[en] The objective of prepulse suppression was met by the carbon plasma gun configuration. Improvements in power flow symmetry, however, were limited by large port-to-port variation in the plasma gun outputs. The large variation in plasma outputs was indicated by Faraday cups and by damage on anode stagnation plates. With the goal of reducing the plasma variation, the authors developed a flashboard system to retrofit to the 18 ports. A single stripline with 9 periodically spaced sets of flashover gaps was energized by a single 1.8 μF capacitor bank with 3 μsec period. Two flashboards and two banks thus replaced the 18 guns and 6 banks. A carbon ballast resistor was added in series to each chain of gaps, both to increase the flux output and to reduce port-to-port fluctuations in plasma. The resultant flux was much more uniform and faster-moving than was seen with the carbon guns. The flashboards have conducted as much as 1 1/2 MA per side (3 MA total), with no evident switch losses, and with steepened current rise into the ion diode. The stand-off distance from the flashboard to the anode stagnation plate is only 5 cm, producing a risetime of the flashboard-produced flux of less than 200 ns

[en] Long-lived fuels require the use of higher enrichments of 235U or other fissile materials. Such high levels of fissile material lead to excessive fuel activity at the beginning of life. To counteract this excessive activity, integral fuel burnable absorbers (IFBA) are added to some rods in the fuel assembly. The two commonly used IFBA elements are gadolinium, which is added as gadolinium-oxide to the UO2 powder, and boron, which is applied as a zirconium-diboride coating on the UO2 pellets using plasma spraying or chemical vapor deposition techniques. The incorporation of IFBA into the fuel has to be performed in a nuclear-regulated facility that is physically separated from the main plant. These operations tend to be very costly because of their small volume and can add from 20 to 30% to the manufacturing cost of the fuel. Other manufacturing issues that impact cost and performance are maintaining the correct levels of dosing, the reduction in fuel melting point due to gadolinium-oxide additions, and parasitic neutron absorption at fuel's end-of-life. The goal of the proposed research is to develop an alternative approach that involves incorporation of boron or gadolinium into the outer surface of the fuel cladding material rather than as an additive to the fuel pellets. This paradigm shift will allow for the introduction of the IFBA in a non-nuclear regulated environment and will obviate the necessity of additional handling and processing of the fuel pellets. This could represent significant cost savings and potentially lead to greater reproducibility and control of the burnable fuel in the early stages of the reactor operation. The surface alloying is being performed using the IBEST (Ion Beam Surface Treatment) process developed at Sandia National Laboratories. IBEST involves the delivery of energetic ion beam pulses onto the surface of a material, near-surface melting, and rapid solidification. The non-equilibrium nature of such processing allows f or surface alloying well in excess of the thermodynamically dictated solubility limits, an effect that is particularly relevant to this research due to the negligible solubility of boron and gadolinium in zirconium. University of Wisconsin is performing the near surface materials characterization and analysis, aiding Sandia in process optimization, and promoting educational activities. Westinghouse is performing process manufacturability and scale-up analysis and is performing autoclave testing of the surface treated samples. The duration of this NERI project is 2 years, from 9/2002 to 9/2004

[en] A plasma opening switch (POS) requires the use of a source to inject plasma, usually into the vacuum section of a transmission line of a pulsed power generator. The injection point is typically just upstream of the generator load. A flashboard, which consists of a network of flashover gaps built into a stripline geometry, is capable of providing the drifting plasma source used in the POS. This paper details a series of measurements aimed at optimizing this source plasma in order to obtain improved performance of the combination POS-load system

[en] A number of nuclear techniques have been developed and used to measure ion-diode voltages for plasma-erosion-opening-switch (PEOS) experiments on the Gamble II pulsed-power generator at NRL. The voltage is determined by measuring the energy of protons or deuterons from the diode. The techniques include neutron time-of-flight, neutron-intensity measurements, delayed activations, and stacked-foil activations. These diagnostics have evolved as the voltage developed in PEOS experiments have increased from less than 1 MV to more than 4 MV. Examples of these diagnostics are presented, and the extension of some of these techniques to voltages of more than 20 MV is described. 14 refs., 12 figs

[en] In the past year an alternative plasma source to the Mendel carbon gun has been tested at NRL for the Plasma Erosion Opening Switch (PEOS) program. This source uses flashboard technology originally developed at Sandia National Laboratory for the AMF ION ion diode. Such flashboards can be more readily adapted to different geometries and provide a more distributed plasma source than the discrete gun arrangement. An array of boards has been used to provide the plasma source for PEOS experiments on both Gamble I and II machines at NRL, in both negative and positive polarity, with both short circuit and finite Z loads. In the coaxial geometry used, the source arrays can be expected to provide a more uniformly symmetric plasma which may reduce losses in the magnetically insulated transmission line between the switch and the load. Preliminary data tends to support this

[en] The successful development of the Plasma Opening Switch (POS) for inductive storage applications has been largely confined to negative polarity operation. Some models of POS behavior suggest that this is because in a positive polarity coaxial configuration, the weaker magnetic field at the cathode position retards the switch opening process. This article describes experiments in which both conductor radii in the POS region were significantly reduced. Anode- and cathode-side current monitors indicate that voltages greater than open-circuit are generated at the POS position, but there is a significant amount of electron flow out of the POS, depending upon load impedance. Flow impedance analysis indicates that a relatively small gap appears in the POS plasma after switch opening. Switch performance is also compared between flashboard and carbon gun plasma sources, with the latter operated both in positive and negative polarity

[en] In order for a plasma opening switch (POS) to open quickly and transfer power efficiently from an inductively charged vacuum transmission line to an applied B ion diode, the load impedance of the ion diode may be required to have an initial low impedance phase. A plasma-filled diode has such an impedance history. To test the effect of a plasma-filled diode on POS-diode coupling, a drifting plasma was introduced from the cathode side of an applied B ion diode operated on the LION accelerator (1.5 MV, 4 Ω, 40 ns) at Cornell University. This plasma readily crossed the 2.1 T magnetic insulation field of the diode, and resulted in both increased diode electrical power, and an increased ability of the ion beam to remove material from a target. The plasma did not appear to have a noticeable effect on local beam steering angle

[en] In Inertial Fusion Energy (IFE), Target Chamber Dynamics (TCD) is an integral part of the target chamber design and performance. TCD includes target output, deposition of target X-rays, ions and neutrons in target chamber gases and structures, melting and vaporization of target chamber materials, radiation-hydrodynamics in target chamber vapors and gases, and chamber conditions at the time of target and beam injections. Pulsed power provides a unique environment for IFE-TCD validation experiments in two important ways: pulsed power devices do not require the very clean conditions that lasers need, and they currently provide large X-ray and ion energy fluences

[en] We report on the continuing development of the LEVIS (Laser Evaporation Ion Source) lithium active ion source for the 15-cm radial focussing ion diode on PBFA-11. We found previously that DC-heating of the anode surface to 150 degrees C maximum for 5 hours resulted in a pure lithium beam. This paper discusses the characterization of LEVIS source uniformity by Faraday cup arrays and multiple lines of sight for visible light spectroscopy. These diagnostics give some evidence of nonuniformity in both A-K gap electric fields and ion current density. Despite this, however, the measured focal spot size appears smaller than with a passive LiF source operated in the same magnetic field topology. Experiments using a curved anode for vertical beam focussing show reduced ion beam turn-on delay by 5 ns by altering the magnetic field topology as well as anode curvature. Another 3--5 ns reduction was achieved by switching from a passive LiF to the active LEVIS source

[en] Pulses of MeV-level ions with fluences of up to 20 J/cm² can be expected to impinge on the first-wall of future laser-driven Inertial Fusion Energy (IFE) power plants. To simulate the effect of these ions, we have exposed candidate dry-wall materials to ion pulses from RHEPP-1, located at Sandia National Laboratories. Various forms of tungsten and tungsten alloy were exposed to up to 1000 pulses, with some samples heated to 600 deg. C. Thresholds for roughening and material removal, and evolution of surface morphology were measured and compared with code predictions for materials response. Tungsten is observed to undergo surface roughening and subsurface crack formation that evolves over hundreds of pulses, and which can occur both below and above the melt threshold. Heating and Re-alloying mitigate, but do not eliminate, these apparently thermomechanically-caused effects. Use of a 3-D geometry, and/or use of the tungsten in thin-film form may offer improved survivability compared to bulk tungsten