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in creator/contributor: "Chen, Y."

open access

Similarity-Guided Streamline Placement with Error Evaluation

Most streamline generation algorithms either provide a particular density of streamlines across the domain or explicitly detect features, such as critical points, and follow customized rules to emphasize those features. However, the former generally includes many redundant streamlines, and the latter requires Boolean decisions on which points are features (and may thus suffer from robustness problems for real-world data). We take a new approach to adaptive streamline placement for steady vector… more

Date: August 15, 2007

Creator: Chen, Y.; Cohen, J. D. & Krolik, J. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Compact Proton Accelerator for Cancer Therapy

An investigation is being made into the feasibility of making a compact proton dielectric wall (DWA) accelerator for medical radiation treatment based on the high gradient insulation (HGI) technology. A small plasma device is used for the proton source. Using only electric focusing fields for transporting and focusing the beam on the patient, the compact DWA proton accelerator m system can deliver wide and independent variable ranges of beam currents, energies and spot sizes.

Date: June 12, 2007

Creator: Chen, Y. & Paul, A. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A Compact Linac for Proton Therapy Based on a Dielectric Wall Accelerator

A novel compact CT-guided intensity modulated proton radiotherapy (IMPT) system is described. The system is being designed to deliver fast IMPT so that larger target volumes and motion management can be accomplished. The system will be ideal for large and complex target volumes in young patients. The basis of the design is the dielectric wall accelerator (DWA) system being developed at the Lawrence Livermore National Laboratory (LLNL). The DWA uses fast switched high voltage transmission lines … more

Date: October 29, 2007

Creator: Caporaso, G. J.; Mackie, T. R.; Sampayan, S.; Chen, Y.; Wang, L.; Blackfield, D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Dielectric Wall Accelerator Technology

The dielectric wall accelerator (DWA) is a compact pulsed power device where the pulse forming lines, switching, and vacuum wall are integrated into a single compact geometry. For this effort, we initiated a extensive compact pulsed power development program and have pursued the study of switching (gas, oil, laser induced surface flashover and photoconductive), dielectrics (ceramics and nanoparticle composites), pulse forming line topologies (asymmetric and symmetric Blumleins and zero integral… more

Date: October 18, 2007

Creator: Sampayan, S.; Caporaso, G.; Chen, Y.; Harris, J.; Hawkins, S.; Holmes, C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Scaled Accelerator Test for the DARHT-II Downstream Transport System

The second axis of the Dual Axial radiography Hydrodynamic Test (DARHT-II) facility at LANL is currently in the commissioning phase[1]. The beam parameters for the DARHT-II machine will be nominally 18 MeV, 2 kA and 1.6 {micro}s. This makes the DARHT-II downstream system the first system ever designed to transport a high current, high energy and long pulse beam [2]. We will test these physics issues of the downstream transport system on a scaled DARHT-II accelerator with a 7.8-MeV and 660-A bea… more

Date: October 3, 2005

Creator: Chen, Y.; Blackfield, D. T.; Caporaso, G. J.; Guethlein, G.; McCarrick, J. F.; Paul, A. C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Advanced Accelerator Applications University Participation Program

Our research tasks span the range of technology areas for transmutation, gas-cooled reactor technology, and high temperature heat exchangers, including separation of actinides from spent nuclear fuel, methods of fuel fabrication, reactor-accelerator coupled experiments, corrosion of materials exposed to lead-bismuth eutectic, and special nuclear materials protection and accountability.

Date: July 25, 2007

Creator: Chen, Y. & Hechanova, A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence

The GEM gyrokinetic {delta}f simulation code [Chen, 2003] [Chen, 2007] is shown to reproduce electron temperature gradient turbulence at the benchmark operating point established in previous work [Nevins, 2006]. The electron thermal transport is within 10% of the expected value, while the turbulent fluctuation spectrum is shown to have the expected intensity and two-point correlation function.

Date: May 7, 2007

Creator: Nevins, W. M.; Parker, S. E.; Chen, Y.; Candy, J.; Dimits, A.; Dorland, W. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Extraction System Design for the Bsns/Rcs.

The BSNS extraction system takes use one of the four dispersion-free straight sections. Five vertical kickers and one Lambertson septum magnet are used for the one-turn extraction. The rise time of less 250 ns and the total kicking angle of 20 mrad are required for the kickers that are grouped into two tanks. The design for the kicker magnets and the PFN is also given. To reduce the low beam loss in the extraction channels due to large halo emittance, large apertures are used for both the kicke… more

Date: June 23, 2006

Creator: Wei, J.; Chen, Y.; Chi, Y. L.; Jiang, Y. L.; Kang, W.; Pang, J. B. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Active Creation of Instrinsically Localized Vibrations in Uranium Using X-Ray and Neutron Scattering

In real materials, nonlinear forces cause the frequencies of vibrating atoms to depend on amplitude. As a consequence, a large-amplitude fluctuation on the scale of the atom spacing can develop a frequency that does not resonate with the normal modes, causing energy to become trapped in an intrinsically localized mode (ILM)--also called 'discrete breather' or 'lattice soliton'. As temperature is increased, entropy is expected to stabilize increased concentrations of these random hotspots. This … more

Date: August 23, 2007

Creator: Manley, M.; Alatas, A.; Trouw, F.; Hults, W.; Leu, B.; Lynn, J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

High Gradient Induction Accelerator

A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is stimulated by the desire for compact flash x-ray radiography sources. Research describing an extreme variant of this technology aimed … more

Date: June 21, 2007

Creator: Caporaso, G. J.; Sampayan, S.; Chen, Y.; Blackfield, D.; Harris, J.; Hawkins, S. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Environmentally Assisted Cracking in Light Water Reactors Annual Report January - December 2005.A

This report summarizes work performed from January to December 2005 by Argonne National Laboratory on fatigue and environmentally assisted cracking in light water reactors (LWRs). Existing statistical models for estimating the fatigue life of carbon and low-alloy steels and austenitic stainless steels (SSs) as a function of material, loading, and environmental conditions were updated. Also, the ASME Code fatigue adjustment factors of 2 on stress and 20 on life were critically reviewed to assess… more

Date: August 31, 2007

Creator: Alexandreanu, B.; Chen, Y.; Chopra, O. K.; Chung, H. M.; Gruber, E. E.; Shack, W. J. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Non-Equilibrium Creation of Intrinsically Localized Vibrations in Uranium Using X-Ray and Neutron Scattering

In an anharmonic crystal, large-amplitude vibrational fluctuations on the scale of the lattice spacing can develop frequencies that do not resonate with the normal modes, causing energy to become trapped in intrinsically localized modes (ILMs)--also called 'discrete breathers' or 'lattice solitons'. This mechanism has been observed in analogous systems on a larger scale, but unambiguous sightings in atomic lattice vibrations, where quantum mechanics may play a role, have proved difficult. Two c… more

Date: July 2, 2007

Creator: Manley, M.; Alatas, A.; Trouw, F.; Leu, B. M.; Lynn, J. W.; Chen, Y. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Vacuum Insulator Development for the Dielectric Wall Accelerator

At Lawrence Livermore National Laboratory, we are developing a new type of accelerator, known as a Dielectric Wall Accelerator, in which compact pulse forming lines directly apply an accelerating field to the beam through an insulating vacuum boundary. The electrical strength of this insulator may define the maximum gradient achievable in these machines. To increase the system gradient, we are using 'High Gradient Insulators' composed of alternating layers of dielectric and metal for the vacuum… more

Date: March 17, 2008

Creator: Harris, J. R.; Blackfield, D.; Caporaso, G. J.; Chen, Y.; Hawkins, S.; Kendig, M. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Design of a relativistic Klystron Two-Beam Accelerator Prototype

We are designing an experiment to study physics, engineering, and costing issues of an extended Relativistic Klystron Two-Beam Accelerator (RK-TBA). The experiment is a prototype for an RK-TBA based microwave power source suitable for driving a 1 TeV linear collider. Major components of the experiment include a 2.5-MV, 1.5-kA electron source, a 11.4-GHz modulator, a bunch compressor, and a 8-m extraction section. The extraction section will be comprised of 4 traveling-wave output structures, ea… more

Date: April 1, 1995

Creator: Westenskow, G.; Caporaso, G.; Chen, Y.; Houck, T.; Yu, S.; Chattopadhyay, S. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Complete momentum and energy resolved TOF electron spectrometerfor time-resolved photoemission spectroscopy

Over the last decade, high-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) has emerged as a tool of choice for studying the electronic structure of solids, in particular, strongly correlated complex materials such as cuprate superconductors. In this paper we present the design of a novel time-of-flight based electron analyzer with capability of 2D in momentum space (kx and ky) and all energies (calculated from time of flight) in the third dimension. This analyzer will utilize an im… more

Date: August 12, 2007

Creator: Hussain, Zahid; Lebedev, G.; Tremsin, A.; Siegmund, O.; Chen, Y.; Shen, Z. X. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Formation of Nanopore-Arrays by Plasma-based Thin FilmDeposition

The ability to fabricate membranes with arrays of apertures only a few nanometers in diameter are important to many fields of research, including ion beam lithography, DNA sequencing, single ion implantations, and single molecule studies. Because even the state-of-the-art lithography tools are limited in their ability to produce nanoscale features, alternative methods of fabricating single pores of nanometer scale have been developed, using ion-beam sculpting and focused-ion-beam assisted depos… more

Date: March 18, 2005

Creator: Ji, Qing; Chen, Y.; Jiang, Ximan; Ji, Lili & Leung, K. N.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Reorientation of misfit dislocations during annealing in InGaAs/GaAs(001) interfaces

Transmission electron microscopy is applied to investigate the effect of postannealing on misfit dislocations in an In[sup 0.2]Ga[sup 0.8]As/GaAs(001) heterostructure. An orthogonal array of 60[degree] dislocations along [110] and [110] directions was observed in the interfaces of the samples grown by MBE at 520C. When the as-grown samples were annealed at temperatures ranging from 600 to 800C, the 60[degree] dislocations were gradually reoriented by dislocation reactions occurring at the 90[de… more

Date: April 1, 1993

Creator: Chen, Y.; Liliental-Weber, Z.; Washburn, J. (Lawrence Berkeley Lab., CA (United States)); Klem, J.F. & Tsao, J.Y. (Sandia National Labs., Albuquerque, NM (United States))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Hydrogen in MgO crystals thermochemically reduced at very high temperatures

Evidence is presented that H/sup -/ ions are the main electron traps responsible for the long-lived luminescence of the F centers observed at 2.3 eV in thermochemically reduced MgO crystals.

Date: August 1, 1982

Creator: Chen, Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Magnetic field quality analysis using ANSYS

The design of superconducting magnets for particles accelerators requires a high quality of the magnetic field. This paper presents an ANSYS 4.4A Post 1 macro that computes the field quality performing a Fourier analysis of the magnetic field. The results show that the ANSYS solution converges toward the analytical solution and that the error on the multipole coefficients depends linearly on the square of the mesh size. This shows the good accuracy of ANSYS in computing the multipole coefficien… more

Date: March 1, 1991

Creator: Dell'Orco, D. & Chen, Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

New concepts for drift pumping a thermal barrier with rf

Pump neutral beams, which are directed into the loss cone of the TMX-U plugs, are normally used to pump ions from the thermal barriers. Because these neutral beams introduce cold gas that reduces pumping efficiency, and require a straight line entrance and exit from the plug, alternate methods are being investigated to provide barrier pumping. To maintain the thermal barrier, either of two classes of particles can be pumped. First, the collisionally trapped ions can be pumped directly. In this … more

Date: May 9, 1985

Creator: Barter, J.D.; Baldwin, D.; Chen, Y. & Poulsen, P.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Experimental studies of electron beam transport in the Maryland periodic solenoid channel

In the University of Maryland electron beam transport experiment, a 5 kV, 0.2 A electron beam from a thermionic electron source (cathode radius r/sub c/ = 1.27 cm and cathode temperature kT = 0.12 eV) is injected into a periodic focusing channel consisting of 38 solenoid lenses with period length S = 13.6 cm. The magnetic focusing fields of the channel, and hence the phase advance without space charge, can be varied over a wide range. We report emittance measurements and results of the effects … more

Date: January 1, 1988

Creator: Kehne,, D.; Low, K.; Reiser, M.; Shea, T.; Chang, C.R. & Chen, Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Small-angle x-ray scattering studies of microvoids in amorphous-silicon-based semiconductors. Annual subcontract report, February 1, 1992--January 31, 1993

Our general objectives are to provide new details of the microstructure for the size scale from about 1 to 30 nm in high-quality a-Si:H and related alloys prepared by current state-of-the-art deposition methods as well as by new and emerging deposition technologies and thereby help determine the role of microvoids and other density fluctuations in controlling the opto-electronic properties. More specifically, the objectives are to determine whether the presence of microstructure as detected by … more

Date: May 1, 1994

Creator: Williamson, D. L.; Jones, S. J. & Chen, Y.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Small-angle x-ray scattering studies of microvoids in amorphous-silicon-based semiconductors. Final subcontract report, 1 February 1991--31 January 1994

This report describes work performed to provide new details of the microstructure for the size scale from about 1 nm to 30 nm in high-quality hydrogenated amorphous-silicon and related alloys prepared by current state-of-the-art deposition methods as well as by new and emerging deposition technologies. The purpose of this work is to help determine the role of microvoids and other density fluctuations in controlling the opto-electronic and photovoltaic properties. The approach involved collabora… more

Date: July 1994

Creator: Williamson, D. L.; Jone, S. J. & Chen, Y.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Beam Transport in a Compact Dielectric Wall Induction Accelerator System for Pulsed Radiography

Using dielectric wall accelerator technology, we are developing a compact induction accelerator system primarily intended for pulsed radiography. The accelerator would provide a 2-kA beam with an energy of 8 MeV, for a 20-30 ns flat-top. The design goal is to generate a 2-mm diameter, 10-rad x-ray source. We have a physics design of the system from injector to the x-ray converter. We present the results of injector modeling and PIC simulations of beam transport. We also discuss the predicted sp… more

Date: May 9, 2005

Creator: McCarrick, J. F.; Caporaso, G. J. & Chen, Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department