R.A. Stuart

Evidence of optical generation of minority carriers from saturated MOS transistors

Abstract Minority carrier injection into the substrate by a MOS transistor operating in saturation presents a reliability problem in dynamic memory circuits such as RAMs and CCDs. The effect has been studied by measuring the substrate and drain currents of stressed transistors as a function of gate and drain voltages, firstly by the accumulation of minority carriers in a charge coupled device, and secondly by the direct detection of light from the drain region of a transistor. These results suggest that light emission associated with multiplication in the drain region is more important than the secondary impact ionization mechanism in the generation of minority carriers.

Gain enhancement for waveguide FEL systems using an optical klystron configuration

The application of an optical klystron configuration to waveguide free electron laser systems is proposed either as a gain enhancement scheme or as a way to reduce the beam current necessary for a given gain requirement. An analytical formulation is developed for these devices in the small signal regime. The feasibility of an optical klystron arrangement for FEL systems operating in the far infrared and submillimetre regions is studied. It is shown that with the excellent beam quality of electrostatic accelerators, the optical klystron scheme is an effective means to improve the small signal gain.

Low-voltage ubitrons for industrial purposes

Abstract Based on a consideration of the industrial constraints likely to be placed on any FEL-based technology, a three-stage programme has been undertaken at Liverpool to produce FEL oscillators operating cw at voltages less than 400 kV with outputs in the range from 10 to 1000 GHz at kW levels. The design for stage 1, a 10 GHz device, is based on a dielectrically loaded guide and is reported in this article. The results of gain calculations are presented.

Low cost undulator magnets for industrial free electron masers

At the University of Liverpool we are developing free electron masers <100 kV as a power source for industrial microwave applications. In order to be considered practical, such a device needs to have a cost comparable with conventional sources of microwave power. To achieve this we required an undulator magnet design which was considerably less expensive than the designs normally used in research-based free electron lasers and free electron masers. This paper describes techniques used to successfully construct low cost undulator magnets.

Thickness and field dependence of defects in silicon dioxide

Abstract The Liquid Crystal Technique is used to determine the variation of saturation defect density with applied field and film thickness, in thermal oxides of silicon. The results are consistent with trap controlled space charge limited currents occurring in the region of a defect. Various parameters of the free charge, and traps, are estimated.

Mode selection in a waveguide FEL

Abstract The use of waveguides in low voltage FELs introduces many new features, among which, that of two positive gain peaks is of most interest. One of the problems encountered in designing a waveguide FEL oscillator is to suppress the lower frequency peak, which may have a higher gain than the more useful higher frequency peak. We propose a technique using a dispersive wiggler to select a desired peak from the various participating cavity modes. The principle of this cavity mode selection technique is discussed, and its feasibility tested with a simple example. It is shown that this technique can have many advantages over alternative techniques.

Polarity dependent oxide defects located using liquid crystals

Abstract Liquid crystals have been used to study, non-destructively, the localized regions of high conductivity known to be present in thin layers of silicon dioxide grown thermally on n type silicon. The polarity dependence of the turbulence in the liquid crystals, together with the growth in the number of defects with time suggests that mobile impurity ions play an important role.

The dependence of the oscillation frequency of an FEM on beam voltage

Abstract A waveguide free electron maser oscillator operating in the X-band frequency range has been constructed. It has been observed that the frequencies of oscillation, although close to the longitudinal modes of the cavity, vary slightly with electron beam voltage. It is proposed that this effect is due to the voltage-dependent variation in the phase of the radiation caused by the interaction with the electron beam. An initial comparison has been made between the observed variation of frequency with voltage and simple calculations carried out using the small signal approximation.

Simulation of an optical klystron waveguide FEL

Abstract It is suggested that an optical klystron FEL operating in a waveguide could provide a compact source of mm wave and far infrared radiation with both a low voltage and a low electron beam requirement. As a first step in determining the feasibility of this suggestion, a method of calculating the small signal gain of a waveguide optical klystron is outlined and some results are presented.

Cut-off mode suppression in a waveguide FEM oscillator

We have constructed a waveguide FEM oscillator for use as a power source in research into industrial microwave applications. We report problems encountered when attempting to increase the output coupling of this device and present the results of our attempted solutions.