654 Matching Results

Search Results

Advanced search parameters have been applied.

Surface Dependent Electron and Negative Ion Density in Inductively Coupled Discharges

Description: Electron and negative ion density have been measured in a modfied Applied Materials DPS metal etch chamber using gas mixtures of BCl{sub 3}, Cl{sub 2} and Ar. Measurements were performed for four dflerent substrate types to examine the influence of surface material on the bulk plasma properties; aluminurq alumina, photoresist and 50 percent patterned aluminum / photoresist. Electron densities in the Cl{sub 2} / BCl{sub 3} mixtures varied from 0.25 to 4 x 10{sup 11} cm{sup -3}. Photodetachment measurements of the negative ion density indicate that the negative ion density was smaller than the electron density and that the electron to negative ion density ratio varied between 1 and 6. The presence of photoresist had a dominant intluence on the electron and negative ion density compared to alumina and aluminum surfaces. In most cases, the electron density above wafers covered with photoresist was a factor of two lower while the negative ion density was a factor of two higher than the aluminum or alumina surfaces.
Date: January 18, 1999
Creator: Blain, M.G.; Hamilton, T.W.; Hebner, G.A.; Jarecki, R.L. & Nichols, C.A.
Partner: UNT Libraries Government Documents Department

Measurements of slant and vertical TEC using data from FORTE and the TRACKER ray-tracing code

Description: In a previous informal report, the author described the FORTE satellite and the analysis techniques used to extract a slant TEC from measurements of the dispersion of a signal transmitted from and EMP generator at Los Alamos. In this report he reports on the use of a ray-tracing/ionospheric model code to deduce the vertical TEC to 800 km from the FORTE measurements.
Date: December 12, 1997
Creator: Massey, R.S.
Partner: UNT Libraries Government Documents Department

Informal report on measurements of slant TEC by FORTE

Description: Los Alamos National Laboratory`s Space and Atmospheric Sciences group is now operating the FORTE satellite, which has two sets of instruments: optical detectors and radio detectors. In this report the author describes work with one set of radio detectors that allow measurements of the total electron content (TEC) traversed by VHF radiation originating at an electromagnetic pulse (EMP) generator located at Los Alamos.
Date: November 21, 1997
Creator: Massey, R.S.
Partner: UNT Libraries Government Documents Department

Simulational studies of the Farley-Buneman in the equatorial electrojet

Description: The Farley-Buneman instability in the equatorial electrojet current system in the E-region of the ionosphere has been identified as the cause of the observed Type I electron density irregularities. The goal of this work was to study the instability in the equatorial region.
Date: July 1, 1995
Creator: Otani, N.; Seyler, C. & Kelley, M.
Partner: UNT Libraries Government Documents Department

Electron-Cloud Build-up in the FNAL Main Injector

Description: We present a summary on ongoing simulation results for the electron-cloud buildup in the context of the proposed FNAL Main Injector (MI) intensity upgrade [1] in a fieldfree region at the location of the RFA electron detector [2]. By combining our simulated results for the electron flux at the vacuum chamber wall with the corresponding measurements obtained with the RFA we infer that the peak secondary electron yield (SEY) {delta}{sub max} is {approx}> 1.4, and the average electron density is n{sub e} {approx}> 10{sup 10} m{sup -3} at transition energy for the specific fill pattern and beam intensities defined below. The sensitivity of our results to several variables remains to be explored in order to reach more definitive results. Effects from the electron cloud on the beam are being investigated separately [3].
Date: June 4, 2007
Creator: Furman, M.A.
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

Decision-Making in Structure Solution using Bayesian Estimates of Map Quality: The PHENIX AutoSol Wizard

Description: Estimates of the quality of experimental maps are important in many stages of structure determination of macromolecules. Map quality is defined here as the correlation between a map and the map calculated based on a final refined model. Here we examine 10 different measures of experimental map quality using a set of 1359 maps calculated by reanalysis of 246 solved MAD, SAD, and MIR datasets. A simple Bayesian approach to estimation of map quality from one or more measures is presented. We find that a Bayesian estimator based on the skew of histograms of electron density is the most accurate of the 10 individual Bayesian estimators of map quality examined, with a correlation between estimated and actual map quality of 0.90. A combination of the skew of electron density with the local correlation of rms density gives a further improvement in estimating map quality, with an overall correlation coefficient of 0.92. The PHENIX AutoSol Wizard carries out automated structure solution based on any combination of SAD, MAD, SIR, or MIR datasets. The Wizard is based on tools from the PHENIX package and uses the Bayesian estimates of map quality described here to choose the highest-quality solutions after experimental phasing.
Date: March 1, 2009
Creator: Terwilliger, T. C.; Adams, P. D.; Read, R. J.; McCoy, A. J.; Moriarty, Nigel W.; Grosse-Kunstleve, R. W. et al.
Partner: UNT Libraries Government Documents Department


Description: OAK A271 PHYSICS OF ELCTRON CYCLOTRON CURRENT DRIVE ON DIII-D. Recent experiments on the DIII-D tokamak have focused on determining the effect of trapped particles on the electron cyclotron current drive (ECCD) efficiency. The measured ECCD efficiency increases as the deposition location is moved towards the inboard midplane or towards smaller minor radius for both co and counter injection. The measured ECCD efficiency also increases with increasing electron density and/or temperature. The experimental ECCD is compared to both the linear theory (Toray-GA) as well as a quasilinear Fokker-Planck model (CQL3D). The experimental ECCD is found to be in better agreement with the more complete Fokker-Planck calculation, especially for cases of high rf power density and/or loop voltage. The narrow width of the measured ECCD profile is consistent with only low levels of radial transport for the current carrying electrons.
Date: September 1, 2002
Partner: UNT Libraries Government Documents Department

A Comparison of Spectroscopic Measurements of an Inductive Plasma Source with the INDUCT Model

Description: Noninvasive spectroscopic measurements of an inductively driven hydrogen plasma source with density and temperature characteristic of plasma processing tools have been made with an ultimate application of cleaning of silicon substrates. These measurements allow full radial and axial profiles of electron density and temperature to be measured from absolutely calibrated multichannel spectroscopic measurements of upper state number densities and a collisional radiative model. Profiles were obtained over a range of powers from 50 to 200 W and pressures from 5 to 50 mTorr in hydrogen in a small cylindrical source. The hydrogen working gas and simple cylindrical geometry was chosen to simplify detailed comparisons with a 2D computational model (INDUCT95) which uses a fluid approximation for tbc plasma and neutral gas. The code calculates the inductive coupling of the 13.56 MHz RF source, the collisional, radiative, and wall losses as well as a chemistry model for electrons, H{sub 2}, H, H{sup +}, H{sub 2}, and H{sub 3}{sup +}. Simulation results were sensitive to the value for the wall coefficient. The simulation and experimental temperature and density profiles in r and z were in rough agreement, but some details were quite different. The simulated axial density profile was located under the coil while the measured density profiles extended well beyond the edges of the coil. The scaling of conditions with pressure and power was in rough agreement between experiment and simulations.
Date: October 3, 1999
Creator: Huebschman, M.L.; Bakshi, V.; Bengtson, R.D.; Ekerdt, J.G.; Vitello, P.; Wiley, J.C. et al.
Partner: UNT Libraries Government Documents Department

Reciprocating and fixed probe measurements of n{sub e} and T{sub e} in the DIII-D divertor

Description: This paper describes divertor density and temperature measurements using both a new reciprocating Langmuir probe (XPT-RCP) which plunges vertically above the divertor floor up to the X-point height and swept, single, Langmuir probes fixed horizontally across the divertor floor. These types of measurements are important for testing models of the SOL and divertor which then are used to design plasma facing components in reactor size tokamaks. This paper presents an overview of the new divertor probe measurements and how they compare with the new divertor Thomson scattering system. The fast time response of the probe measurements allows detailed study of ELMs.
Date: November 1, 1996
Creator: Watkins, J.G.; Moyer, R.A.; Cuthbertson, J.W.; Buchenauer, D.A.; Carlstrom, T.N.; Hill, D.N. et al.
Partner: UNT Libraries Government Documents Department

Edge density modification with rf on TFTR and DIII-D

Description: Modification of the electron density profile in front of rf antennas has been observed on TFTR and DIII-D using reflectometers installed in-antenna to ensure localization to the antenna environment. The modification of the edge density gradient has two components: a flattening of the gradient in the private flux zone, and an increase in the edge density inside the last closed flux surface. In general, these modifications result in a significant decrease in the electron density over most of the private flux zone with a sharp rise in the density near the last closed flux surface. Data from TFTR is used to infer the dependence of this edge modification with antenna strap phasing and rf power. Initial results from DIII-D showing edge modification will also be discussed. Antenna modeling has shown that this modification in the private flux zone has only small effects on the antenna loading and launched spectrum.
Date: September 1, 1995
Creator: Hanson, G.R.; England, A.C. & Wilgen, J.B.
Partner: UNT Libraries Government Documents Department

Propagation of electromagnetic waves in a structured ionosphere

Description: The ionosphere is a birefringent medium which strongly affects the transmission of very high frequency (vhf) radio signals. These effects must be understood in detail if one wishes to look at the propagation of wide bandwidth coherent signals through the ionosphere. We develop a general perturbative solution of Maxwell`s equations for vhf signals propagating in the ionosphere, subject only to mild restrictions on the ionospheric structure. This solution can be extended to give the propagating field to any desired degree of precision. The case of a laminar ionosphere with harmonic waves is developed in greater detail, and we show how to calculate the ray path in this case. This solution is used to elucidate the effects of refraction on the phase of the signal, and we calculate the spatial- and frequency-coherence functions. The electric field for a laminar ionosphere without waves is analyzed to clarify the physical origins of the terms modifying the signal phase. We then calculate the solution in this case for the Appleton-Hartree model of the ionospheric dielectric function and express the result as a series in inverse powers of frequency. We conclude by calculating the ray path for a model ionosphere using the Appleton-Hartree dielectric function and a parabolic layer for the electron density.
Date: June 1, 1996
Creator: Murphy, T.
Partner: UNT Libraries Government Documents Department

Build up of electron cloud with different bunch pattern in the presence of solenoidal field

Description: We have augmented the code POSINST to include solenoid fields, and used it to simulate the build up of electron cloud due to electron multipacting in the PEP-II positron ring. We find that the distribution of electrons is strongly affected by the resonances associated with the cyclotron period and bunch spacing. In addition, we discover a threshold beyond which the electron density grows exponentially until it reaches the space charge limit. The threshold does not depend on the bunch spacing but does depend on the positron bunch population.
Date: April 1, 2004
Creator: Cai, Y.; Furman, M.A. & Pivi, M.
Partner: UNT Libraries Government Documents Department

Heavy Neutral Beam Probe for Edge Plasma Analysis in Tokamaks

Description: The Heavy Neutral Beam Probe (HNBP) developed initially with DOE funding under the Small Business Innovation Research (SBIR) program was installed on the Tokamak de Varennes (TdeV) at the CCFM. This diagnostic was designed to perform fundamental measurements of edge plasma properties. The hardware was capable of measuring electron density and potential profiles with high spatial and temporal resolution. Fluctuation spectra for these parameters were obtained with HNBP for transport studies.
Date: January 4, 2001
Creator: Castracane, J.
Partner: UNT Libraries Government Documents Department

Suppression of Impurity Back Scattering in Double Quantum Wires: Theory Beyond the Born Approximation

Description: The effect of higher-order corrections to the Born approximation is studied for the previously obtained giant conductance enhancement in tunnel-coupled double quantum wires in a parallel magnetic field. The relative correction is found to be significant and depends on various effects such as the magnetic field, electron and impurity densities, impurity positions, symmetric and asymmetric doping profiles, and center barrier thickness.
Date: August 9, 1999
Creator: Huang, Danhong & Lyo, S.K.
Partner: UNT Libraries Government Documents Department

Experimental and theoretical evaluation of density sensitive N VII, Ar XIV and Fe XXII line ratios

Description: The line ratios of the 2p-3d transitions in the B-like spectra Ar XIV and Fe XXII have been measured using the electron beam ion traps at Livermore. Radiative-collisional model calculations show these line ratios to be sensitive to the electron density in the ranges ne = 10{sup 10} to 10{sup 12} cm{sup -3} and ne = 10{sup 13} to 10{sup 15} cm{sup -3}, respectively. In our experiment, the electron beam density of about 10{sup 11} cm{sup -3} was varied by about a factor of 5. Our data show a density effect for the line doublet in Ar XIV, and good agreement with theory is found. The relative intensity of the Fe XXII doublet shows good agreement with our predicted low density limit. The N VI K-shell spectrum was used to infer the actual electron density in the overlap region of ion cloud and electron beam, and systematic measurements and calculations of this spectrum are presented as well. The Ar XIV and Fe XXII spectra promise to be reliable density diagnostics for stellar coronae, complementing the K-shell diagnostics of helium-like ions.
Date: January 9, 2004
Creator: Chen, H; Beiersdorfer, P; Heeter, L A; Liedahl, D A; Naranjo-Rivera, K L; Trabert, E et al.
Partner: UNT Libraries Government Documents Department

Iterative model-building, structure refinement, and density modification with the PHENIX AutoBuild Wizard

Description: The PHENIX AutoBuild Wizard is a highly automated tool for iterative model-building, structure refinement and density modification using RESOLVE or TEXTAL model-building, RESOLVE statistical density modification, and phenix.refine structure refinement. Recent advances in the AutoBuild Wizard and phenix.refine include automated detection and application of NCS from models as they are built, extensive model completion algorithms, and automated solvent molecule picking. Model completion algorithms in the AutoBuild Wizard include loop-building, crossovers between chains in different models of a structure, and side-chain optimization. The AutoBuild Wizard has been applied to a set of 48 structures at resolutions ranging from 1.1 {angstrom} to 3.2 {angstrom}, resulting in a mean R-factor of 0.24 and a mean free R factor of 0.29. The R-factor of the final model is dependent on the quality of the starting electron density, and relatively independent of resolution.
Date: April 29, 2007
Creator: Los Alamos National Laboratory, Mailstop M888, Los Alamos, NM 87545, USA; Lawrence Berkeley National Laboratory, One Cyclotron Road, Building 64R0121, Berkeley, CA 94720, USA; Department of Haematology, University of Cambridge, Cambridge CB2 0XY, England; Terwilliger, Thomas; Terwilliger, T.C.; Grosse-Kunstleve, Ralf Wilhelm et al.
Partner: UNT Libraries Government Documents Department

The Free Radical from Perinaphthene

Description: The electron spin resonance spectrum of the perinaphthene free radical is reported and a discussion of electron spin density in this radical is given.
Date: January 31, 1957
Creator: Sogo, Power B.; Nakazaki, Masao & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Simulation of Electron Cloud Density Distributions in RHIC Dipoles at Injection and Transition and Estimates for Scrubbing Times

Description: In this report we summarize electron-cloud simulations for the RHIC dipole regions at injection and transition to estimate if scrubbing over practical time scales at injection would reduce the electron cloud density at transition to significantly lower values. The lower electron cloud density at transition will allow for an increase in the ion intensity.
Date: January 2, 2009
Creator: He,P.; Blaskiewicz, M. & Fischer, W.
Partner: UNT Libraries Government Documents Department

Observations of Plasmons in Warm Dense Matter

Description: We present the first collective x-ray scattering measurements of plasmons in solid-density plasmas. The forward scattering spectra of a laser-produced narrow-band x-ray line from isochorically heated beryllium show that the plasmon frequency is a sensitive measure of the electron density. Dynamic structure calculations that include collisions and detailed balance match the measured plasmon spectrum indicating that this technique will enable new applications to determine the equation of state and compressibility of dense matter.
Date: September 5, 2006
Creator: Glenzer, S H; Landen, O L; Neumayer, P; Lee, R W; Widmann, K; Pollaine, S W et al.
Partner: UNT Libraries Government Documents Department