218 Matching Results

Results open in a new window/tab.

PROGRESS IN 2 mm GLOW DISCHARGE POLYMER MANDREL DEVELOPMENT FOR NIF (open access)

PROGRESS IN 2 mm GLOW DISCHARGE POLYMER MANDREL DEVELOPMENT FOR NIF

OAK-B135 All planned National Ignition Facility (NIF) capsule targets except machined beryllium require a glow discharge polymer (GDP) mandrel upon which the albator is applied. This mandrel, {approx} 2 mm in diameter, must at least meet if not exceed the symmetry and surface finish requirements of the final capsule. Such mandrels are currently produced by the three-step depolymerizable mandrel technique. The quality of the final mandrel depends upon precise optimization and execution of each of the three steps. They had shown previously that fabrication of a mandrel which met the symmetry and surface finish requirements was feasible using this technique. In this paper they will discuss recent progress towards converting this process into a high yield, production scale process.
Date: June 1, 2003
Creator: Nikroo, A.; Bousquet, J.; Cook, R.; Mcquillan, B. W.; Paguio, R. & Takagi, M.
System: The UNT Digital Library
Searches for new physics at D0 (open access)

Searches for new physics at D0

The integrated luminosity at Run 2 of the Tevatron is approaching the Run 1 total, and data analysis is progressing. New results in searches for new physics by the D0 experiment are presented in a variety of channels, demonstrating good performance of the detector and detailed understanding of the data.
Date: June 4, 2003
Creator: Brooijmans, Gustaaf
System: The UNT Digital Library
Fermilab booster modeling and space charge study (open access)

Fermilab booster modeling and space charge study

The Fermilab Booster is a bottleneck limiting the proton beam intensity in the accelerator complex. A study group has been formed in order to have a better understanding of this old machine and seek possible improvements. The work includes lattice modeling, numerical simulations, bench measurements and beam studies. Based on newly obtained information, it has been found that the machine acceptance is severely compromised by the orbit bump and dogleg magnets. This, accompanied by emittance dilution from space charge at injection, is a major cause of the large beam loss at the early stage of the cycle. Measures to tackle this problem are being pursued.
Date: June 4, 2003
Creator: al., Weiren Chou et
System: The UNT Digital Library
Lattice function measurements of the Fermilab recycler ring (open access)

Lattice function measurements of the Fermilab recycler ring

The Fermilab Recycler ring, designed and built as an 8-GeV anti-proton storage ring, is at the final stage of its commissioning. Once integrated into the accelerator complex it is expected to help achieve the luminosity goal of Run II at Fermilab. The Recycler Ring is made up mostly of combined function magnets with a substantial sextupole component. Any orbit error could cause higher order feed-down and potentially change the machine. Lattice function measurements had been taken at various stages of the machine and the results are presented here.
Date: June 4, 2003
Creator: Yang, Ming-Jen; Marchionni, Alberto & Mishra, Shekhar
System: The UNT Digital Library
Nb3Sn accelerator magnet development around the world (open access)

Nb3Sn accelerator magnet development around the world

During the past 30 years superconducting magnet systems have enabled accelerators to achieve energies and luminosities that would have been impractical if not impossible with resistive magnets. By far, NbTi has been the preferred conductor for this application because of its ductility and insensitivity of Jc to mechanical strain. This is despite the fact that Nb{sub 3}Sn has a more favorable Jc vs. B dependence and can operate at much higher temperatures. Unfortunately, NbTi conductor is reaching the limit of it usefulness for high field applications. Despite incremental increases in Jc and operation at superfluid temperatures, magnets are limited to approximately a 10 T field. Improvements in conductor performance combined with future requirements for accelerator magnets to have bore fields greater than 10 T or operate in areas of large beam-induced heat loads now make Nb{sub 3}Sn look attractive. Thus, laboratories in several countries are actively engaged in programs to develop Nb{sub 3}Sn accelerator magnets for future accelerator applications. A summary of this important research activity is presented along with a brief history of Nb{sub 3}Sn accelerator magnet development and a discussion of requirements for future accelerator magnets.
Date: June 23, 2003
Creator: Lamm, Michael J.
System: The UNT Digital Library
Barrier RF stacking at Fermilab (open access)

Barrier RF stacking at Fermilab

A key issue to upgrade the luminosity of the Tevatron Run2 program and to meet the neutrino requirement of the NuMI experiment at Fermilab is to increase the proton intensity on the target. This paper introduces a new scheme to double the number of protons from the Main Injector (MI) to the pbar production target (Run2) and to the pion production target (NuMI). It is based on the fact that the MI momentum acceptance is about a factor of four larger than the momentum spread of the Booster beam. Two RF barriers--one fixed, another moving--are employed to confine the proton beam. The Booster beams are injected off-momentum into the MI and are continuously reflected and compressed by the two barriers. Calculations and simulations show that this scheme could work provided that the Booster beam momentum spread can be kept under control. Compared with slip stacking, a main advantage of this new method is small beam loading effect thanks to the low peak beam current. The RF barriers can be generated by an inductive device, which uses nanocrystal magnet alloy (Finemet) cores and fast high voltage MOSFET switches. This device has been designed and fabricated by a Fermilab-KEK-Caltech team. The first …
Date: June 4, 2003
Creator: al., Weiren Chou et
System: The UNT Digital Library
The New York Transmission Congestion Contract Market: Is It Truly Working Efficiently? (open access)

The New York Transmission Congestion Contract Market: Is It Truly Working Efficiently?

None
Date: June 30, 2003
Creator: Bartholomew, Emily S.; Siddiqui, Afzal S.; Marnay, Chris & Oren, Shmuel S.
System: The UNT Digital Library
A new-generation EM system for the detection and classification of buried metallic objects (open access)

A new-generation EM system for the detection and classification of buried metallic objects

A prime requirement in discrimination between UXO and non-UXO metallic fragments (clutter) is to determine accurately the response parameters that characterize a metallic object in the ground. Lawrence Berkeley National Laboratory has been involved in assessing and comparing existing systems, and designing an optimum system for UXO detection. A prototype of a new electromagnetic system will be built based on the results of this study. The detection and characterization of metallic objects can be considered a two-step process: location and identification. A multi-component transmitter-receiver system is essential for the identifying of the principal dipole moments of a target. The ground response imposes an early time limit on the time window available for target discrimination. Once the target response falls below the ground response, it will be poorly resolved, especially since the ground response itself will be variable due to the inhomogeneous nature of the near surface. For a given range of targets and given ambient noise characteristics, one can optimize system bandwidth so as to maximize the observable signal-to-noise ratio. A sensor with four or more decades of flat frequency response is needed to record the secondary magnetic fields associated with the target.
Date: June 1, 2003
Creator: Gasperikova, Erika
System: The UNT Digital Library
Charm physics at the Tevatron (open access)

Charm physics at the Tevatron

The cross section of p{bar p} into charm is very high compared to e{sup +}e{sup -}-machines, but it is orders of magnitude smaller than the total cross section of {approx} 100mb. This explains the need for a good trigger mechanism. Traditionally charm physics at hadron colliders relies on a lepton signature. For example, the decay of the J{psi} into two leptons or semi-leptonic decays of D-mesons. Both detectors at the Tevatron, CDF and D0 have undergone substantial upgrades for RUN II. CDF now exploits a new trigger technique selecting more abundant hadronic decays. First charm physics results from the CDF and D0 experiments at the Tevatron Run II are presented. With the addition of the Secondary Vertex Trigger CDF has become a competitive charm experiment.
Date: June 4, 2003
Creator: Korn, A.
System: The UNT Digital Library
2 MW upgrade of the Fermilab Main Injector (open access)

2 MW upgrade of the Fermilab Main Injector

In January 2002, the Fermilab Director initiated a design study for a high average power, modest energy proton facility. An intensity upgrade to Fermilab's 120-GeV Main Injector (MI) represents an attractive concept for such a facility, which would leverage existing beam lines and experimental areas and would greatly enhance physics opportunities at Fermilab and in the U.S. With a Proton Driver replacing the present Booster, the beam intensity of the MI is expected to be increased by a factor of five. Accompanied by a shorter cycle, the beam power would reach 2 MW. This would make the MI a more powerful machine than the SNS or the J-PARC. Moreover, the high beam energy (120 GeV) and tunable energy range (8-120 GeV) would make it a unique high power proton facility. The upgrade study has been completed and published. This paper gives a summary report.
Date: June 4, 2003
Creator: Chou, Weiren
System: The UNT Digital Library
Theoretical studies of beam-beam effects in the Tevatron at collision energy (open access)

Theoretical studies of beam-beam effects in the Tevatron at collision energy

The dynamics due to the long-range beam-beam interactions depends on several beam parameters such as tunes, coupling, chromaticities, beam separations, intensities and emittances. They have developed analytical tools to calculate, for example, amplitude dependent tune shifts and chromaticities, beam-beam induced coupling, and betatron and synchro-betatron resonance widths. They report on these calculations and dynamic aperture calculations with long-term tracking. These theoretical results are compared with observations at collision energy and used to predict performance at design values of beam intensities and emittances.
Date: June 9, 2003
Creator: Sen, T.; Erdelyi, B. & Xiao, M.
System: The UNT Digital Library
Subsurface void detection using seismic tomographic imaging (open access)

Subsurface void detection using seismic tomographic imaging

Tomographic imaging has been widely used in scientific and medical fields to remotely image media in a nondestructive way. This paper introduces a spectrum of seismic imaging applications to detect and characterize voids in coal mines. The application of seismic waves to detect changes in coal relies on two types of waves: body waves refracted along the interface between coal and bedrock (i.e., refracted P-waves) and channel waves that propagate directly through the coal (dispersive wave trains of the Rayleigh or Love type). For example, a P-wave tomography study to find underlying old mine workings in a coal mine in England, produced velocity patterns that revealed increases in velocity where high stress concentrations occur in the rock, which are most likely connected to old pillars left in support of the old working areas. At the same time, low velocities were found in areas of low stress concentrations, which are related to roof collapses indicating the locations of mined areas below. The application of channel wave tomography to directly image the presence of gaseous CO{sub 2} in a low velocity oil reservoir showed that the injected CO{sub 2} followed an ancient flow channel in the reservoir migrating from the injector to …
Date: June 26, 2003
Creator: Gritto, Roland
System: The UNT Digital Library
Simulation studies of a XUV/soft X-ray harmonic-cascade FEL for the proposed LBNL recirculating linac* (open access)

Simulation studies of a XUV/soft X-ray harmonic-cascade FEL for the proposed LBNL recirculating linac*

Presently there is significant interest at LBNL in designing and building a facility for ultrafast (i.e. femtosecond time scale) x-ray science based upon a superconducting, recirculating RF linac (see Corlett et al. for more details). In addition to producing synchrotron radiation pulses in the 1-15 keV energy range, we are also considering adding one or more free-electron laser (FEL) beamlines using a harmonic cascade approach to produce coherent XUV soft X-ray emission beginning with a strong input seed at {approx}200 nm wavelength obtained from a ''conventional'' laser. Each cascade is composed of a radiator together with a modulator section, separated by a magnetic chicane. The chicane temporally delays the electron beam pulse in order that a ''virgin'' pulse region (with undegraded energy spread) be brought into synchronism with the radiation pulse, which together then undergo FEL action in the modulator. We present various results obtained with the GINGER simulation code examining final output sensitivity to initial electron beam parameters. We also discuss the effects of spontaneous emission and shot noise upon this particular cascade approach which can limit the final output coherence.
Date: June 2, 2003
Creator: Fawley, W. M.; Barletta, W. A.; Corlett, J. N. & Zholents, A.
System: The UNT Digital Library
New aspects of beam-beam interactions in hadron colliders (open access)

New aspects of beam-beam interactions in hadron colliders

Beam-beam phenomena have until now limited the beam currents and luminosity achievable in the Tevatron. injected proton currents are about ten times larger than the anti-proton currents so beam-beam effects have largely acted on the anti-protons and at all stages of the operational cycle. The effects of the anti-protons on the protons have until now been relatively benign but that may change at higher anti-proton currents. After 36 bunches of protons are injected and placed on the proton helix, anti-protons are injected four bunches at a time. After all bunches are injected, acceleration to top energy takes bout 85 seconds. After reaching flat top, the optics around the interaction regions (IRs) is changed to lower {beta}* from 1.6 m to 0.35 m at B0 and D0. The beams are brought into collision by collapsing the separation bumps around the IPs. During a high energy physics store each bunch experiences two head-on collisions with bunches in the opposing beam and seventy long-range interactions. At all other stages of the operational cycle, each bunch experiences only long-range interactions--seventy two in all. Performance limitations from beam-beam effects until now have been primarily due to these long-range interactions. The anti-proton losses at 150 GeV …
Date: June 2, 2003
Creator: Sen, Tanaji
System: The UNT Digital Library
Top quark production cross-section at the Tevatron Run 2 (open access)

Top quark production cross-section at the Tevatron Run 2

The top quark pair production cross-section {sigma}{sub t{bar t}} has been measured in p{bar p} collisions at center of mass energies of 1.96 TeV using Tevatron Run 2 data. In the beginning of Run 2 both CDF and D0 {sigma}{sub t{bar t}} measurements in the dilepton channel t{bar t} {yields} WbW{bar b} {yields} {bar {ell}}{nu}{sub {ell}}b{ell}{prime} {bar {nu}}{sub {ell}{prime}}{bar b} and in the lepton plus jets channel t{bar t} {yields} WbW{bar b} {yields} q{bar q}{prime} b{ell}{bar {nu}}{sub {ell}}{bar b} + {bar {ell}}{nu}{sub {ell}}bq{bar q}{prime} {bar b} agree with the NLO (Next-to-Leading-Order) theoretical predictions. The presence of a top signal in Tevatron data has been reestablished.
Date: June 4, 2003
Creator: Cabrera, S.
System: The UNT Digital Library
Performance and costs of particle air filtration in HVAC supply airstreams (open access)

Performance and costs of particle air filtration in HVAC supply airstreams

None
Date: June 1, 2003
Creator: Fisk, William J.; Faulkner, David; Palonen, Jari & Seppanen, Olli
System: The UNT Digital Library
Electroweak and top physics at CDF in Run II (open access)

Electroweak and top physics at CDF in Run II

The CDF experiment at the Tevatron has used p{bar p} collisions at {radical}s = 1.96 TeV to measure the production cross sections of W and Z bosons using several leptonic final states. An indirect measurement of the W width and the ratio of tau and electron electroweak couplings have been extracted. The forward-backward charge asymmetry, A{sub FB}, in Drell-Yan dilectron production has been measured up to an invariant mass of 600 GeV/c{sup 2}. CDF has also started looking for WW production in the dilepton channel, WW{prime} {yields} ll{prime}vv, with the aim of measuring its cross section and derive limits on the anomalous WWZ and WW{gamma} couplings. The presence of a top quark signal in the Tevatron data has been reestablished by measuring the top quark pair production cross section in the dilepton channel, t{bar t} {yields} WbW{bar b} {yields} {bar l}v{sub l}bl{prime}{bar v}{sub l{prime}}{bar b} and in the lepton plus jets channel, t{bar t} {yields} WbW{bar b} {yields} q{bar q}lbl{bar b}{sub l}{bar b} + {bar l}v{sub l}bq{bar q}{prime}{bar b}. A pre-tagged lepton plus jets sample has also been used to reconstruct the top quark mass.
Date: June 12, 2003
Creator: Taffard, A.
System: The UNT Digital Library
Repair of a Melter Pour Spout Using an Expanding Ring (open access)

Repair of a Melter Pour Spout Using an Expanding Ring

An expanding ring was developed that provided remote repair of the pour spout for a radioactive waste vitrification melter. This passive device used gas pressure to expand a metal ring against the irregularly shaped pour spout wall. Laboratory modeling and testing were performed for proof of concept and optimization before final design and field deployment. The ring expanded radially more than 4.8 mm and successfully repaired the melter pour spout allowing continued glass pouring operation.
Date: June 17, 2003
Creator: Imrich, K. J.
System: The UNT Digital Library
Jet Breakup and Spray Formation in a Diesel Engine (open access)

Jet Breakup and Spray Formation in a Diesel Engine

The breakup of injected fuel into spray is of key interest to the design of a fuel efficient, nonpolluting diesel engine. We report preliminary progress on the numerical simulation of diesel fuel injection spray with the front tracking code FronTier. Our simulation design is set to match experiments at ANL, and our present agreement is semi-quantitative. Future efforts will include mesh refinement studies, which will better model the turbulent flow.
Date: June 17, 2003
Creator: Glimm, J.; Li, X.; Kim, M. N.; Oh, W.; Marchese, A.; Samulyak, R. et al.
System: The UNT Digital Library
Longitudinal Bunch Dynamics in the Tevatron (open access)

Longitudinal Bunch Dynamics in the Tevatron

The authors present their observations of the longitudinal bunch dynamics in Tevatron for uncoalesced proton bunches at 150 GeV and coalesced proton bunches at 150 GeV and 980 GeV. They have observed long-term (> 15 minutes) coherent oscillations of uncoalesced protons that preserve already existing oscillations from upstream accelerators. A single-bunch instability in large intensity protons bunches at 980 GeV has also been observed.
Date: June 2, 2003
Creator: Moore, R.; Balbekov, V.; Jansson, A.; Lebedev, V.; Ng, K. Y. & Shiltsev, V.
System: The UNT Digital Library
A new security model for collaborative environments (open access)

A new security model for collaborative environments

Prevalent authentication and authorization models for distributed systems provide for the protection of computer systems and resources from unauthorized use. The rules and policies that drive the access decisions in such systems are typically configured up front and require trust establishment before the systems can be used. This approach does not work well for computer software that moderates human-to-human interaction. This work proposes a new model for trust establishment and management in computer systems supporting collaborative work. The model supports the dynamic addition of new users to a collaboration with very little initial trust placed into their identity and supports the incremental building of trust relationships through endorsements from established collaborators. It also recognizes the strength of a users authentication when making trust decisions. By mimicking the way humans build trust naturally the model can support a wide variety of usage scenarios. Its particular strength lies in the support for ad-hoc and dynamic collaborations and the ubiquitous access to a Computer Supported Collaboration Workspace (CSCW) system from locations with varying levels of trust and security.
Date: June 6, 2003
Creator: Agarwal, Deborah; Lorch, Markus; Thompson, Mary & Perry, Marcia
System: The UNT Digital Library
B physics at CDF (open access)

B physics at CDF

B physics is at the core of the CDF agenda for Run II. With the Tevatron performance gradually improving, samples of data corresponding to about 70 pb{sup -1} are now available. Due to improved detector capabilities these data already allow one to improve a number of Run I results, as well as perform a series of new measurements. We present an overview of the current state of B physics at CDF.
Date: June 4, 2003
Creator: Anikeev, K.
System: The UNT Digital Library
Slip stacking experiments at Fermilab main injector (open access)

Slip stacking experiments at Fermilab main injector

In order to achieve an increase in proton intensity, Fermilab Main Injector will use a stacking process called ''slip stacking''. The intensity will be doubled by injecting one train of bunches at a slightly lower energy, another at a slightly higher energy, then bringing them together for the final capture. Beam studies have started for this process and we have already verified that, at least for a low beam intensity, the stacking procedure works as expected. For high intensity operation, development work of the feedback and feedforward systems is under way.
Date: June 2, 2003
Creator: al., Kiyomi Koba et
System: The UNT Digital Library
FNAL booster: Experiment and modeling (open access)

FNAL booster: Experiment and modeling

We present measurements of transverse and longitudinal beam phase space evolution during the first two hundred turns of the FNAL Booster cycle. We discuss the experimental technique, which allowed us to obtain turn-by-turn measurements of the beam profile. The experimental results are compared with the prediction of the Synergia 3D space charge simulation code.
Date: June 2, 2003
Creator: Spentzouris, Panagiotis & Amundson, James
System: The UNT Digital Library