Showing papers on "Power density published in 1984"

Cascaded pyroelectric energy converter

Abstract: A regenerative pyroelectric converter employing multiple staging has been constructed and tested. Operating between the temperatures of 150°C and 180°C the device converted heat into electrical energy. Measurements of the conversion efficiency and power density as functions of frequency (0.05 to 0.3 Hz) are reported. The converter's maximum power density was 33 Watts per liter of pyroelectric ceramic at 0.26 Hz.

Numerical analysis of thermomagnetic generators

Abstract: Thermomagnetic generators allow direct conversion of heat energy to electrical energy. Temperature cycling about or near the Curie temperature causes changes in magnetization, resulting in time variant magnetic flux and induced voltage in a surrounding conductor. Numerical analyses of regenerative thermomagnetic generators with perfect regeneration have been performed for three working materials: iron, gadolinium, and Ho69Fe31. Power density above 20 W/kg of shunt material and efficiency approaching Carnot limits are possible over temperature differences of 50 K. Analytical studies performed during the 1950s predicted maximum power density less than 7 W/kg and efficiency less than 1% for nonregenerative cycles.

Inertial confinement fusion: Review and perspective

Abstract: Inertial Confinement Fusion (ICF) refers to the extraction of energy from fusion reactions ignited in small fuel pellets by the deposition of energy at extremely high power. The pellets of thermonuclear fuel, nominally deuterium and tritium, are compressed to densities on the order of one thousand times liquid density before the center reaches ignition temperature and burn propagates outward. Each pellet will produce an energy yield the equivalent of hundreds of pounds of explosive. For such a system to be a potential producer of electric power, it is necessary that an efficient source of sufficient power density and coupling properties to drive the implosion be developed. A target capable of producing high gain from this deposited power must be designed and manufactured. And a reactor which effectively contains the explosions and transfers the energy to usable form must be built. This paper surveys progress in ICF research in these areas from 1972 through 1983.

Method and apparatus for generating short intensive pulses of electromagnetic radiation in the wavelength range below about 100 nm

Abstract: In a method and an apparatus for generating a hot plasma which emits elecmagnetic radiation in the wavelength range below about 100 nm in a predetermined volume, in which a laser radiation pulse of short duration with sufficient energy and power density is focused into the volume containing a target material, the laser radiation energy which is necessary for generating the plasma emitting the radiation is radiated into the target volume by a focused laser radiation pulse which is shorter than one picosecond. The method may be used in ASE X-ray laser comprising an axicon focusing optics.

Picosecond degenerate four‐wave mixing through orientation and concentration gratings in GaAs

Abstract: We report the observation of degenerate four‐wave mixing in GaAs above the band gap, using tunable picosecond pulses in the 1.53–1.61‐eV region. A very fast contribution due to orientational gratings of electron‐hole pairs is isolated with orthogonally polarized beams. This is observed for incident intensities down to 5 MW/cm2, i.e., two orders of magnitude lower than recently reported for germanium. Even at this relatively low power density, higher order effects are important, as evidenced by the power dependence of the conversion efficiency.

Application of magnetic wedges to large motors

Abstract: Although high output power density can be achieved in electrical machines by increasing airgap flux density, this also increases tooth ripple flux density with a subsequent increase in pole surface loss. This loss, however, can be reduced with magnetic wedges. This paper describes the calculation of pole surface losses and ripple flux density, and the effect of magnetic wedges on the characteristics of practical motors is shown experimentally.

On fluctuations and transients in injection lasers

Abstract: A new computer model of the semiconductor injection laser is described. The electron-photon interactions are introduced using a Monte Carlo technique in combination with multimode rate equations to compute laser output versus time and to compute output power probability density. Laser turn-on initially in a side mode, followed by evolution to the normal equilibrium modal power distribution, is shown to be intrinsic and a natural consequence of fluctuations in the modal powers at the moment the laser passes through threshold. Calculations of fluctuations in the equilibrium power levels show that occasional dropouts of the main-mode power are also a natural consequence of electron-photon interactions. Reduction in equilibrium fluctuations and in turn-on fluctuations can be achieved by increasing the laser power-output level, by increasing the mirror reflectivities, and by decreasing the laser length. This work indicates that conventional injection lasers must be operated at or above the 1 mW level in order to assure an error rate of 10-9in digital systems. The well-known transition from thermal-noise statistics below threshold to Poisson statistics well above threshold is still evolving in the 0.5-2 mW region in the injection laser.

Low temperature growth of silicon dioxide on silicon

Abstract: A low temperature, high power method of plasma oxidation for silicon dioxide films is disclosed. The method includes the use of magnetron electrodes which effectively increase the power density of the plasma. The effective power density should be between 1 and 15 Watts/cm2 and preferably about 6 Watts/cm2. By maintaining the substrate temperature below about 300° C., and preferably at about 130° C., it has been found that a high quality silicon dioxide film up to about 1000Å in thickness is grown. The films produced by this process have an excellent interface with the silicon, good electrical properties and good density.

Experimental observations of nonlinearly enhanced 2ωUH electromagnetic radiation excited by steady‐state colliding electron beams

Abstract: Counterstreaming large-diameter electron beams in a steady-state laboratory experiment are observed to generate transverse radiation at twice the upper-hybrid frequency (2omega-UH) with a quadrupole radiation pattern. The electromagnetic wave power density is nonlinearly enhanced over the power density obtained from a single beam-plasma system. Electromagnetic power density scales exponentially with beam energy and increases with ion mass. Weak turbulence theory can predict similar (but weaker) beam energy scaling but not the high power density, or the predominance of the 2omega-UH radiation peak over the omega-UH peak. Significant noise near the upper-hybrid and ion plasma frequencies is also measured, with normalized electrostatic wave energy density W(ES)/n(e)T(e) approximately 0.01.

Controlled slow Q-switch

Abstract: By applying to a laser Q-switch a staircase-shaped control signal, a plurality of laser pulses are emitted with controlled energy and time separation. Compared with conventional Q-switching, the invention enables the laser to emit pulses with shorter time intervals, narrower linewidths, higher output energy, and more uniform power density across the laser beam cross section. The apparatus and method are particularly well-suited for use with low-gain lasers, such as alexandrite.

Pulsed laser evaporation of Cd3As2

Abstract: A pulsed Nd:yttrium aluminum garnet (YAG) laser, power density 4–10×107 W/cm2, was used to prepare thin films of Cd3As2 by evaporation onto room‐temperature substrates. The net deposition rate was 105 A/s. The film microstructure was composed of amorphous agglomerates, 600–2000 A in size. The films obtained with power density 7–10×107 W/cm2 were stoichiometric and they had electron concentrations of 2.6–10×1018 cm−3 and electron mobilities of 210–520 cm2/Vs at 300 K.

Nonabsorbing-mirror (NAM) CDH-LOC diode lasers

Abstract: CDH-LOC lasers with lateral and transverse mode control in nonabsorbing mirror regions are realised by a single etch-and-regrowth cycle. The maximum achieved peak-pulsed output power (100 ns) and catastrophic-optical-damage (power-density) levels are 1.5 W and (20–30) MW/cm2, respectively. A linear power density of 200 mW/μm is reached at catastrophic damage. Fundamental-mode operation is obtained to 80 mW in narrow beams (θ∥≅7°; θ⟂≅15°).

Pulsed heating of semiconductors

Abstract: A new approach in temperature calculations for a semiconductor wafer subjected to pulsed heating with intense light is developed. The heating processes are distinguished as adiabatic ( 10−2s) whereas the last includes transient and steady-state (isothermal) phases. Thermal flux and heat balance regimes being the most practically important ones are analysed in detail for Si, Ge, GaAs, InSb heated with ruby laser, xenon and halogen lamp rediation. Temperature profiles as well as their time evolution are numerically calculated for semiconductor wafers 200 to 800 μm of thick exposed to an energy density of 5 to 150 J/cm2 in the millisecond range and a power density of 5 to 65 W/cm2 in the pulse duration interval of seconds. [Russian Text Ignored].

New power-density calculation method by three-dimensional finite elements

Abstract: A new method to calculate the absorbed power density in closed microwave systems is presented. The method, which is based on the use of a dual variational principle and three-dimensional finite elements, extracts more information from the field solution than a previously published method. The calculation of the total incident and reflected power in a microwave cavity is discussed.

A 900 MHz 100 W VD-MOSFET with silicide gate self-aligned channel

Abstract: A planar vertical double-diffused field-effect transistor (VD-MOSFET) that can deliver maximum output power of 100 W with 8-dB gain at 900 MHz has been developed. Silicide gate (MoSi 2 ) is employed for the reduction of gate series resistance. Also, the silicide is used as a shield plate beneath the bonding area of the gate to reduce the feedback capacitance Cgd. One-micron-long self-aligned channel is formed by using the gate as a mask against the double diffusion of boron and phosphorous. Power gain is increased by 3 dB due to the decrease of the feedback capacitance Cgd, when the shield plate is grounded. Parallel operation of the MOSFETs has been successfully achieved to deliver maximim output power of 100 W CW with 8-dB gain and 46 % drain efficiency at Vds = 45 V and f = 900 MHz in a common-source, push-pull configuration. Power density is 11 W/mm2, twice as high as that of conventional lateral MOSFETs.

Charged particle spectra from U-235 and B-10 micropellets and slab coatings

Abstract: A novel method of utilizing fluorescence generated from the products of nuclear reactions offers the prospect of compact, high efficiency, multi-megajoule lasers. To overcome the problems associated with traditional laser (or energy converter)-fissile material interfaces, such as a uranium coating (low power density and low efficiency) or a gaseous uranium compound (low power density and deleterious effects on the laser kinetics and photon transport), a method suggested elsewhere of employing a reactor using a uranium aerosol fuel, interspersed with a fluorescer medium, is briefly reviewed. The charged particles produced by nuclear reactions in the fuel produce fluorescence in the core region of the reactor, through interactions with the fluorescer. This fluorescence can then be concentrated, to increase the effective power density in the laser medium, and used to drive a photolytic laser.One key issue in the above process is the charged particle spectrum from the fissile aerosol. These issues can be addressed theoretically based on the Dirac chord length distribution technique and an Arcen's function. The charged particle spectrum from a UO2 coating has been generated and benchmarked with the experimental data of Kahn et al., and Redmond et al. Agreement is generally good except near the end of the fission fragment tracks. The validity of this simple technique in approximating the rate of ion energy loss lends confidence to the generation of fission fragment spectra for other geometries (i.e. spherical in which transport efficiencies of over 60% appear achievable) using U, UO2 and U3O8. Work is also extended to the case of B-10 in a variety of configurations which are frequently used in modern energy conversion experimental devices.

Nearfield pressures and surface intensity for cylindrical vibrators

Abstract: A numerical approach is presented to evaluate the acoustic nearfield of cylindrical vibrators with specified harmonic radial velocity distributions The approach is based on the use of a combined Green’s function and FFT method The acoustic field is first represented in terms of a Fourier transform of the specified radial velocity A normalized axial power density at the surface of the vibrator is then introduced This quantity provides a useful measure of the local power transfer into the fluid per unit length of the vibrator The resulting spectral representation of the acoustic field and power density can be rapidly evaluated via the use of FFT methods to obtain the spatial characteristics of the acoustic field and the local power transfer into the fluid Numerical results are presented to illustrate the spatial characteristics of the acoustic fields and power density of finite length vibrators with axisymmetric and nonaxisymmetric distributions

Dynamical Aspects of Pulsed Laser Annealing of Ion-Implanted Silicon

Abstract: The transient reflectivity of ion-implanted silicon during picosecond and nanosecond pulsed laser annealing was measured by using probe light of various wavelengths. The threshold and energy range for annealing were found to be determined by the incident energy density (J/cm2) on the surface but not by the power density (W/cm2), and were independent of whether picosecond or nanosecond pulses were used. The characteristics of picosecond pulsed laser annealing were similar to those of nanosecond pulsed laser annealing. No differences in the duration of the enhanced reflectivity at various probe wavelengths were observed, and the enhanced reflectivity had the same value of ~70%. The experimental results obtained are consistent with calculations based on the surface melting model. It is pointed out that the plasma model cannot explain the experimental results.

ICRF heating experiments on JIPP T-II

Abstract: Data of JIPP T-II ICRF heating experiments are presented. The experiment covers three typical cases: the low-concentration hydrogen minority case, the high-concentration hydrogen minority case, and the 3He-minority case. The best heating efficiency is obtained for the 3He-minority case. It is shown through power balance analysis that the two H-minority cases are different in the wave energy deposition profile. The difference is explained by the presence of a local cavity mode in the high-concentration minority case. The ion temperature stops rising at a power density level of 0.65 W-cm−3 for the hydrogen minority experiments. No such deterioration is found in the case of the 3He minority experiment up to a power density level of 0.45 kW-cm−3. This is the maximum possible to attain within the maximum power injection (180 kW) up to which the experiment is conducted. An analytic solution of the Fokker-Planck equation is derived in order to interpret the deterioration of the heating efficiency.

Time Resolved Surface Temperature Measurements of the DITE MkII Bundle Divertor Target Plate Using a Scanning Infrared Camera

Abstract: The DITE tokamak has a bundle divertor capable of operating in the maximum toroidal field of 2.7 T. A scanning infrared camera with a framing rate of 50 f.p.s. has been used to determine the power and power density at the divertor target. For discharges with 1.4 MW of neutral injection, peak diverted powers of nearly 400 kW were observed during the neutral injection period, representing 24% of the total input power. Power densities on the ion drift side of the target of up to 30 MW m/sup -2/ were measured for these discharges. Discharges without neutral injection show a maximum power diversion when the gas puffing is switched off.

Guided-Wave Characteristics And Optical Damage In LiNb0 3 Waveguides

Abstract: High power optical performances of Ti-indiffused and ion-exchanged waveguides were investigated and discussed. It was experimentally confirmed that Ti-indiffused waveguide suffered a serious optical damage at the output power density less than 0.1 mW/mm at A = 0.6328 pm. For x-propagating guided waves in y-cut crystal, the throughput decay time, by which we could characterize the dependences of optical damage, was revealed to be inversely propor-tional to square of initial guided power, P2, for TE modes, and to P3 for TM modes, and also confirmed to increase with an exponential function of wavelength λ. No optical damage was found for z-propagating guided waves. Proton-exchanged waveguides exhibited to have a good damage resistance. Their surface acoustic wave(SAW) performances, however, were found to be degraded; an IDT's insertion loss of 45 dB was measured, which was much larger than 13 - 14 dB available for Ti-indiffused waveguides. According to the experimental results of infrared absorption spectra, we speculate that the deterioration of SAW performances is attributed to the formation of a HNbO3 phase. A preliminary study using electron spin resonance(ESR) at 77 K provided us a good evidence of the close relation between impurities such as iron and free electrons in the crystal under UV light irradiation.

Studies of Photoluminescence Intensity in the InP/InGaAsP/InP Double Heterostructure

Abstract: Photoluminescence intensity and spectrum of the InGaAsP layer in the double heterostructure with either n-InP/n-InGaAsP or p-InP/n-InGaAsP are investigated over a wide range of excitation power density 10-1–104 Wcm-2 by using a Nd:YAG laser with a wavelength of 1.064 µm transparent to the top InP layer. From analysis of photoluminescence intensity, an interface recombination velocity smaller than 2.5 cm s-1 is estimated. It is found from photoluminescence spectra that carrier temperature becomes higher than lattice temperature at high excitations. The excitation power dependence of photoluminescence intensity of samples with a p-n junction differs from that of samples with an n-n junction. The former shows a low internal quantum efficiency at low excitations and subsequent rapid recovery with increasing excitation power, while the latter shows a linear dependence of photoluminescence intensity over a wide excitation range.

Backing plate for laser working

Abstract: PURPOSE:To reduce the power density of a beam with a small volume by disposing a fume suction port, and a reflection surface and absorption surface for a beam in the cavity under the beam working part. CONSTITUTION:A part of a laser beam 10 transmits the material 12 to be worked and the beam 10 is irradiated directly to the lower side where there is no material 12 in the stage of working the material 12 in a beam working part 14 by the condensed beam 10. The transmitted or irradiated beam is reflected and spreaded in a lateral direction on a reflection surface 22 by which the reflected light is absorbed on an absorption surface 26. The surface 26 does not have a perpendicular wall surface and disperses and absorbs the beam 10 in the widest possible area. The power density of the beam 10 is decreased with the small volume even if said powder density is high.

Parametric Amplification and Oscillation

Abstract: Efficient parametric amplification and oscillation in the optical frequency regime require large pump intensities along a considerable interaction length. Due to the confinement of the optical power within the small cross section of a waveguide, diffraction is avoided and a high power density can be generated with a relatively low input power. Provided the waveguide attenuation is low a large optical intensity can be maintained over a considerably longer interaction length than in bulk optics.

Electrode Design for a Magnetically Stabilized Glow Discharge

Abstract: The operational characteristics of a magnetically stabilized glow discharge are investigated for several different experimental electrode configurations. In this parametric study, successive geometries were designed to accommodate and/or control specific aspects of the plasma glow process. In this manner, an electrode structure which optimizes discharge stability and promotes glow uniformity over an extended active volume, was ultimately achieved. The study teaches a promising new technique for significantly increasing the power density of high power gas lasers. Experimental data is in excellent correlation with predictions provided by a previous numerical study of this magnetic stabilization process.

Temperature Distribution Measurement of Laser Produced Plasma by X-Ray Photodiode Array

Abstract: A multi-slit camera with an X-ray photodiode array has been developed to measure the electron temperature of a laser produced plasma. The fourth harmonic of Nd: glass laser output is irradiated on an aluminum plane target with a power density of 3×1014 W/cm2. The camera is set to view the plasma side. The profiles of X-ray intensity are obtained immediately. Using Abel inversion, the spatially resolved electron temperature distribution with 300 eV at the center is calculated by the absorption method assuming the Maxwellian distribution of free electrons.

Manufacture of photoconductive element

Abstract: PURPOSE:To enable to control the uptake amount of oxygen atoms in an amorphous Si in the first photoconductive layer to a necessary quantity by a method wherein the power impressed to generate a plasma state is made smaller in forming the first photoconductive layer than the other case, when a photoconductive element composed of the multi-layer structure of the first photoconductive layer containing oxygen and the second photoconductive layer is manufactured by the plasma state of a gas which contains silicon. CONSTITUTION:The first photoconductive layer 27 is formed to film on a substrate 12 by impressing a high frequency power of the power density at 0.0424W/cm under SiH4 gas and O2 gas, a high frequency power is impressed at the power density of approx. 1.7W/cm by removing the O2 gas, thus the amorphous Si layer 28, the second photoconductive layer, is formed to film, and next a SiO2 film 29 is formed to film under the same condition as the beginning. Such a method enables a charge generation layer 28 to function as a photoconductor by receiving light and then generating charges, accordingly the first and third layers 27 and 29 can obtain dark resistance at approx. 10 OMEGAcm and surface potential at approx. 500V, and therefore a contrast necessary in case of the use for electronic-photography purpose can be obtained.