The cathode region of a quasi-steady magnetoplasmadynamic arcjet, supplement 8

Electric and magnetic field measurements in cathode region of quasi-steady magnetoplasmadynamic arcje

The Effects of Magnetic Nozzle Configurations on Plasma Thrusters

Over the course of eight years, the Ohio State University has performed research in support of electric propulsion development efforts at the NASA Lewis Research Center, Cleveland, OH. This research has been largely devoted to plasma propulsion systems including MagnetoPlasmaDynamic (MPD) thrusters with externally-applied, solenoidal magnetic fields, hollow cathodes, and Pulsed Plasma Microthrusters (PPT's). Both experimental and theoretical work has been performed, as documented in four master's theses, two doctoral dissertations, and numerous technical papers. The present document is the final report for the grant period 5 December 1987 to 31 December 1995, and summarizes all activities. Detailed discussions of each area of activity are provided in appendices: Appendix 1 - Experimental studies of magnetic nozzle effects on plasma thrusters; Appendix 2 - Numerical modeling of applied-field MPD thrusters; Appendix 3 - Theoretical and experimental studies of hollow cathodes; and Appendix 4 -Theoretical, numerical and experimental studies of pulsed plasma thrusters. Especially notable results include the efficacy of using a solenoidal magnetic field downstream of a plasma thruster to collimate the exhaust flow, the development of a new understanding of applied-field MPD thrusters (based on experimentally-validated results from state-of-the art, numerical simulation) leading to predictions of improved performance, an experimentally-validated, first-principles model for orificed, hollow-cathode behavior, and the first time-dependent, two-dimensional calculations of ablation-fed, pulsed plasma thrusters

Report on Characterization of U-10 wt.% Zr Alloy

This report summarizes the chemical and structural characterization results for a U-10 wt.% Zr alloy to be used in an ultra-high burn-up nuclear fuel concept. The as-cast alloy material was received from Texas A and M University. Characterization and an initial heat treatment of the alloy material were conducted at Lawrence Livermore National Laboratory. The as-received ingot was sectioned for X-ray analysis, metallography, SEM, TEM, and heat treatments, as shown in Figure 1

An Assessment of the Net Value of CSP Systems Integrated with Thermal Energy Storage

AbstractWithin this study, we evaluate the operational and capacity value—or total system value—for multiple concentrating solar power (CSP)plant configurations under an assumed 33% renewable penetration scenario in California. We calculate the first-year bid price for two CSP plants, including a 2013 molten-salt tower integrated with a conventional Rankine cycle and a hypothetical 2020 molten-salt tower system integrated with an advanced supercritical carbon-dioxide power block. The overall benefit to the regional grid, defined in this study as the net value, is calculated by subtracting the first-year bid price from the total system value.Re--sults of this study indicate a positive net value for a variety of scenarios, depending on technology assumptions and assumed values for natural gas price and tax incentives. We provide results for the 2013 and 2020 CSP configurations as a function of thermal energy storage capacity and solar field size. We provide a sensitivity of these results to natural gas price, which influence the operation value and thus the total system value. We also investigate the sensitivity of the net value to current and anticipated tax incentives

STABILITY AND ORDERING PROPERTIES OF FCC ALLOYS BASED ON RH, IR, PD, AND PT

Stability properties and ordering trends for the six face-centered cubic binary combinations of the four transition metals Rh, Ir, Pd, and Pt are examined in the context of electronic structure calculations. The method is based on a Green function description of the electronic structure of random alloys. Configurational order is treated within the generalized perturbation method. On one hand, the three alloys, Pd-Rh, Pd-Ir and Pt-Ir that have been studied experimentally are confirmed to behave like phase separating systems. On the other hand, the other three mixtures, Pd-Pt, Rh-Ir, and Pt-Rh for which phase separating trends have been inferred from experiments are found to display chemical order with ordering of the (1 0 0), (1 1/2 0) family-types and a mixture of both, respectively. The origin of these results is discussed in terms of electronic structure properties

Modeling multi effect distillation powered by CSP in TRNSYS

This work presents the results of using a new tool to simulate the cogeneration of water and electricity with Concentrating Solar Power (CSP) and Forward Feed Multi-Effect-Desalination (FF-MED) plants, by adding a new functionality to the System Advisor Model (SAM) developed by the US National Renewable Energy Laboratory (NREL). The controlling strategy of the MED model is presented in detail, and a case study application is shown. This study compares the results obtained with a CSP plant operating in San Diego, CA, with four different cooling systems: an MED/Seawater Cooling Circuit (SWCC), dry cooling, wet cooling, and a SWCC standalone. The results show that the usage of an MED/SWCC system in cogeneration with a CSP plant can be feasible and has the potential to be economically interesting

Effects of magnetic field and disorder on electronic properties of Carbon Nanotubes

Electronic properties of metallic and semiconducting carbon nanotubes are investigated in presence of magnetic field perpendicular to the CN-axis, and disorder introduced through energy site randomness. The magnetic field field is shown to induce a metal-insulator transition (MIT) in absence of disorder, and surprisingly disorder does not affect significantly the MIT. These results may find confirmation through tunneling experimentsComment: 4 pages, 6 figures. Phys. Rev. B (in press

A tight-binding potential for atomistic simulations of carbon interacting with transition metals: Application to the Ni-C system

We present a tight-binding potential for transition metals, carbon, and transition metal carbides, which has been optimized through a systematic fitting procedure. A minimal basis, including the s, p electrons of carbon and the d electrons of the transition metal, is used to obtain a transferable tight-binding model of the carbon-carbon, metal-metal and metal-carbon interactions applicable to binary systems. The Ni-C system is more specifically discussed. The successful validation of the potential for different atomic configurations indicates a good transferability of the model and makes it a good choice for atomistic simulations sampling a large configuration space. This approach appears to be very efficient to describe interactions in systems containing carbon and transition metal elements

Studies of Vibrational Properties in Ga Stabilized d-Pu by Extended X-ray Absorption Fine Structure

Temperature dependent extended x-ray absorption fine structure (EXAFS) spectra were measured for a 3.3 at% Ga stabilized Pu alloy over the range T= 20 - 300 K at both the Ga K-edge and the Pu L_III-edge. The temperature dependence of the pair-distance distribution widths, \sigma(T) was accurately modeled using a correlated-Debye model for the lattice vibrational properties, suggesting Debye-like behavior in this material. We obtain pair- specific correlated-Debye temperatures, \Theta_cD, of 110.7 +/- 1.7 K and 202.6 +/- 3.7 K, for the Pu-Pu and Ga-Pu pairs, respectively. These results represent the first unambiguous determination of Ga-specific vibrational properties in PuGa alloys, and indicate the Ga-Pu bonds are significantly stronger than the Pu-Pu bonds. This effect has important implications for lattice stabilization mechanisms in these alloys.Comment: 7 pages, 4 figures, Phys. Rev. B in pres

The interplay between double exchange, super-exchange, and Lifshitz localization in doped manganites

Considering the disorder caused in manganites by the substitution of Mn by Fe or Ga, we accomplish a systematic study of doped manganites begun in previous papers. To this end, a disordered model is formulated and solved using the Variational Mean Field technique. The subtle interplay between double exchange, super-exchange, and disorder causes similar effects on the dependence of T_C on the percentage of Mn substitution in the cases considered. Yet, in La$_{2/3}$Ca$_{1/3}$Mn$_{1-y}$Ga$_y$O$_3$ our results suggest a quantum critical point (QCP) for $y\approx 0.1-0.2$, associated to the localization of the electronic states of the conduction band. In the case of La$_x$Ca$_x$Mn$_{1-y}$Fe$_y$O$_3$ (with $x=1/3,3/8$) no such QCP is expected.Comment: 6 pages + 3 postscript figures. Largely extended discussio