Table of contents

After recalling the characteristic properties of a superconductor, the authors present theoretical and experimental results concerning the microwave surface resistance and upper-limit values of the radio frequency fields in a resonant cavity. Details are also given on technological processes used for the fabrication of resonators with high-quality metal surfaces. A great part of the paper is then devoted to the most important field of applications of superconducting resonators: the frequency stabilisation of microwave generators for metrological purposes, and the realisation of electron (or ion) continuous-wave linear accelerators. Other applications also based upon a very low surface resistance are briefly reviewed. Microwave Josephson devices are not considered.

By the use of ceramic-to-metal high-vacuum sealing technology, a sealed-off, miniature, high-power nitrogen laser operating at 337.1 nm has been constructed. The laser is excited transversely by a fast Blumlein pulser and uses UV photoionisation stabilisation. Peak output powers exceed 150 kW with pulse lengths ranging from 0.3 to 1 ns. No deterioration of the output was observed over more than 10⁸ shots.

A simple eddy-current method for the measurement of the electrical resistivity of cylindrical, metallic, non-magnetic samples is presented. The method has proven to be well suited for the study of resistivity changes in phase transitions since it works quasi-continuously during variations of the temperature.

A rotating-head-type torque magnetometer with negative feedback is described. The rotation of the head is effected by a geared stepper motor under direct control of a low-cost dedicated microcomputer, which may be programmed for on-line data processing. Alternatively, the head may be rotated by a small synchronous motor and the analogue output observed on a X-Y pen recorder. The measurable range of torques is from about 10^-8 to 3*10^-4 N m and samples with a maximum mass of about 10 g may be used.

An acoustic surface wave probe has been developed for use in broadband non-destructive testing and in seismological modelling. The probe has a bandwidth of about 0.5-4 MHz but the design is suitable for use up to centre frequencies of about 5 MHz. It takes a negligible amount of energy from the ultrasonic beam and appears to reproduce accurately the shape of an ultrasonic pulse. The probe is characterised by simplicity of construction and operation.

A simple method of measurement of bulk resistivity of soil using an autoranging digital voltmeter is described. The apparatus is battery-operated, portable and weighs only 6 kg. It can be easily constructed using readily available integrated circuits and other electronic components. The use of the method in conjunction with digital data-processing techniques in an archaeological survey is demonstrated.

The design and evaluation of an improved apparatus for the sensitive detection of small thermoelectric effects in insulating samples are reported.

The effect of solder contacts on magnetoresistance measurements has been systematically examined using superconducting materials for the contacts. The results indicate that solder contacts in the conventional four-terminal method can cause severe current distortion and partial shunting of the potential probes, even in fields up to 2.5 T. In these cases the magnetoresistance measurements may not be representative of the intrinsic behaviour of the sample.

A magnetically shielded sampling technique is developed which permits determination of plasma parameters by orifice probe, electrostatic analyser or mass spectrometer for medium-pressure magnetised plasmas. Experimental results show that: for a retarded-electron current no abnormal peak or non-exponential potential dependence of current potential characteristics as observed by previous orifice probe measurements in a magnetised plasma is observed; electron temperature measurements agree to within 10% with recent positive-column electron temperature theory; and plasma density measurements agree to within a factor of 3 with electrostatic probe measurements.

A method of gating the emission from the laser-produced plasmas of solid targets is described. A Pockels cell is operated between parallel polarisers and used as an optical shutter. If the shutter is opened after the continuum and multiply ionised species emission has subsided, a considerably simplified spectrum containing only singly ionised and atomic lines is obtained. Gated spectra from Mg, Al and Fe plasmas are shown.

Certain semiconductors and ionic salts can be made amorphous only under drastic quenching conditions, such as vapour deposition on to a cold substrate. Studies of light scattering by such thin films are most efficiently undertaken using waveguide methods. A prism-film coupler has been developed that can be incorporated into a conventional optical cryostat. Evaporation of the films, optical absorption measurements and trapping of the laser beam in the thin sample film can be performed without breaking the vacuum. This new technique has been used to record for the first time the polarised and depolarised Raman spectra of a non-crystalline BaFCl film condensed on to vitreous silica at liquid nitrogen temperature.

A high-vacuum feedthrough is described which is small and simple to construct and incorporates rigorous screening against noise pick-up. Rotary and linear displacements can be transmitted across the vacuum interface by the feedthrough.

A general criterion is presented for the applicability of the cavity perturbation method to the measurement of the complex dielectric constants of high-loss materials. The criterion has been tested in measurements on water at 10 GHz in the temperature range 0-60 degrees C.

The design and construction of a carbon monoxide waveguide laser is described. An output power of 280 mW was achieved with the laser coolant maintained near room temperature, Laser oscillation on a number of lines, mostly in the nu =14 to nu =13 transition was observed.

The need for, construction and application of three designs of cell are described. The first is for dark conductivity measurements with solid metal electrodes, but adaptable to the observation of photoeffects; the second is for photoeffects but adaptable for dark conductivity; and the third is a simple design for the rapid application of mercury contacts for dark conductimetry.

A pneumatic, horizontal force transducer has been developed and calibrated in the range 0-100 N. An approximate analysis shows that the calibration depends on two of its dimensions only. Tests were carried out to determine the effects of supply pressure and ambient temperature variations. It was found that a 25% change in supply pressure and a 28 degrees C change in ambient temperature caused the calibration to change by 4.0% and 2.2% respectively. The transducer is extremely stiff (a movement of 43 mu m was measured at full load), is easy to manufacture, requires no complex readout devices, and is capable of measuring forces over a wide range. The device operates at a supply pressure of 400 kPa with an air consumption of approximately 1.3*10^-3 m³ s^-1.

An ultrasonic interferometer for the study of liquids in the frequency range 0.1-1.5 GHz has been designed and constructed. The apparatus is robust, simple to operate and, apart from the crystals and their holders, uses standard components. An accuracy of +or-3% in absorption and of +or-1% in velocity has been achieved in measurements of water and cyclohexane.

A combined ion-scattering and secondary-ion mass spectrometer, for use in studies of low-energy ion bombardment of solids, is described. The secondary ions from the target (both sputtered and scattered) are analysed by a momentum analyser having a 14 cm radius and 90 degrees magnetic sector which provides their positive identification in mass and energy. It is an ultrahigh-vacuum instrument; inert-gas primary ions of energies in the range 15-2000 eV are used. The principle of operation, constructional details and capabilities are presented. The use of the instrument in secondary-ion mass spectrometry and ion-scattering studies is discussed. The magnetic analysis used allows the sputtered and scattered ions to be distinguished even at very low primary-ion energies (below 100 eV).

A method of using a two-channel signal averager to obtain simultaneously the AC electric birefringence signals from two Kerr cells mounted in series is described. When one of the cells contains a standard sample this method enables the relative birefringence of the liquid in the second cell to be determined even when turbulence, such as is produced by Joule heating, in the second cell is causing the intensity of the transmitted light to fluctuate. The use of the signal averager together with a linear method of detection enables signals to be obtained from water with field strengths as low as 5*10⁴ V m^-1. Results of measurements of p-xylene, toluene, chloroform and water are given.

A miniature, wideband, horizontal-component feedback seismometer has been developed and compared with conventional seismometers. The instrument employs an inverted pendulum of mass 0.04 kg supported with a natural period of 0.6 s and a Q factor of about 20. Displacements of the mass are sensed by a differential capacitive transducer and feedback is applied via an electromagnetic system to maintain the mass stationary with respect to its supports. The instrument has a response defined by feedback from DC to 100 Hz and has a Brownian noise level of 5*10^-10 m s^-2. Overall dimensions, including an evacuated jacket, are 15 cm*10 cm diameter making it suitable for borehole applications. The instrument has been operated for several weeks with conventional long-period seismometers and has been found to compare satisfactorily.

A method of determining the dielectric relaxation frequency of ionic defect pairs which carry a permanent electric dipole moment is described. The electron paramagnetic resonance (EPR) spectrum of a paramagnetic ion incorporated as a probe in the defect pair is modulated with electric and magnetic fields simultaneously, and a signal proportional to the quadrature component of the electric-field-induced polarisation is detected. This signal is also proportional to that part of the bulk complex permittivity component in " due to the dielectric relaxation of the defect pair, and has the same Debye shape. Thus the new technique makes it possible to identify a peak in the dielectric relaxation spectrum with a particular defect structure determined by EPR. The method is limited to defect pairs which incorporate a paramagnetic ion whose EPR spectrum is visible over a wide temperature range. The successful application of the method to a test case of gadolinium-doped calcium fluoride is described.

New techniques for the interferometric measurement of quasi-static and dynamic pressure variations are discussed. The pressure variations are transmitted through oil contained in a closed cavity and the measurements depend on an experimental calibration constant derived solely from measurements of mass and length. The sensitivities of the interferometers (a Michelson and a Jamin) are adjusted so that pressure variations produce phase changes of less than +or- pi /2; this then allows the pressure variations to be directly displayed. In an application of the technique pressure transducers are calibrated by mounting the elements in the side of the cavity. Their outputs are then compared with pressure variations measured over the frequency range from 0 (quasi-static pressure changes) to 6 kHz.

A fast flashlight is described, the light of which is absorbed in a solution resulting in a temperature jump used for chemical relaxation measurements in the time range from 20 mu s to 0.1 s. The changes in concentrations are measured using a conductivity bridge. The apparatus is also applicable to flash photolysis studies provided that the photolysis is accompanied by a conductivity change.

A non-contacting bore gauge is described which makes use of the fringing capacitance between two live electrodes. The performance characteristics of experimental probes are described together with the temperature sensitivity of the device and the various possible sources of error.

A time-of-flight mass spectrometer with a quadrupole doublet in its flight path has been built up at the Bochum Dynamitron Tandem Laboratory (DTL). The quadrupole doublet allows extension of the flight path and thereby improvement of mass resolution and suppression of background radiation. Using a flight path of 2.60 m we get a mass resolution of 0.95% for alpha particles and of 1.1% for ¹⁶O ions; the solid angle of the spectrometer amounts to 0.94 msr. The ion optical properties of the spectrometer are discussed and illustrated by means of a thick-target scattering experiment.

The position of the movable mirror in a Michelson interferometer may be controlled by means of three capacitor probes situated symmetrically about the mirror. An aluminium-coated portion of the mirror flat serves as one of the capacitor plates, the other being attached to the supporting framework. The mirror itself is positioned at either of its two extremes by means of three piezoelectric elements. Servo-systems are used to compare the capacitance of each probe with a standard capacitor and to apply the resulting error signal to the appropriate piezoelectric support. In this way the stability of the mirror is ultimately limited by the stability of the reference capacitors and supporting framework.

The results of some space charge concentration and electric field measurements made downstream of a source of positive ions in a low-turbulence wind tunnel are described. The plume expansion due to electrostatic effects is compared with the predictions of a simple theory. The experimental technique, previously used for full-scale diffusion experiments in the open air, could probably be adapted for wind tunnel work.

An image converter with an S1 photocathode and a silicon diode array target Vidicon are compared with Kodak High-Speed Infrared film for recording infrared cathodoluminescence from a specimen surface flooded with an electron beam of energy 20-30 kV and current density 1-5 mu A mm^-2, a magnified image of the surface being projected on to the detector by a simple optical system. Test objects were platelet defects in diamond, with platelet diameters ranging from 40 mu m downwards, and the infrared platelet emission lying in a band peaking at 1.25 eV and falling to half-peak intensity at about 1.4 and 1.1 eV. Apparatus arrangements are described, and the results illustrated, in experiments involving cine-recording of the television monitor output of the infrared-sensitive Vidicon, and the visual, photographic and television observation of the output of the infrared image converter used alone and also with further stages of electronic image intensification.

A controlled power supply for the electrolytic enrichment of tritium in environmental samples is described. By use of an alkaline solution of sodium hydroxide as electrolyte, a reservoir feed system, a mild steel cathode and probe and a pure nickel anode a control loop circuit is created, maintaining a constant current density throughout the entire electrolysis. Tritium enrichment factors of *10-70 are obtained with volume enrichment factors of *20-100 with corresponding tritium recoveries of 62.3+1.5%.

The paper 'An apparatus to measure circular dichroism of phototransients' by Slifkin and Allos (see ibid., vol.10, p.508 (1977)) claims to represent the first measurements of the circular dichroism (CD) of transient species induced by photolysis. It is pointed out that Ferrone et al. (1974) reported a system for measuring the transient CD of carbonmonoxy-haemoglobin following photolysis. More importantly, it is believed that the system described by Slifkin and Allos is based on a misconception.

Using pulsed-probe plasma diagnostics (Wokock et al., 1977) for investigating neutral molecular reactions in weakly ionised plasmas, a simultaneous dissociation of two bonds in arsenic trioxide, caused by a single electron impact, has been detected. Wokock and Bradaczek (1977) showed that non-thermal, slowly drifting electrons (6 eV) have a high probability of reacting with neutral plasma molecules. The case of arsenic trioxide vapour has been investigated at a pressure of about 1 Pa and a density of unscattered plasma electrons of 10¹⁴ m^-3. At this pressure, non-maintained discharges can only be realised by a special electrode system (Wokock, 1977).