the gain of the system as a whole was 25. The width of the output spectrum was 1–4 A. The radiation was emitted in the form of 0.25 J pulses of 20 nsec duration. The radiation power density reaching the grating was 0.6 MW/cm2. The construction of the system should make it possible to increase the angular brightness of the radiation and to reduce the modulation of the spectral-energy tuning characteristic.

01 Mar 1975
TL;DR: In this article, a program computes specific power output, specific fuel consumption, and cycle efficiency for power systems having any number of shafts up to a maximum of five and maximum temperatures no higher than about 2000 K (3140 F).
Abstract: Program computes specific power output, specific fuel consumption, and cycle efficiency for power systems having any number os shafts up to maximum of five. Maximum temperatures should be no higher than about 2000 K (3140 F) because molecular dissociation is not included in stoichiometry.


Journal ArticleDOI
TL;DR: In this article, surface temperatures of ion-bombarded silicon and gallium arsenide were measured using an infrared detector, and the change in temperature depended only on beam power, target material, and sample mounting technique.
Abstract: Surface temperatures of ion‐bombarded silicon and gallium arsenide have been measured using an infrared detector. Ion beams of N+, N+2, O+, O+2, C+, CO+, and H+ were used at energies from 1–2.0 MeV and at current densities up to 12 μA⋅cm−2. No temperature dependence was found on ion species, energy, or current. The change in temperature depended only on beam power, target material, and sample mounting technique. With proper mounting temperature increases of 20 °C for silicon and 65 °C for gallium arsenide were observed for a beam power density of 1.0 W⋅cm−2.