Showing papers on "Marx generator published in 1990"

Repetitive flash x‐ray generator utilizing a simple diode with a new type of energy‐selective function

Abstract: The construction and the fundamental studies of a repetitive flash x‐ray generator having a simple diode with an energy‐selective function are described. This generator consisted of the following components: a constant high‐voltage power supply, a high‐voltage pulser, a repetitive high‐energy impulse switching system, a turbo molecular pump, and a flash x‐ray tube. The circuit of this pulser employed a modified two‐stage surge Marx generator with a capacity during main discharge of 425pF. The x‐ray tube was of the demountable‐diode type which was connected to the turbo molecular pump and consisted of the following major devices: a rod‐shaped anode tip made of tungsten, a disk cathode made of graphite, an aluminum filter, and a tube body made of glass. Two condensers inside of the pulser were charged from 40 to 60 kV, and the output voltage was about 1.9 times the charging voltage. The peak tube voltage was primarily determined by the anode‐cathode (A‐C) space, and the peak tube current was less than 0.6 kA. The peak tube voltage slightly increased when the charging voltage was increased, but the amount of change rate was small. Thus, the maximum photon energy could be easily controlled by varying the A‐C space. The pulse width ranged from 40 to 100 ns, and the x‐ray intensity was less than 1.0 μC/kg at 0.3 m per pulse. The repetitive frequency was less than 50 Hz, and the effective focal spot size was determined by the diameter of the anode tip and ranged from 0.5 to 3.0 mm in diameter.

Compact high voltage power supply

Abstract: A high voltage power supply having energy storage, charging and switching elements and using an interruptible switch as the switching element for efficient, compact and safe operation. In a specific embodiment, the interruptible switch is implemented with at least one cold cathode grid-controlled, crossed field plasma switch and associated control circuit. The charging element is a Marx bank which can be capacitive or inductive. Embodiments with a single master-slave control arrangement, a pulse-forming network providing high voltage regulation, an inductive implementation with a plurality of switching elements in a single envelope with the cathode of at least one switching element being the anode of the next switching element are disclosed. A current amplifier and voltage regulator implemented with a cold cathode grid-controlled, crossed field plasma switch having a cathode, an anode and a control grid therebetween are disclosed.

Discharge kinetics and emission characteristics of a large-area-cold cathode flash X-ray tube: parametric study and numerical modelling.

Abstract: A pulsed X-ray tube is described which consists of a large-area (80-400 cm2) cold carbon felt cathode and a tantalum foil anode arranged in transmission geometry. It is driven by a Marx generator with an output voltage between 60 and 140 kV. The dose and the dose rate of the X-ray flash together with the diode current are studied as a function of anode-cathode distance, the cathode area and the charging voltage. The tube characteristics are numerically well described by a simple model which considers cathode plasma migration and a space-charge limited current in the remaining vacuum gap.

Compact, mega-volt, rep-rated Marx generators

Abstract: A concept for compact, megavolt Marx generators has been developed, resulting in several functional designs which are approximately 1/2 the diameter and 1/4 to 1/2 the height of conventional units. The customized Marx capacitor assemblies utilize multiple windings which have been incorporated into a single common capacitor case. Spark gap switch electrodes extend directly from the external capacitor terminals, eliminating the need for additional buswork. In order to construct the Marx generator, two such capacitor assemblies are positioned directly opposite each other so that the electrodes line up in a vertical column between the two assemblies. More than 10000 shots have been recorded to date with a test system with no major system failures. The entire Marx bank, charging inductors, and trigger circuit are contained in a cylindrical gas vessel 30 in. in diameter and 22 in. in height, weighing approximately 160 lb. >

An optically triggered, glow switch Marx bank

Abstract: Operation of high-powers lasers, electron and other accelerators, and other devices is often limited by power modulator performance. Results of an investigation of a concept for modulator switching that has the potential to significantly extend these limitations presented. The switching device is a three-stage Marx bank based on back-lighted thyratrons that are triggered using optical fibers. Potential advantages include optical isolation of triggering, operation of the switches in a glow mode, no external cathode heater, reduced volume and supporting systems, and high-precision (subnanosecond) triggering. A three-stage proof-of-principle Marx bank has been operated at 105 kV with a rise time of >

The Bushing Test Facility: A new megavolt-class, meter-scale vacuum insulation test facility

Abstract: Construction of the Bushing Test Facility (BTF) was completed at the Los Alamos National Laboratory (LANL) in the fall of 1989. The BTF is a new megavolt-class, meter-scale vacuum insulation test facility built to meet two primary objectives: (1) to qualify high-voltage vacuum feedthrough bushings before their installation in the electron-beam diodes of the Aurora KrF laser amplifiers and (2) to investigate fundamental issues related to surface flashover and electrical breakdown in vacuum, thereby enabling us to improve the performance and reliability of high-voltage components for future laser systems. The BTF voltage source is a low-energy (<4.4-kJ), 1-MV Marx generator whose output pulse width is variable from 100 ns to a few microseconds. The large BTF test chamber (2.1 m in diameter and 1.5 m long) allows full-sized Aurora bushings or other large-scale vacuum insulators to be tested at background pressures down to about 10{sup {minus}7} torr. This paper will further describe the facility, its experimental checkout and first bushing tests, and the plans for future vacuum insulation research. 11 refs., 5 figs.

Generation of a high power electron beam from a 2.6 MV vacuum field emission diode

Abstract: A ∼ 94 GW pulsed electron beam has been generated from a 2.6 MV high impedance vacuum field emission diode with a dielectric field shaper. The voltage pulse applied to the diode was produced from a high power system consisting of a 1.2 MV. 21 kJ Marx generator, a 9.2 ω water filled Blumlein line and a tapered coaxial impedance transformer (9.2 ω → 23 ω ). The maximum beam energy and beam current are 2.6 MeV and 36 kA, which is in accordance with the equivalent circuit predictions. When this beam hits a 50 μm tantalum anode, a bremsstrahlung pulse of ∼ 7.5 R and ∼ 70 ns pulse width is obtained 1 m behind the anode.