Showing papers on "Power density published in 1986"

Computer modeling of heat flow in welds

Abstract: This paper summarizes progress in the development of methods, models, and software for analyzing or simulating the flow of heat in welds as realistically and accurately as possible. First the fundamental equations for heat transfer are presented and then a formulation for a nonlinear transient finite element analysis (FEA) to solve them is described. Next the magnetohydrodynamics of the arc and the fluid mechanics of the weld pool are approximated by a flux or power density distribution selected to predict the temperature field as accurately as possible. To assess the accuracy of a model, the computed and experimentally determined fusion zone boundaries are compared. For arc welds, accurate results are obtained with a power density distribution in which surfaces of constant power density are ellipsoids and on radial lines the power density obeys a Gaussian distribution. Three dimensional, in-plane and cross-sectional kinematic models for heat flow are defined. Guidelines for spatial and time discretization are discussed. The FEA computed and experimentally measured temperature field,T(x, y, z, t), for several welding situations is used to demonstrate the effect of temperature dependent thermal properties, radiation, convection, and the distribution of energy in the arc.

A Model for the Bulk Plasma in an RF Chlorne Discharge

Abstract: A model has been constructed to describe the electrical characteristics of the central bulk plasma region in a 13.56-MHz parallel-plate discharge in chlorine at pressures of about 1 torr. This region is modeled as a volume-controlled plasma with the electron balance dominated by single-step electron-impact ionization and attachment and with the electron energy distribution function in equilibrium with the local instantaneous electric field. Relationships between the ionization frequency, the attachment frequency, the electron drift velocity, and the electric field are provided by solutions of the Boltzmann equation for mixtures of Cl2 and Cl which result from Cl2 dissociation. From a measured current waveform and Cl2/Cl density ratio, the model generates the local electric-field waveform, the time-varying electron density, and the power density in the central portion of the bulk plasma. The calculated time-averaged power input per unit discharge length compares well with experimentally determined values.

Novel process for direct conversion of free energy of mixing into electric power

Abstract: Direct conversion of salinity gradients into electric power as well as production of an acid and a base, simultaneous to generation of electricity, was investigated. Devices that combined features of an electrodialytic pile with those of fuel cells or of electrochemical half cells were designed. Electrodes of the electrochemical half cells were restored to their initial condition by simple reversal of the flow pattern. Fuel cells in the investigated system used water as the fuel and air as the oxidant. Energy extracted from salinity gradients at power density of up to 1 W/m/sup 2/ of the membrane yields up to 0.6 MW of electric power per m/sup 3//s of river or brackish water. Sodium hydroxide is obtained in an amount which corresponds to the number of coulombs of electricity generated in the process. Part of the produced HCI is, however, lost.

High-efficiency millimeter-wave GaAs/GaAlAs power HEMT's

Abstract: The power, gain, and efficiency of 0.5-µm gate-length, 75- and 50-µm gate-width multiple heterojunction high electron mobility transistors (HEMT's) have been evaluated from 10 to 60 GHz. At 10 GHz, with a source-to-drain voltage as low as 2.4 V, the device delivers a power density of 0.37 W/mm with 13.4-dB gain and 60.8-percent efficiency. At 60 GHz, a 50-µm device gave 0.4 W/mm with 3.6-dB gain and 14-percent efficiency. The power density and efficiency of these 0.5- µm gate-length HEMT's above 40 GHz are the best reported for a three-terminal device. Fundamental frequency oscillations up to 104 GHz were observed when a device was bonded as a free-running oscillator.

Transient performance investigation of a space power system heat pipe

Abstract: Start-up, shut-down, and peak power tests have been conducted with a molybdenum-lithium heat pipe at temperatures to 1500 K The heat pipe was radiation coupled to a water cooled calorimeter for the tests with rf induction heating used for the input to the evaporator region Maximum power throughput in the tests was 368 kw corresponding to a power density of 23 kw/cm/sup 2/ for the 14 cm diameter vapor space of the annular wick heat pipe The corresponding evaporator flux density was approximately 150 w/cm/sup 2/ over an evaporator length of 40 cm at peak power Condenser length for the tests was approximately 30 m A variable geometry radiation shield was used to vary the load on the heat pipe during the tests Results of the tests showed that liquid depletion in the evaporator region of the heat pipe could occur in shut-down and prevent restart of the heat pipe Changes in surface emissivity of the heat pipe condenser surface were shown to affect the shut-down and re-start limits 12 figs

Nonlinear Guided Waves

Abstract: Since its inception in the 1960s, nonlinear optics has led to a rich variety of wave-mixing interactions that have applications to basic materials research [1–2], to the generation of new frequencies [1], and most recently to all-optical signal processing [3]. In general, nonlinear optical interactions occur whenever the optical fields associated with one or more laser beams propagating in a material are large enough to produce polarization fields proportional to the product of two or more of the incident fields. These nonlinear polarization fields radiate electric fields at the nonlinear frequency. For some interactions, the generated fields grow linearly with propagation distance under optimum conditions of phase-matching. Typically, the efficiency of any nonlinear optical interaction depends on (1) the product of the power densities of the input and output waves, raised to some power, and (2) the interaction distance raised to some power greater than or equal to unity. Since power density is power per unit area, the efficiency of any nonlinear interaction can be enhanced by reducing the cross-sectional area of the interacting beams. For plane waves this can be achieved by focusing with a lens. There is a tradeoff, of course, because the high power density can be maintained only over the depth of focus of the lens, which limits the effective interaction length.

Magnetic self-compression in laboratory plasmas, quasars and radio galaxies. Part II

Abstract: A model of quasars and their associated jets as phenomena of magnetic selfcompression is presented. Magnetic field self-compression, as observed in laboratory plasma focus devices, results in increases in energy density of more than 108 and in even larger increases in transferred power density. Our model, based on the scaling of these phenomena to astrophysical dimensions, avoids the problems of gravitationallyconfined approaches. It presents a mechanism by which the energy of a quasar is immediately derived from a volume nearly 106 times larger than the observed quasar radiating volume and is ultimately derived from the volume of an entire protogalactic plasma cloud. The model's predictions of quasar energy, radiated power, lifetime, dimensions, density and rotational velocity are in good agreement with observations. Part II of this paper extends the model to radio galaxies and briefly discusses the role of similar self-compression processes in the origin of filamentary super-clusters of galaxies.

High-power high-efficiency stable indium phosphide MISFETs

Abstract: In P MISFETs with gate widths up to 1 mm using SiO 2 as the gate insulator have been fabricated. At 9.7 GHz the highest power output with 4 dB gain was 4.5 W at 46% power-added efficiency corresponding to a power density of 4.5 W/mm of gate width. The maximum power-added efficiency for the same device and frequency was 50% at 3.8 W and 3.8 dB gain. This power is more than 3.5 times the previously reported maximum for InP FETs at 15% higher power-added efficiency and the power per unit gate width is more than three times that of the best GaAs FET. Power output was stable to within 2% over 167 hours of continuous operation.

Frequency stabilized microwave power system and method

Abstract: System and method for applying microwave power of substantially constant frequency and variable power level to a work load. A microwave power source having an operating frequency which varies with power level is operated at a substantially constant power level and frequency. Power from the source is applied to a dummy load, and a portion of the power is diverted away from the dummy load to the work load to vary the amount of power applied to the work load without changing the power level or frequency at which the source is operated.

A 100 GHz gyrotron—results and future prospects

Abstract: High efficiency (~40%) gyrotrons have been built by other workers in the frequency range from 28–70 GHz with output powers of 200 kW or more in pulses of 0 · 1–1 second, and some have operated in CW. In this frequency range, we have developed a single cavity oscillator at 35 GHz. Table 2 includes a summary of results obtained with this tube. Of course, it is required to produce tubes for higher frequencies and higher powers. According to the laws of electron dynamics and electromagnetics in vacuo, simple scaling in frequency requires a scaling in dimensions with invariant voltages, currents, and powers. Most quantities in that case are not invariant, e.g. electric field E ~ƒ, magnetic induction B ~ ƒ, current density J ~ ƒ, power density J ~ƒ2, power density due to electron impact (Pel/S) ~ƒ2,Rf ohmics losses, assuming classical skin effect ~ƒ5/2, and losses in dielectric present complex variation with frequency depending upon their nature. This type of scaling cannot be applied indefinitely to higher fre...

Surface structures produced in 1C–1.5Cr and 0.38C-Ni-Cr-Mo steels by high-power CO2 laser processing

Abstract: The effects of surface high-power laser processing were studied for 1C-1.5Cr and 0.38C-Ni-Cr-Mo steels by changing the incident power density and laser-material interaction time. Both melted and solid-state transformed regions were produced, and studied by means of depth-selective surface Mossbauer measurements, X-ray diffraction analyses, metallogmphy and microhardness measurements. The results are compared with those previously obtained by laser surface-melting of OAC carbon steel, and are discussed with reference to the carbon content in the base alloys as well as the conditions of laser processing.

GaAs/AlGaAs heterojunction MISFET's having 1-W/mm power density at 18.5 GHz

Abstract: The previously reported GaAs/AlGaAs heterojunction MISFET with an undoped AlGaAs layer as an insulator has been further optimized for power operation at upper Ku band. A 300-µm gate-width device generated 320 mW of output power with 33-percent efficiency at 18.5 GHz. The corresponding power density exceeds 1 W/mm. When optimized for efficiency, the device has achieved a power added efficiency of 43 percent at 19 GHz.

Mode-correlation times and dynamical instabilities in a multimode cw dye laser

Abstract: Correlation times of mode amplitudes in a multimode cw dye-laser system have been measured using intracavity absorption spectroscopy The dependence of the mode-correlation times on the spectral power density in the laser cavity has been investigated in detail At low spectral power densities, surprising discontinuities are observed and interpreted as dynamical instabilities in the laser system At high spectral power densities, the mode-correlation time approaches a constant value These observations are described by a system of two nested, self-referential feedback loops explaining the behavior of the laser system The resulting model is discussed within the concepts of generalized multistability and presumably chaotic behavior

Measuring the Quality of High Power Laser Beams

Abstract: The characteristic properties of high power laser beams are the time and spatial dependent power density distribution, the power, the polarization and the so called focusability, d , χ which is the product of beam diameter and beam divergence. These four parameters have a large influence on penetration depth and/or processing speed during material processing as sell 23 on the quality of the processed material. In the following two measuring devices are explained to measure the above mentioned properties of a 5 kW-CO 2 -laser beam with the exception of the polarization degree.

High Performance Monolithic Power Amplifier Using a Unique Ion Implantation Process

Abstract: State-of-the-art X-band power FETs and monolithic amplifiers have been fabricated by a high yield planar process using a unique double-peaked implant profile. A 1-mm FET has achieved 40 percent power added efficiency with 720 mW output power and 6.3 dB gain at 10 GHz. A two-stage monolithic amplifier has delivered 2.2 W output power at 9.5 GHz for a record 0.6 W/mm power density. The monolithic amplifier chips have also achieved 20 percent dc-yield and 5 percent uniformity in /sup I/DSS and /sup V/PO.

Transversely excited atmospheric‐pressure copper‐vapor laser

Abstract: We report the results of the measurements of the performance parameters of the transversely excited atmospheric‐pressure (TEA) copper‐vapor laser (CVL). A specific laser energy density of 36 μJ/cm3 was achieved in an excited volume of 0.6×1×20 cm3. This corresponds to a specific power density of 3.6 kW/cm3 for a 10‐ns pulse. Because of the high buffer gas pressure that can be used in the TEA‐CVL, containment of the copper vapor in the heated zone can be maintained for an extended period, making a sealed system possible.

Power deposition profiles and Poynting vector distribution of phased antenna arrays in the ion-cyclotron resonance heating of a NET/INTOR-type tokamak

Abstract: The heating produced by magnetosonic waves launched from phased antenna arrays in the ioncyclotron range of frequencies is studied for a large tokamak with NET/INTOR-like parameters. The model used combines a 3-D planar, cold-plasma, antenna-plasma coupling code and a 3-D non-circular, toroidal, hot-plasma/ray-tracing code. First, the fractional power absorption of a ray during a single transit through the absorption layer is studied in a D-T plasma indicating total absorption in all INTOR cases except during the initial state characterized by low plasma temperature and density. However, in this case the single-pass wave absorption can be increased considerably by adding a few per cent of hydrogen. Further, complete power deposition profiles and Poynting vector distributions are presented for 'symmetric' and 'antisymmetric' 2 ? 2 antenna array configurations with k||-shaping. Excitation of coaxial modes has, for the first time, been demonstrated explicitly by analysis of the Poynting vector distribution in real space. An antenna configuration with a ?-phasing in the z-direction (such that the radiated power spectrum peaks at k|| 5 m?1) and the choice of 3?/4 long antenna elements with 'symmetric' excitation in the y-direction, are found to produce central RF power deposition profiles in the secondharmonic and minority heating of INTOR. Finally, from a comparison of results for circular and non-circular NET/INTOR plasmas with elongation ? = 1.6, it is found that in the latter wave focusing is greatly reduced and that the power density figures are lower by approximately a factor of 1.9 for the case treated.

A thermal absorber for high power density photon beams

Abstract: The high power density of multipole wiggler radiation from the X-ray ring at the National Synchrotron Light Source at Brookhaven National Laboratory precludes the use of normal incidence water cooled masks and shutters due to high metal temperatures and resulting high stresses and/or deflections and the possibility of cooling water boiling. One way the power density can be reduced is by positioning the absorber surface at a small angle to the beam, a technique first developed by Lawrence Berkeley Laboratory. Finite element analyses results for temperatures, displacements and stresses are presented in this paper for a thermal absorber designed for ultrahigh vacuum operation.

Characterization of radiative efficiency in double heterostructures of InGaAsP/InP by photoluminescence intensity analysis

Abstract: The photoluminescence (PL) intensity of an InGaAsP layer has been investigated as a function of excitation power density over a wide range of five orders. Two samples with n -InP/ n -InGaAsP isotype and p -InP/ n -InGaAsP heterotype doping have quite different excitation power dependences on PL intensity. The heterotype sample has notable nonlinear dependence. The excitation power dependences of PL intensity are theoretically analyzed. The estimated interface recombination velocity of the InP/InGaAsP heterojunction is found to be very low (smaller than a few cm/sec), compared with that of a GaAs/GaAlAs heterojunction. This PL intensity analysis has been applied to study the effect of an InP buffer layer and thermal degradation of radiative efficiency. The effective non-radiative recombination life time has been estimated as about 2×10 −9 s for the double heterostructure with no buffer layer. Annealing in conditions of low phosphorus pressure leads to degradation of radiative efficiency, and the degradation is attributed to decrease in the nonradiative life time in the quaternary layer rather than increase in the interface recombination velocity. Sufficient phosphorus pressure prevents degradation of radiative efficiency. The correlation between PL intensity and output optical power of the light emitting diode has also been investigated. The PL intensity must be measured at high excitation power if it is to accurately predict the output power as a light emitting diode.

High Frequency Excitation of CO2 Lasers

Abstract: In the field of material processing there is an increassing need for compact high power CO2 lasers which are pulsable in the 10- or even 100 kHz range. In d.c.-excited systems compactness is limited by the achievable power density of about 10 Wcm-3, whereas the maximal pulse frequency does not exceed the kHz region.

Energy characteristics of cw gas-discharge lasers utilizing self-terminating atomic transitions. I. Experimental investigation of quasi-cw barium vapor lasers

Abstract: An investigation was made of the characteristics of lasing due to the self-terminating transition 6p1P1–5d1D2 of the barium atom when barium vapor was excited in a quasi-cw discharge. A train of stimulated emission pulses was generated in a longitudinal discharge, the average specific power in a train being ~150 mW/cm3. This figure exceeded the average specific laser output power from pulsed barium vapor lasers. In a hollow-cathode discharge a specific power for quasi-cw lasing of ~20 mW/cm3 was obtained. The discharge parameters needed for quasi-cw lasing were estimated.

Electron gun for surface treatment of materials

Abstract: This paper describes a diode-type plasma electron gun with a carbon fiber cathode for surface treatment of materials. The power density is controlled by varying the current density, which is determined by the distance between the anode and the cathode, which is varied without disruption of the vacuum conditions in the diode. The electron gun has a current density of 100-1600 A/cm/sup 2/ and an electron energy of 100-150 keV.

Manufacture of p-type amorphous silicon thin film

Abstract: PURPOSE:To increase a doping efficiency and to reduce the amount of doped B by a method wherein a mixed gas of diborane and silane is sent into a reaction vessel within a specified range of a mixed gas pressure and a high-frequency power density and a P-type amorphous silicon thin film is made to grow on a ground layer by glow discharge decomposition of the mixed gas. CONSTITUTION:While a reaction chamber is evacuated through an exhaust port 22 by operating pumps 32 and 34, a substrate 14 is set at a temperature of 200-300 deg.C by a heater 12. In this state, B2H6 and SiH4 gases are controlled by a flow controller 26 to be set at values within a range from the case wherein B is not doped to the case wherein the mixture ratio [B2H6]/[SiH4] is about 10 , and they are introduced into the reaction chamber with the entire flow rate set at 300-700SCCM. After the internal pressure is set at a value of 100-300Pa, an RF power density is set at a value of 0.2-0.5w/cm , and glow discharge is generated between the substrate 14 and an external electrode 18, whereby a film is prepared. The growing speed of the film is so high as 1,000Angstrom /min or above. With the increase in a growing speed, a doping efficiency is improved.

Transfer Standards For Energy And Peak Power Of Low-Level 1.064 Micrometer Laser Pulses And Continuous Wave Laser Power

Abstract: For the first time traceable transfer standards have been developed for measuring 1.064 µm laser pulses with duration of about 10 to 100 ns, peak power density of about 10-8 to 10-4 W/cm2, and energy density of about 10-16 to 10-11 J/cm2. These power and energy transfer standards use avalanche (APD) and PIN silicon photodiode detectors, respectively. They are stable and have total uncertainties of about 10%. The system for calibrating them and other devices consists of a cw Nd:YAG laser beam acousto-optically modulated to provide low-level laser pulses of known peak power and energy. With pulse height analyzer readout, the PIN transfer standard system may record each pulse, from which the mean pulse energy and laser stability may be evaluated. With integrating voltmeter readout, this system can measure energy or average power. These pulsed and cw measurement techniques can be extended to the visible and other near-infrared wavelengths.

Application of Two-Dimensional Hadamard Transform to Photoacoustic Microscopy

Abstract: The conventional method of focused laser scanning limits the application domain of photoacoustic microscopy (PAM) because o f the high power density of the illuminating laser beam at the sample surface, H. Coufal et al. have introduced Hadamard Transform ( HT ) technique to photoacoustics for solving this problem in onedimension (1-D). The present paper describes the application of two-dimension ( 2-D ) HT to PAM in both theory and experiment. Our results show that 2-D HT is more effective in improving SNR as well as in reducing the high power density than 1-D HT. The local power density at the sample surface in our experiment is reduced about 1000 times as much as that of the focused laser scanning method. A laminated imaging method by using 2-D HT is presented.

Gas laser with different positional dependent mutual spacings between the electrodes

Abstract: A gas laser which has transverse high frequency exitation and which is improved in efficiency and in power density by the use of a coupling structure which assures a roughly positional independent electrical field strength for each neutral particle density in the full discharge space and this is accomplished with capacitance electrodes (2) between which the discharge space of a laser are arranged in a cavity resonator and wherein the mutual spacings between the capacitive electrodes (2) are positionally dependent and are selected such that they assure that an electrical field strength proportional to the neutral particle density occurs.

Production of coated steel

Abstract: PURPOSE:To improve the performance of a coated steel tool, etc. by using a high-frequency power source and DC power source in combination for a plasma excitation source, maintaining a base material at a negative potential and controlling high-frequency power density, the absolute value of a DC voltage and gaseous atmosphere pressure. CONSTITUTION:The high-frequency power source and DC power source are used in combination for the plasma excitation source to form stable plasma in the stage of coating a hard material onto the surface of the steel base material by a plasma CVD method. The steel base material is maintained at the negative potential by the DC power source so that the positive ions contributing to reaction are preferentially attracted toward the base material surface. The density of the high-frequency electric power to the thrown to the plasma forming space is controlled to 0.01-1.0W/cm , the absolute value of the DC voltage to <=1,500V and the pressure of the gaseous atmosphere to 0.5-5Torr. The plasma CVD coated steel obtd. by the above-mentioned method has the performance which compares favorably with the performance of a PVD coated steel.

Evaluation And Control Of The Properties Of Thin Sputtered Silver Films For Spectrally Selective Coatings.

Abstract: The influence of the deposition parameters on the electrical and optical properties of very thin silver films prepared by magnetron sputtering was studied. To evaluate the film properties a method was used, which is based on simple optical transmission measurements, and was proposed recently by one of the authors /1/. The results show that the specific resistivity, the plasma energy and the optical resistivity of films below 30 nm thickness are very sensitive to deposition parameters as cathode power density. It is concluded that the obtained variations in the optical and electrical properties are related to the density of the sputtered films.

Free Electron Masers for Tokamak Applications

Abstract: Electron cyclotron heating (ECH) has been proposed as the primary heating and current drive source for tokamaks. Other uses of ECH include profile control and stabilization of m = 1 and m = 2 oscillations. The stabilization may be accomplished by steady heating to alter the current profile or by the more efficient alternative of driving current within the m = 1 or m = 2 islands with synchronous ECH. This could result in disruption avoidance, better energy confinement, increased ..beta../sub c/, and higher maximum ohmic heating power density. Advantages of ECH include wave penetration at full density, precise power absorption zones, avoidance of alpha resonances, and simple launching structures. The technology of the free electron maser (FEM) has advanced to where it is now an attractive source on ECH power at reasonable cost. To adapt the FEM concept to a high power, tunable, CW device, TRW has developed a concept that is based on two key ideas: first, the use of a high-quality (low energy spread and low emittance) electron beam of moderate current (< 50 A) and a large-amplitude wiggler ensures high-gain operation with good efficiency. Second, the small-diameter, cylindrical spent beam has a relatively low energy spreadmore » making a highly efficient current and energy recovery system feasible. An FEM experiment using a 3-MeV, 2-A electron beam has demonstrated an energy recovery efficiency of 99%. To advance the FEM for fusion and other applications, TRW is in the process of building a device based on the principles just described.« less