US Government as Represented by the Secretary of the Army

Lawrence J Bovino

Maurice Weiner

Anderson H Kim

Terence Burke

Louis J Jasper, Jr

Robert J Youmans

William H Wright, Jr

A high power, solid state burst generator for producing RF pulses includes a plurality of transmission lines, such as coaxial cables, having one end connected across a load via a plurality of photoconductive switches, one for each line. The other end of the transmission lines are terminated in open ends and connected to a charging DC voltage. One set of lines is connected to a positive DC voltage +V while other set is connected to a negative DC voltage -V. A laser is coupled to one end of a plurality of fiber optic lines, each having a different length, for simultaneously launching switch pulses thereon. The other ends of the fiber optic lines are each coupled to a different one of the photoconductive switches for closing and opening the switches in a sequential fashion such that the lines are sequentially discharged through the load to generate a cyclic series of pulses.

High power, solid state RF pulse generators

A spark gap switch having a mid-plane or triggering electrode is brought o a conductive state using a photoconductive switch or other suitable switch, closed by a laser pulse on other pulsed light source. The photoconductive switch is connected between one of the primary electrodes and the mid-plane electrode and brings the potential of the mid-plane electrode to the same potential as the primary electrode when the photoconductive switch is closed. The use of the photoconductive switch permits shorter closing times and eliminates the need for high voltage auxiliary triggering circuits. Plural photoconductive switches, which are triggered in a precise predetermined sequence, improve the operation of Marx generators and other multi-spark gap switch applications.

Triggering technique for multi-electrode spark gap switch

Waveform configuration and/or power accumulation are accomplished with a ial transmission line that includes a pair of electrodes. One electrode is segmented to have at least two independent sections disposed in radial sequence relative to an axis passing perpendicularly through the electrodes. Individual voltage levels are applied between each independent section and the other electrode, while optical switches are disposed between each radially adjacent pair of independent sections for controlling electrical conductivity therebetween. The magnitude of the individual voltages, as well as the phasing of the optical switches are determined in accordance with the desired waveform configuration and power level. For purposes of power accumulation only, a plurality of such radial transmission lines may be connected in series to a load through a coaxial waveguide, with each being arranged to generate the same waveform, while the waveform generated by each is delayed to enhance the cumulative waveform amplitude that passes thereto from the immediately preceding radial transmisison line in the conductive path to the load.

Radial transmission line for waveform generation and power accumulation

An electromagnetic launcher or railgun includes a projectile or armature which is comprised of an optically activated semiconductor switch device including a body of bulk semiconductor material, such as gallium arsenide (GaAs) or gallium arsenide doped with chromium (Cr: GaAs), located between a pair of rails across which is connected a relatively high current source. A source of optical energy, such as a pulsed laser, directs optical energy to at least one surface of the semiconductor switch device where the conductivity of the semiconductor body is thereby increased and current from the source is transferred between the rails through the semiconductor body, causing an electromagnetic Lorentz type drive force to be built up behind the armature, which is set into motion and rapidly accelerated along the rails.

Laser controlled semiconductor armature for electromagnetic launchers

Utilizing sections of charged transmission line cables and optically-actied semiconductor switches, the direct generation of high power RF is demonstrated.

High power RF generation with optically activated bulk GaAs devices

A Marx high voltage generator with a fast rise time. Photoconductive semiconductor switches are sequentially triggered by a single laser via fiber optic bundles of different lengths. The switches serve to series connect a group of charged capacitors. Output is taken from the last capacitor which receives the voltage accumulated on all of the previous capacitors. Proper timing of the activation of each switch produces a fast rise time.

Asynchronous marx generator utilizing photo-conductive semiconductor

A high energy, optically controlled kilovolt semiconductor switch is provd including a bulk piece of high resistivity semiconductor for illumination by a high speed laser, said semiconductor having a thick highly doped epitaxial layer of P+ impurity grown on one side of the semiconductor, and a thick highly doped epitaxial layer of N+ impurity grown on the opposite side of the semiconductor with metallic electrodes deposited on the respective epitaxial layers using standard ohmic contact procedures.

High energy optically controlled kilovolt semiconductor switch

Solid state optically activated switches in which a plurality of spaced cacts are arranged in a line on one of the broad surfaces of a semiconductor wafer and one or more bridging electrodes are arranged on the opposite broad surface thereof. The two end contacts are the switch terminals. This arrangement directs the electric field and the load current into the bulk of the semiconductor in a zig-zag fashion to provide a high hold-off voltage and a short conduction path. Also the bridging electrode can be used as a control electrode. A novel circuit utilizing such switches is shown.

Multiple gap optically activated switch

A high power solid state source of microwave and millimeter wave signals is provided by an optically triggered body of bulk semiconductor material selected from the Group III-V compounds including GaAs, Cr:GaAs, and Fe:InP and having a relatively long gap length which is in the order of 0.5 to 10.0 mm as well as having a resistivity which is greater than 1.times.10.sup.7 ohm-cm. The device is further dc biased to a field of between 15 kV/cm and 35 kV/cm. Under such conditions, a very low dc current flows without any oscillatory behavior; however, illumination of the semiconductor body with a fast rising optical pulse having a wavelength suitable for carrier generation causes electrons to be lifted to the conduction band which is accompanied by a rapid reduction of the resistivity. At the same time, the electric field across the gap length decreases to a value just above the oscillation threshold whereupon high power RF oscillations are generated whose frequency is a function of the recombination time of the excited carriers.

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Eatontown, NJ, United States of America

Lawrence J Bovino