High Energy Extraction Efficiency Research Articles

Tapered helical undulator system for high efficiency energy extraction from a high brightness electron beam

In this paper we discuss the design choices and construction strategy of the tapered undulator system designed for a high energy extraction efficiency experiment in the ultraviolet region of the electromagnetic spectrum planned for installation at the Argonne National Laboratory Linac Extension Area (LEA) beamline. The undulator is comprised of 4 sections pure permanent magnet Halbach array separated by short break sections, each one of them housing a focusing quadrupole doublet and a phase shifter. The quadrupoles use a novel hybrid design which allows one to vary the gradient and match the beam transversely. The undulator tapering profile is optimized to maximize the energy conversion efficiency from a 343 MeV 1 kA beam into coherent 257.5 nm radiation taking into account the longitudinal current profile generated by the linac.

An adaptive plate at flapping wing’s trailing edge in promoting energy extraction performance

As is known, the maximum thickness position plays a key role in determining the energy extraction properties for flapping wing airfoils. Previous work demonstrated that the energy extraction efficiency might increase when we move the maximum thickness position towards the leading-edge direction. Inspired from this phenomenon, we propose in this work the addition of a flat plate at the tail of the flapping wings. Under two different Reynolds numbers (Re = 1100 and Re = 5×105), the effect of adding a rigid flat plate or a flexible flat plate to the trailing edge of the flapping wing on the flapping wing’s energy efficiency was investigated. The corresponding results were also compared with that of the original flapping wing. Results show that the addition of a rigid flat plate is sufficient for the amelioration of the flapping wing’s energy extraction efficiency in low Reynolds number cases. At high Reynolds number cases, the flapping wing with flexible flat plate trailing edge can maintain a relatively high energy extraction efficiency over a wide range of frequency, while the flapping wing with rigid flat plate trailing edge can only improve the energy extraction efficiency in the low frequency region. Therefore, we propose the application of flapping wings with flexible flat plate trailing edge for increasing the energy extraction efficiency under high Reynolds number conditions.

New insights into aerodynamic characteristics of oscillating wings and performance as wind power generator

Summary In this paper, the effects of nondimensional frequency f*, pitch amplitude θ0, and airfoil thickness on the energy extraction performance of an oscillating wing wind power generator were numerically investigated. It is found that the optimum value of f* or θ0 exists to achieve the maximum energy efficiency. Additionally, the thickness of airfoil also significantly affects the efficiency and the flow patterns around the oscillating foil. For thin airfoils, a relatively large-scale vortex was normally generated at its leading edge. This vortex detached from leading edge might be able to be “caught” by the airfoil again and then reutilized to increase its work capacity. By contrast, no induced leading edge vortex is formed on the upper surface of a thick airfoil. Nevertheless, the pressure difference between the upper and lower surface of the oscillating thick airfoil is greater than that of thin airfoil. Thus, the portion of the output power contributed by the oscillatory heaving motion is greatly increased and high energy extraction efficiency can still be achieved. For airfoils with moderate thickness, both flow phenomena observed on thin and thick oscillating airfoils that have high wind energy utilization efficiency are all likely to occur, depending on the adopted motion parameters.

A cavity mode size adjustable high average power Ti: sapphire femtosecond regenerative amplifier

High average power femtosecond lasers based on Ti:sapphire are widely used in strong-field physics and ultrafast dynamics.Continued advances include isolated attosecond pulse generation,few-cycle pulse generation,ultrafast spectroscopy,time-resolved photo-chemical reaction dynamics and laser micro-machining benefit greatly from use of such laser systems.The regenerative amplifiers are mostly utilized and have inherent advantages over multipass ones for applications in chirped pulse amplification.In this paper we describe a design,performance,and the characterizations of a novel linear cavity regenerative amplifier which has produced 4.8 W average power with 35 fs pulse durations at 1 kHz repetition rate. The main difficulty in designing and constructing a high average power Ti:sapphire regenerative cavity is thermal lensing effect.In order to generate amplified pulses with an output power exceeding 5 W at 1 kHz,a green pump power higher than 20 W is required.Meanwhile,the focal pump beam diameter on the surface of Ti:sapphire crystal should have sub-millimeter mode size to demonstrate large pump fluence,inducing a focal length of a thermal lens about 100 mm,i.e.,which is much less than the scale of the cavity length.For our experiments,a cavity mode size adjustable geometry is employed to counteract thermal lensing effect and to optimize the conversion efficiency of the amplifier.We first characterize the cavity stability by applying the well-known ABCD matrix formalism.The cavity consisting of R=900 mm concave mirror,an 2=800 mm lens and a plane mirror has two stability ranges with increasing the focal length of the thermal lens.In order to obtain a highest thermal tolerance,the optimal cavity parameters are resolved when two stability zones merge into one.After characterizing the cavity in detail,we calculate the cavity mode and the pump beam size at the position of the Ti:sapphire rod as a function of the thermal focal length.The optimal mode radius occurs at 312 m,corresponding to the intersection point of two curves.Stability curve exhibits a weak thermal sensitivity which is defined as the change of radius of cavity mode size per unit focal power change of thermal lens, keeping well below 10 m/D in a range of 2 D-4 D.The calculated results show that the active compensation for thermal lens focal length from 100 mm to could be achieved by adjusting the lens position,without changing the cavity. 20 fs,3 nJ pulses at a repetition rate of 82 MHz produced by a home-made Kerr-lens mode-locked oscillator are first sent to a Martinez stretcher by using a 1200 lines/mm holographic reflectance grating,which temporally stretches the laser pulses to 200 ps.The seed pulses out of the stretcher is then injected into the regenerative cavity depicted above. The 20 mJ pumping energy at 1 kHz is focused through the R=900 mm concave mirror into a 10 mm Brewster-cut Ti:sapphire rod,which is cooled to 250 K by thermoelectric elements.Condensation was avoided by placing the crystal into a small evacuated chamber.Mode matchings of pump and laser beam are found to be of critical importance for high energy extraction efficiency and high beam quality.In our experiments it is accomplished by fine adjusting the F=800 mm cavity lens and the pump beam size.The amplified power of 6.5 W at 1 kHz is obtained with minimum beam distortion,giving a 33.6% slope efficiency.The trapped pulse is built-up quickly and saturated after 8-round trips. The beam size of the amplified laser is expanded to 15 mm in diameter before compressor.A transmission efficiency of 73.8% is achieved through the grating-pair Treacy-type compressor,leading to a 4.8 mJ pulse energy.The grating has a groove density of 1500 lines/mm,and the compressed output spectrum has a full width at half maximum of 29 nm. The pulse duration measurement is performed by using an interferometric autocorrelation.As a result,a typical autocorrelation trace corresponding to a 35 fs pulse width is displayed,and agrees well with the 32 fs transform limit.The far-field beam profile after the compressor is round and Gaussian in both s and p planes,respectively.This scheme is also sufficiently reliable and robust so that no components of the laser system were damaged over a year of operation. In summary,the theoretical analysis and experimental results show that the regenerative cavity developed in this work exhibits a high conversion efficiency and an extraordinary thermal stability,and it is very suitable for high power and high efficient amplification of femtosecond Ti:sapphire pulses.

Extracting black-hole rotational energy: The generalized Penrose process

In the case involving particles the necessary and sufficient condition for the Penrose process to extract energy from a rotating black hole is absorption of particles with negative energies and angular momenta. No torque at the black-hole horizon occurs. In this article we consider the case of arbitrary fields or matter described by an unspecified, general energy-momentum tensor $T_{\mu \nu}$ and show that the necessary and sufficient condition for extraction of a black hole's rotational energy is analogous to that in the mechanical Penrose process: absorption of negative energy and negative angular momentum. We also show that a necessary condition for the Penrose process to occur is for the Noether current (the conserved energy-momentum density vector) to be spacelike or past directed (timelike or null) on some part of the horizon. In the particle case, our general criterion for the occurrence of a Penrose process reproduces the standard result. In the case of relativistic jet-producing "magnetically arrested disks" we show that the negative energy and angular-momentum absorption condition is obeyed when the Blandford-Znajek mechanism is at work, and hence the high energy extraction efficiency up to $\sim 300\%$ found in recent numerical simulations of such accretion flows results from tapping the black hole's rotational energy through the Penrose process. We show how black-hole rotational energy extraction works in this case by describing the Penrose process in terms of the Noether current.

Design of ultrahigh energy laser amplifier system with high storage energy extraction

A design concept of realizing high storage energy extraction efficiency is presented for an ultrahigh energy laser system, stressing the advantage of variable-diameter aperture structure for the multistage amplifier system over the constant-aperture design. Based on the established modeling, the conceptual schematic of an amplifier system with optimized high storage energy extraction is developed, which is expected to produce 15 kJ output energy from three stages, with an extremely high storage extraction efficiency of 50.3%.

High Beam Quality and Efficiency in Plasma-Based Accelerators

The question of what beam quality and efficiency are ultimately achievable in plasma-based accelerators is addressed analytically and through self-consistent particle-in-cell simulations. A strategy for phasing and beam loading to minimize energy spread while at the same time achieving high energy extraction efficiency is proposed. Preservation of beam emittance is facilitated by the use of a hollow channel. {copyright} {ital 1998} {ital The American Physical Society }

Demonstration of high energy extraction efficiency in a laser-diode pumped high gain Nd:YAG regenerative amplifier

High energy extraction efficiency of 48±4% for the cavity mode cross section (17.5%±1% for the entire lasant cross section) and high energy gain of 71±1 dB have been demonstrated simultaneously, for the first time, in a laser-diode pumped Nd:YAG regenerative amplifier (RA). The RA was operated at an initial small-signal gain of 3.15±0.20, an input pulse energy of 0.5±0.1 nJ (pulse width of 910±12 ps), an amplified output pulse energy of 6.0±0.3 mJ (pulse width <1 ns), and a repetition rate of 50 Hz. The dependence of energy extraction efficiency on initial small-signal gain of the RA was shown to be well fitted with the theory of Lowdermilk and Murray [J. Appl. Phys. 51, 2436 (1980)].

Reflectivity and oscillation conditions of a gain medium in a self-conjugating loop geometry

The intensity-dependent reflectivity of a gain medium in a self-phase-conjugating loop geometry is numerically modeled by use of exact integration equations without restriction on the degree of gain saturation. High conjugate reflectivity and high energy extraction efficiency of the gain medium are predicted. A weak saturation analysis is also presented to derive useful expressions for the threshold input intensity for oscillation of the backward conjugate mode and the resonant oscillation frequencies.

Q-switched neodymium-doped phosphate glass fiber lasers

The operation of a short-pulse, Q-switched, neodymium-doped fiber laser operating at 1.054 mu m is described experimentally and theoretically. The laser is efficiently pumped with a single-stripe AlGaAs laser diode and emits >1 kW pulses. It is seen that due to high gain short pulses with high energy extraction efficiency can be obtained. The feature of broad emission lines associated with rare-earth-doped glasses is exploited to demonstrate tunable, Q-switched operation over a 40-nm tuning range.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Present Status of Laser-Diode Pumped High-Power Nd:YAG Lasers.

The present status of laser-diode (LD) pumped high-power Nd: YAG lasers at 1.06μm is reviewed. With a side-pumped rod geometry, an output of of 1.25J per pulse is demonstrated. The LD-end-pumped Nd: YAG laser can produce an output power of CW 60W in a near-diffraction-limited beam. A one Joule per Q-switched pulse LD-pumped Nd: YAG zigzag-slab laser is constructed. A 1-kW average-power LD array-pumped folded zigzag-slab Nd: YAG laser is demonstrated at 2.25 kHz. A phase conjugated LD-pumped Nd: YAG MOPA laser architecture is proposed to have a 1 kW average power in a near-diffraction-limited beam. An LD pumped Nd: YAG regenerative amplifier is achieved simultaneously with a high gain (71dB) and a high energy extraction efficiency (48%) .

High-repetition-rate laser systems based on a high-energy phase-conjugated multiple-pass amplifier and a low-power oscillator

A high-gain, high-energy extraction efficiency, phase-conjugated, multiple-pass amplifier was developed using Nd:YAG. The amplifier was used with a low-energy, self-injection locked, passively <i>Q</i>-switched, highrepetition-rate oscillator to obtain energies of 0.85 J in SLM laser pulses of durations variable between <7 and >17 ns. At high repetition rates (20 Hz), the average power reached 14.5 W. Beam quality was better than 2 x diffraction limited. A two-dimensional multiple-pass model was developed for the purpose of interpretation and design.

Resonant optical interactions in active dielectric films

An investigation of oblique plane-wave electromagnetic scattering in active dielectric films reveals the existence of anomalously large resonances that occur at discrete plane-wave angles of incidence. These resonances may be understood from a ‘‘leaky wave’’ phase matching condition whose predictions for the first three modes agree to within a few percent of those obtained from a rigorous treatment using Maxwell’s equations. Experiments using finite-diameter pump and probe laser beams verify the existence of these scattering resonances with enhancements of the scattered field intensities on the order of 100 observed in active dielectric films as thin as 6 μm. Saturation effects are discussed in the context of a very simple model whose predictions agree qualitatively with experimental measurements. Two novel laser oscillator configurations based upon resonant leaky waveguide interactions were tested and found to have very high-energy extraction efficiency (≥18%) with oscillation being easily achieved using active dielectric films as thin as 6 μm.

Line tunable tea CO 2 laser using SFUR configuration

We present the first TEA CO 2 line tunable laser to be obtained using the SFUR (Self Filtering Unstable Resonator) technique. Tunability over 64 lines with high energy extraction efficiency ( E=3.8 J on the 10P20 line), single transverse and longitudinal mode operation and diffraction limited divergence are reported. The laser has been developed for the ENEA lidar facility at Frascati.

The revived Penrose process can power the central engine in active galactic nuclei

Using the fact that the efficiency of the revived (Wagh et al 1985) Penrose process of energy extraction from black holes immersed in electromagnetic fields can be very high (Parthasarathy et al, 1986) we show that this process can comfortably power the ‘central engine’ in Active Galactic Nuclei. The microphysical Penrose process energized particles will be ultrarelativistic in the asymptotic frame. Hence the kinematical analysis of escaping photons by Piran and Shaham (1977) will be a good approximation to the kinematics of these particles. From this analysis one expects the energized particles to emerge within an angle∼ 40° above and below the equatorial plane. These energetic particles, which are collimated in the funnel of an accretion disk and further on by the magnetic field, then, form supersonic, relativistic, bilateral jets. The relativistic Y factor for such jets can be expected to be ∼ 2 since these ultrarelativistic particles will effectively mimick radiation in ‘dragging’ the matter already injected inside the funnel. Various implications of high energy extraction efficiency are illustrated.

Développement larvaire et bilan d'utilisation d'énergie en fonction de l'hygrométrie chez Tinea pellionella L. (Lepidoptera : Tineidae)

We studied the ability of the case-bearing clothes moth (Tinea pellionella L.) larva to develop in a dry environment and we examined the strategy developed by this species to survive under dry conditions. In a dry environment the larval development was characterized by a high level of mortality and a reduced growth rate. The weight of the fully grown larva was twice as low at 5% relative humidity (RH) as at 95% RH. The consumption index was higher at 5% RH than at 95% RH but the oxygen consumption per day was unchanged. For the same quantity of food ingested, oxygen consumption was higher at 5% RH than at 95% RH. The digestibility of ingested food was low under dry conditions and the efficiency with which digested food was converted to body substance was much reduced at 5% RH. A large proportion of digested food was utilized by the larva for water production. In spite of a high energy extraction efficiency, the larval production was greatly reduced in a dry medium because of the low efficiency of storage of metabolizable energy. In a dry environment the amount of energy required for water production is so large (24% of ingested energy) that it does not allow optimal development; only survival is possible under these conditions.