Table of contents

A review is made of the field of long-range atmospheric wind velocity measurements by laser anemometry. Scattering from atmospheric aerosols of both visible (Ar⁺) and infrared (CO₂) wavelength laser beams with both transit time and Doppler processing are considered. Special attention is paid to the transverse type of measurements required for wind power development as an example and, of many possible systems, a critical assessment is made for selection on grounds of spatial resolution, number of velocity components required, safety, efficiency and cost.

Precision microwave ferrite phase shifters/attenuators designed for use in cryogenic systems are described. Superconducting field coils enable phase shift or attenuation to be precisely controlled in two independent operating regimes.

A novel design of a water-cooled helical hollow cathode device (HCD) is presented. The simple construction, that is conveniently manufactured, offers discharge and laser properties superior to those obtained with conventional HCDs. This is demonstrated for a CW IR Cu II laser.

The realisation of a three-axis magnetic field test station is described. A field homogeneity of approximately 10^-5 and a linear gradient homogeneity of approximately 10^-3 in a 10*10 cm³ volume was achieved. The absolute value of the field is known with an uncertainty less than 10^-3 and can reach an intensity higher than that of the earth's steady field. The three-axis field facility consists of four coils per direction wound on a 2*2*2 m³ wooden structure. A three-channel current generator with adjustable phases was designed for driving the coils.

A simple and inexpensive tensile testing machine for evaporated thin metal films has been developed. Fragile thin specimens can be mounted in the equipment without suffering from any mechanical damage which would give rise to variations in the experimental data, and thus the examination of stress-strain relations become possible. The in situ microscopic observation of the deforming specimens is also possible in this system. Some experimental results and design advantages are presented to show the potential of the apparatus.

A DPS calorimeter for measuring in heating and cooling modes is described. It can be used for investigation of thermally induced hysteretic effects of biopolymer systems in dilute solution forming long-lived metastable states. The calorimeter works on the principle of 'environmental scanning' and is controlled by a programmable desktop computer. To test the device, phase transitions of phospholipids and transitions of model nucleotides have been examined.

A measuring system is described which maps the spatial and temporal positions of the periodic turbulent bursts which appear in the boundary layer growing on a surface immersed in an oscillatory travelling-wave type of flow. The basic principle of the system is that whereby a 'window' of controllable duration and phase relative to the oscillatory flow is opened and the flow is observed during this opening to examine whether it is laminar or turbulent. The system uses both analogue signal-processing components and digital circuitry under the control of a programmable desk calculator. Some typical results are presented for the growth of turbulent patches in the boundary layer on a flat plate mounted in one of the QMC gust tunnels.

The implementation of a field data-logging system to measure atmospheric winds and temperatures is described. The data acquisition unit is essentially an analogue device with universal inputs for alternative applications. Six channels of data are integrated and recorded simultaneously, each having a resolution better than 1% of maximum input amplitude over two minutes of recording time. The whole unit will run unattended for one month, consuming 55 mW of power. The system has wider application for use at remote stations where low-power, unattended systems providing good reliability at low cost are required.

The design and construction of a DC discharge (Wood's tube), used as source for an atomic hydrogen target in collision experiments with multiply charged ions, is described and the characteristic parameters (nozzle diameter, wall temperature, pumping speed, discharge tube preparation and discharge pressure) are investigated. The ratio obtained for the atomic and molecular hydrogen target thickness was of the order of four in the collision region. The target thickness of the atomic hydrogen could be varied between 5*10¹⁶ m^-2 and approximately 3*10¹⁷ m^-2. The effectiveness of the arrangement is demonstrated by charge transfer measurements of multiply charged Kr^q+ ions in atomic hydrogen.

A measuring cell for the dielectric study of liquid crystals is presented. This cell allows one to perform measurements for samples having high phase transition temperatures (up to 200 degrees C) within a wide frequency range (1 Hz-1 GHz). Moreover, a small quantity of sample is used and the study of anisotropic phases is easy. After the description of the cell, the authors report dielectric results obtained for two liquid crystals. Various dielectric spectra obtained have shown that this cell have a good behaviour with regard to the temperature and frequency ranges.

A method of measuring ultra-high and -low temperatures is described, whereby the heating or cooling curve of a body is interrogated to yield the temperature gradient at the start of the heating or cooling cycle. It is shown that the asymptotic temperature is proportional to the fourth root of the gradient, hence standard sensors can be used to measure temperatures much greater than their destruction values. Experimental evidence is given in support of the theory and suggested applications are discussed.

Prolonged operation of compact sealed CO₂ TEA lasers has been achieved at pulsed repetition frequencies up to 100 Hz, with the high CO₂ levels (50% and above) needed for maximum peak power output per unit discharge volume. This has hitherto been prevented by the inability to recombine the dissociation products CO and O₂ rapidly enough in high-CO₂, high-PRF conditions. This has now been achieved through the first use of an unheated SnO₂-Pd catalyst (active at -26°C) placed in the mainstream of gas circulated inside the laser. More than 2.5 × 10⁶pulses have been obtained, with no evidence of a limit to the life through decline in catalyst activity or deterioration of the gas discharge

No existing instruments are suitable for use in three-dimensional and oscillatory velocity measurements of water particles in breaking waves so that no such measurements have been reported previously. A new flow meter for the measurements has therefore been designed and constructed. The three velocity components of water particles in a plunging breaker have successfully been measured concurrently using the present flow meter for the first time by considering the flow drag trio of 'tension threads' with each measuring a separate velocity component.

Aperture aberrations affecting the width of the line-focused beam are accurately obtained by using a new shadow-image technique for electrostatic quadrupoles of axial lengths of 20 and 30 mm with an aperture radius of 5 mm. Experimental values are in satisfactory agreement with those calculated by the modified bell-shaped model. The results show that an electrostatic quadrupole lens is very useful for forming fine line patterns. Precision grids, fine gratings and interdigital electrode patterns have been fabricated by using a line-focused beam.

Two single pole piece electron lenses of equal dimensions, one with a cylindrical pole and the other with a spherical pole, are described. The projector focal properties of both lenses were calculated from the experimentally measured axial flux density distributions at different diameters of the axial bore in the pole piece. A comparison is made between the electron optical properties of the two experimental lenses including their projector focal length, radial and spiral distortion. The effect of the pole piece shape and the size of the axial bore on the projector focal properties are discussed in detail. Empirical equations concerning some electron optical properties of single pole piece lenses are put forward. The results should be useful in the design of single pole piece projector lenses for the transmission electron microscope.