Table of contents

Avalanche diodes are finding an increasing number of applications as sources of microwave power in the frequency rane 1-100 GHz. There are two basic modes of operation; the IMPATT mode in which the diode behaves as a negative conductance in a resonant circuit, and the TRAPATT mode in which the diode acts as a fast switch which periodically discharges the circuit elements. The basic features of the two modes are explained in terms of the physical mechanisms involved, and the performances of practical devices are reviewed. It is seen that both IMPATT and TRAPATT diodes will operate as amplifiers as well as oscillators and the properties of a typical X-band IMPATT amplifier are described. Examples of applications which are suitable for IMPATT and TRAPATT devices are also discussed.

The principles upon which accurate measurements of kinetic energy of kilovolt ions are based are illustrated, and the design of an instrument for focusing the ions formed by reactions in a field-free region is described. Reactions that have been studied include spontaneous decompositions as well as charge-stripping, charge-exchange and charge- inversion both for rare gases and for organic compounds. The results give information on the energies of excited states, on double ionization potentials and on electron affinities.

The design of a water-cooled nonsymmetrical RF sputtering electrode suitable for a general purpose vacuum coating unit is described. The reliable bonding techniques of the target to the electrode are also described. Hot pressed targets have been bonded with conducting epoxy resin, and sintered targets by an alloy soldering method.

Some recording instruments produce chart records with axes that may be nonperpendicular and/or nonrectilinear. Difficulties are encountered in attempting to digitize such records with a digitizing instrument mechanically constrained to move only in two perpendicular directions. A computer controlled incremental plotter can be used to simulate the mode in which the data are recorded and to provide an equispaced digital time series for further processing.

A new concept for the elimination of the air buoyancy correction in absolute measurement, i.e. true mass measurement, of small quantities of various substances, such as radioactive sources, precious metals etc., is presented.

A novel method is described for forming narrow, very uniform, graduation marks on the surface of glass tubes used in apparatus for the precise measurement of volumes. The graduation mark is formed by first grooving the surface with a fine hot tungsten wire and then 'pencilling' in with cold zirconium foil.

When a diameter is defined by surfaces unsuitable for mechanical contact, then a low-angle reflection setting technique may offer a means of measurement. The arrangement described here involves telescopes for setting and, for convenience, a laser interferometer for measurement. Several applications are possible including diameter measurements from 5 mm upwards with an uncertainty of 1.7 mu m. Factors affecting the overall accuracy are discussed, constructional details are given and several likely applications are listed.

A servo controlled Fabry-Perot interferometer using capacitance micrometers to sense departures from parallelism and variations in the mean spacing of the Fabry-Perot plates is described. The parallelism and mean spacing of the plates is maintained over the full 75 mm aperture of the instrument to an accuracy better than the surface quality of the plates ( approximately lambda /150 at 500 nm).

A time-of-flight machine for the velocity analysis of molecular beams is described together with an experimental investigation of systematic errors. A velocity selecting chopper is used to measure all delay times, including the delay in the beam detector due to the extraction time from the ionizer and the flight time of the ions in the quadrupole mass filter. With the ionizer no memory effects occur at emission currents smaller than 1 mA. Memory effects in the detector chamber due to the direct reflection of beam particles are eliminated.

An interpolation equation for a 470 Omega , 0.5 W Speer resistor has been found, which with 20 calibration points enables an interpolation accuracy of better than 3 mK to be obtained in the range 0.3-4 K and in magnetic fields of up to 6.5 T.

A calibration system has been designed and built at the NPL for the calibration of ultrahigh vacuum gauges in a well distributed maxwellian gas. The system has a base pressure of approximately 2 nPa, and calculable gas pressures can be generated using the orifice flow technique. The apparatus uses a cryopump in a novel way to condense the gas molecules passing through the primary orifice. A full description is given of the metrology of the apparatus and an error analysis is also included. It is concluded that known pressure increments can be produced in the range 3 nPa to 0.1 mPa to within +or-7%.

High peak power output has been obtained from a transversely excited CO₂ laser in a single longitudinal mode, operating on a single rotational line and the lowest order transverse mode at 9.3, 9.6 and 10.6 mu m. The laser was designed to operate with high efficiency at reduced pressures and low voltage. Mode selection was by means of an intracavity germanium etalon.

An automatic photomultiplier cooler for a photon counting system has been constructed with thermo-elements. The apparatus has a high sensitivity of 0.0025 degrees C and a stability of +or-0.005 degrees C. The photomultiplier temperature is adjustable between room temperature and -20 degrees C.

A theoretical analysis has been undertaken of the application of an indicator dilution technique, using bolus injection, to the measurement of flow rate, mean transit time and vessel volume in a straight tube, for both mixed and laminar flow. Under laminar flow conditions, formulae previously utilized may be substantially wrong. Alternative methods and formulae are proposed and experimental confirmation made of their validity over a wide range of flow conditions.

A simple method of correcting hot wire probe measurements of conduction losses is presented. Such losses are particularly important in low density flows where they are frequently larger than the convective heat losses to be measured. The correction scheme has been tested experimentally and found to give satisfactory results.

A cylindrical electrostatic particle guide incorporating a 90 degrees bend has been constructed and tested. Transmission efficiency and beam profile are investigated for 500 eV. electrons and the results suggest that the technique will be particularly suited to low energy ion beam transport over nonrectilinear trajectories.

The authors discuss the use of Pt-Pt/13%Rh thermocouples coated with (1) silica and (2) quartz tubing. The protection from surface reaction, and catalysis effects on the surface are discussed.

A description of the use of the Casella dew point apparatus (T9308) for the determination of atmospheric dew point. The instrument consists of two chambers, thermally in contact but separated by a heat-conducting polished metal mirror.