In this paper we report on the experimentation conducted on vertical optically activated switches fabricated from GaAs grown by Liquid Encapsulated Czochralski (LEC) and Vertical Gradient Freeze (VGF) techniques. Heavily doped contact regions have been grown on the bulk GaAs to form n-SI GaAs-n and p-S1 GaAs-n structures. Dark dc I-V characterisation has been used to assess the voltage withstand characteristics of the devices demonstrating 3.5kV hold-off for reverse biased LEC and VGF p-SI GaAs-n devices. Optical activation has achieved a ins switch closure time with VGF p+-SI GaAs-n devices reverse biased at 7kV and 2ns switch closure times for VGF n-SI GaAs-n devices biased at 4.5kV. The voltage drop across the optically activated switches was characterised in terms of two components; a constant and a resistive voltage drop.
Abslracl-This paper presents the results from an experimental investigation of plasma armature behaviour in the Culham Laboratory HTF rail launcher. The object of this work was to gain further insight into the conditions which lead
OBJECTIVESThe main objectives of this work were: --to the formation of secondary plasma arcs in the rail launcher. The railgun was operated with a 1 cm square bore formed . from glass reinforced epoxy insulators and either stainless steel or copper rails. A 1 MJ, 8 kV capacitor bank was used as the power supply; this was arranged in five 200 kJ modules. The modules were sequentially fired, to produce a current waveform approximating to a linear ramp in the railgun. B-dot probes were used to measure the behaviour of the plasma armatures in the launcher. A number of calibration checks were performed to assess the quality of the B-dot probe measurements, with regard to both spatial resolution and rail current measurement. Experimental results were obtained with projectile muzzle velocities ranging from 1.5 km/s to 3.0 kmls; two free arc shots also occurred during the test series. The results show that the launcher performed much better with copper rails than with stainless steel rails. The results also show that the glass epoxy insulators performed much better than the acetyl copolymer material previously used in HTF.
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