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One of the most promising approaches to reach a high gain in inertial confinement fusion is the fast ignition scheme. In this scheme, a relativistic electron beam is generated; this passes through the imploded plasma and deposits parts of its energy in the core. However, the large angular spread of the relativistic electron beam and the poorly controlled compression of the target affect realization of the fast ignition technique. Here, we demonstrate that indirectly driven (that is, driven by X-rays generated inside a gold hohlraum) implosions with a ‘high-foot’ and a short-coast time of less than 200 ps allow us to tightly compress the shell. Furthermore, we show the ability to optimize the symmetry of the imploding shell by changing the hohlraum length, successfully tuning a suitable tube-shaped shell to compensate for the large angular spread of the relativistic electron beam and to enhance the electron-to-core coupling efficiency via resistive magnetic fields. Benefiting from those experimental techniques, a significant enhancement in neutron yield was achieved in our indirectly driven fast ignition experiments. These results pave the way towards high-coupling fast ignition experiments with indirectly driven targets similar to those at the National Ignition Facility. Experiments realizing the indirect-drive fast ignition scheme for inertial confinement fusion are reported. Enabled by a tightly compressed target, an increase of neutron yield is observed.

This paper will discuss the design and construction of BESIII, which is designed to study physics in the tau-charm energy region utilizing the new high luminosity BEPCII double ring e+e- collider. The expected performance will be given based on Monte Carlo simulations and results of cosmic ray and beam tests. In BESIII, tracking and momentum measurements for charged particles are made by a cylindrical multilayer drift chamber in a 1 T superconducting solenoid. Charged particles are identified with a time-of-flight system based on plastic scintillators in conjunction with dE/dx (energy loss per unit pathlength) measurements in the drift chamber. Energies of electromagnetic showers are measured by a CsI(Tl) crystal calorimeter located inside the solenoid magnet. Muons are identified by arrays of resistive plate chambers in the steel magnetic flux return. The level 1 trigger system, Data Acquisition system and the event filter system based on networked computers will also be described., 57 pages, 75 figures

Characteristics of laser-ultrasound signals are presented from photoacoustic interaction with a layered, optically absorbing medium surrounded by a transparent fluid. A thermoelastic model is presented describing the interaction, with signal predictions in the fluid arising from polymer transducer detection. By taking the optical absorption coefficient and finite layer thickness into account, the amplitude and shape of transient elastic waves are calculated for both forward and backward travelling directions. Additionally, wave interaction with the PVDF transducer has been characterised using a discrete-time algorithm for the transducer response. With just three constants to define transducer response characteristics, the response function may be used to predict voltage signals. Good agreement with experimental waveforms is demonstrated, so that the response function may form the basis of system modelling when miniature laser-ultrasound probes are used in various applications.

To detect ultrasound remotely, an optical detection scheme is described which uses a confocal Fabry-Perot interferometer and conjugate detection. A conjugate signal is derived from the interferometer by making simultaneous use of signals derived from optical back reflection, and optical transmission, through the interferometer. Theoretical analysis and experimental results have demonstrated that the new scheme has a higher sensitivity than those described previously. Sensitivity enhancements between 2 and 17 times can be expected. Depending on mirror reflectivity, the frequency response is approximately flat in the range of 10 MHz and above, limited only by the free spectral range of the interferometer device.

The analytical magnetization versus time expressions for several flux‐pinning models for high‐Tc superconductors are deduced. Magnetic relaxation and hysteresis studies have been performed on a zone‐melted YBa2Cu3O6+x sample by SQUID. Nonlogarithmic magnetization decay is observed at relatively high temperatures; we attribute this to the nonlinear U(J) relationship which may arise from the local pinning potential Up(x), rather than collective pinning. At 70 K, the experimental data fits extremely well to the expression M(t)=M0+a(T)ln ln(t/τ) which is the result of the exponential U(J) relationship. Based on this U(J) law, the local pinning potential is determined to be Up(x)=U0(x/x0)[1−ln (x/x0)]. The voltage–current E(J) resulting from the observed U(J) relationship, as well as the role of the Y2BaCuO5 (211) phase in zone‐melted YBCO is discussed.

A laser confocal Fabry-Perot interferometer (CFPI) is described for the sensing of ultrasound in opaque solids having optically rough surfaces. Stabilization was required to eliminate the optical frequency drift arising from various sources in both the CFPI and the argon-ion laser. Measurements showed that conventional proportional control was inadequate when using feedback to the piezoelectrically-controlled interferometer mirror. Instead, a cascade control system was developed with a digital proportional-integral controller as the primary controller and an analogue proportional controller as the secondary controller. Two control loops were nested, with the secondary loop used to stabilize fast fluctuations and the primary loop used to eliminate the drift. When the interferometer mirror reaches the limit of its dynamic range, the intelligent digital controller was able to reset automatically the interferometer at a new operating point within its proper dynamic range. In this way, it is shown that the interferometer sensor can be used in a fully automatic way for on-line monitoring applications.

Through-transmission ultrasonic NDT measurements have been performed with a non-contact laser combination system. High power (~2 MW) laser pulses were used for the generation of longitudinal pulses in metallic samples. On reaching the far surface, ultrasound was detected with a 50 cm confocal Fabry-Perot interferometer. The interferometer analysed speckle from back-scattered laser light so that measurements could be made from samples with only a machine finish. Signal-to-noise ratios were sufficiently good for two-dimensional scans to be performed, producing optical images of artificial defects. For improved image quality, signals were normalised taking into account changes in sample surface reflectivity. Median filtering was also used. Results show that images of 4-mm diameter drill holes can be obtained with resolutions of ±0·5 mm.

A non-contact scanning system is described which is capable of producing two-dimensional ultrasonic images of defects in opaque materials. Lasers are used both for generation and detection of ultrasound. Short-duration high-power ( approximately 2 MW) laser pulses are used to generate ultrasound on the surface of a sample. Such ultrasound in the form of steps or pulses propagates through the sample and after interaction with defects are monitored by a 50 cm confocal Fabry-Perot interferometer. The interferometer uses back-scattered laser light from the sample's surface, which can be diffuse in nature. System sensitivity is sufficient for applications on optically rough surfaces. Two-dimensional scans have been performed, leading to computer-generated images of artificial defects in aluminium.

The thickness of thin polyester film has been measured using ultrasonic Lamb waves which were generated and detected using noncontacting laser techniques. The uncertainty analysis of such a measurement technique has been examined. Systematic errors in both time of flight and distance between laser generation and detection points were estimated and reduced with the assistance of computerized X‐scan translation techniques. Thickness measurements with uncertainties of less than 3% have been achieved.

A modulated continuous wave diode laser was used to generate ultrasonic Lamb waves in a thin steel plate. No surface damage was evident on the sample, a feature due to the low power density of the acoustic source in contrast to the high power pulsed laser systems usually employed for laser-ultrasound generation. The Lamb waves were monitored using a surface bonded optical fiber interferometer whose output was correlated with the pseudorandom binary sequence used to modulate the laser diode. In this fashion, it was possible to record a time domain history of the ultrasonic propagation in the sample.

Convenient and reliable temperature monitoring systems are increasingly demanded in vehicle refrigerators. However, difficulties exist in wiring between temperature recorders and sensors in vehicles such as trailer-tractor. To solve this problem, this paper provides a novel solution: wireless temperature sensors using Bluetooth. A prototype of the wireless temperature sensors has been developed. The technologies and mathematical models used are presented in this paper.

To detect ultrasound remotely, an optical detection scheme is described which uses a confocal Fabry-Perot interferometer and conjugate detection. A conjugate signal is derived from the interferometer by making simultaneous use of optical back-reflection, and optical transmission, through the interferometer. Theoretical and experimental results have demonstrated that the new scheme has higher sensitivity than established transmission schemes. Sensitivity enhancements between 2 and 17 times can be expected. Depending on mirror reflectivity, the frequency response is approximately flat in the range of 10 MHz and above, limited only by the free spectral range of the interferometer device.

This paper presents an investigation into technologies of wireless intelligent sensor networks for refrigerated delivery vehicle. The investigation has reviewed the latest wireless communication technologies such as Bluetooth and Zigbee, and artificial intelligent technologies such as neural network, fuzzy logic and neuro-fuzzy. A proposed solution of future sensor networks for cold chain area has been addressed.

Surface‐breaking tight fatigue cracks in mild steel have been examined with laser‐generated ultrasonic pulses. Before the arrival of transmitted Rayleigh waves arriving at the detector, evidence is presented of a fast skimming longitudinal pulse which is also transmitted through the crack. Additionally, another ultrasonic feature is consistent with a longitudinal wave which is mode converted to a diffracted shear pulse by the tip of the fatigue crack. Such an interaction mechanism can form the basis of laser‐based fatigue crack depth measurements.

The authors describe the application of laser-ultrasonic sources in combination with interferometric detectors to monitorultrasonic Lamb waves propagaing in metal and composite structure plate samples. Using a high powered pulsed lasersource, and temporally and spatially sampling the resultant acoustic field, it was possible to directly measure the Lamb wavephase velocities of several modes simultaneously. A further development has been the demonstration of a low power CW laser source capable of generating Lamb waves in a steel sample at a power density well below the ablation damage threshold.Keywords: Lamb waves, materials characterisation, laser ultrasound INTRODUCTION The choice of appropriate acoustic probing mode for ultrasonic materials characterisation and evaluation depends upon thegeometry of the sample under inspection. This paper describes application of plate testing using ultrasonic Lamb waves,which are guided acoustic waves that propagate in plate-like structures parallel to the surface boundary layers. Previouswork by the authors has concentrated on the detection of defects in composite materials using a combination of embeddedoptical fibre sensors and structurally integrated acoustic sources [1-3]. Lamb waves 141 are often the preferred candidate ofacoustic wave modes for the inspection of plate samples due to their propagation along the length of the plate, thus offeringa saving in time over C-scanning of the sample. Many applications of Lamb wave testing have been described for thedetection of defects in metals [5] and composite plates [6,71. In general Lamb wave inspection relies on the generation and

Conventional ultrasonic Lamb wave testing of materials often relies on the efficient generation and detection of a single Lamb wave mode that propagates in a relatively non- dispersive region of its characteristic. Such an approach allows identification of defect sites within the material by looking for distinct pulse reflections in the time domain. The fundamental symmetric mode is often utilized due to its low dispersion and relatively high velocity. However, this mode is restricted to a low frequency-plate thickness product where its wavelength may be several tens of millimeters with obvious implications for defect sensitivity. An alternative approach to single mode excitation is to utilize broadband Lamb wave measurements. Since a wider portion of the Lamb wave spectrum is now excited it is anticipated that defect resolution could be enhanced. We have investigated the propagation characteristics of ultrasonic Lamb waves in thin plates of metal and composite structure. Ultrasonic generation and detection was accomplished using a combination of non- contacting optical techniques, material integrated optical fiber sensor and conventional piezoelectric sources. Utilizing the broad optical techniques, material integrated optical fiber sensor and conventional piezoelectric sources. Utilizing the broad temporal and spatial bandwidth of a pulsed laser source combined with a point detector, it was possible to simultaneously measure the dispersion characteristics of several propagating Lamb wave modes in both aluminium and carbon fiber composite plates. An alternative approach to signal interpretation was undertaken by developing a NARMAX model of composite plates. An alternative approach to signal interpretation was undertaken by developing a NARMAX model of Lamb wave propagation in a sample plate and correlating properties of the model to damage in the samples. A possible extension to this techniques using a modulated laser diode for acoustic generation is also described. It is anticipated that these related techniques could be used to identify the presence of defects in addition to material ageing effects in composites.

Coating technology is used in a variety of applications, for example to improve the wear properties or to improve the bonding properties of a surface. The properties of such surfaces depend on the mechanical properties of the coating, namely its Young’s modulus and its thickness. To be able to predict the performance of such coatings it is necessary to be able to measure these properties in a nondestructive way. Conventional ultrasound is one nondestructive method that has been used for coating measurement [1]. It has the disadvantage of needing a transducer to be placed in direct contact with the material surface, often with the use of a couplant. This is sometimes inconvenient and risks contaminating the surface. Laser ultrasound offers a complete noncontact technique that prevents any surface contamination. It also offers scanning possibilities and laser sensor systems can possess very broad frequency bandwidths [2,3].

C-scan images are presented of artificial defects in carbon fiber composite materials derived from a laser ultrasound imaging system. Detection of ultrasound has been achieved from natural material surfaces, by an actively stabilized Fabry-Perot interferometer in conjunction with an argon-ion laser source. Recent measurements have been made in what is known as the thermoelastic regime, so that the sample did not suffer surface damage from any plasma spark. However, signals were averaged in order to produce good quality images. These were further processed using a separable median filter to give images which compared favorably with X-ray radiography measurements. Using 0.25 mm pixel separation in the scanning process, images with size resolution better than 0.5 mm were achieved.

We have previously reported our observations that, at laser wavelengths of 1,064 and 532 nm, following repeated exposure to short pulses at power density levels well below those reported to cause permanent damage to biological tissue, the photoacoustic signal detected using an ultrasound probe diminishes significantly. Examination by electron microscopy of such tissue at the site at which repeated laser pulse exposures have been made reveals little evidence of structural changes to the tissue. The effect that we have observed remains unexplained.

A confocal Fabry-Perot interferometer for the detection of laser-ultrasound has been employed for C-scan image applications on industrial samples without special surface preparation. Automatic stabilisation of the interferometer has made this possible. A cascade control system has been developed to overcome the complex de-stabilising mechanism inherent in this type of interferometry. It was based on a special version of proportional integral (PI) control, implemented digitally and tailored to the Fabry-Perot characteristics. This was combined with an analogue processing loop to provide a system capable of long term stabilisation throughout C-scan measurements.

By measuring the velocity of Lamb waves using photoacoustic generation, the molecular orientation in biaxially-stretched polymer film has been investigated.