449 Matching Results

Search Results

Advanced search parameters have been applied.

The Electrostatic Potential About an Atomic Nucleus in an Ionized Gas

Description: From introduction: "The object of this paper is to derive a simple approximate expression for the average potential about an atomic nucleus in an ionized gas. It was desired that the expression be simple in the sense that its analytic form would be convenient in Born approximation calculations. It was also desired that the results would be valid over a large range of temperature and density for all elements with perhaps the exception of those with low atomic number."
Date: June 1958
Creator: Kidder, R. E.
Partner: UNT Libraries Government Documents Department

Design and Formation of a Large, Tetrahedral, Metal-ligand Cluster Using 1,1'-Binaphthyl Ligands

Description: Many chemists have been fascinated with the development of discrete supramolecular structures that encapsulate guest molecules. These structures can be assembled through covalent or hydrogen bonds, electrostatic or metal-ligand interactions. These host structures have provided valuable insight into the forces involved in small molecule recognition. Our work has focused on the design and study of metal-ligand clusters of varying sizes. The naphthalene [M{sub 4}L{sub 6}]{sup 12-} cluster 1, shown in Figure 1, has demonstrated diastereoselective guest binding and chiral induction properties as well as the ability to catalyze reactions carried out inside the cavity in an enzyme-like manner. However, the size of the cavity (ca. 300-500 {angstrom}{sup 3}) has often limited the scope of substrates for these transformations.
Date: March 13, 2008
Creator: Biros, Shannon M.; Yeh, Robert M. & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department

Compact High-Current Heavy-Ion Injector

Description: To provide a compact high-brightness heavy-ion beam source for Heavy Ion Fusion (HIF), we have been experimenting with merging multi-beamlets in an injector which uses an RF plasma source. An array of converging beamlets was used to produce a beam with the envelope radius, convergence, and ellipticity matched to an electrostatic quadrupole (ESQ) channel. Experimental results were in good quantitative agreement with simulation and have demonstrated the feasibility of this concept. The size of a driver-scale injector system using this approach will be several times smaller than one designed using traditional single large-aperture beams. The success of this experiment has possible significant economical and technical impacts on the architecture of HIF drivers.
Date: October 5, 2005
Creator: Westenskow, G. A.; Grote, D. P.; Kwan, J. W. & Bieniosek, F.
Partner: UNT Libraries Government Documents Department

The HIBEAM Manual

Description: HIBEAM is a 2 1/2D particle-in-cell (PIC) simulation code developed in the late 1990's in the Heavy-Ion Fusion research program at Lawrence Berkeley National Laboratory. The major purpose of HIBEAM is to simulate the transverse (i.e., X-Y) dynamics of a space-charge-dominated, non-relativistic heavy-ion beam being transported in a static accelerator focusing lattice. HIBEAM has been used to study beam combining systems, effective dynamic apertures in electrostatic quadrupole lattices, and emittance growth due to transverse misalignments. At present, HIBEAM runs on the CRAY vector machines (C90 and J90's) at NERSC, although it would be relatively simple to port the code to UNIX workstations so long as IMSL math routines were available.
Date: February 1, 2000
Creator: Fawley, William M.
Partner: UNT Libraries Government Documents Department

NANOSCALE SCIENCE AND TECHNOLOGY FOR THE DEVELOPMENT OF ENVIRONMENTAL SENSORS

Description: Under this funding, we proposed to: i) develop a ChemFET sensor platform, ii) develop a ChemDiode sensor platform, iii) synthesize receptor molecules suitable for chemical sensing, iv) study the electrostatic potential changes induced by receptor/target binding on surfaces and v) develop VLSI fabrication approaches for micron-scale chemical sensor devices. The accomplishments under these various thrusts are summarized in this section.
Date: January 3, 2007
Creator: Ronald Andres, School of Chemical Engineering, Purdue University David Janes, School of Electrical and Computer Engineering, Purdue University Clifford Kubiak, Dept. of Chemistry, UCSD Ronald Reifenberger, Dept. of Physics, Purdue University
Partner: UNT Libraries Government Documents Department

Electron Cloud induced instabilities in the Fermilab Main Injector(MI) for the High Intensity Neutrino Source (HINS) project

Description: The electrostatic particle-in-cell codeWARP is currently being expanded in order to study electron cloud effects on the dynamics of the beam in storage rings. Results for the Fermilab main injector (MI) show the existence of a threshold in the electron density beyond which there is rapid emittance growth. The Fermilab MI is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort, which will result in a significant increasing of the bunch intensity relative to its present value, placing it in a regime where electron-cloud effects are expected to become important. Various results from the simulations using WARP are discussed here.
Date: April 15, 2006
Creator: Sonnad, Kiran G.; Furman, Miguel A.; Vay, Jean-Luc; Venturini,Marco; Celata, Christine & Grote, David
Partner: UNT Libraries Government Documents Department

Simulations of Electron Cloud Effects on the Beam Dynamics for theFNAL Main Injector Upgrade

Description: The Fermilab main injector (MI) is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort. This upgrade will involve a significant increasing of the bunch intensity relative to its present value. Such an increase will place the MI in a regime in which electron-cloud effects are expected to become important. We have used the electrostatic particle-in-cell code WARP, recently augmented with new modeling capabilities and simulation techniques, to study the dynamics of beam-electron cloud interaction. This work in progress involves a systematic assessment of beam instabilities due to the presence of electron clouds.
Date: April 15, 2006
Creator: G., Sonnad Kiran; Furman, Miguel; Vay, Jean-Luc; Venturini, Marco; Celata, Christine M. & Grote, David
Partner: UNT Libraries Government Documents Department

Electrostatic microvalves utilizing conductive nanoparticles for improved speed, lower power, and higher force actuation.

Description: We have designed and built electrostatically actuated microvalves compatible with integration into a PDMS based microfluidic system. The key innovation for electrostatic actuation was the incorporation of carbon nanotubes into the PDMS valve membrane, allowing for electrostatic charging of the PDMS layer and subsequent discharging, while still allowing for significant distention of the valveseat for low voltage control of the system. Nanoparticles were applied to semi-cured PDMS using a stamp transfer method, and then cured fully to make the valve seats. DC actuation in air of these valves yielded operational voltages as low as 15V, by using a supporting structure above the valve seat that allowed sufficient restoring forces to be applied while not enhancing actuation forces to raise the valve actuation potential. Both actuate to open and actuate to close valves have been demonstrated, and integrated into a microfluidic platform, and demonstrated fluidic control using electrostatic valves.
Date: September 1, 2009
Creator: Ten Eyck, Gregory A.; Branson, Eric D.; Kenis, Paul J. A. (University of Illinois, Champaign Urbana); Desai, Amit (University of Illinois, Champaign Urbana); Schudel, Ben (University of Illinois, Champaign Urbana); Givler, Richard C. et al.
Partner: UNT Libraries Government Documents Department

Polymer/inorganic superhydrophobic surfaces.

Description: We have designed and built electrostatically actuated microvalves compatible with integration into a PDMS based microfluidic system. The key innovation for electrostatic actuation was the incorporation of carbon nanotubes into the PDMS valve membrane, allowing for electrostatic charging of the PDMS layer and subsequent discharging, while still allowing for significant distention of the valveseat for low voltage control of the system. Nanoparticles were applied to semi-cured PDMS using a stamp transfer method, and then cured fully to make the valve seats. DC actuation in air of these valves yielded operational voltages as low as 15V, by using a supporting structure above the valve seat that allowed sufficient restoring forces to be applied while not enhancing actuation forces to raise the valve actuation potential. Both actuate to open and actuate to close valves have been demonstrated, and integrated into a microfluidic platform, and demonstrated fluidic control using electrostatic valves.
Date: September 1, 2009
Creator: Collord, Andrew; Kissel, David J.; Brinker, C. Jeffrey; Apblett, Christopher Alan & Branson, Eric D.
Partner: UNT Libraries Government Documents Department

Stereo soft x-ray microscopy and elemental mapping of hematite and clay suspensions

Description: The spatial arrangements of hematite particles within aqueous soil and clay samples are investigated with soft X-ray microscopy, taking advantage of the elemental contrast at the Fe-L edge around E = 707 eV. In combination with stereo microscopy, information about spatial arrangements are revealed and correlated to electrostatic interactions of the different mixtures. Manipulation of a sample mounted to the microscope is possible and particles added while imaging can be detected.
Date: September 1, 2008
Creator: Gleber, S.-C.; Thieme, J.; Chao, W. & Fischer, P.
Partner: UNT Libraries Government Documents Department

Charge and fluence lifetime measurements of a dc high voltage GaAs photogun at high average current

Description: GaAs-based dc high voltage photoguns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. This paper describes techniques to maintain good vacuum while delivering beam, and techniques that minimize the ill effects of ion bombardment, the dominant mechanism that reduces photocathode yield of a GaAs-based dc high voltage photogun. Experimental results presented here demonstrate enhanced lifetime at high beam currents by: (a) operating with the drive laser beam positioned away from the electrostatic center of the photocathode, (b) limiting the photocathode active area to eliminate photoemission from regions of the photocathode that do not support efficient beam delivery, (c) using a large drive laser beam to distribute ion damage over a larger area, and (d) by applying a relatively low bias voltage to the anode to repel ions created within the downstream beam line. A combination of these techniques provided the best total charge extracted lifetimes in excess of 1000 C at dc beam currents up to 9.5 mA, using green light illumination of bulk GaAs inside a 100 kV photogun.
Date: April 1, 2011
Creator: J. Grames, R. Suleiman, P.A. Adderley, J. Clark, J. Hansknecht, D. Machie, M. Poelker, M.L. Stutzman
Partner: UNT Libraries Government Documents Department

Electrostatic Modeling of Vacuum Insulator Triple Junctions

Description: A comprehensive matrix of 60 tests was designed to explore the effect of calcium chloride vs. sodium chloride and the ratio R of nitrate concentration over chloride concentration on the repassivation potential of Alloy 22. Tests were conducted using the cyclic potentiodynamic polarization (CPP) technique at 75 C and at 90 C. Results show that at a ratio R of 0.18 and higher nitrate was able to inhibit the crevice corrosion in Alloy 22 induced by chloride. Current results fail to show in a consistent way a different effect on the repassivation potential of Alloy 22 for calcium chloride solutions than for sodium chloride solutions.
Date: August 13, 2007
Creator: Tully, L. K.; White, A. D.; Goerz, D. A.; Javedani, J. B. & Houck, T. L.
Partner: UNT Libraries Government Documents Department

Simulation studies of non-neutral plasma equilibria in anelectrostatic trap with magnetic mirror

Description: The equilibrium of an infinitely long, strongly magnetized, non-neutral plasma confined in a Penning-Malmberg trap with an additional mirror coil has been solved analytically [J. Fajans, Phys. Plasmas 10, 1209 (2003)] and shown to exhibit unusual features. Particles not only reflect near the mirror in the low field region, but also may be weakly trapped in part of in the high field region. The plasma satisfies a Boltzmann distribution along field lines; however, the density and the potential vary along field lines. Some other simplifying assumptions were employed in order to analytically characterize the equilibrium; for example the interface region between the low and high field regions was not considered. The earlier results are confirmed in the present study, where two-dimensional particle-in-cell simulations are performed with the Warp code in a more realistic configuration with an arbitrary (but physical) density profile, realistic trap geometry and magnetic field. A range of temperatures and radial plasma sizes are considered. Particle tracking is used to identify populations of trapped and untrapped particles. The present study also shows that it is possible to obtain local equilibria of non-neutral plasmas using a collisionless PIC code, by a scheme that uses the inherent numerical collisionality as a proxy for physical collisions.
Date: June 1, 2006
Creator: Gomberoff, K.; Fajans, J.; Wurtele, J.; Friedman, A.; Grote,D.P.; Cohen, R.H. et al.
Partner: UNT Libraries Government Documents Department

Simulating Electron Clouds in High-Current Ion Accelerators withSolenoid Focusing

Description: Contamination from electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high-energy-density physics (HEDP). These electrons are produced directly by beam ions hitting lattice elements and intercepting diagnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the Solenoid Transport Experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to included the physics needed to simulate electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and electrons.
Date: September 20, 2006
Creator: Sharp, W.M.; Grote, D.P.; Cohen, R.H.; Friedman, A.; Vay, J.-L.; Seidl, P.A. et al.
Partner: UNT Libraries Government Documents Department

A Compact Multi-Beamlets High Current Injector for HIFDrivers

Description: Using curved electrodes in the injector, an array of converging beamlets can produce a beam with the envelope radius, convergence, and ellipticity matched to an electrostatic quadrupole (ESQ) channel. Experimental results were in good quantitative agreement with simulation and have demonstrated the feasibility of this concept. The size of a driver-scale injector system using this approach will be several times smaller than the one designed using traditional single large-aperture beams, so the success of this experiment has significant economical and technical impacts on the architecture of heavy ion fusion (HIF) drivers.
Date: September 6, 2005
Creator: Kwan, J.W.; Bieniosek, F.M.; Grote, D.P. & Westenskow, G.A.
Partner: UNT Libraries Government Documents Department

Electrical Design of Electrostatic Deflectors for Sector-FocusedCyclotrons

Description: The new sector-focused cyclotrons have more energetic and better focused beams at the extraction radius than do ordinary cyclotrons. While the first characteristic requires a more intense electric field, the second permits this field to extend over a smaller volume. By tailoring the electrode geometry to these characteristics of the beam, the required deflector gap and electrode surface become smaller, and a higher gradient can be held without sparking. A different compromise between radioactivity, power dissipation, and resistance to spark damage must be made in selecting electrode materials. Carefully designed electrostatic deflectors perform very well in sector-focused cyclotrons of intermediate energy. Deflector efficiencies of about 50% and external-beam intensities of 20 {micro}A have been obtained in the Lawrence Laboratory's 88 -Inch Cyclotron.
Date: March 25, 1963
Creator: Smith, Bob H. & Grunder, Hermann A.
Partner: UNT Libraries Government Documents Department

Domain evolution and polarization of continuously graded ferroelectric films

Description: A thermodynamic analysis of graded ferroelectric films demonstrates that in the equilibrium state the films are subdivided into a single-domain band and a polydomain band which consists of wedge-shape domains. Polarization under an external electrostatic field proceeds through an inter-band boundary movement due to growth or shrinkage of the wedge domains. It is shown how the domain structure and evolution are determined by the principal characteristics of the film: the distribution of the spontaneous polarization and dielectric constant. Graded films exhibit a sharp increase of polarization with the field for weak fields, with a drop of the dielectric constant when the field is increasing. A general approach to finding the dependence of the displacement and the wedge-domain shape on the field as well as analytical solutions for the p{sup 4} Landau-Devonshire and parabolic potentials are presented.
Date: January 1, 2008
Creator: Roytburd, A. & Roytburd, V.
Partner: UNT Libraries Government Documents Department

Nonlinear integrable ion traps

Description: Quadrupole ion traps can be transformed into nonlinear traps with integrable motion by adding special electrostatic potentials. This can be done with both stationary potentials (electrostatic plus a uniform magnetic field) and with time-dependent electric potentials. These potentials are chosen such that the single particle Hamilton-Jacobi equations of motion are separable in some coordinate systems. The electrostatic potentials have several free adjustable parameters allowing for a quadrupole trap to be transformed into, for example, a double-well or a toroidal-well system. The particle motion remains regular, non-chaotic, integrable in quadratures, and stable for a wide range of parameters. We present two examples of how to realize such a system in case of a time-independent (the Penning trap) as well as a time-dependent (the Paul trap) configuration.
Date: October 1, 2011
Creator: Nagaitsev, S.; /Fermilab; Danilov, V. & /SNS Project, Oak Ridge
Partner: UNT Libraries Government Documents Department

Spherical Aberration Corrections for the Electrostatic Gridded Lens

Description: Two methods of spherical aberration corrections of an electrostatic gridded lens have been studied with ray tracing simulations. Both methods are based on modifying electrostatic field on the periphery of the lens. In a simplest case such modification is done by extending the part of the grid support on its radial periphery in axial direction. In alternative method the electric field on the radial periphery of the lens is modified by applying an optimum voltage on an electrically isolated correcting electrode. It was demonstrated, that for a given focal length the voltage on this lens can be optimized for minimum aberration The performance of lenses is presented as a lens contribution to the beam RMS normalized emittance.
Date: May 1, 2008
Creator: Pikin,A.
Partner: UNT Libraries Government Documents Department

Implementation of an interactive matching scheme for the Kapchinskij-Vladimirskij equations in the WARP code

Description: The WARP code is a robust electrostatic particle-in-cell simulation package used to model charged particle beams with strong space-charge forces. A fundamental operation associated with seeding detailed simulations of a beam transport channel is to generate initial conditions where the beam distribution is matched to the structure of a periodic focusing lattice. This is done by solving for periodic, matched solutions to a coupled set of ODEs called the Kapchinskij-Vladimirskij (KV) envelope equations, which describe the evolution of low-order beam moments subject to applied lattice focusing, space-charge defocusing, and thermal defocusing forces. Recently, an iterative numerical method was developed (Lund, Chilton, and Lee, Efficient computation of matched solutions to the KV envelope equations for periodic focusing lattices, Physical Review Special Topics-Accelerators and Beams 9, 064201 2006) to generate matching conditions in a highly flexible, convergent, and fail-safe manner. This method is extended and implemented in the WARP code as a Python package to vastly ease the setup of detailed simulations. In particular, the Python package accommodates any linear applied lattice focusing functions without skew coupling, and a more general set of beam parameter specifications than its predecessor. Lattice strength iteration tools were added to facilitate the implementation of problems with specific applied focusing strengths.
Date: April 15, 2008
Creator: Chilton, Sven H.
Partner: UNT Libraries Government Documents Department