Showing papers on "Power density published in 1985"

Fourfold to threefold transition in diamondlike amorphous carbon films: A study of optical and electrical properties

Abstract: Hard, diamond‐like amorphous carbon films (a‐C) were prepared as a function of sputtering power density by employing dc planar magnetron sputtering of a graphite target in pure argon. Films deposited at 300 K and at increasing sputtering power density in the range 0.25–25 W cm−2 show a transition of optical and electrical properties, with the room temperature electrical conductivity increasing from 5×10−4 to 5 Ω−1 cm−1 and the optical gap decreasing from 0.74 to 0.40 eV. The imaginary part e2 of the complex dielectric function is determined in the photon energy range 0.5–7 eV and shows a clear dependence on sputtering power density. The e2 spectra for a a‐C films possess features typical of amorphous semiconductors. neff, the effective number of valence electrons per carbon atom taking part in optical transitions, is determined via a sum rule operation on e2. Comparisons of neff for each a‐C film with that for crystalline graphite allow the average coordination of the carbon atom to be determined. We observe a systematic four‐fold to three‐fold transition, with the ratio of carbon atoms having four‐fold sp3 configuration (diamond‐like) to carbon atoms with three‐fold sp2 configuration (graphite) varying from 3:1 to 1:1.

Time‐resolved proton focus of a high‐power ion diode

Abstract: An improved understanding of the factors that control the axial focus of applied‐B ion diodes was obtained from time‐resolved diagnostics of ion‐beam trajectories. This resulted in a new selection of anode shape that produced a proton focus of 1.3‐mm diameter from a 4.5‐cm‐radius diode, which is a factor of 2 improvement over previous results. We have achieved a peak proton power density of 1.5±0.2 TW/cm2 on the 1‐TW Proto I accelerator. The radial convergence of this proton beam, defined as the ratio of the anode diameter to focused beam FWHM, is 70. Time‐resolved information about virtual cathode evolution, the self‐ and applied‐magnetic‐field bending, and the horizontal focus of the beam was also obtained. In addition, the diffusion of the magnetic field into the anode plasma is estimated by measuring the horizontal focal position as a function of time. Finally, we discuss the effects of gas cell scattering on the beam focus.

Process for producing by-product oxygen from turbine power generation

Abstract: A method is set forth for the generation of net power and the recovery of by-product oxygen-enriched gas at low power requirements. Air is compressed to elevated temperature and pressure, at least a portion of the air is combusted and a portion of the oxygen is removed from the air or combustion effluent through a membrane or adsorbent before the oxygen lean combustion effluent is expanded through a turbine to recover power for the process and net power.

Electromagnetic applicator for localizing hyperthermia heating in a system

Abstract: An electromagnetic applicator (10) is provided for heating internal biological tissue, such as cancerous tumors, where applicators generate an electromagnetic field propagating across a gap (20) for forming a relative maximum power density adjacent the internal tumor volume. Conductive elements (12, 14) are spaced a predetermined distance to form a gap (20) and power is applied at radio frequencies through a balancing and matching circuit to generate the electromagnetic field which propagates across the gap (20). A plurality of applicators (10) may be placed about a body location to enable the maximum relative power density to be placed at a selected location within the body portion. A radiating dipole antenna (46) may be used to radiate a signal from which transmitted signal parameters are derived for forming a local power density maximum at a location approximated by the radiating dipole antenna (46). A controller (42) provides power source (40) outputs to applicators (10) having the same relative amplitudes and opposite phase angles of signals received from the transmitting dipole antenna (46) at locations approximating the locations of applicators (10) at the desired body location.

Power density spectrum controller

Abstract: A power density spectrum controller circuit which incorporates a programming element in conjunction with a voltage controlled oscillator and which uses spread spectrum techniques to provide a relatively clean output signal having little or no ripple, little or no noise and little or no signature while having a minimum output filtering requirement.

Alkali Metal Thermoelectric Conversion (AMTEC) for space nuclear power systems

Abstract: Performance parameters of the Alkali Metal Thermoelectric Converter (AMTEC) for a 100 kW electric power system have been calculated at four technological levels assuming a heat pipe-cooled nuclear reactor heat source. The most advanced level considered would operate between 1180 K converter temperature and 711 K radiator temperature at 16 percent efficiency, and would weigh 1850 kg with a radiator area of 43 sq m. In addition, electrode research studies for the AMTEC systems have been conducted utilizing an experimental test cell of Bankston et al. (1983) and Mo and several Mo-Ti electrodes. It was found that the Mo-Ti electrodes offered no improvement in lifetime characteristics over the pure Mo electrodes, however, oxygen treatment of a degraded Mo electrode restored its specific power output to 90 percent of its original specific power and maintained this level for 60 hr, thus offering a potential for lifetime stability.

Ray-tracing analysis of ICRH power-deposition profiles in non-circular large Tokamaks

Abstract: Using self-consistent initial conditions obtained from the full-wave solution of the field radiated by an ion-cyclotron resonance heating (ICRH) antenna, the ray-tracing technique is applied to generate r.f. power-deposition profiles in non-circular large Tokamaks such as JET and NET/INTOR. An analytic expression has been used to simulate the shape of the flux surfaces, which fit reasonably well to the numerical solutions of the Grad-Shafranov equation describing the Tokamak equilibrium, by adjusting three free parameters: the flux-surface shift Delta , the elongation ratio kappa and the triangularity parameter delta . For an elliptic INTOR plasma, it is found that the focussing of rays is much reduced and when the absorption layer is located in the center, the r.f. power density figures are lower approximately by a factor of 1.9 compared to that obtained in an equivalent circular case. This reduction in power density is not so significant when the power is deposited off-center, as demonstrated by an example treated for the JET D-shaped plasma.

Deposition of III-V semiconductor materials

Abstract: A low temperature procedure for depositing III-V semiconductor materials that offers the possibility of higher deposition rates together with abrupt junction formation has been found. This process involves the irradiation at a deposition substrate with a high power density radiation source of deposition gases such as organometallic materials, e.g., trimethyl gallium and trimethyl indium. By utilizing a sufficiently high power density, multiphoton processes are induced in the deposition gas that, in turn, lead to advantageous deposited materials.

Low‐energy optical generation and detection of acoustic pulses in metals and nonmetals

Abstract: Acoustic pulses have been generated in both metals and nonmetals using a low‐energy tunable dye laser emitting 6‐ns pulses with 20–210‐μJ energies. The acoustic waveforms have been detected optically with a calibrated laser interferometer having improved signal‐to‐noise ratio. In this fashion, noncontact characterization of nonmetallic, as well as metallic samples of small size, has been shown to be feasible, using a potentially portable system. In addition between the relationship acoustic signal level and incident laser energy (and power density) has been measured for a polyimide‐glass‐fiber composite material.

Transverse-discharge copper-vapor laser

Abstract: A novel transverse-discharge copper-vapor laser has been developed using a flat-plate Blumlein pulse-forming circuit. This copper-vapor laser system generates a current pulse with a fast rise time ( 1 \times 1 \times 20 cm3volume, producing a specific power density of 2.8 kW/cm3. The results of the preliminary measurements of the laser parameters are presented.

Efficient High Power-Density Operation Regime of KrF*-Laser Amplifiers for Fusion Driver

Abstract: The kinetics in electron-beam-excited KrF*-medium is numerically analysed in order to study the dependence of the fundamental laser characteristics on gas constitution, specific pump power and cavity flux. There appears the prospect of the compact fusion driver operating at considerably higher laser intensity (~100 MW/cm2) and higher intrinsic efficiency (~20%) in Kr-rich media at the pump power density of 10 MW/cm3 than in conventional Ar-diluted mixtures.

Study of the saturation effect and output power of optically pumped FIR laser

Abstract: Solutions are presented for the density matrix equation of a six-level optically pumped far-IR laser. Output power density is obtained by an iterative method, and the system's saturation effect is studied by means of numerical calculations. Sets of curves are obtained for laser output vs. length with different pumping detunings and optimum operating pressures. The values obtained are in agreement with published data. 6 references

A High Efficiency I.C.F. Driver Employing Magnetically Confined Plasma Rings

Abstract: We discuss the possibility of achieving energy, power and power density necessary for ICF by magnetically accelerating plasma confined by a compact torus (CT) field configuration. The CT, which consists of a dipole (poloidal) field and imbedded toroidal field formed by force-free, plasma current, is compressed and accelerated between coaxial electrodes by B/sub THETA/ fields as in a coaxial railgun. Compression and acceleration over several meters by a 9.4 MJ capacitor bank is predicted to give a 5.7 cm radius, 0.001 gm CT 5 MJ kinetic energy (10/sup 7/ m/sec). Transport and focussing several meters by a disposable lithium pipe across the containment vessel is predicted to bring 4.8 MJ into the pellet region in 0.5 cm/sup 2/ area in 0.3 ns. The high efficiency (approx.50%) and high energy delivery of the CT accelerator could lead to low cost, few hundred MW power plants that are economically viable.

Acceleration and deceleration method for charged particle

Abstract: PURPOSE: To make it possible that high voltage low current acceleration and low voltage high current acceleration can be performed by the same power supply, by switching the arrangement of a plurality of power supplies arranged for performing high voltage low current acceleration during acceleration of charged particles to the arrangement for low voltage high current acceleration during deceleration thereof through changing the power supply connection. CONSTITUTION: During extracting acceleration, a power supply A is employed for an extracting power supply 5 and two power supplies B connected in parallel to reach other and employed for an accelerating power supply 6. And during extracting deceleration, the power supply A and B connected in parallel to each other are used for a power supply 8 and the power supply B is used for a power supply 9. In the case where the power supplies are employed in forms of aforementioned connections, the power supply 8 operates during extracting deceleration as a power supply of 60kV and 75mA by the power supplies A and B, and the power supply 9 supplies the extracting voltage for a beam 11 applied to an extracting electrode 2 so that an extracting beam current can be increased one and a half times. Furthermore, power supplies of the same size may be used although the extracting beam amount is increased as mentioned above. COPYRIGHT: (C)1987,JPO&Japio

Determination of multiphoton ionization cross sections in focused laser experiments

Abstract: A model is presented for the interaction between a focused laser beam and a gas at low pressure, which allows the determination of accurate multiphoton ionization cross sections. The slope of the curves representing the ion yield vs. the power density of the laser beam, the effective interaction volume and the time of interaction, which are usually taken into account in such a determination, are thoroughly studied. The model is applied to the determination of the multiphoton ionization cross section for krypton.

High power density reactors based on direct cooled particle beds

Abstract: Reactors based on direct cooled HTGR type particle fuel are described. The small diameter particle fuel is packed between concentric porous cylinders to make annular fuel elements, with the inlet coolant gas flowing inwards. Hot exit gas flows out long the central channel of each element. Because of the very large heat transfer area in the packed beds, power densities in particle bed reactors (PBR's) are extremely high resulting in compact, lightweight systems. Coolant exit temperatures are high, because of the ceramic fuel temperature capabilities, and the reactors can be ramped to full power and temperature very rapidly. PBR systems can generate very high burst power levels using open cycle hydrogen coolant, or high continuous powers using closed cycle helium coolant. PBR technology is described and development requirements assessed. 12 figs.

Far-field 2.45 GHz irradiation system for cellular monolayers in vitro.

Abstract: A 2.45-GHz microwave exposure facility was developed for long-term TEM irradiation of cellular monolayers. Culture flasks with cells attached to the inside bottom surface were filled with medium, submerged in a 60 X 60 X 12-cm water bath on the field central axis, and exposed in the far-field 2 m below the ceiling-mounted antenna. A quarter-wave transformer plate increased the power transmitted into the water bath, and treatment temperatures were maintained by closed circulation with an external temperature control reservoir. Power density mapped below the quarter-wave plate indicated uniform TEM fields in the 25 X 25-cm region where flasks were located. With 1 kW of forward power to the antenna, the SAR [W/kg] = 45 exp(-0.607d) where d [cm] is the depth in water at any point within this area.

Experimental study of laser induced decomposition based processing of a brittle plastic, CR-39 (allyl diglycol carbonate)

Abstract: A cw CO2 laser, coupled with an astigmatism free beam focussing mirrors arrangement is used for processing a brittle plastic, CR-39 without producing cracks, vents or chips. The processing is based on the formation of volatile products of laser-induced decomposition in the plastic. Threshold fluence for the decomposition (found to be independent of the power density and beam residence time) in CR-39 atλ=10.6μm is determined to be 25 J cm−2 and the decomposition threshold power density for cw irradiation 2.1±0.5 W cm−2. The depth and width of the tapered laser processed region are observed to increase with power density and beam residence time. The widths attain a steady state value of ∼ 1 mm at beam residence time above 65 ms, for a fixed power density (2.5×104 W cm−2) and sheet thickness (250 μm). Taper angle of the edges decreases with increasing power density and/or beam residence time. The heat affected zone (measured in crossed polarisers) around the processed region is found to extend with increasing beam residence time but remains unaffected on changing power density. The results are discussed in terms of the optical and thermophysical properties of CR-39 and the parameters of the interacting laser beam.

Detection of anomalous plasma resistivity at high RF-power densities

Abstract: In a linear magnetoplasma, excited with RF-waves in the region of the lower hybrid resonance, radial power density profiles are recorded by use of a modulation technique involving time-resolved intensity measurements of He I spectral lines. Computations of these profiles within the framework of a linear fluid description-neglecting temperature and density gradients-show typical geometric structures, which are not verified by the observations. Discrepancies are resolved if anomalous plasma resistivity is taken into account. This behaviour is characterized by an effective collision frequency nu eff for momentum loss, the value of which can be determined by comparing the experimental data with the theoretical predictions. The plasma loading resistances calculated with nu eff are in good agreement with the results of electrical measurements.

Materials Considerations for a High Power-Density Accelerator

Abstract: A 100-mA 50-MeV H- accelerator is being designed at Los Alamos. The accelerating structures will operate at 425-MHz and will consist of a radio-frequency quadrupole (RFQ) to 2-MeV and a drift-tube linac (DTL) from 2 to 50-MeV. Design parameters have been specified to match the maximum operating capabilities of the rf system: 2-ms pulse length and 6% duty factor. The accelerating gradient in the DTL will be 4-MV/m; the maximum electric field will be approximately 1.2 times the Kilpatrick limit. These design parameters are substantially more ambitious than those of the accelerator test stand (ATS). The larger accelerating gradient and increased duty factor will increase the average power density in the DTL to approximately 25 times the design values for the ATS DTL. The increased duty factor will raise the average power density on the proposed RFQ to approximately 6 times the operating values of the ATS RFQ. The instantaneous power density on the drift tubes is predicted to be 60 W/sq cm, and the average power density is predicted to be 4 W/sq cm. These power densities are not excessive, but do represent design challenges in specific areas. Some components where thermal difficulties may be encountered include RFQ vanes, drift tubes, post couplers, slug tuners, rf seals, and tuning bars. That copper will be used on the rf-structure surfaces is not in question. Concern with residual activation and thermal management forces the investigation of materials other than the traditional carbon- and stainless-steel base materials used at Los Alamos.

Analysis of alkali liquid metal Rankine space power systems

Abstract: Space power systems must have both high power density (kW/m/sup 3/) and high specific power output (kW/kg), while maintaining high reliability. Several power source and conversion options are available. A sketch of the Rankine system under consideration is shown. The design for the 100 kWe system analyzed here uses the same basic design concept as described by Jones for a 5 MWe system. In brief, it consists of a uranium nitride fuel pin reactor core with a tungsten/lithium hydride shield. Potassium at approx. 25% quality exits the reactor core. A separator is used to provide potassium vapor (at approx. 99%+ quality) to a full impulse turbine. Liquid from the separator is recirculated back to the core inlet using jet pumps. A heat pipe radiator condenses the vapor exiting the turbine while a separate turbine driven boiler feed pump returns the condensed liquid to the core inlet. Sizes and weights for the various system components were determined using design algorithms or were scaled from previous design studies.

The optimum pumping power for optically pumped FIR lasers

Abstract: The relations between the output power of optically pumped FIR laser and the pumping power were studied theoretically by solving the density matrix equation of four-level system by means of the matrix signal flow graph method. The output power density of FIR laser was calculated by iteration method. A set of curves of output FIR power density against pumping power has been obtained. It has found that every of each curve has a maximum point of which the position is different for different pumping detuning. According the these results we predicted that there would exist an optimum pumping power density for an optically pumped FIR laser with certain pumping detuning. This theoretical results would help us to design the optically pumped FIR lasers.

Some features of the evaporation of magnesium and lead by quasi-cw laser radiation

Abstract: An investigation was made of the action of quasi-cw neodymium laser radiation of approximately 0.6 msec duration and having a power density q <10 MW/cm2 on magnesium and lead targets at reduced densities of the surrounding air. Measurements were made of the average recoil pressures on the target and the distribution of the refractive index n over the volume of the vapor jet was determined for various q. It was found that the increase in n with increasing q ceased at q≈2 MW/cm2 for magnesium and at q≈1MW/cm2 for lead, whereas the pressures remained proportional to q. This result can be attributed to an increase in the electron density in the vapor jet.

The effect of impurity gas on Mo-Cu-permalloy films prepared by RF sputtering

Abstract: The dependence of Mo-Cu-Permalloy films on the depostion parameters in rf diode sputtering has been investigated. It was found that soft magnetism of Mo-Cu-Permalloy films depended strongly on the background pressure P b before sputtering, argon gas pressure, P Ar during deposition, and the power density. The films deposited at high P Ar were contaminated with oxygen and presented clear columnar texture. They, therefore, exhibited rotatable anisotropy and did not have soft magnetism. Films with excellent soft magnetic properties have been prepared at low P Ar and high power density. Typical magnetic properties of rf sputtered Mo -Cu-Permalloy film deposited at P Ar of 2.2 mTorr and power density of 3.3 W/cm2were as follows ; 20 mOe in coercivity, 7.5 kGauss in 4πMs, 1500 in effective permeability at 1 MHz and 750 in Vickers hardness.

Light-ion beams for inertial confinement fusion

Abstract: Inertial confinement fusion requires the generation and focusing of several megajoules of energy at > 100 TW power and > 100 TW·cm−2 power density onto a target for approximately 10 ns. Lasers and particle beam drivers have been developed for this purpose. Lightion beams offer the potential for a cost-effective, efficient and versatile driver with excellent energy deposition and no significant preheat. The research and development to date has emphasized technology development of the driver. Advances in pulsed power technology, magnetically insulated power flow, intense ion beam generation, focusing and transport, and ion beam deposition have led to the Particle Beam Fusion Accelerator II at Sandia National Laboratories which will begin operation in January 1986. This accelerator has the potential for achieving ignition of thermonuclear fuel in the laboratory.

Absolute Power Density Spectra

Abstract: For various reasons, few people are concerned with absolute power density spectra. This is evidenced by the way people display plots of spectral estimates. Often, the spectra are plotted so that their maximum or minimum values are the same or the spectra all start with the same value at zero frequency. For really meaningful comparisons, spectra should be plotted in absolute terms. To do this, we need to go back to fundamentals and look at what a power density spectrum really is.

Performance scaling of fusion reactors using the deuterium-tritium and advanced fuel cycles

Abstract: How the plasma stability index beta and the fusion power density influence three performance parameters of fusion reactors burning deuterium-tritium and four advanced fusion fuel cycles was determined. The performance parameters include the total power produced per unit length of the reactor, the mass per unit length, and the specific mass in kilograms per kilowatt. The scaling of these parameters with beta and fusion power density was examined for a common set of conservative engineering assumptions on the allowable wall loading limits, the maximum magnetic field existing in the plasma, the average blanket mass density, etc. It was found that one should employ an entirely different strategy for the design of an engineering test reactor, designed to test components under high wall loadings and neutron fluences, than one would employ in designing a power plant reactor intended to produce the cheapest possible thermal power. An ETR should not be merely a scaled-down power plant reactor, but should operate at substantially different values of beta and plasma power density, and in some circumstances even use a different confinement concept and fusion fuel cycle.

Repetitive Pulse Accelerator Technology for Light Ion Inertial Confinement Fusion

Abstract: Successful ignition of an inertial confinement fusion (ICF) pellet is calculated to require that several megajoules of energy be deposited in the pellet's centimeter-sized shell within 10 ns. This implies a driver power of several hundreds of terawatts and power density around 100 TW/cm2 . The Sandia ICF approach is to deposit the energy with beams of 30 MV lithium ions. The first accelerator capable of producing these beams (PBFA II, 100 TW) will be used to study beam formation and target physics on a single pulse basis. To utilize this technology for power production, repetitive pulsing at rates that may be as high as 10 Hz will be required. This paper will overview the technologies being studied for a repetitively pulsed ICF accelerator. As presently conceived, power is supplied by rotating machinery providing 16 MJ in 1 ms. The generator output is transformed to 3 MV, then switched into a pulse compression system using laser triggered spark gaps. These must be synchronized to about 1 ns. Pulse compression is performed with saturable inductor switches, the output being 40 ns, 1.5 MV pulses. These are transformed to 30 MV in a self-magnetically insulated cavity adder structure. Space charge limited ion beams are drawn from anode plasmas with electron counter streaming being magnetically inhibited. The ions are ballistically focused into the entrances of guiding discharge channels for transport to the pellet. The status of component development from the prime power to the ion source will be reviewed.

Transmission of laser radiation by an optical discharge plasma and the channel discharge model

Abstract: An experimental investigation was made of the structure of optical discharges in air and in argon in a quasi-cw CO2 laser beam. Measurements of the fraction of the laser power transmitted by the discharge plasma and of the power density at the center of the focal spot, when the plasma was present, showed that the heating of the plasma in the beam propagation zone to temperatures above 17 kK was accompanied by its bleaching in the beam and by a peaking of the beam intensity distribution in the focal plane. A channel model of the optical discharge is proposed to provide an analytical description of its temperature distribution in the laser beam. Sufficient conditions for the discharge bleaching regime are determined.