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[show abstract]
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ABSTRACT: UCHII G25.4NW is a bright IR source in the inner Galaxy region.
New HI images from the VLA Galactic Plane Survey (VGPS) show clear absorption
features associated with the UCHII region up to 95 km s$^{-1}$, and there is
not any other absorptions up to the tangential velocity.
It reveals that G25.4NW is at a near-side distance of 5.7 kpc, and it is
located in the inner Galactic molecular ring region.
Using the new distance, the bolometric luminosity of G25.4NW is estimated as
$10^{5.6} L_{\odot}$, which corresponds to an O6 star.
It contains 460 $M_{\odot}$ of ionized gas. High-resolution $^{13}$CO image
from the Galactic Ring Survey (GRS) reveals that G25.4NW is part of a more
extended star-formation complex with about $10^{4} M_{\odot}$ molecular gas.
04/2013;
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[show abstract]
[hide abstract]
ABSTRACT: The Monoceros Loop (SNR G205.5+0.5) is a large shell-type supernova remnant
located in the Rosette Complex region. It was suggested to be interacting with
the Rosette Nebula. We aim to re-examine the radio spectral index and its
spatial variation over the Monoceros SNR, and study its properties of evolution
within the complex interstellar medium. We extracted radio continuum data for
the Monoceros complex region from the Effelsberg 21 cm and 11 cm surveys and
the Urumqi 6 cm polarization survey. We used the new Arecibo GALFA-HI survey
data with much higher resolution and sensitivity than that previously available
to identify the HI shell related with the SNR. Multi-wavelengths data are
included to investigate the properties of the SNR. The spectral index $\alpha$
($S_{\nu}\propto\nu^{\alpha}$) averaged over the SNR is $-0.41 \pm$0.16. The
TT-plots and the distribution of $\alpha$ over the SNR show spatial variations
which steepen towards the inner western filamentary shell. Polarized emission
is prominent on the western filamentary shell region. The RM there is estimated
to be about 30$\pm$77n rad m$^{-2}$, where the n=1 solution is preferred, and
the magnetic field has a strength of about 9.5 $\mu$G. From the HI channel
maps, further evidence is provided for an interaction between the Monoceros SNR
and the Rosette Nebula. We identify partial neutral hydrogen shell structures
in the northwestern region at LSR velocities of +15 km s$^{-1}$ circumscribing
the continuum emission. The HI shell has swept up a mass of about 4000
M$_{\odot}$ for a distance of 1.6 kpc. The western HI shell, well associated
with the dust mission, is found to lie outside of the radio shell. We suggest
that the Monoceros SNR is evolving within a cavity blown-out by the progenitor,
and has triggered part of the star formation in the Rosette Nebula.
07/2012;
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G Burt,
P Ambattu,
R. Carter,
A Dexter,
I Tahir,
C Beard,
M. Dykes,
P Goudket,
A Kalinin,
L Ma, [......],
R. M. Jones,
L Bellantoni,
B. Chase,
M. Church,
T. Khabouline,
A Latina,
C. Adolphsen,
Z Li,
A. Seryei, L Xiao
[show abstract]
[hide abstract]
ABSTRACT: Crab cavities have been proposed for a wide number of accelerators and interest in crab cavities has recently increased after the successful operation of a pair of crab cavities in KEK-B. In particular crab cavities are required for both the ILC and CLIC linear colliders for bunch alignment. Consideration of bunch structure and size constraints favour a 3.9 GHz superconducting, multi-cell cavity as the solution for ILC, whilst bunch structure and beam-loading considerations suggest an X-band copper travelling wave structure for CLIC. These two cavity solutions are very different in design but share complex design issues. Phase stabilisation, beam loading, wakefields and mode damping are fundamental issues for these crab cavities. Requirements and potential design solutions will be discussed for both colliders. Comment: 3 pages. To be published in proceedings of LINAC 2008, Victoria, Canada
10/2008;
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C Ng,
V Akcelik,
A Candel,
S Chen,
L Ge,
A Kabel,
Lie-Quan Lee,
Z Li,
E Prudencio,
G Schussman,
R Uplenchwar, L Xiao,
K Ko,
T Austin,
J R Cary,
S Ovtchinnikov,
D N Smith,
G R Werner,
L Bellantoni
[show abstract]
[hide abstract]
ABSTRACT: SciDAC-1, with its support for the 'Advanced Computing for 21st Century Accelerator Science and Technology' project, witnessed dramatic advances in electromagnetic (EM) simulations for the design and optimization of important accelerators across the Office of Science. In SciDAC2, EM simulations continue to play an important role in the 'Community Petascale Project for Accelerator Science and Simulation' (ComPASS), through close collaborations with SciDAC Centers and Insitutes in computational science. Existing codes will be improved and new multi-physics tools will be developed to model large accelerator systems with unprecedented realism and high accuracy using computing resources at petascale. These tools aim at targeting the most challenging problems facing the ComPASS project. Supported by advances in computational science research, they have been successfully applied to the International Linear Collider and the Large Hadron Collider in high energy physics, the JLab 12-GeV Upgrade in nuclear physics, and the Spallation Neutron Source and the Linac Coherent Light Source in basic energy sciences.
Journal of Physics Conference Series 08/2008; 125(1):012003.
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L Lee,
V Akcelik,
L Ge,
S Chen,
G Schussman,
A Candel,
Z Li, L Xiao,
A Kabel,
R Uplenchwar,
C Ng,
K Ko
[show abstract]
[hide abstract]
ABSTRACT: Computational science research components were vital parts of the SciDAC-1 accelerator project and are continuing to play a critical role in the SciDAC-2 accelerator project, the Community Petascale Project for Accelerator Science and Simulation (ComPASS). Presented here are recent advances and achievements in the area of computational science research in support of petascale electromagnetic modeling for accelerator design analysis, which include shape determination of superconducting RF cavities, mesh-based multilevel preconditioner for solving highly indefinite linear systems, moving window using h- or p-refinement for time-domain short-range wakefield calculations, and improved scalable application I/O.
Journal of Physics Conference Series 08/2008; 125(1):012077.
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L. Xiao,
K. Ko,
Z. Li,
C. Ng,
G. Schussman,
A. Seryi,
R. Uplenchwar,
G. Burt,
P. Goudket,
P. McIntosh,
L. Bellantoni
[show abstract]
[hide abstract]
ABSTRACT: The FNAL 9-cell 3.9 GHz deflecting cavity designed for the CKM experiment was chosen as the baseline design for the ILC BDS crab cavity. Effective damping is required for the lower-order TM<sub>010</sub> modes (LOM), the same-order TM<sub>110</sub> pi-mode (SOM) as well as the higher-order modes (HOM) to minimize the beam loading and beam centroid steering due to wakefields. Simulation results of the original CKM design using the eigensolver Omega3P showed that both the notch filters of the HOM/LOM couplers are too sensitive to the notch gap, and the damping of the SOM is insufficient for the ILC. To meet the ILC requirements, the couplers were redesigned to improve the damping and tuning sensitivity. With the new design, the damping of the LOM/SOM/HOM modes is significantly improved, the sensitivity of the notch filter for the HOM coupler is reduced by one order of magnitude and mechanically feasible, and the LOM coupler is simplified by aligning it on the same plane as the SOM coupler and by eliminating the notch filter. In this paper, we will present the coupler optimization, tolerance studies and multipacting analysis for the crab cavity.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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[show abstract]
[hide abstract]
ABSTRACT: The actual cell shapes of the TESLA cavities differ from the ideal due to fabrication errors, the addition of stiffening rings and the frequency tuning process. Cavity imperfection shifts the dipole mode frequencies and alters the Qext's from those computed for the ideal cavity. Qext increase could be problematic if its value exceeds the limit required for ILC beam stability. To study these effects, a cavity imperfection model was established using a mesh distortion method. The eigensolver Omega3P was then used to find the critical dimensions that contribute to the Qext spread and frequency shift by comparing predictions to TESLA cavity measurement data. Using the imperfection parameters obtained from these studies, fiducial cavity imperfection models are generated for the studies of wake fields.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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Z. Li,
L. Ge,
L. Lee,
C. Ng,
G. Schussman, L. Xiao,
K. Ko,
J. Sekutowicz,
P. Kneisel,
T. Higo,
Y. Morozumi,
K. Saito
[show abstract]
[hide abstract]
ABSTRACT: The low-loss shape cavity design has been proposed as a possible alternative to the baseline TESLA cavity design for the ILC main linacs. The advantages of this design over the TESLA cavity are its lower cryogenic loss, and higher achievable gradient due to lower surface fields. High gradient prototypes for such designs have been tested at KEK (ICHIRO) and TJNAF (LL). However, issues related to HOM damping and multipacting still need to be addressed. Preliminary numerical studies of the prototype cavities have shown unacceptable damping factors for some higher-order dipole modes if the typical TESLA HOM couplers are directly adapted to the design. The resulting wakefield will dilute the beam emittance thus reducing the machine luminosity. Furthermore, high gradient tests on a 9-cell prototype at KEK have experienced multipacting barriers although a single LL cell had achieved a high gradient. From simulations, multipacting activities are found to occur in the end-groups of the cavity. In this paper, we will present the optimization results of the end-groups for the low-loss designs for effective HOM damping and alleviation of multipacting.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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J. Sekutowicz,
J. Iversen,
D. Klinke,
D. Kostin,
W. Moller,
A. Muhs,
P. Kneisel,
J. Smedley,
T. Rao,
P. Strzyzewski,
A. Soltan,
Z. Li,
K. Ko, L. Xiao,
R. Lefferts,
A. Lipski,
M. Ferrario
[show abstract]
[hide abstract]
ABSTRACT: We report on the progress and status of an electron RF* gun made of two superconductors: niobium and lead [1]. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead. The design of RF-gun and performance of 3 test cavities without and with the emitting lead spot are reported in this contribution. Measured quantum efficiency for lead at 2 K is presented briefly. More details are reported in [9].
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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Z. Li,
V. Akcelik,
A. Candel,
S. Chen,
L. Ge,
A. Kabel,
L.-Q. Lee,
C. Ng,
E. Prudencio,
G. Schussman,
R. Uplenchwar, L. Xiao,
K. Ko
[show abstract]
[hide abstract]
ABSTRACT: Under the support of the U.S. DOE SciDAC program, SLAC has been developing a suite of 3D parallel finite- element codes aimed at high-accuracy, high-fidelity electromagnetic and beam physics simulations for the design and optimization of next-generation particle accelerators. Running on the latest supercomputers, these codes have made great strides in advancing the state of the art in applied math and computer science at the petascale that enable the integrated modeling of electromagnetics, self-consistent Particle-In-Cell (PIC) particle dynamics as well as thermal, mechanical, and multi-physics effects. This paper will present 3D results of trapped mode calculations in an ILC cryomodule and the modeling of the ILC Sheet Beam klystron, shape determination of superconducting RF (SCRF) cavities and multipacting studies of SCRF HOM couplers, as well as PIC simulation results of the LCLS RF gun.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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A. Seryi,
J. Amann,
R. Arnold,
F. Asiri,
K. Bane,
P. Bellomo,
E. Doyle,
A. Fasso,
K. Jonghoon,
L. Keller, [......],
T. Mattison,
J. Carwardine,
C. Saunders,
R. Appleby,
E. Torrence,
J. Gronberg,
T. Sanuki,
Y. Iwashita,
V. Telnov,
D. Warner
[show abstract]
[hide abstract]
ABSTRACT: The beam delivery system for the linear collider focuses beams to nanometer sizes at its interaction point, collimates the beam halo to provide acceptable background in the detector and has a provision for state-of-the art beam instrumentation in order to reach the ILC's physics goals. This paper describes the design details and status of the baseline configuration considered for the reference design and also lists alternatives.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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[show abstract]
[hide abstract]
ABSTRACT: The FNAL 9-cell 3.9GHz deflecting mode cavity designed for the CKM experiment was chosen as the baseline design for the ILC BDS crab cavity. The full 9-cell CKM cavity including the coupler end-groups was simulated using the parallel eigensolver Omega3P and scattering parameter solver S3P. It was found that both the notch filters for the HOM/LOM couplers are very sensitive to the notch gap, which is about 1.6MHz/micron and is more than 10 times more sensitive than the TTF cavity. It was also found in the simulation that the unwanted vertical {pi}-mode (SOM) is strongly coupled to the horizontal 7{pi}/9 mode which causes x-y coupling and reduces the effectiveness of the SOM damping. To meet the ILC requirements, the HOM/LOM couplers are redesigned to address these issues. With the new designs, the damping of the HOM/LOM modes is improved. The sensitivity of the notch filter for the HOM coupler is reduced by one order of magnitude. The notch filter for the LOM coupler is eliminated in the new design which significantly simplifies the geometry. In this paper, we will present the simulation results of the original CKM cavity and the progresses on the HOM/LOM coupler re-design and optimization.
04/2007;
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K Ko,
N Folwell,
L Ge,
A Guetz,
V Ivanov,
A Kabel,
M Kowalski,
L Lee,
Z Li,
C Ng,
E Prudencio,
G Schussman,
R Uplenchwar, L Xiao,
ISICs/SAPP Collaborators
[show abstract]
[hide abstract]
ABSTRACT: Electromagnetic Modelling led by SLAC is a principal component of the "Advanced Computing for 21st Century Accelerator Science and Technology" SciDAC project funded through the Office of High Energy Physics. This large team effort comprises three other national laboratories (LBNL, LLNL, SNL) and six universities (CMU, Columbia, RPI, Stanford, UC Davis and U of Wisconsin) with the goal to develop a set of parallel electromagnetic codes based on unstructured grids to target challenging problems in accelerators, and solve them to unprecedented realism and accuracy. Essential to the code development are the collaborations with the ISICs/SAPP in eigensolvers, meshing, adaptive refinement, shape optimization and visualization (see "Achievements in ISICs/SAPP Collaborations for Electromagnetic Modelling of Accelerators"). Supported by these advances in computational science, we have successfully performed the large-scale simulations that have impacted important accelerator projects across the Office of Science (SC) including the Positron Electron Project (PEP) -II, Next Linear Collider (NLC) and the International Linear Collider (ILC) in High Energy Physics (HEP), the Rare Isotope Accelerator (RIA) in Nuclear Physics (NP) and the Linac Coherent Light Source (LCLS) in Basic Energy Science (BES).
Journal of Physics Conference Series 08/2005; 16(1):195.
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J. Sekutowicz,
K. Ko,
L. Ge,
L. Lee,
Z. Li,
C. Ng,
G. Schussman, L. Xiao,
I. Gonin,
T. Khabibouline,
N. Solyak,
Y. Morozumi,
K. Saito,
P. Kneisel
[show abstract]
[hide abstract]
ABSTRACT: An international team comprising SLAC, KEK, FNAL, JLAB and DESY is collaborating on the design, fabrication and test of a low loss, 1.3 GHz 9-cell SRF structure as a potential improvement for the ILC main linac. The advantages of this structure over the TESLA structure include lower cryogenic loss, shorter rise time, and less stored energy. Among the issues to be addressed in this design are HOM damping, Lorentz force detuning and multipacting. We will report on HOM damping calculations using the parallel finite element eigenmode solver Omega3P and the progress made towards an optimized design. Studies on multipacting and estimates of the Lorentz force detuning will also be presented.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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Z Li,
DESY Maschinenphysik,
L. Ge,
K Ko,
L. Lee,
C. Ng,
G. Schussman, L Xiao,
J. Sekutowicz,
P. Kneisel,
T. Higo,
Yu. Morozumi,
K Saito
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J. Sekutowicz,
DESY Maschinenphysik,
J. Iversen,
D. Klinke,
D. Kostin,
W. Moeller,
I. Ben-Zvi,
A. Burrill,
T. Rao,
J. Smedley,
M. Ferrario,
P. Kneisel,
R. Lefferts,
A. Lipski,
K Ko, L Xiao,
J. Langner,
P. Strzyzewski,
J. Rosenzweig,
K. Szalowski
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A. Seryi,
J. Amann,
R Arnold,
F. Asiri,
K. Bane,
P. Bellomo,
E. Doyle,
A. Fasso,
K. Jonghoon,
L Keller, [......],
T Mattison,
J. Carwardine,
C Saunders,
R. Appleby,
E Torrence,
J Gronberg,
T. Sanukii,
Y Iwashita,
V. Telnov,
D. Warner
[show abstract]
[hide abstract]
ABSTRACT: The beam delivery system for the linear collider focuses beams to nanometer sizes at its interaction point, collimates the beam halo to provide acceptable background in the detector and has a provision for state-of-the-art beam instrumentation in order to reach the ILCs physics goals. this paper describes the design details and status of the baseline configuration considered for the reference design and also lists alternatives.
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A. Seryi,
J.A. Amann,
R Arnold,
F. Asiri,
K.L.F. Bane,
P. Bellomo,
E. Doyle,
A.F. Fasso,
L Keller,
J Kim, [......],
Y Iwashita,
W Lohmann,
L Ma,
T.M. Mattison,
T.S. Sanuki,
V I Telnov,
E.T. Torrence,
D. Warner,
N K Watson,
H.Y. Yamamoto
22nd Particle Accelerator Conference,Albuquerque,USA (2007),1985.
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