Table of contents

Various methods of determining temperature distributions in hot gases and plasmas by spectroscopic techniques are reviewed. A large range of temperature from approximately 10³ to 20*10³ K is considered. Particular attention is paid to the meaning of temperature at these high temperatures, and in this context the concept of 'local thermodynamic equilibrium' is introduced and approximate conditions for its validity are discussed. A brief account is given of recent work on the use of a wall-stabilized arc as a standard of very high temperature and standard of radiation in the vacuum ultraviolet.

A method is described of measuring the position and velocity of a sodium liquid-vapour interface during transient boiling of sodium in a tube. The technique is based on measuring the changes in electrical resistance due to voiding in a sodium-filled tube and is an adaptation of the Jodel probe method previously applicable only to experiments using high constant direct current heating. The present method, using simple apparatus, is independent of the heating method used and is unaffected by the temperature changes occurring during the experiment. A spatial resolution of less than 1 cm and measurement of velocities up to a few metres per second have been achieved.

A cryostat is described in which a sample may be rapidly cooled or linearly heated at various rates to any final temperature in the range 77-800 K. The controlled heating rate ranges from 3 to 50 K min^-1 with linearity to better than 1%. The final temperature may be stabilized to better than 0.1 K, for long periods of time. This cryostat may be used for electrical, optical glow curve measurements.

It is shown that the heat conductivity of a bismuth solder joint at T approximately=0.1 K is much larger than the heat conductivity of connections made with superconducting solder. 'Lambda tight' joints can be made with bismuth solder.

A device for UHV cleavage of crystal specimens is described for use with LEED-Auger apparatus. The device is designed to minimize stress on the crystal holder and to be entirely removable from the area in front of the LEED screen.

By keeping constant the pick-up radius of the Talyrond 73 roundness measuring machine through a series of records it is possible to obtain relative diameters at different heights of a cylinder. Accuracy in diameter is of the order of 0.2 mu m.

A microelectronic structure is described for the measurement of the photoconductivity of various semiconductor dyes. A consequence of the employment of a structure of such small size is that the technique has several important advantages over others commonly used for photoconductivity measurements. Results are presented for cosine and pinacyanol using the new structure.

The design and construction of a gland system used to seal instrumentation wires is discussed. The gland was designed to operate with hydraulic pressures of 3000 lb in^-2 (20700 kPa), and tests have shown that the system functions with pressures of 7200 lb in^-2 (49600 kPa).

The construction is described of a linear, variable range, tensile load cell for use at loads of up to 50 kg.

An approach to a linear variation of the switch thermal conductance K with temperature below 1 K is reported for a mechanical heat switch using copper jaws gripping a gold-plated fin. The conductance follows the relationship K=0.024T+0.011T² mWK^-1.

A description is given of the characteristics of a thin-film gold-palladium photosource arranged for back-illumination by UV photons. The emitter is found to have both a useful service life when operated in air or vapours of organic liquids and to exhibit a high photoelectric yield.

The existence and magnitude of the influence of fluid property variations on the perturbation response of a constant-current hot-wire anemometer is investigated. Analysis and experiments indicate that unless the current injection technique is used for calibrating a constant-current hot-wire anemometer substantial errors will be introduced into the perturbation sensitivity calculation owing to omissions in the usually assumed form of the heat transfer relation for a hot wire.

A compact spark light source has been developed that provides electrically triggered light flashes at high repetition rates. The flashes are of duration about 20 ns (measured between half-peak intensity points) and are subject to a time jitter of less than 5 ns relative to the input trigger pulses. When used with photoelastic and schlieren techniques in the visualization of repetitive pulsed ultrasound the source can stroboscopically resolve the wave features of ultrasound of frequency as high as 10 MHz.

A direct fabrication system has been developed for semiconductor devices. It allows the recording of submicrometre patterns by an electron resist on a semiconductor wafer, using a fine electron beam controlled by a digital computer. The accelerating voltage, incident current and beam diameter are 15 kV, 100 pA and less than 0.2 mu m, respectively. The beam scans the unit field of 0.5 mm square, and an area of 25 mm square on the wafer can be irradiated by means of mechanical stepping and repeating. Four kinds of distortions (amplitude, rotation, trapezoid and shift) can be eliminated so that a registration accuracy of +or-0.2 mu m can be obtained over the whole area. Some microelectronic devices have been fabricated by using this system.

The synchronized astable multivibrator bridge using time delay between pulses, is a new temperature- stabilized linear transducer and a measuring device with a digital counter of R or C parameter changes or corresponding nonelectric quantities. It is used as an error detector, compatible with an electronic relay, bistable multivibrator or corresponding flip-flop integrated circuit, in a simple and reliable on-off servomechanism whose hysteresis or dead zone corresponds to relative changes of a variable element of about 10^-5. This servomechanism is convenient for measurement, control, command or recording, especially for remote operations. Applied with thyristors it can be used as a sensitive and contactless thermostat or switcher.

A novel method for the study of nonlinear dielectric effects has been developed, which allows, for the first time, measurements to be carried out on conductive media such as water. The sample is contained in a dielectric cell which is part of the tank circuit of an oscillator. A rectangular electric field pulse of up to 15 MV m^-1 is applied to the sample, and the resulting frequency change of the oscillator due to the nonlinear dielectric effect is measured using a computing frequency counter. This frequency change is simply related to the change in relative permittivity Delta epsilon . By sampling the frequency of the oscillator at different points throughout the duration of the electric field pulse, a very faithful reproduction of the profile of the nonlinear effect can be built up. Details are given of the instrumentation along with illustrative results for diethyl ether.

A new type of fast ionization gauge is described to measure neutral particle densities in the presence of a plasma in a magnetic field. The gauge has a sensitivity of 6.5m Torr^-1 for nitrogen over the pressure range 70 n Torr to 0.3m Torr. The notable features of the gauge are its small volume, 2.2 cm³, low emission current, 1 mu A, and power dissipation, 2W. With the appropriate choice of electrode potentials the sensitivity changes by no more than 20% when the magnetic field intensity is varied in the range 1.8-3.0 kG. The gauge may be rotated so that its axis makes and angle of +or-15 degrees with the direction of the magnetic field before the sensitivity changes by +or-10%. Its speed of response to a fast rising pulse of gas is less than 300 mu s. A venetian blind type of structure is used to shield the gauge from charged plasma particles. The gauge has been used to monitor the neutral particle density in the PROTO-CLEO stellarator during the plasma confinement period.

A method is described for establishing a linear relationship between a controlling voltage and the ohmic value of a silicon photoconductor in an electrically isolated circuit. Gallium arsenide lamps are used to achieve a wide bandwidth, although it is found that this decreases as the operational range of resistance change increases.

An improved Auger electron spectrometer is presented, using concentric hemispheres accessed by retarding electron lenses. Two modes of operation are available. The first is a constant resolving power mode in which the resolving power is variable from 500 to 4000, by selection of working distance and applied potentials. The collection efficiency is 0.2% of 2 pi sr at a resolving power of 500. The second is a constant hemisphere pass energy mode. By consecutive use of the two modes, the spectrometer will scan from 1 eV to 2 keV. The collection efficiency can be increased to 3% at a resolving power of 300 but aberrations degrade the performance. The analyser is mounted on an 8 in Conflat flange. Finally, the Auger spectrum of lithium is presented.

An adiabatic scanning calorimeter has been made with a controlled heating rate. The sample used was relatively small (3-10g), but the accuracy of the calorimeter was found to be within 2% in temperatures ranging from room temperature to 1000K. It is shown that the temperature distribution in the sample vessel produced in the continuous heating type calorimeter is proportional to the heating rate and inversely proportional to the thermal diffusivity in the sample vessel. An estimate of, and the correction for, the error due to the temperature distribution in the sample vessel has been made. The dehydration reaction of CuSO₄5H₂O was studied, and very sharp, separate, endothermic peaks of the dehydration reaction were obtained.

A miniature Mattauch-Herzog mass spectrometer is described. The electric field radius is 4.3 cm. Detector slits are placed in the magnet focal plane at positions corresponding to magnetic field radii of 1.0 and 2.5 cm. Information pertaining to the resolution and dynamic range is reported.

Symmetrical electrostatic lenses consisting of three apertures of equal diameter were investigated by computer analysis. All the results are represented approximately by three charts. One chart gives the projector focal length, the location of principal plane and the coefficients of spherical and chromatic aberrations as functions of lens strength k and 1/e and width of the axial potential distribution d, and other charts give k and d as functions of lens dimensions. The differences between the projector focal lengths obtained from the charts and those obtained by accurate computations are of the order of several per cent, except for extreme cases. The charts are useful for practical design purposes of the electrostatic lenses.

A device is described which has been designed for the measurement of internal friction Q^-1 and dynamic elastic moduli of piezoelectric crystal resonators. The principle of operation is to excite vibrations in a sample, interrupt the driving signal and count the number of cycles of the freely decaying vibration between two known, preselected amplitudes of oscillation. This method is especially suitable for measuring internal friction of specimens, whose resonant frequencies depend strongly on temperature, because of the very short time required for a single measurement. The apparatus to be described can also be used to investigate samples of materials which are not piezoelectric. In this case additional driver and detector units have to be provided. Generally, this instrument may be used to measure the rate of decay of any vibration provided that it is exponential. The frequency range of the device is 10 Hz to 40 MHz for values of Q between some tens and some millions.

A new system has been designed for measuring circular dichroism with resolution Delta A approximately 10^-5, at approximately 2 ms time constant, and used for stopped-flow circular dichroism spectroscopy. Expressions are derived for signal-to-noise ratio and circular dichroism resolution including contributions from signal current and detector dark current shot noise, and thermal and amplifier noise. An experimental system has been constructed using a mercury arc, piezo-optical birefringence modulator (50 kHz) and silicon photodiode detector. Transient CD signals have been monitored for rapid reactions conducted in a stopped-flow mixing device with dead time less than 1 ms. Phase sensitive detection and analogue division are used for CD signal recovery. The resolution achieved is close to the theoretical prediction. Applications are indicated for the study of ligand-induced conformational changes in biological systems.

The electrical potential in a cylindrically symmetric electrostatic filter lens is developed in a power series. From this is derived the low current limit on the calibration and the resolution of such a lens when using it as an energy analyser in a homogeneous static magnetic field. The results are tabulated as a function of the lens parameter L/a, where 2L is the length and 2a the diameter of the filter lens.

An apparatus for determining the wavelength of maximum reflection of light lambda _R of cholesteric mesophases at high static pressures is described. The arrangement of the whole high pressure equipment is briefly outlined. The pressure chamber allows optical measurements up to 5000 bar and can be thermostated by oil on the outside. Details of the sample cell are illustrated. The generated oil pressure is transmitted to the sample layer of 25 mu m by means of a thin Teflon membrane. By way of example the effect of pressure on the reflection of a cholesteric mixture of cholesteryloleylcarbonate and cholesterylchloride is shown. In a definite pressure range the sensitivity of lambda _R to pressure is so large that it can provide a new accurate means of pressure measurement. This behaviour is probably caused by a pretransition effect of the mesophase.

A two-stage etching technique enables the substrates to be removed from thin p-type layers of gallium arsenide over large areas. An n-type 'blocking layer' is used to retard the etching front during the selective first stage and this is subsequently removed using a nonselective etch. Greater precision is offered by this method than by conventional etching techniques.