National Ignition Facility laser performance status

The National Ignition Facility (NIF) is the world's largest laser system. It contains a 192 beam neodymium glass laser that is designed to deliver 1.8 MJ at 500 TW at 351 nm in order to achieve energy gain (ignition) in a deuterium-tritium nuclear fusion target. To meet this goal, laser design criteria include the ability to generate pulses of up to 1.8 MJ total energy, with peak power of 500 TW and temporal pulse shapes spanning 2 orders of magnitude at the third harmonic (351 nm or 3omega) of the laser wavelength. The focal-spot fluence distribution of these pulses is carefully controlled, through a combination of special optics in the 1omega (1053 nm) portion of the laser (continuous phase plates), smoothing by spectral dispersion, and the overlapping of multiple beams with orthogonal polarization (polarization smoothing). We report performance qualification tests of the first eight beams of the NIF laser. Measurements are reported at both 1omega and 3omega, both with and without focal-spot conditioning. When scaled to full 192 beam operation, these results demonstrate, to the best of our knowledge for the first time, that the NIF will meet its laser performance design criteria, and that the NIF can simultaneously meet the temporal pulse shaping, focal-spot conditioning, and peak power requirements for two candidate indirect drive ignition designs.     

Imaging performance of the liquid-crystal-adaptive lens with conductive ladder meshing

The liquid-crystal-adaptive lens (LCAL) is an electro-optical device that utilizes a graded index of refraction to bring light to focus. A set of electrodes controls the index variation in a liquid-crystal thin film. One can vary the focal length of the LCAL by changing the voltages applied to the device. The discrete nature of the electrodes causes phase aberrations. We introduce a novel electrode architecture, called conductive ladder meshing (CLM), that we developed to greatly reduce the static phase aberration (caused by the electrode structure). To reduce the dynamic phase aberration (associated with inaccurate voltages), we used a simulated-annealing voltage-dithering technique. The coherent transfer function of the LCAL was derived so that the performance of the CLM LCAL could be predicted theoretically. Theoretical analysis indicates that the CLM LCAL scatters less than 30% of incident light compared with scattering of 65% in the previous version. The focal-spot performance of the spherical LCAL was measured under coherent illumination for plane-wave illumination. Because of the improved quality of the spherical LCAL, true imaging experiments are demonstrated for a single incoming polarization under white-light illumination. Images formed by the spherical LCAL are comparable with those formed by a fixed lens in terms of resolution, although the contrast is worse.     

Performance improvement of terrestrial free-space optical communications by mitigating the focal-spot wandering

Abstract

Focal-spot wandering is the main cause for the major power loss in free-space optical communications. Thus,mitigating it is a primary requirement for the successful performance improvement. In order to prove this prerequisite, an experimental set-up using 155-Mbps data transmission is built for the link range of 0.5 km at an altitude of 15.25 m. In the experiment, the receiver is equiped with a control system to stabilize the received optical propagation at the detector plane which is called as focal-spot wandering mitigation control so as to couple the power in bucket perfectly to the photodetector. The performance improvements due to mitigating focal-spot wandering are regressively investigated in terms of various quality assessment key parameters. Maximum radial distance of 0.25 mm, maximum effective scintillation index of 0.17, optical signal-to-noise ratio of 9 dB, minimum eye-opening of ±0.37 V, minimum eye-height of ±0.51 V, controlled bit-error-rate of 6.45 × 10^?9 to 7.09 × 10^?8 and the link margin of 1.83 dB are attained even during strong turbulence level while mitigating focal-spot wandering.     

A frequency modulated envelope delay FSCW radar for multiple-targetapplications

A frequency modulated (FM) FSCW radar technique that uses the envelope delay to determine range information is described. The analysis shows that the measured delay produced by the FM FSCW system consists of a term proportional to the delay of the strongest reflection and a superimposed oscillation with a period equal to the difference in the target delays. A practical system able to measure target distance by determining the delay experienced by a tone modulated FM test signal reflected from the two targets is described, A feature of this design is the use of a digital phase detector based upon an IQ correlation algorithm to accurately measure the modulation phase delay and, hence, distance. While the system is being developed to measure the bagasse-water interface at the diffuser in a sugar milling process, the technique is quite general and could be applied to other close-range radar problems     

The determination of volume ratios by gas depletion through multiple expansions

We present a new technique for the determination of the volume ratio of two vacuum chambers connected through a valve. The method is based on the measurement of the pressure in a chamber filled with a gas that is repeatedly depleted by expansion in a second chamber that was previously evacuated. Our calculation shows that under the reported measurement conditions, this technique has an uncertainty comparable to that obtained from the gas accumulation technique [Elliott KWT, Clapham PB.The accurate measurement of the volume ratios of vacuum vessels. NPL Report MOM 28, January 1978]. An excellent equivalence between the results obtained with this new technique and the measurements obtained by the gas accumulation technique is demonstrated.     

Multiple-phase retrieval for optical security systems by use of random-phase encoding

The technique of the multiple phase encoding for optical security and verification systems is presented in this paper. This technique is based on a 4-f optical correlator that is a common architecture for optical image encryption and verification systems. However, two or more phase masks are iteratively retrieved by use of the proposed multiple phases retrieval algorithm (MPRA) to obtain the target image. The convergent speed of the iteration process in the MPRA is significantly increased and the recovered image is much more similar to the target image than those in previous approaches. In addition, the quantization effects due to the finite resolution of the phase levels in practical implementation are discussed. The relationships between the number of phase masks and the quantized phase levels are also investigated. According to the simulation results, two and three phase masks are enough to design an efficient security verification system with 64 and 32 phase levels, respectively.     

Phase anomalies in fourier-transform spectrometers: an absorbing beam splitter is neither sufficient nor necessary

Recently it has been a topic of some discussion that the phase associated with part of the self-emission of a Fourier-transform spectrometer may differ neither by 0 nor by pi rad from the phase of an external target if there is absorption in the beam splitter. The conventional interpretation of this has been to separate the self-emission into three terms: instrument emission from the input port, in phase with the external target; emission from the secondary input port, pi rad from the target; and emission from an absorbing beam splitter with an anomalous phase (neither 0 nor pi rad with respect to the target). There is another necessary condition that has not received much attention, that the instrument not be isothermal. For polarized radiation there is an additional condition that suppresses the anomalous phase, and for unpolarized radiation there is a way to produce an anomalous phase without beam-splitter absorption.     

Bombardon: an apparatus for investigating the influence of 5–20 keV ions on metal targets

An apparatus for ion bombardment in the energy range of 5–20 keV is described. The ion beam, produced by a duoplasmatron ion source, is purified by a magnetic sector field and directed into a target chamber 60 cm in diameter. The chamber is evacuated by sputter ion and titanium sublimation pumps with a total pumping speed of 20000 ls^?1 for H₂. The energy and angular distributions of particles backscattered from metal targets can be measured with an electrostatic spherical condenser which can be pivoted around the target. The whole apparatus is bakeable up to 250°C. With a 100 μA proton beam a pressure of 10^?9 torr is maintained in the target chamber. The black off pressure is a few 10^?11 torr.     

A segmented target chamber for (n,p) studies at TRIUMF

We have developed an (n, p) target chamber consisting of six target layers sandwiched between seven gas detector layers. This target chamber is now commonly used with the new (n, p) facility at TRIUMF. With this arrangement, large total (n, p) target thicknesses (> 1 g/cm²) can be used and yet the target contribution to overall energy resolution is moderate, typically less than 500 keV. The simultaneous accumulation of data from six target layers has proven to be highly advantageous with a number of applications, such as; (1) using multiple thicknesses of one target material, (2) including a target of known cross-section in the target stack for normalization, (3) adding a target to obtain simultaneous spectra for later subtraction of contamination lines and (4) the use of several target materials at once.     

Wiener–Hopf approach for predicting the transmission loss of a circular silencer with a locally reacting lining

The propagation of sound in an infinite rigid circular cylindrical duct with an inserted expansion chamber whose walls are treated with an acoustically absorbent, locally-reacting material is investigated rigorously through the Wiener–Hopf technique. The expansion chamber is separated from the central airway which contain a uniform main gas flow by a perforated cylindrical screen which also increases the silencing performance. The influence of the expansion chamber radius, lining impedances, the mean flow and the acoustical impedance of the central perforated tube on the transmission loss are displayed graphically.     

Real Time,in situ Observation of the Photocatalytic Destruction of Saccharomyces cerevisiae Cells by Palladium-modified Nitrogen-doped Titanium Oxide Thin Film

Palladium-modified nitrogen-doped titanium oxide(TiON/PdO) thin film was synthesized by the ion-beamassisted deposition technique,which enabled a heavy nitrogen doping and the subsequent light absorption extension to ~700 nm for a better usage of the solar spectrum.Based on TiON/PdO thin film and a phase contrast microscope,a micro-reaction chamber was developed,which allowed the simultaneous optical excitation of the photocatalytic thin film and the phase contrast image observation of cells in it.The real time,in situ observation of the photocatalytic destruction of Saccharomyces cerevisiae(S.cerevisiae),an essential eukaryotic unicellular model of living cells,was conducted with this new observation technique,which demonstrated clearly that the photocatalytic destruction effect was much stronger than the photodamage effect caused by the visible light irradiation alone in the disinfection process.     

The effect of processing parameters on the synthesis of tungsten oxide nanomaterials by a modified plasma arc gas condensation technique

In the present study, tungsten oxide nanomaterials were synthesized by a modified plasma arc gas condensation technique. The effects of processing parameters (plasma current ranged from 70-90 A and chamber pressure ranged from 200-600 torr) on the preparation of tungsten oxide nanomaterials were investigated. X-ray diffraction results showed that all of the nanomaterials synthesized in the present study exhibited W5O14 phase. Field emission scanning electron microscopy and transmission electron microscopy examinations revealed that the tungsten oxide nanomaterials were equiaxed when prepared at a relatively low plasma current of 70 A, and turned into rod-like nanoparticles with increasing plasma current (80 or 90 A). Generally, the relative amount, diameter, and length of tungsten oxide nanorods increased with increasing plasma currents or chamber pressures. The aspect ratio of the as-prepared tungsten oxide nanorods reached a maximum of 12.7 when a plasma current of 90 A and a chamber pressure of 400 torr were used. A growth mechanism for tungsten oxide nanorods was proposed.     

Gains in sensitivity with a device that mixes microarray hybridization solution in a 25-microm-thick chamber

A microarray hybridization system that allows mixing in volumes comparable to those used by glass coverslips is presented. This system is composed of a disposable flexible lid that binds to 1 in. x 3 in. glass slides via an adhesive gasket, forming a uniform 25-microm-thick hybridization chamber. This chamber rests on a base unit for temperature control. The lid contains two air-driven bladders that continuously mix the hybridization fluid. Mixing enhances sensitivity from a typical microarray experiment 2-3-fold. Mixing is particularly effective at high spotted probe and low labeled target concentrations and overcoming local target depletion that occurs when homologous probes are spotted in close proximity. Mixing appears to be compatible with most hybridization conditions; however, mix versus no-mix control experiments should be performed. Also covered are a number of microfluidic issues related to manufacturing, filling, mixing, and packaging.     

一种新型复合加速离子注入动力学研究

提出了一种基于靶台(工件)二次加速的束线离子注入的新方法,基本原理是将传统束线离子注入和等离子体离子注入有效复合。采用二维Particle-in-cell(PIC)模型对这种注入方法进行了数值仿真研究。考察了靶台加负偏压情况下靶台表面空间电势、离子密度变化以及离子的运动状态的时空演化。统计分析了不同时刻离子注入剂量、注入能量和注入角度的分布规律。结果表明:靶台施加偏压对束流离子起到了很好的二次加速效果,束线离子复合加速离子注入这种新方法理论上是切实可行的。同时发现在靶台附近空间电场的作用下,离子束会发生小角度偏转,由柱状形逐渐变成"喇叭口"形,靶台表面有效注入范围扩大。靶台表面注入剂量分布呈中心区域高边缘区域低的趋势。这种新方法有助于减缓电源硬件加工的难度,增加了工艺的灵活性。     

The Open University planetary impact facility: A compact two-stage light gas gun for all impact angles

For liquid and planetary regolith target studies, requiring a horizontal target plain, a two-stage light gas gun (LGG) was designed by UniSpaceKent and constructed at the Open University. Based on a 4.7 mm bore launch facility, supplied by Physics Applications International (PIA), the design provides high mechanical rigidity under varying angles of launch, using an integral small target chamber (200 mm diameter) or an intermediate planetary target chamber; the entire gun and target chambers can be rotated from horizontal to vertical. It can also move horizontally and rotated to mate with fixed larger target facilities beneath its mezzanine location; for this configuration pre-set angles through vacuum ports are used. The position of the axis of rotation, assisted by trim weights, provides for balancing out of residual force moments.     

A cryogenic target within an electric field

A liquid hydrogen target is placed inside a streamer chamber which has an electric field equal to 20 kV cm^?1. A flask of the target is made from mylar. Its diameter is 35 mm, its length is 198 mm and its thickness is 100 microns. The target box is made from polystyrene foam. The diameter of the box is 59 mm and its thickness is 7 mm. A source of cold for the target is a cooling gas machine having a power of 100 W.     

Topology optimization of muffler internal partitions for improving acoustical attenuation performance

The internal partition configuration of an expansion chamber muffler affects significantly its acoustical transmission characteristics, but the use of systematic optimization methods to muffler design problems is rare. The main objective of this research is to maximize the transmission loss at target frequencies by optimizing partition layouts inside a muffler chamber by formulating an acoustical topology optimization problem. The selected target frequencies include the deep frequencies of a nominal muffler in order to see the critical effects of partition configurations on the acoustical transmission characteristics. The effects of partition volume constraint ratios are also investigated and physics behind the optimized layouts is investigated. Numerical results show that mufflers with optimized partition layouts outperform nominal mufflers considerably, but the shapes and locations of the optimized partitions should be much different from those of conventional partitions. Copyright © 2009 John Wiley & Sons, Ltd.     

The mechanism of TiO2 deposition by direct current magnetron reactive sputtering

Thin films are generally thought of as being the product of a reaction between the surface and atoms and/or molecules in the gas phase. However, a relatively new theory, the theory of charged clusters (TCC), suggests that charged clusters nucleate in the gas phase and become the growth unit for a thin film. The aim of this study was to determine whether or not TiO₂ thin film deposition by DC reactive sputtering occurs via this mechanism. TiO₂ was deposited on unheated transmission electron microscopy grids to observe TiO₂ clusters, as well as glass and silicon substrates to observe the resulting thin films. The results showed that TiO₂ clusters were indeed produced in the chamber of a direct current reactive sputtering system. Furthermore, these clusters were observed as close as 50 mm away from the target. Clusters 3 nm and <2 nm in diameter were found 250 mm and 50 mm away from the target, respectively The cluster size was found to have a direct effect on the film deposited. Smaller clusters produced a facetted crystalline anatase film whereas larger clusters produced an amorphous film.     

Boundary element analysis of the droplet dynamics induced by spark-generated bubble

Spark bubble droplet generation (SBDG) method is the most recently developed drop-on-demand droplet generation technique where the oscillation of a spark-generated bubble near a circular aperture causes a single droplet quite smaller than the aperture to form and break off. This paper investigates the fluid dynamics of the droplet generated through a flat plate aperture as well as through the nozzle of an axisymmetric chamber using boundary element method and high-speed photography. The results revealed that the bottom wall of the chamber would strongly influence the behavior of the bubble oscillating inside. In addition, it was found that with the same normalized nozzle size and bubble distance from air–liquid interface, a relatively smaller and faster droplet is generated from the chamber nozzle as compared with that formed through the flat plate aperture. Furthermore, although the droplet size decreases, its pinch-off time was found to increase by increasing the size of chamber feeder canal.