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Enabling technologies are being developed at Sandia National Laboratories to improve the performance and flexibility of compact pulsed-power drivers for magnetically driven dynamic materials properties research. We have designed a modular system that is capable of precision current pulse shaping through the selective triggering of pulse-forming components into a disk transmission line feeding a strip line load. The system is composed of 240 200-kV 60-kA modules in a low-inductance configuration that is capable of producing 250–350 kbar of magnetic pressure in a 1.75-nH 20-mm-wide strip line load. The system, called Genesis , measures approximately 5 m in diameter and is capable of producing shaped currents that are greater than 5 MA. This performance is enabled through the use of a serviceable solid-dielectric insulator system which minimizes the system inductance and reduces the stored energy and operating voltage requirements. Genesis can be programmed by the user to generate precision pulse shapes with rise times of 220–500 ns, allowing characterization of a range of materials from tungsten to polypropylene. This paper provides an overview of the Genesis design, including the use of genetic optimization to shape currents through selective module triggering. [ABSTRACT FROM PUBLISHER]

The applied electrical fields required to initiate surface flashover of different types of dielectric material immersed in insulating oil have been investigated, by applying impulses of increasing peak voltage until surface flashover occurred. The behavior of the materials in repeatedly over-volted gaps was also analyzed in terms of breakdown mode (some bulk sample breakdown behaviour was witnessed in this regime), time to breakdown, and breakdown voltage. Cylindrical samples of polypropylene, low-density polyethylene, ultra-high molecular weight polyethylene, and Rexolite, were held between two electrodes immersed in insulating oil, and subjected to average applied electrical fields up to 870 kV/cm. Tests were performed in both uniform- and nonuniform- fields, and with different sample topologies. In applied field measurements, polypropylene required the highest levels of average applied field to initiate flashover in all electrode configurations tested, settling at ~600 kV/cm in uniform fields, and ~325 kV/cm in non-uniform fields. In over-volted point-plane gaps, ultra-high molecular weight polyethylene exhibited the longest pre-breakdown delay times. The results will provide comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage, pulsed-power machines. [ABSTRACT FROM AUTHOR]

Corona-stabilised plasma closing switches, filled with electronegative gases such as SF6 and air, have been used in pulsed-power applications as repetitive switching devices for the last 10 years. Their high repetition-rate capabilities coupled with their relatively simple design and construction have made them suitable alternatives to thyratrons and semi-conductor switches. As well as having repetitive switching capabilities, corona-stabilised plasma closing switches have the potential to operate at elevated voltages through the incorporation of multiple electrode sets. This allows high-voltage operation with inherent voltage grading between the electrodes. A further feature of such switches is that they can have relatively low jitter under triggered condition. This paper reports on some of the operational features of a new design of corona-stabilised, cascade switch that utilises air as the insulating gas. At pressures between 0 and 1 bar gauge the switch has be shown to operate over the voltage range of 40 to 100 kV with a jitter below 2 ns. [ABSTRACT FROM AUTHOR]

We are studying the behavior of self-breaking, high-voltage water switches for the Z refurbishment project. In Z-20, three or four water switches in parallel are charged to 4 MV in ∼220 ns. The water gap between switch electrodes is 13-15 cm, and the enhancement of the positive and negative electrodes is varied to study time-evolution of the breakdown arcs, current sharing, and switch simultaneity. In addition to the standard electrical diagnostics (V, I), we are looking at one or more of the switches during the breakdown phase with two optical diagnostics: a streak camera and a fast framing camera. The streak camera has ∼1 -ns resolution, and the framing camera provides seven frames with >5 ns exposure times. For identical electric fields, the streamers originating on the positive electrode form earlier and move more rapidly than the streamers originating on the negative electrode. We observe four distinct phases in the closure of the water switches that depend on the macroscopic electric fields in the water: 1) No streamers propagate at E-fields below ∼ 100 kV/cm from positive electrodes or voltages below ∼ 140 kV/cm for negative electrodes; 2) streamers propagate with constant velocity between 100 and ∼ 300 kV/cm; 3) above 300 kVlcm, the streamer velocities become linearly proportional to the electric field; 4) above 600 kVlcm, the velocity of streamers from the negative electrodes appears to saturate at ∼ 100 cm/ps. The velocity of the streamers from the positive electrode continues to increase with E-field, reaching sim;1% of the speed of light when the switch reaches closure. [ABSTRACT FROM AUTHOR]

Examines the incidence of subnanosecond corona inception in an ultrawideband environment. Diagram of the pulsed corona system; Electrical characteristics of the corona chamber; Correlation between transmitted power and luminosity.

Presents a study which characterized the design, fabrication and testing of a pulser with a parabolic reflector antenna. Role of a transverse electromagnetic structure to the parabolic reflector; Elements of the pulse and antenna system.

Shows that digital image processing methods can be applied to enhance the quality of X-ray microscopic images. What are image restoration methods based on; Application of a iterative image-processing-restoration method to pictures obtained with the Gottingen transmission X-ray microscope at BESSY; Conclusions reached.