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Improved Prediction of the Doppler Effect in TRISO Fuel

Description: The Doppler feedback mechanism is a major contributor to the passive safety of gas-cooled, graphite-moderated High Temperature Reactors that use fuel based on TRISO particles. It follows that the correct prediction of the magnitude and time-dependence of this feedback effect is essential to the conduct of safety analyses for these reactors. Since the effect is directly dependent on the actual temperature reached by the fuel during transients, the underlying phenomena of heat transfer and temper… more
Date: May 1, 2009
Creator: Ortensi, J. & Ougouag, A.M.
Partner: UNT Libraries Government Documents Department
open access

Analysis of an Earthquake-Initiated-Transient in a PBR

Description: One of the Design Basis Accidents (DBA) for a Pebble Bed Reactor has been identified as the “Safe shutdown earthquake with core conduction cooling to passive mode of Reactor Cavity Cooling System.” A new methodology to analyze this particular DBA has been developed at the Idaho National Laboratory (INL). During the seismic event the reactor core experiences the densification of the pebbles, which produce small reactivity insertions due to the effective fuel densification. In addition, a decreas… more
Date: May 1, 2009
Creator: Ougouag, A. M.; Ortensi, J. & Hiruta, H.
Partner: UNT Libraries Government Documents Department
open access

Benchmarking Multipacting Simulations in VORPAL

Description: We will present the results of benchmarking simulations run to test the ability of VORPAL to model multipacting processes in Superconducting Radio Frequency structures. VORPAL is an electromagnetic (FDTD) particle-in-cell simulation code originally developed for applications in plasma and beam physics. The addition of conformal boundaries and algorithms for secondary electron emission allow VORPAL to be applied to multipacting processes. We start with simulations of multipacting between paralle… more
Date: May 1, 2009
Creator: C. Nieter, C. Roark, P. Stoltz, K. Tian
Partner: UNT Libraries Government Documents Department
open access

Application of Goubau Surface Wave Transmission Line for Improved Bench Testing of Diagnostic Beamline Elements

Description: In-air test fixtures for beamline elements typically utilize an X-Y positioning stage, and a wire antenna excited by an RF source. In most cases, the antenna contains a standing wave, and is useful only for coarse alignment measurements in CW mode. A surface-wave (SW) based transmission line permits RF energy to be launched on the wire, travel through the beamline component, and then be absorbed in a load. Since SW transmission lines employ travelling waves, the RF energy can be made to resembl… more
Date: May 1, 2009
Creator: John Musson, Keith Cole, Sheldon Rubin
Partner: UNT Libraries Government Documents Department
open access

Improved DC Gun Insulator

Description: Many user facilities such as synchrotron light sources and free electron lasers require accelerating structures that support electric fields of 10-100 MV/m, especially at the start of the accelerator chain where ceramic insulators are used for very high gradient DC guns. These insulators are difficult to manufacture, require long commissioning times, and have poor reliability, in part because energetic electrons bury themselves in the ceramic, creating a buildup of charge and causing eventual p… more
Date: May 1, 2009
Creator: M.L. Neubauer, K.B. Beard, R. Sah, C. Hernandez-Garcia, G. Neil
Partner: UNT Libraries Government Documents Department
open access

SRF Cavity High-Gradient Study at 805 MHz for Proton and Other Applications

Description: 805 MHz elliptical SRF cavities have been used for SNS as the first application for protons. At LANL, an R&D started to explore a capability of getting high-gradient cavities (40-50 MV/m) at this frequency for the future applications such as proton and muon based interrogation testing facility added to the LANSCE accelerator and a power upgrade of the LANSCE accelerator for the fission and fusion material test station. Optimized cell designs for “standard”, “low-loss” and “re-entrant” shape… more
Date: May 1, 2009
Creator: Tajima, T; Chacon, P; Edwards, R L; Eremeev, G V; Krawczyk, F L; Roybal, R J et al.
Partner: UNT Libraries Government Documents Department
open access

Thermal Analysis of SRF Cavity Couplers Using Parallel Multiphysics Tool TEM3P

Description: SLAC has developed a multi-physics simulation code TEM3P for simulating integrated effects of electromagnetic, thermal and structural loads. TEM3P shares the same software infrastructure with SLAC’s paralell finite element electromagnetic codes, thus enabling all physics simulations within a single framework. The finite-element approach allows high fidelity, high-accuracy simulations and the parallel implementation facilitates large-scale computation with fast turnaround times. In this paper, T… more
Date: May 1, 2009
Creator: Akcelik, V, Lee, L.-Q., Li, Z., Ng, C.-K., Ko, K.,Cheng, G., Rimmer, R., Wang, H.
Partner: UNT Libraries Government Documents Department
open access

Reverse Emittance Exchange for Muon Colliders

Description: Muon collider luminosity depends on the number of muons in the storage ring and on the transverse size of the beams in collision. Ionization cooling as it is currently envisioned will not cool the beam sizes sufficiently well to provide adequate luminosity without large muon intensities. Six-dimensional cooling schemes will reduce the longitudinal emittance of a muon beam so that smaller high frequency RF cavities can be used for later stages of cooling and for acceleration. However, the bunch … more
Date: May 1, 2009
Creator: V. Ivanov, A. Afanasev, C.M. Ankenbrandt, R.P. Johnson, G.M. Wang, S.A. Bogacz, Y.S. Derbenev
Partner: UNT Libraries Government Documents Department
open access

Cryogenic Test of the Nb-Pb SRF Photoinjector Cavities

Description: In this contribution, we report progress on the development of a hybrid lead/niobium superconducting RF (SRF) photoinjector. The goal of this effort is to build a Nb injector with the superconducting cathode made of lead, which demonstrated in the past superior quantum efficiency (QE) compared to Nb Three prototype hybrid devices, consisting of an all-niobium cavity with an arc-deposited spot of lead in the cathode region, have been constructed and tested. We present the cold test results of th… more
Date: May 1, 2009
Creator: Sekutowicz, J. K.; Muhs, A.; Kneisel, P. & Nietubyc, R.
Partner: UNT Libraries Government Documents Department
open access

Pion Cloud and the Sea of the Nucleon

Description: I review recent progress in understanding the structure of the nucleon sea and the role of the nucleon's pion cloud. In particular, I discuss the consequences of the pion cloud for the d-bar - u-bar asymmetry in the proton, the neutron's electric form factor, and the proton's electric to magnetic form factor ratio.
Date: May 1, 2009
Creator: Melnitchouk, Wally
Partner: UNT Libraries Government Documents Department
open access

Design and Construction of a 15 T, 120 mm Bore Ir Quadrupole Magnet for LARP

Description: Pushing accelerator magnets beyond 10 T holds a promise of future upgrades to machines like the Large Hadron Collider (LHC) at CERN. Nb{sub 3}Sn conductor is at the present time the only practical superconductor capable of generating fields beyond 10 T. In support of the LHC Phase-II upgrade, the US LHC Accelerator Research Program (LARP) is developing a large bore (120 mm) IR quadrupole (HQ) capable of reaching 15 T at its conductor peak field and a peak gradient of 219 T/m at 1.9 K. While exp… more
Date: May 4, 2009
Creator: Caspi, S.; Cheng, D.; Dietderich, D.; Felice, H.; Ferracin, P.; Hafalia, R. et al.
Partner: UNT Libraries Government Documents Department
open access

Analysis of Contribution from Edge Radiation to Optical Diffraction Radiation

Description: Beam size measurement with near-field optical diffraction radiation (ODR) has been carried out successfully at CEBAF. The ODR station is installed on the Hall-A beam line after eight bending magnets. The ODR images were affected by an unexpected radiation. Some calculations for analyzing the source of the radiation will be presented. Furthermore, two schemes will be proposed to alleviate the contamination.
Date: May 1, 2009
Creator: C. Liu, P. Evtushenko, A. Freyberger, C. Liu, A.H. Lumpkin
Partner: UNT Libraries Government Documents Department
open access

Status of Electron-Cloud Build-Up Simulations for the Main Injector

Description: We provide a brief status report on measurements and simulations of the electron cloud in the Fermilab Main Injector. Areas of agreement and disagreement are spelled out, along with their possible significance.
Date: May 4, 2009
Creator: Furman, M. A.; Kourbanis, I. & Zwaska, R. M.
Partner: UNT Libraries Government Documents Department
open access

R&D for the Sponge Cleaning of Superconducting RF Cavity

Description: The Electro-polishing process is the best candidate of final surface treatment for the production of ILC cavities. Nevertheless, the broad distribution of the gradient caused by field emitters in cavities is sitll a serious problem for the EP process. Ethanole- and degreaser-rinse processes after the EP process were found to be effective to decrease the field emmitter in recent studies, however, these are not perfect yet. We tried to test the sponge cleaning as the post EP process to remove the… more
Date: May 1, 2009
Creator: Saeki, T.; Hayano, H; Kato, S.; Nishiwaki, M.; Sawabe, M.; Ueno, K. et al.
Partner: UNT Libraries Government Documents Department
open access

Options for an 11 GeV RF Beam Separator for the Jefferson Lab CEBAF Upgrade

Description: The CEBAF accelerator at Jefferson Lab has had, since first demonstration in 1996, the ability to deliver a 5-pass electron beam to experimental halls (A, B, and C) simultaneously. This capability was provided by a set of three, room temperature 499 MHz rf separators in the 5th pass beamline. The separator was two-rod, TEM mode type resonator, which has a high shunt impedance. The maximum rf power to deflect the 6 GeV beams was about 3.4kW. The 12 GeV baseline design does not preserve the capab… more
Date: May 1, 2009
Creator: Jean Delayen, Michael Spata, Haipeng Wang
Partner: UNT Libraries Government Documents Department
open access

Enhanced Method for Cavity Impedance Calculations

Description: With the proposal of medium to high average current accelerator facilities the demand for cavities with extremely low Higher Order Mode (HOM) impedances is increasing. Modern numerical tools are still under development to more thoroughly predict impedances that need to take into account complex absorbing boundaries and lossy materials. With the usually large problem size it is preferable to utilize massive parallel computing when applicable and available. Apart from such computational issues, w… more
Date: May 1, 2009
Creator: Marhauser, Frank; Rimmer, Robert; Tian, Kai & Wang, Haipeng
Partner: UNT Libraries Government Documents Department
open access

The “SF” System of Sextupoles for the JLAB 10 KW Free Electron Laser Upgrade

Description: The characteristics of the system of “SF” Sextupoles for the infrared Free Electron Laser Upgrade1 at the Thomas Jefferson National Accelerator Facility (JLab) are described. These eleven sextupoles possess a large field integral (2.15 T/m) with +/- 0.2%
Date: May 1, 2009
Creator: George Biallas, Mark Augustine, Kenneth Baggett, David Douglas, Robin Wines
Partner: UNT Libraries Government Documents Department
open access

High Power Co-Axial SRF Coupler

Description: There are over 35 coupler designs for SRF cavities ranging in frequency from 325 to 1500 MHz. Two-thirds of these designs are coaxial couplers using disk or cylindrical ceramics in various combinations and configurations. While it is well known that dielectric losses go down by several orders of magnitude at cryogenic temperatures, it not well known that the thermal conductivity also goes down, and it is the ratio of thermal conductivity to loss tangent (SRF ceramic Quality Factor) and ceramic … more
Date: May 1, 2009
Creator: M.L. Neubauer, R.A. Rimmer
Partner: UNT Libraries Government Documents Department
open access

Time-Dependent Phase-Space Mapping of Space-Charge-Dominated Beams

Description: In this paper we report on a proof of principle experiment for demonstrating the possibility of reconstructing the time resolved-phase-space distribution of a space-charge dominated beam by a tomographic technique which provides us with far more information than a time-sliced emittance. We emphasize that this work describes and demonstrates a new methodology which can be applicable to any beam pulse using imaging methods with the appropriate time resolution for the pulse duration. The combinati… more
Date: May 2009
Creator: Stratakis, D.; Fiorito, R. B.; Haber, I.; Kishek, R. A.; O'Shea, P. G.; Reiser, M. et al.
Partner: UNT Libraries Government Documents Department
open access

Nb3Sn superconducting magnets for electron cyclotron resonance ion sources

Description: Electron cyclotron resonance (ECR) ion sources are an essential component of heavy-ion accelerators. Over the past few decades advances in magnet technology and an improved understanding of the ECR ion source plasma physics have led to remarkable performance improvements of ECR ion sources. Currently third generation high field superconducting ECR ion sources operating at frequencies around 28 GHz are the state of the art ion injectors and several devices are either under commissioning or under… more
Date: May 4, 2009
Creator: Ferracin, P.; Caspi, S.; Felice, H.; Leitner, D.; Lyneis, C. M.; Prestemon, S. et al.
Partner: UNT Libraries Government Documents Department
open access

Buffered Electropolishing – A New Way for Achieving Extremely Smooth Surface Finish on Nb SRF Cavities to be Used in Particle Accelerators

Description: Future accelerators require unprecedented cavity performance, which is strongly influenced by interior surface nano-smoothness. Electropolishing (EP) is the technique of choice to be developed for high-field superconducting radio frequency (SRF) cavities. Electrochemical impedance spectroscopy (EIS) and related techniques point to the electropolishing mechanism of Nb in a sulphuric and hydrofluoric acid electrolyte controlled by a compact surface salt film under F- diffusion-limited mass transp… more
Date: May 1, 2009
Creator: Hui Tian, Charles Reece, Michael Kelley
Partner: UNT Libraries Government Documents Department
open access

Oxidation in Environments with Elevated CO2 Levels

Description: Efforts to reduce greenhouse gas emissions from fossil energy power productions focus primarily on either pre- or post-combustion removal of CO2. The research presented here examines corrosion and oxidation issues associated with two types of post-combustion CO2 removal processes—oxyfuel combustion in refit boilers and oxyfuel turbines.
Date: May 1, 2009
Creator: Holcomb, Gordon H.
Partner: UNT Libraries Government Documents Department
open access

Superconducting Multi-Cell Deflecting Cavity for Short-Pulse X-Ray Generation at the Advanced Photon Source

Description: A superconducting multi-cell cavity for the production of short x-ray pulses at the Advanced Photon Source (APS) has been explored as an alternative to a single-cell cavity design in order to improve the packing factor and potentially reduce the number of high-power RF systems and low-level RF controls required. The cavity will operate at 2815 MHz in the APS storage ring and will require heavy damping of parasitic modes to maintain stable beam operation. Novel on-cell dampers, attached directly… more
Date: May 1, 2009
Creator: G.J. Waldschmidt, L.H. Morrison, R. Nassiri, R.A. Rimmer, K. Tian, H. Wang
Partner: UNT Libraries Government Documents Department
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