Showing papers on "Power density published in 1989"

Nested-cone transformer antenna

Abstract: A plurality of conical transmission lines are concentrically nested to formn output antenna for pulsed-power, radio-frequency, and microwave sources. The diverging conical conductors enable a high power input density across a bulk dielectric to be reduced below a breakdown power density at the antenna interface with the transmitting medium. The plurality of cones maintain a spacing between conductors which minimizes the generation of high order modes between the conductors. Further, the power input feeds are isolated at the input while enabling the output electromagnetic waves to add at the transmission interface. Thus, very large power signals from a pulse rf, or microwave source can be radiated.

Microchannel heat sinks for two-dimensional high-power-density diode laser arrays

Abstract: The operation of a two-dimensional GaInAsP/InP diode laser array with CW power dissipation up to 500 W/cm/sup 2/ into a Si microchannel heat sink is discussed. The approximately 1*4-mm/sup 2/ laser array was used to characterize the heat sink, and the value of 0.040 degrees C cm/sup 2//W was obtained for the thermal resistance per unit area. The extrapolated value for a 1-cm/sup 2/ heated area is 0.070 degrees C cm/sup 2//W. >

CO2 large‐area discharge laser using an unstable‐waveguide hybrid resonator

Abstract: A one‐dimensional unstable resonator combining free‐space and waveguide propagation is used to efficiently extract power from a large‐area gain medium in a slab waveguide CO2 laser. A power of 240 W in a near‐diffraction‐limited beam has been attained at 12% conversion efficiency from a 38 cm gain length in a compact sealed‐off laser head, corresponding to a specific power extraction of 14 kW m−2 of discharge area.

Chalcogenide glass fiber with a core–cladding structure

Abstract: GeAsSeTe, GeSeTeTl, and GeSeTe glass fibers with a core-cladding structure were prepared by one of two methods: crucible drawing or preform drawing. The diameter of the core was 340 microm and that of the cladding was 440 microm. The transmission loss spectra of the fibers were measured by the cut-back method. The crucible drawing method was preferable to reduce the loss due to structural imperfections at the interface of the core and cladding. The lowest loss of 1.7 dB/m was achieved at 10.6 microm (the wavelength of the CO(2) laser) in the fibers with a GeSeTe core and a GeAsSeTe cladding. Transmission of CO(2) laser power was examined using a 1.5-m long fiber and an output power of 2 W (2.2 kW/cm(2) in power density) was obtained.

The effect of electrode design on the efficiency of delivery of radiofrequency energy to cardiac tissue in vitro.

Abstract: Four types of electrodes were studied with respect to efficiency of delivery of radiofrequency energy (RFE) and characteristics of the lesions produced in dog ventricular muscle in vitro. An imbeddable needle electrode was found to be the most efficient of the four types studied, with a lesion volume/energy-delivered ratio of 1.10 mm3/joule at an optimum power level of 2.8 watts and power density at the electrode surface of 0.45 watt/mm2. Lesion volume was linearly related to energy delivered at all power levels used below a power density of 0.64 watt/mm2, at and above which tissue impedance increased abruptly. The electrode catheter typically used for RFE ablations was the least efficient at 0.15 mm3/joule and a power density at the electrode surface of 0.50 watt/mm2 at 6.27 watts. masking 2/3 of the electrode surface with electrically insulating epoxy caused the RFE current to be directed into the tissue, resulting in a threefold increase in efficiency (0.46 mm3/joule) at less than half the power (2.79 watts). A flat, thermally insulated electrode with larger (10 mm2) contact area approached the efficiency of the imbedded electrode with a ratio of 0.69 mm3/joule at a low power density of 0.19 watt/mm2 and 1.85 watt power level. Characteristics of an "ideal" electrode for RFE lesion production in cardiac tissue are discussed.

Design for a high power-density Astron reactor

Abstract: A liquid lithium blanket surrounding the plasma volume is described. The liquid lithium flows along magnetic flux tubes at a high speed. There is no vacuum wall between the blanket and the plasma. The E-layer of relativistic particles within which the plasma is confined serves as a vacuum wall protecting the plasma from the lithium vapor, which is continuously produced at the surface of the blanket, by ionizing the lithium atoms and ejecting the same along open magnetic lines. The heat load at the surface of the blanket generated by 14 MeV neutrons can be several hundred MW per square meter.

Determination of the power and current densities in argon and oxygen plasmas by in situ temperature measurements

Abstract: In situ temperature measurements of silicon wafers in argon and oxygen plasmas are presented. The processes which determine the heat flow from and to the wafer have been established. It is found that conduction of heat to the electrode does not contribute to the heat loss of the wafer. Radiation of heat and conduction of heat by the gas are the main loss processes. The heat flux qp from the plasma to the wafer is independent of time and temperature. This is attributed to the flux of high‐energy ions to the wafer. By measuring the plasma potential, the energy of the ions is estimated. The ion current density is calculated from qp and the energy of the ions. The value which is obtained is compared to those obtained with other methods. It is concluded that the power density on the electrode can differ by almost an order of magnitude from an estimation using the dissipated rf power and the electrode area.

Microwave and millimeter-wave QWITT diode oscillators

Abstract: The authors present DC, microwave, and millimeter-wave characteristics of different quantum-well-injection transit-time (QWITT) devices. Small-signal and large-signal device models are used to provide physical design parameters to maximize the output power density at any desired frequency of operation. A peak output power density of 3.5-5 kW/cm/sup 2/ in the frequency range 5-8 GHz has been obtained from a planar QWITT oscillator. This appears to be the highest output power density obtained from any quantum-well oscillator at any frequency. This result also represents the first planar circuit implementation of a quantum-well oscillator. Good qualitative agreement between DC and RF characteristics of QWITT devices and theoretical predictions based on small-signal and large-signal analyses is achieved. The device efficiency has been increased from 3% to 5% by optimizing the design of the drift region in the device through the use of a doping spike with optimized concentration, without compromising the output power at X-band. Self-oscillating QWITT diode mixers are also demonstrated at X-band in both waveguide and planar circuits. The self-oscillating mixer exhibits a conversion gain of about 10 dB in a narrow bandwidth and a conversion loss of about 5 dB if broadband operation is desired. >

Plasma processing apparatus

Abstract: A plasma processing apparatus wherein a means is provided to apply the proper negative DC voltage through a filter circuit to an electrode for generating the low-temperature plasma through the feed of the high-frequency power When the high-frequency power has been fed in the higher high-frequency power density to the electrode for generating the low temperature plasma, the sparks (abnormal discharge) easy to be generated are prevented from being caused to generate the stable low-temperature plasma for better plasma processing

Preparation and Characterization of Highly Conductive (100 S/cm) Phosphorus Doped νc-Si:H Films Deposited Using the VHF-GD Technique

Abstract: We report on the preparation and characterization of phosphorus doped gc-Si:H films produced by the very high frequency glow discharge (VHF-GD) at a plasma excitation frequency of 70 MHz. We present a systematic study of the deposition parameters i.e. hydrogen dilution of silane, VHF power density, gas phase doping ratio and deposition temperature and their influences on the electrical and structural properties of the material. In contrast to 13.56 MHz GD the VHF plasma conditions favour microcrystalline formation at low power densities; the resulting conductivities are significantly higher than those obtained at 13.56 MHz.

A 0.25- mu m gate-length pseudomorphic HFET with 32-mW output power at 94 GHz

Abstract: The 94-GHz power performance of a 0.25*75- mu m doped-channel pseudomorphic heterostructure FET (HFET) is reported. A maximum output power of 32 mW, corresponding to a power density of 0.43 W/mm, was obtained with 15% power-added efficiency and 3.0 dB gain. >

AlGaAs/InGaAs heterostructures with doped channels for discrete devices and monolithic amplifiers

Abstract: AlGaAs/InGaAs/GaAs-type heterostructure with one or two doped channels have been used to fabricate both discrete devices and monolithic amplifiers for millimeter-wave operation. Maximum current densities of 1 A/mm and maximum transconductances of 530 mS/mm were obtained. 0.25*50 mu m discrete devices delivered a power density of 1 W/mm with 2.9-dB gain and 25% efficiency at 60 GHz. A 100- mu m monolithic one-stage amplifier demonstrated 93 mW (0.93-W/mm power density) at 31.5 GHz with 4.2-dB gain and 29% efficiency. A record 34% efficiency was achieved with a 53.7-mW output power and 4.8-dB gain. >

Method for manufacturing oxide superconducting films by laser evaporation

Abstract: A method of manufacturing a layer of a superconducting high-T c -material. For this purpose, an appropriate target material is deposited on a predetermined substrate by a pulsed laser with a wavelength in the ultraviolet range and, by applying a heat treatment and an oxygen treatment, the desired superconducting metal-oxide phase is formed with an ordered crystal structure. The heat treatment and oxygen treatment are performed simultaneously during the vaporizing step, whereby a power density of the laser radiation of over 3 J/cm 2 at the target material is provided, the pulse power of the laser is at least 1.5 J/pulse, the temperature of the substrate is raised to 600° C. to 800° C., and an oxygen atmosphere of between 0.02 mbar and 1 mbar is provided.

Efficient generation of acoustic pressure waves by short laser pulses

Abstract: The displacement of laser-generated ultrasonic bulk waves in polycrystalline metal samples consists of signals travelling with pressure wave velocity as well as with shear wave velocity. The waveform obtained depends on the incident laser power density and the laser energy. It is found that there is a specific power density I 0 at which only a maximum pressure pulse is generated whose magnitude is proportional to the laser energy. Furthermore, the angular distribution of the pressure pulse shows that most of the acoustic energy is radiated in the forward direction. The Fourier spectrum of the pressure pulse is also evaluated.

Multilayer mirrors as power filters in insertion device beamlines

Abstract: The power‐filtering capabilities of multilayer bandpass x‐ray mirrors relative to total reflection low‐pass mirrors are presented Results are based on calculations assuming proposed wiggler sources on the upcoming generation of low‐energy (15 GeV) and high‐energy (70 GeV) synchrotron radiation sources Results show that multilayers outperform total reflection mirrors in terms of reduction in reflected power by roughly an order of magnitude, with relatively small increases in total absorbed power and power density over total reflection mirrors, and with comparable reflected flux values Various aspects of this potential application of multilayer x‐ray optics are discussed

Comparison of etch rates of silicon nitride, silicon dioxide, and polycrystalline silicon upon O2 dilution of CF4 plasmas

Abstract: The etch rates of Si3N4, SiO2, and doped polycrystalline silicon with CF4 plasmas have been examined as a function of O2 dilution and radio frequency (rf) (13.56 MHz) power density at constant residence time (25 mTorr and 25 sccm total process gas flow rate) at 22±2 °C in a batch reactor. At fixed reactor pressure and process gas composition, the etch rates of these materials increase linearly, with different slopes, with increasing rf power density. Under the conditions studied, the etch rates of SiO2 are lower than those of the other two materials and are primarily a function of rf power for CF4 plasmas that are diluted with 0%–25% O2 by flow rate. In comparison, the etch rates of Si3N4 and doped polycrystalline silicon are functions of both rf power density and gas composition, although at each rf power level (200, 300, and 400 W) the Si3N4 etch rate reaches a plateau at an O2 dilution of ∼10%–15% by flow rate. Although the doped polycrystalline silicon etch rate exhibits similar behavior at 200 and 300 W, a steady increase in etch rate is noted at 400 W over the range of O2 dilution examined in this work. At low O2 dilutions, the Si3N4 etch rate is greater than the doped polycrystalline silicon etch rate. However, with increasing O2 dilution, the doped polycrystalline silicon etch rate exceeds the Si3N4 etch rate, with the intersections of these etch rate curves shifting to greater O2 dilution at higher rf power settings.

Development of a high-power KrF laser system, ASHURA

Abstract: The present status of the development of a high-power KrF laser system, Ashura, is described. The main amplifier has generated 710 J (95 ns) at the pumping density of 1·lMW/cm 3 with the wall plug efficiency of 2·0%. Maximum power of 9·0 GW (200 J/22 ns) per beam has been obtained from the beam lines of six-time pulse multiplexing. Power density of 1 × 10 14 W/cm 2 has been achieved on target with a 10 −6 pre-pulse.

Arrangement of fuel cells based on a solid electrolyte operating at a high temperature, consisting of zirconium oxide, to obtain maximum possible power

Abstract: An arrangement of fuel cells based on a solid electrolyte (1) operating at high temperature and consisting of stabilised ZrO2 to obtain the maximum possible power in the smallest possible space by electrically connecting in series and mechanically stacking a multiplicity of shallow, flat plate-type fuel cells (1; 2; 3) on the filter press principle. The oxygen electrode (2) of one fuel cell is in each case connected to the fuel electrode (3) of the subsequent fuel cell by an electrically conducting element (4) which contains flow channels for the gaseous media. The electrically conducting elements are designed as bipolar plates (4) with projections (11). Cross-current principle. A chequerboard arrangement of a plurality of fuel cell stacks (33) alongside one another gives the best space utilisation and the highest power density. … …

Fission-fragment energy deposition in argon

Abstract: The gas-dynamic response of argon to fission-fragment energy deposition is simulated, for the first time explicitly including the coupling between the gas density, which is spatially and temporally varying, and the power density. In simulations of three experiments with different initial fill pressures of argon, good agreement was found between calculated and observed pressure rises, after the experimental pressure rise data from one case were used as a calibration. However, in each case, the calculated thermal energy deposition corresponding to the experimental pressure data was about half the fission-fragment kinetic energy release into the gas predicted by neutron and fission-fragment transport calculations. Also, the experimental pressure data exhibited a decay not seen in the simulations, which did not incorporate an energy-loss mechanism.

Etch rates and surface chemistry of GaAs and AlGaAs reactively ion etched in C2H6/H2

Abstract: The etch rates of GaAs and AlxGa1−xAs (x=0.09–1) in C2H6/H2 were investigated as a function of time (1–12 min), gas flow rate (5–25 sccm), total pressure (4–30 mTorr), plasma power density (0.56–1.32 W cm−2), and percentage of C2H6 in the discharge (10%–50%). The etch rates are constant with time, and decrease with increasing Al content in the AlGaAs. The maximum etch rates occur at 25% by volume C2H6 in H2 and increase linearly with increasing power density. Increasing the total pressure at constant gas composition reduces the etch rates by approximately a factor of 2 between 4 and 30 mTorr. The etched surfaces have smooth morphologies for C2H6 concentrations less than ∼40% of the total gas volume. A layer of subsurface dislocations approximately 40 A deep were observed in GaAs by transmission electron microscopy for the highest‐power density discharges, while the surfaces for all samples are As‐deficient to a depth of ∼30 A after reactive ion etching. Polymer deposition is not significant for C2H6 volum...

Electrothermal accelerators: the power conditioning point of view

Abstract: The authors advance the concept of a single-element power supply for ET (electrothermal) guns, showing that compulsator-type machines with waveform flexibility (pulse-shaping capability) can satisfy all the ET gun power supply and conditioning requirements while maintaining a high efficiency and low mass. Specifically, it is shown that such a compulsator is an optimal power supply for an ET accelerator due to its capability to conform to the load requirements while still performing the energy storage and electromechanical energy conversion functions in one element. Compulsators also have the highest power density reported for an electrical machine and have demonstrated repetitive rate operation at 60 Hz. A simulation of an existing laboratory-based 60-MJ HPG (homopolar generator) power supply driving an ET gun is also presented. >

Measurements of gain and absorption saturation in an electron-beam-pumped KrF amplifier

Abstract: A detailed study of energy deposition and the amplification and absorption characteristics of an electron-beam-pumped KrF laser is discussed. In particular, the gain and absorption were measured over the 241-257-nm wavelength range with and without extraction, to investigate saturation effects. Detailed measurements were made of pulsed power characteristics and energy deposition in the laser medium. Peak deposition in the medium is approximately 70 J/l in a 62-ns pulse for a power density of approximately 1.1 MW/cm/sup 3/. Measurements of gain and absorption, using a frequency-doubled tunable dye laser give a small signal net gain of 9.9+or-0.5%/cm, a small-signal absorption coefficient of 1.6+or-0.1%/cm, and a nonsaturable absorption coefficient of 1.1+or-0.4%/cm. These results are compared with other experimental measurements and with the results of numerical modeling. >

Silicon deposition in diode and hollow-cathode systems

Abstract: Deposition of silicon from silane discharges is studied in diode and hollow‐cathode systems. Using the single‐target (‘‘diode’’) configuration as a reference, it is shown that discharge confinement results in substantial increases in deposition rate and efficiency. The ‘‘target‐confined hollow cathode’’ exhibits the best performance; in comparison with a diode discharge at 2‐Pa silane pressure, rates are 20–50× higher at fixed applied rf voltage and 5× higher at fixed input power density. Alternatively, for a fixed deposition rate this new configuration allows the applied rf voltage to be reduced by ∼10 and the power density to be reduced by ∼20, again at a 2‐Pa pressure. Planarizing films are obtained at low pressures and/or low gas flows, while high pressures yield more directional deposition over surface steps. Good agreement with this profile study, and with our deposition rate data, is given by a model wherein ion bombardment is the dominant film forming and etching mechanism at low pressures, and wherein trapping of both excited neutrals and of electrons may contribute to the high efficiencies and rates observed.

Mercury vapour lamp with solid-body recombination structure - is excited by HF energy in discharge space contg. fibre with specified surface-vol. ratio

Abstract: A flat rectangular bulb (1) of glass is coated internally with a protective layer of e.g. SiO2 (2) and a fluorescent aluminate layer (3). It filling comprises 1mg of Hg in excess and 2 torr Ne. The recombination structure (4) of rockwool is distributed in the discharge space to the extent of 0.1mg per c.c. with an average fibre dia. of 12 microns. Outer electrodes (5) of e.g. Cu sheet are connected to a generator (6) of 13.56 MHz frequency. USE/ADVANTAGE - Esp. with capacitively coupled lamps. The density of illumination when the power density is increased shows practically no saturation.