High Power Extraction Research Articles

Effect of Control Strategies and Power Take-Off Efficiency on the Power Capture From Sea Waves

The choice of the most suitable control strategy for wave energy converters (WECs) is often evaluated with reference to the sinusoidal assumption for incident waves. Under this hypothesis, linear techniques for the control of the extracted power, as passive loading and optimum control, are well known and widely analyzed. It can be shown, however, how their performances are fundamentally different when irregular waves are considered and the theoretical superiority of optimum control is questionable under real wave conditions. Moreover, the global optimization of WECs implies a rational design of the power electronics equipment. This requires the analysis of the instantaneous extracted power in addition to the average one. In this paper, the impact of irregular waves on the power extraction when using different control techniques is analyzed in the case of a point absorber in heave. It is also shown how a convenient tradeoff between high average power extraction and limited power electronics overrating can be obtained by applying simple power saturation techniques. Moreover, the impact of power conversion efficiency on the control strategy is analyzed.

Tapered multi-mode interference couplers for high order mode power extraction

Tapered 1 × 1 multi-mode interference (MMI) devices are proposed for high order to fundamental modeconversion. Like adiabatic tapers, the device provides a down-tapered image of theinput fundamental mode, while acting as a short taper for higher even-orderedmodes. This is the first tapering scheme capable of near 100% transmission ofthe input fundamental mode, as well as mode conversion for the input higherorder modes. When directly excited by diode lasers, the tapered MMI couplerpresented can convert the fundamental and second-order transverse modes ofdifferent wavelengths into the fundamental mode signals of a single-mode outputwaveguide.

Pseudo-Capacitor Structure for Direct Nuclear Energy Conversion

AbstractThe advanced space missions need for more power opened the way for advanced nuclear reactors and for alternative power conversion procedures. The most advanced power systems available in space are the fuel cells and nuclear reactors. Both systems manifest low efficiencies for converting the primary energy into electricity and as consequence are requiring high heat dump into space mainly by infrared radiation. The thermo-nuclear power generator also requires a high temperature gas turbine and a mechano-electric generator, finally driving to low conversion efficiencies. The new nano-materials offer the possibility of creating direct energy conversion devices able of achieving high conversion efficiencies up to 99% in the cryogenic versions. The interest for direct conversion of the nuclear energy into electricity appeared in early 1940th, by the invention of the thermo-ionic fission device by Linder. Then a series of patents and scientific papers improved gradually the designs and performances of the devices, up to the actual concepts of beta-voltaic and liquid-electronics. The most intuitive direct conversion device looks mainly like a super mirror- or a heterogeneous super-capacitor. The issues on its operation are related to global conversion efficiencies and the stable operation life-time in high radiation field. There are combinations of nano-structures and actinides assuring both the neutron flux stability, by meeting criticality conditions and the direct conversion or the nuclear energy into electricity. Achieving a high efficiency internal conversion of the nuclear energy into electricity is not enough if it is not completed by a high efficiency power extraction system from the nuclear reactor core into the outside load. The development of the new MEMS devices and micro electronics in the 40 nm technologies provides an excellent background for the production of the electric power harvesting and conversion devices embedded in the fuel. The new nano-structured materials may be produced as radiation energy harvesting tiles that are free of actinides, using them for harvesting the energy of radioactive sources and controlled fusion devices, or may include actinides in their structure achieving critical or sub-critical accelerator driven nuclear reactor assemblies. Another predictable advantage of the nano-structure is the property of self-repairing and self-organizing to compensate the radiation damage and improve the lifetime. Due to direct conversion the power density of the new materials may increase from the actual average of 0.2 kw/cm3 to about 1 kw/mm3 driving to miniaturization of nuclear power sources and reductions of the shield weight. At these dimensions and power densities of few thousands horse power per liter the nuclear power source becomes suitable for mobile applications as powering trains, strategic airplanes, etc. These new developments may drive to the production of high power solid-state compact nuclear battery for space applications, leading to a new development stage.

Efficiency enhancement in free-electron lasers by means of concurrent rf acceleration.

Efficiency enhancement in free-electron lasers (FELs) using rf beam acceleration in the wiggler is described. Since the beam tube is a waveguide, there are low and high frequency resonances. Injection of low frequency power can act as an inverse-FEL accelerator concurrently with high frequency power extraction. Simulation of a FEL using this technique shows that substantial efficiency enhancements are possible without significant increases in the beam energy spread, which facilitates the use of energy recovery schemes. The technique is applicable to amplifier and oscillator configurations.

An Asymmetric Sampled Grating Laser and Its Application to Multi-Wavelength Laser Array

We propose an asymmetric sampled grating laser and a multi-wavelength laser array associated with it. Asymmetric sampling periods combined with an index shifter make it possible to use first order reflection for lasing operations. With the structure of our design, we achieved a simple fabrication procedure as well as a high yield without using complex and time-consuming e-beam lithography for multi-period gratings. We analyzed the effect of mirror coating by numerical analysis to improve single mode and power extraction performance. By using high reflection-antireflection coatings, we obtained high power extraction efficiency without degradation of the single mode property. For the multi-wavelength laser array, to gain wavelength control, we varied the sampling periods from one laser to an adjacent laser across the array. With this approach, we showed the feasibility of an array of up to 30 channels with 100 GHz wavelength spacing.

First lasing of the regenerative amplifier FEL

The regenerative amplifier free-electron laser (RAFEL) is a high-gain RF-linac FEL capable of producing high optical power from a compact design. The combination of a high-gain and small optical feedback enables the FEL to reach saturation and produce a high optical power and high extraction efficiency without the risk of optical damage to the mirrors. This paper summarizes the first lasing of the regenerative amplifier FEL and describes recent experimental results. The highest optical energy achieved thus far at 16.3 μm is 1.7 J over a train of 900 micropulses. We infer pulse energy of 1.9 mJ in each 16 ps micropulse, corresponding to a peak power of 120 MW.

High efficiency diffraction limited operation of a copper vapor laser

Recently, a novel unstable resonator (SFUR) has been proposed, which employes a self-filtering intracavity aperture. This configuration is particularly suited for high gain lasers. In this work we present an experimental study on the application of the SFUR to a small size copper vapor device, demonstrating diffraction limited emission with high efficiency power extraction.

Power extraction study of an e-beam-pumped atmospheric pressure, Kr-rich KrF laser amplifier

Single-pass (50-cm) amplification characteristics of a short-pulse [65 ns full width half maximum (FWHM)] e-beam-pumped KrF laser amplifier with an atmospheric pressure Kr-rich and Kr/F2 mixture were investigated theoretically for wide excitation rate from 0.1 to 2.0 MW/cm3. We have constructed a one-dimensional propagation amplifier model which considers the gain depletion and the saturated absorption spatially and temporally in the amplifying medium. With this numerical model, good agreement was obtained between the calculated result and the experiment. As a result of this theoretical study, extraction efficiencies of over 40% and power efficiencies of over 10% are obtainable at the highest output powers for all atmospheric mixtures containing 10%–99% Kr gas for excitation rates ranging from 0.5 to 2.0 MW/cm3 using a 30-ns (FWHM) input laser pulse, indicating that high efficiency power extraction from an atmospheric pressure KrF laser amplifier is achievable.

Picosecond high power extraction from an unstable resonator based injection-locked XeCl laser

Single pulse peak power of over 0.3 GW with good beam quality was obtained from an injection-locked XeCl laser based on a positive branch confocal unstable resonator. The high power thus obtained has the potential of generating efficient high power tunable picosecond pulses from organic dyes in the UV and near UV region of the spectrum by pumping in a synchronous scheme.