Publications

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

High voltage vacuum systems with stringent vacuum requirements are often designed with ceramic insulators which have low flashover strength. In this paper, we report on experimental results comparing pulsed high voltage flashover of Rexolite®(cross-linked polystyrene), a pulsed power industry standard vacuum insulator, to Kel-F® (polyclorotrifluoroethylene), a plastic with significantly lower vacuum outgassing. Our results show similar surface flashover results with the two materials, with both exhibiting large spread in flashover electric field. The average electric field for flashover of each material agree well with predictions based on previously published results.

Here we present details of the design, simulation, and performance of a 100-GW linear transformer driver (LTD) cavity at Sandia National Laboratories. The cavity consists of 20 “bricks.” Each brick is comprised of two 80 nF, 100 kV capacitors connected electrically in series with a custom, 200 kV, three-electrode, field-distortion gas switch. The brick capacitors are bipolar charged to ±100 kV for a total switch voltage of 200 kV. Typical brick circuit parameters are 40 nF capacitance (two 80 nF capacitors in series) and 160 nH inductance. The switch electrodes are fabricated from a WCu alloy and are operated with breathable air. Over the course of 6,556 shots the cavity generated a peak electrical current and power of 1.03 MA (±1.8%) and 106 GW (±3.1%). Experimental results are consistent (to within uncertainties) with circuit simulations for normal operation, and expected failure modes including prefire and late-fire events. New features of this development that are reported here in detail include: (1) 100 ns, 1 MA, 100-GW output from a 2.2 m diameter LTD into a 0.1 Ω load, (2) high-impedance solid charging resistors that are optimized for this application, and (3) evaluation of maintenance-free trigger circuits using capacitive coupling and inductive isolation.

The results presented here were obtained with a self-magnetic pinch (SMP) diode mounted at the front high voltage end of the RITS accelerator. RITS is a Self-Magnetically Insulated Transmission Line (MITL) voltage adder that adds the voltage pulse of six 1.3 MV inductively insulated cavities. The RITS driver together with the SMP diode has produced x-ray spots of the order of 1 mm in diameter and doses adequate for the radiographic imaging of high area density objects. Although, through the years, a number of different types of radiographic electron diodes have been utilized with SABER, HERMES III and RITS accelerators, the SMP diode appears to be the most successful and simplest diode for the radiographic investigation of various objects. Our experiments had two objectives: first to measure the contribution of the back-streaming ion currents emitted from the anode target and second to try to evaluate the energy of those ions and hence the Anode-Cathode (A-K) gap actual voltage. In any very high voltage inductive voltage adder utilizing MITLs to transmit the power to the diode load, the precise knowledge of the accelerating voltage applied on the A-K gap is problematic. This is even more difficult in an SMP diode where the A-K gap is very small (∼1 cm) and the diode region very hostile. The accelerating voltage quoted in the literature is from estimates based on the measurements of the anode and cathode currents of the MITL far upstream from the diode and utilizing the para-potential flow theories and inductive corrections. Thus, it would be interesting to have another independent measurement to evaluate the A-K voltage. The diode's anode is made of a number of high-Z metals in order to produce copious and energetic flash x-rays. It was established experimentally that the back-streaming ion currents are a strong function of the anode materials and their stage of cleanness. We have measured the back-streaming ion currents emitted from the anode and propagating through a hollow cathode tip for various diode configurations and different techniques of target cleaning treatment: namely, heating at very high temperatures with DC and pulsed current, with RF plasma cleaning, and with both plasma cleaning and heating. We have also evaluated the A-K gap voltage by energy filtering technique. Experimental results in comparison with LSP simulations are presented.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

In this study, we have developed a conceptual design of a next-generation pulsed-power accelerator that is optmized for driving megajoule-class dynamic-material-physics experiments at pressures as high as 1 TPa. The design is based on an accelerator architecture that is founded on three concepts: single-stage electrical-pulse compression, impedance matching, and transit-time-isolated drive circuits. Since much of the accelerator is water insulated, we refer to this machine as Neptune. The prime power source of Neptune consists of 600 independent impedance-matched Marx generators. As much as 0.8 MJ and 20 MA can be delivered in a 300-ns pulse to a 16-mΩ physics load; hence Neptune is a megajoule-class 20-MA arbitrary waveform generator. Neptune will allow the international scientific community to conduct dynamic equation-of-state, phase-transition, mechanical-property, and other material-physics experiments with a wide variety of well-defined drive-pressure time histories. Because Neptune can deliver on the order of a megajoule to a load, such experiments can be conducted on centimeter-scale samples at terapascal pressures with time histories as long as 1 μs.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Presently the Self Magnetic Pinch (SMP) diode is successfully utilized for flash radiography with pulsed power drivers. However, it is not capable of more than one pulse. Multi-pulse single-Axis radiography is most preferred since it provides images of time-evolving dynamic targets. In an SMP diode, because the anode cathode (A-K) gap is very small (∼1-2 cm), the debris from the anode converter target arrives soon after the first pulse and completely destroy the cathode electron emitter, and thus the diode cannot produce a second pulse. We propose a feasibility study to scientifically evaluate the idea of decoupling the anode converter from the cathode electron emitter. This work will be based on two successful previous works we have accomplished: first, making a very small pencil-like beam in a magnetically immersed foilless diode (M.G. Mazarakis et al., Applied Physics Letters, 7, pp. 832 (1996)); and second, successfully demonstrating the two-pulse operation of a foilless diode with the RIIM accelerator (M. G. Mazarakis et al., Applied Physics 64 part I pp. 4815, (1988) Our approach will combine the above experimentally demonstrated successful work. The generated beam of 40-50 kA will be propagated in the same diode magnetic solenoid for a sufficient distance before striking the converter target. This way the diode could be multi-pulsed before the target debris reaches the cathode. Although the above describes the option of a foilless diode and a solenoidal transport system, a similar design could be made for a non-immersed low emittance 10 kA velvet emitter foilless diode.

Abstract not provided.

Abstract not provided.

Abstract not provided.