Yellow laser light generation by frequency doubling of the output from a master oscillator fiber power amplifier system

We present a power-scalable approach for yellow laser-light generation based on standard Ytterbium (Yb) doped fibers. To force the cavity to lase at 1154 nm, far above the gain-maximum, measures must be taken to fulfill lasing condition and to suppress competing amplified spontaneous emission (ASE) in the high-gain region. To prove the principle we built a fiber-laser cavity and a fiber-amplifier both at 1154 nm. In between cavity and amplifier we suppressed the ASE by 70 dB using a fiber Bragg grating (FBG) based filter. Finally we demonstrated efficient single pass frequency doubling to 577 nm with a periodically poled lithium niobate crystal (PPLN). With our linearly polarized 1154 nm master oscillator power fiber amplifier (MOFA) system we achieved slope efficiencies of more than 15 % inside the cavity and 24 % with the fiber-amplifier. The frequency doubling followed the predicted optimal efficiency achievable with a PPLN crystal. So far we generated 1.5 W at 1154nm and 90 mW at 577 nm. Our MOFA approach for generation of 1154 nm laser radiation is power-scalable by using multi-stage amplifiers and large mode-area fibers and is therefore very promising for building a high power yellow laser-light source of several tens of Watt.

Current Mode with RMS Voltage and Offset Control Loops for a Single-Phase Aircraft Inverter Suitable for Parallel and 3-Phase Operation Modes

Rms voltage regulation may be an attractive possibility for controlling power inverters. Combined with a Hall Effect sensor for current control, it keeps its parallel operation capability while increasing its noise immunity, which may lead to a reduction of the Total Harmonic Distortion (THD). Besides, as voltage regulation is designed in DC, a simple PI regulator can provide accurate voltage tracking. Nevertheless, this approach does not lack drawbacks. Its narrow voltage bandwidth makes transients last longer and it increases the voltage THD when feeding non-linear loads, such as rectifying stages. On the other hand, the implementation can fall into offset voltage error. Furthermore, the information of the output voltage phase is hidden for the control as well, making the synchronization of a 3-phase setup not trivial. This paper explains the concept, design and implementation of the whole control scheme, in an on board inverter able to run in parallel and within a 3-phase setup. Special attention is paid to solve the problems foreseen at implementation level: a third analog loop accounts for the offset level is added and a digital algorithm guarantees 3-phase voltage synchronization.

A proposed two-stage two-tether scientific mission at Jupiter

A two-stage mission to place a spacecraft (SC) below the Jovian radiation belts, using a spinning bare tether with plasma contactors at both ends to provide propulsion and power,is proposed. Capture by Lorentz drag on the tether, at the periapsis of a barely hyperbolic equatorial orbit, is followed by a sequence of orbits at near-constant periapsis, drag finally bringing the SC down to a circular orbit below the halo ring. Although increasing both tether heating and bowing, retrograde motion can substantially reduce accumulated dose as compared with prograde motion, at equal tether-to-SC mass ratio. In the second stage,the tether is cut to a segment one order of magnitude smaller, with a single plasma contactor, making the SC to slowly spiral inward over severalmonths while generating large onboard power, which would allow multiple scientific applications, including in situ study of Jovian grains, auroral sounding of upper atmosphere, and space- and time-resolved observations of surface and subsurface.

Performance metrics for small-signal stability assessment of DC-distributed power-system-architecture comparisons

The objective of this paper is to provide performance metrics for small-signal stability assessment of a given system architecture. The stability margins are stated utilizing a concept of maximum peak criteria (MPC) derived from the behavior of an impedance-based sensitivity function. For each minor-loop gain defined at every system interface, a single number to state the robustness of stability is provided based on the computed maximum value of the corresponding sensitivity function. In order to compare various power-architecture solutions in terms of stability, a parameter providing an overall measure of the whole system stability is required. The selected figure of merit is geometric average of each maximum peak value within the system. It provides a meaningful metrics for system comparisons: the best system in terms of robust stability is the one that minimizes this index. In addition, the largest peak value within the system interfaces is given thus detecting the weakest point of the system in terms of robustness.

Experimental analysis of a photovoltaic concentrator based on a single reflective stage immersed in an optical fluid

This article reviews all the experimental tests carried out to analyze the performance of a FluidReflex photovoltaic concentrator. This novel concentrator concept consists of a single reflective stage immersed in an optical fluid. The presence of the fluid entails significant advantages. It not only allows a high system optical efficiency and increases the attainable concentration but also enhances the heat dissipation from the cell. In addition, the electrical insulation is improved, and the problem of water vapor condensation inside the module is avoided. A complete characterization is addressed in this paper. Among the experimental results, a measured optical efficiency of 83.5% for a concentration of 1035× stands out

Supercritical Steam power cycle for Line-Focus Solar Power Plants

The supercritical Rankine power cycle offers a net improvement in plant efficiency compared with a subcritical Rankine cycle. For fossil power plants the minimum supercritical steam turbine size is about 450MW. A recent study between Sandia National Laboratories and Siemens Energy, Inc., published on March 2013, confirmed the feasibility of adapting the Siemens turbine SST-900 for supercritical steam in concentrated solar power plants, with a live steam conditions 230-260 bar and output range between 140-200 MWe. In this context, this analysis is focused on integrating a line-focus solar field with a supercritical Rankine power cycle. For this purpose two heat transfer fluids were assessed: direct steam generation and molten salt Hitec XL. To isolate solar field from high pressure supercritical water power cycle, an intermediate heat exchanger was installed between linear solar collectors and balance of plant. Due to receiver selective coating temperature limitations, turbine inlet temperature was fixed 550ºC. The design-point conditions were 550ºC and 260 bar at turbine inlet, and 165 MWe Gross power output. Plant performance was assessed at design-point in the supercritical power plant (between 43-45% net plant efficiency depending on balance of plantconfiguration), and in the subcritical plant configuration (~40% net plant efficiency). Regarding the balance of plant configuration, direct reheating was adopted as the optimum solution to avoid any intermediate heat exchanger. One direct reheating stage between high pressure turbine and intermediate pressure turbine is the common practice; however, General Electric ultrasupercritical(350 bar) fossil power plants also considered doubled-reheat applications. In this study were analyzed heat balances with single-reheat, double-reheat and even three reheating stages. In all cases were adopted the proper reheating solar field configurations to limit solar collectors pressure drops. As main conclusion, it was confirmed net plant efficiency improvements in supercritical Rankine line-focus (parabolic or linear Fresnel) solar plant configurations are mainly due to the following two reasons: higher number of feed-water preheaters (up to seven)delivering hotter water at solar field inlet, and two or even three direct reheating stages (550ºC reheating temperature) in high or intermediate pressure turbines. However, the turbine manufacturer should confirm the equipment constrains regarding reheating stages and number of steam extractions to feed-water heaters.

Life cycle assessment of concentrated solar power (CSP) and the influence of hybridising with natural gas

Purpose Concentrating Solar Power (CSP) plants based on parabolic troughs utilize auxiliary fuels (usually natural gas) to facilitate start-up operations, avoid freezing of HTF and increase power output. This practice has a significant effect on the environmental performance of the technology. The aim of this paper is to quantify the sustainability of CSP and to analyse how this is affected by hybridisation with different natural gas (NG) inputs. Methods A complete Life Cycle (LC) inventory was gathered for a commercial wet-cooled 50 MWe CSP plant based on parabolic troughs. A sensitivity analysis was conducted to evaluate the environmental performance of the plant operating with different NG inputs (between 0 and 35% of gross electricity generation). ReCiPe Europe (H) was used as LCA methodology. CML 2 baseline 2000 World and ReCiPe Europe E were used for comparative purposes. Cumulative Energy Demands (CED) and Energy Payback Times (EPT) were also determined for each scenario. Results and discussion Operation of CSP using solar energy only produced the following environmental profile: climate change 26.6 kg CO2 eq/KWh, human toxicity 13.1 kg 1,4-DB eq/KWh, marine ecotoxicity 276 g 1,4-DB eq/KWh, natural land transformation 0.005 m2/KWh, eutrophication 10.1 g P eq/KWh, acidification 166 g SO2 eq/KWh. Most of these impacts are associated with extraction of raw materials and manufacturing of plant components. The utilization NG transformed the environmental profile of the technology, placing increasing weight on impacts related to its operation and maintenance. Significantly higher impacts were observed on categories like climate change (311 kg CO2 eq/MWh when using 35 % NG), natural land transformation, terrestrial acidification and fossil depletion. Despite its fossil nature, the use of NG had a beneficial effect on other impact categories (human and marine toxicity, freshwater eutrophication and natural land transformation) due to the higher electricity output achieved. The overall environmental performance of CSP significantly deteriorated with the use of NG (single score 3.52 pt in solar only operation compared to 36.1 pt when using 35 % NG). Other sustainability parameters like EPT and CED also increased substantially as a result of higher NG inputs. Quasilinear second-degree polynomial relationships were calculated between various environmental performance parameters and NG contributions. Conclusions Energy input from auxiliary NG determines the environmental profile of the CSP plant. Aggregated analysis shows a deleterious effect on the overall environmental performance of the technology as a result of NG utilization. This is due primarily to higher impacts on environmental categories like climate change, natural land transformation, fossil fuel depletion and terrestrial acidification. NG may be used in a more sustainable and cost-effective manner in combined cycle power plants, which achieve higher energy conversion efficiencies.

Ultra high temperature latent heat energy storage and thermophotovoltaic energy conversion

A conceptual energy storage system design that utilizes ultra high temperature phase change materials is presented. In this system, the energy is stored in the form of latent heat and converted to electricity upon demand by TPV (thermophotovoltaic) cells. Silicon is considered in this study as PCM (phase change material) due to its extremely high latent heat (1800 J/g or 500 Wh/kg), melting point (1410 C), thermal conductivity (~25 W/mK), low cost (less than $2/kg or $4/kWh) and abundance on earth. The proposed system enables an enormous thermal energy storage density of ~1 MWh/m3, which is 10e20 times higher than that of lead-acid batteries, 2e6 times than that of Li-ion batteries and 5e10 times than that of the current state of the art LHTES systems utilized in CSP (concentrated solar power) applications. The discharge efficiency of the system is ultimately determined by the TPV converter, which theoretically can exceed 50%. However, realistic discharge efficiencies utilizing single junction TPV cells are in the range of 20e45%, depending on the semiconductor bandgap and quality, and the photon recycling efficiency. This concept has the potential to achieve output electric energy densities in the range of 200-450 kWhe/m3, which is comparable to the best performing state of the art Lithium-ion batteries.

Isotopic power and thermionic conversion : a literature search /

Included are 88 references on thermionic conversion of heat energy and the use of radioisotopes as power sources. References on thermoelectric conversion are included if the primary energy source is a radioisotope.

Direct energy conversion and systems for nuclear auxiliary power (SNAP) : a literature search /

Mode of access: Internet.

Direct energy conversion and systems for nuclear auxiliary power (SNAP) : A literature search /

January 1963.