Thin film oxide phosphors are prospective for low-voltage field-emission display applications due to their appropriate color coordinates, high efficiency, and possibility of creation of increased conductivity in them. Long-term stability of phosphors is also very important for practical application. Therefore, long-term stability of the most efficient thin film oxide phosphors Y{sub 2}O{sub 3}:Eu, Zn{sub 2}SiO{sub 4}:Mn, Zn{sub 2}SiO{sub 4}:Ti, and Y{sub 2}SiO{sub 5}:Ce was investigated in present work.

Studies conducted over the past several years have shown that electron attachment to highly-excited states of molecules have extremely large cross sections. We will discuss the implications of this for pulsed discharges used for H^- generation, material processing, and plasma remediation.

A Discontinuous Galerkin (DG) method is applied to hyperbolic systems that contain stiff relaxation terms. We demonstrate that when the relaxation time is under-resolved, DG is accurate in the sense that the method accurately represents the system's Chapman-Enskog (or ''diffusion'') approximation. Moreover, we demonstrate that a high-resolution, finite-volume method using the same time-integration method as DG is very inaccurate in the diffusion limit. Results for DG are presented for the hyperbolic heat equation, the Broadwell model of gas kinetics, and coupled radiation-hydrodynamics.

Ceramics with their hardness, chemical stability, and refractoriness could be used to design more efficient energy generation and conversion systems as well as numerous other applications. However, we have needed to develop a fundamental understanding of how to tailor ceramics to improve their performance, especially to overcome their brittle nature. One of the advances in this respect was the incorporation of very strong microscopic rod-like reinforcements in the form of whiskers that serve to hold the ceramic together making it tougher and resistant to fracture. This microscopic reinforcement approach has a number of features that are similar to continuous fiber-reinforced ceramics; however, some of the details are modified. For instance, the strengths of the microscopic reinforcements must be higher as they typically have much stronger interfaces. For instance, single crystal silicon carbide whiskers can have tensile strengths in excess of {ge}7 GPa or >2 times that of continuous fibers. Furthermore, reinforcement pullout is limited to lengths of a few microns in the case of microscopic reinforcement due as much to the higher interfacial shear resistance as to the limit of the reinforcement lengths. On the other hand, the microscopic reinforcement approach can be generated in-situ during the processing of ceramics. …

The problem considered is the use of time series data to do model updating in nonlinear structural systems for which the mathematical form of the system nonlinearities is known ahead of time. This work is a departure from most classical model updating work, which utilizes model data to update linear structural dynamics models. In the present application a singular value decomposition (SVD) of the measured data (e.g., m of the N coordinates are measured at n sampling times) is the basis of the updating. The SVD produces a representation of the data as a linear combination of the so-called principal components, which are analogous to modal coordinate time histories in a linear system. The structural dynamics model parameters are updated by minimizing the differences in the SVD's of the experimental data and the model simulations. This method, proposed by Hasselman et al (IMAC 1998), has been applied to both simulated and actual experimental data for low degree of freedom spring-mass systems with cubic nonlinearity and light damping. The main results that will be presented are the following: (1) the SVD updating is robust in the presence of noise, (2) SVD based updating is effective for both linear and nonlinear systems, …

Atlas is a pulsed-power facility under development at Los Alamos National Laboratory to drive high-energy density experiments. Design has been completed for this new generation pulsed-power machine consisting of an azimuthal array of 24, 240-kV Marx modules and transmission lines supplying current to the load region at the machine center. The transmission line consists of a cable header, load protection switch, and tri-plate assembly interfacing to the center transition section. The cable header interface to the Marx module provides a mechanism to remove the Marx module for maintenance without removing other components of the transmission line. The load protection switch provides a mechanism for protecting the load during charging of the Marx in the event of a pre-fire condition. The aluminum tri-plate is a low-inductance transmission line carries radial current flow from the Marx energy storage system at the machine periphery toward the load. All transmission line components are oil insulated except the solid-dielectric insulated power flow channel connected directly to the load. The transition region at the machine center consists of several components that enable the radial converging vertical transmission lines to interface to a horizontal disk/conical power flow channel delivering current to the load. The current carrying transition …

Atlas is a high-energy pulsed-power facility under construction at Los Alamos National Laboratory. When completed in late 2000, Atlas will provide a laboratory environment to perform shock compression experiments in regimes presently unattainable by other methods. The high-energy-density environment on Atlas will be produced by the rapid ({approximately}4{micro}s) implosion of a 20--40 gram, {approximately}4cm radius, 4 cm length cylindrical aluminum or aluminum/high-Z composite liner, driven by a fast current pulse of {approximately}32 MA from a 24 MJ capacitor bank. Implosion velocities up to 20 km/s are predicted, allowing Hugoniot experiments to {approximately}20 Mbar and quasi-adiabatic compression to several Mbar. However, many issues face scientist in performing such experiments, including how to diagnose conditions inside the imploding liner, how to correct results for distortions and density gradients created by the cylindrical geometry and magnetic drive, and how to prevent geometric distortions and instabilities from degrading results. In this paper, liner performance is predicted for a shock compression experiment utilizing 1-D MHD simulations, and the effect of gradients in density, pressure, and velocity in the impactor prior to collision are discussed.

The authors are developing the Ranchero high explosive pulsed power (HEPP) system to power cylindrically imploding solid-density liners for hydrodynamics experiments. The near-term goal is to conduct experiments in the regime pertinent to the Atlas Capacitor bank. That is, they will attempt to implode liners of {approximately}50 g mass at velocities approaching 15 km/sec. The basic building block of the HEPP system is a coaxial generator with a 304.8 mm diameter stator, and an initial armature diameter of 152 mm. The armature is expanded by a high explosive (HE) charge detonated simultaneously along its axis. They have reported a variety of experiments conducted with generator modules 43 cm long and have presented an initial design for hydrodynamic liner experiments. In this paper they give a synopsis of their first system test, and a status report on the development of a generator module that is 1.4 m long.

An instrument was developed for the direct mass flow calibration of gas flowmeters that does not require measurement of temperature, pressure, or specific volume. This instrument measures the weight of gas collected in a container and makes measuring those thermodynamic variables unnecessary. The need to measure the weight of the gas container is eliminated by submerging it in a liquid (presently water) and balancing its weight with the force of buoyancy. The accuracy of this Gravimetric Calibrator is unaffected by the pressure and temperature of the gas. The Calibrator can also measure reactive, corrosive, and non-ideal gases. The container remains connected to the process by a torsion capillary, and a load cell measures the changing gas weight continuously throughout the measuring process. A prototype was designed for gas flows ranging from 1 sccm of hydrogen to 10,000 sccm of tungsten hexafluoride, constructed, tested, and used to calibrate flow devices. Experience with the prototype and results are presented, and plans for further developments are discussed.

Use of a hydrodynamics code for experimental data fitting purposes (an optimization problem) requires information about how a computed result changes when the model parameters change. These so-called sensitivities provide the gradient that determines the search direction for modifying the parameters to find an optimal result. Here, the authors apply code-based automatic differentiation (AD) techniques applied in the forward and adjoint modes to two problems with 12 parameters to obtain these gradients and compare the computational efficiency and accuracy of the various methods. They fit the pressure trace from a one-dimensional flyer-plate experiment and examine the accuracy for a two-dimensional jet-formation problem. For the flyer-plate experiment, the adjoint mode requires similar or less computer time than the forward methods. Additional parameters will not change the adjoint mode run time appreciably, which is a distinct advantage for this method. Obtaining ''accurate'' sensitivities for the j et problem parameters remains problematic.

The development of voltage and current probes for measuring an electron beam's current and position associated with several microsecond-long pulses from advanced Linear Induction Accelerators requires a precision pulser that can deliver both high voltages and high currents to a diagnostics Test Line. Seven-stage, type-E PFNs have been utilized in both a transformer and 4-stage Marx (plus/minus) configuration. The resulting 50-ohm pulser delivers to the Test Line a repeatable 100 kV, ca. 2 {micro}s flat-top ({+-} 1%), 2.5 {micro}s FWHM pulse with a rise time of 175 ns and 500 ns for the transformer and Marx options, respectively. Methods of reducing the rise time for both options are discussed and modeled. The coaxial Test Line is insulated at up to two atmospheres with SF{sub 6} and includes two transition regions to hold and test different diameter beam current and position monitors (BPMs). The center conductor incorporates both translation and tip/tilt with an accuracy of 100 {micro}m. Finally, the line is terminated in a matched radial resistor that provides a planar region at fields up to 40 kV/cm for the testing of voltage probes. Both the transformer and Marx options are modeled and compared to experimental results.