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Carl Ekdahl,
E. O. Abeyta,
R. Archuleta,
H. Bender,
W. Broste,
C. Carlson,
G. Cook,
D. Frayer,
J. Harrison,
T. Hughes, [......],
E. Jacquez,
B. Trent McCuistian,
N. Montoya,
S. Nath,
K. Nielsen,
C. Rose,
M. Schulze,
H. V. Smith,
C. Thoma,
C. Y. Tom
Phys. Rev. ST Accel. Beams. 12/2011; 14.
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ABSTRACT: Current link adaptation algorithms for IEEE 802.11 WLANs exhibit behavior which makes them unsuitable for transmission of multiple simultaneous real-time uplink video streams. First, these algorithms do not consider the properties of the video codec, and hence, are unaware of the impact of PHY rate selection on the perceptual quality of the received video. Second, they do not differentiate between channel errors and collisions, and hence severely malfunction when the collision probability is non-negligible. In this paper, we propose a link adaptation strategy that not only optimizes the perceptual quality of the received video, but also maintains network stability by preventing catastrophic failure due to collisions. We show that switching to a lower PHY rate improves the SNR/BER performance, but increases channel contention (and hence the collision probability). Then, we use this information plus knowledge of the video codec and network transport protocol to estimate the received perceptual video quality at the current and adjacent PHY rates. The PHY rate that yields the best perceptual quality is chosen for each Group of Pictures (GOP). We support the proposed algorithm through experiments with real wireless cameras on which we have implemented our algorithm.
Communications (ICC), 2010 IEEE International Conference on; 06/2010
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ABSTRACT: This paper summarizes the results of an ongoing design effort to miniaturize HF antennas for HFSWR and OTHR systems. The proposed design is based on a meander antenna described in [1]. Design modifications include a multi-element folding to increase the radiation efficiency and improve the impedance matching and also the incorporation of a back conducting plane reflector to improve the gain. Based on simulation results using the FEKO and IE3D software and experimental measurements, we were able to successfully demonstrate the anticipated advantages of the proposed prototype design.
Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
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Carl Ekdahl,
E. O. Abeyta,
P. Aragon,
R. Archuleta,
G. Cook,
D. Dalmas,
K. Esquibel,
R. Gallegos,
R. Garnett,
J. Harrison, [......],
C. Carlson,
D. Frayer,
D. Johnson,
C. Y. Tom,
C. Trainham,
R. Temple,
H. Bender,
J. Williams,
B. Prichard,
M. Schulze
linac 2008, Victoria, BC, Canada; 09/2008
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Martin Schulze,
R. Archuleta,
J. Barazza,
D. Dalmas,
C. Ekdahl,
W. Gregory,
J. Harrison, J. Johnson,
E. Jacquez,
P. Marroquin, [......],
C. Carlson,
D. Frayer,
D. Johnson,
C. Thoma,
E. O. Abeyta,
R. Anaya,
J. Weir,
H. Bender,
C. Y. Tom,
T. P. Hughes
linac 2008, Victoria, BC, Canada; 09/2008
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ABSTRACT: It is well known that SRAM-based FPGAs are susceptible to single-event upsets (SEUs) in radiation environments. A variety of mitigation strategies have been demonstrated to provide appropriate mitigation and correction of SEUs in these environments. While full mitigation of SEUs is appropriate for some situations, some systems may tolerate SEUs as long as these upsets are detected quickly and correctly. These systems require effective error detection techniques rather than costly error correction methods. This work leverages a well-known error detection technique for FPGAs called duplication with compare (DWC). This technique has been shown to be very effective at quickly and accurately detecting SEUs using fault injection and radiation testing.
Aerospace Conference, 2008 IEEE; 04/2008
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C. Ekdahl,
E.O. Abeyta,
P. Aragon,
R. Archuleta,
R. Bartsch,
D. Dalmas,
S. Eversole,
R. Gallegos,
J. Harrison, J. Johnson, [......],
M. Schauer,
G. Seitz,
H. Bender,
W. Broste,
C. Carlson,
D. Frayer,
D. Johnson,
A. Tipton,
C.Y. Tom,
M. Schulze
[show abstract]
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ABSTRACT: When completed, the DARHT-II accelerator will produce a 2-kA, 17-MeV beam in a 1600-ns pulse. After exiting the accelerator, the long pulse will be sliced into four short pulses by a kicker and quadrupole septum and then transported for several meters to a tantalum target for conversion to bremsstrahlung for radiography. In order to provide early tests of the kicker, septum, transport, and multi-pulse converter target we assembled a short accelerator from the first available refurbished cells, which are now capable of operating of operating at over 200 kV. This scaled accelerator was operated at ~8 MeV and ~1 kA, which provides a beam with approximately the same beam dynamics in the downstream transport as the final 17-MeV, 2-kA beam.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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M. Schulze,
E.O. Abeyta,
P. Aragon,
R. Archuleta,
J. Barraza,
D. Dalmas,
C. Ekdahl,
K. Esquibel,
S. Eversole,
R. Gallegos, [......],
H. Bender,
W. Broste,
C. Carlson,
D. Frayer,
D. Johnson,
A. Tipton,
C.Y. Tom,
T.C. Genoni,
T.P. Hughes,
C. Thoma
[show abstract]
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ABSTRACT: The DARHT-II accelerator will produce a 2-kA, 17-MeV beam in a 1600-ns pulse when completed mid-2007. After exiting the accelerator, the pulse is sliced into four short pulses by a kicker and quadrupole septum and then transported for several meters to a tantalum target for conversion to X-rays for radiography. We describe tests of the kicker, septum, transport, and multi-pulse converter target using a short accelerator assembled from the first available refurbished cells. This scaled accelerator was operated at ~8 MeV and ~1 kA, providing a beam with approximately the same v/gamma as the final 18-MeV, 2-kA beam, and therefore the same beam dynamics in the downstream transport. The results of beam measurements made during the commissioning of this scaled accelerator downstream transport are described.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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C. Ekdahl,
E.O. Abeyta,
P. Aragon,
R. Archuleta,
R. Bartsch,
H. Bender,
R. Briggs,
W. Broste,
C. Carlson,
K.C.D. Chan, [......],
S. Nath,
D. Oro,
L. Rowton,
M. Sanchez,
R. Scarpetti,
M. Schauer,
M. Schulze,
Y. Tang,
A. Tipton,
C.Y. Tom
[show abstract]
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ABSTRACT: When completed, the DARHT-II linear induction accelerator (LIA) will produce a 2-kA, 17-MeV electron beam in a 1600-ns flat-top pulse. In initial tests, DARHT-II accelerated beams with current pulse lengths from 500 to 1200 ns full-width at half-maximum (FWHM) with more than 1.2-kA, 12.5-MeV peak current and energy. Experiments have now been done with a ∼1600-ns pulse length. These pulse lengths are all significantly longer than any other multimegaelectronvolt LIA, and they define a novel regime for high-current beam dynamics, especially with regard to beam stability. Although the initial tests demonstrated insignificant beam-breakup instability (BBU), the pulse length was too short to determine whether ion-hose instability would be present toward the end of a long, 1600-ns pulse. The 1600-ns pulse experiments reported here resolved these issues for the long-pulse DARHT-II LIA.
IEEE Transactions on Plasma Science 05/2006; · 1.17 Impact Factor
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C. Ekdahl,
P. Aragon,
E.O. Abeyta,
R. Bartsch,
L. Caudill,
K.C.D. Chan,
D. Dalmas,
S. Eversole,
R. Gallegos,
J. Harrison, [......],
A. Meidinger,
K. Moy,
R. Sturgess,
A. Tipton,
C.Y. Tom,
M. Schulze,
T. Hughes,
C. Mostrom,
Y. Tang,
R. Briggs
[show abstract]
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ABSTRACT: When completed, the DARHT-II linear induction accelerator (LIA) will produce a 2-kA, 18-MeV electron beam with more than 1500-ns current/energy "flat-top." In initial tests DARHT-II has already accelerated beams with current pulse lengths from 500-ns to 1200-ns full- width at half maximum (FWHM) with more than 1.2- kA, 12.5-MeV peak current and energy. New experiments are planned with a ~1600-ns pulse length but with reduced current and energy. These pulse lengths are all significantly longer than any other multi-MeV LIA, and they define a novel regime for high-current beam dynamics, especially with regard to beam stability. Although the initial tests demonstrated absence of BBU, the pulse length was too short to determine whether ion- hose instability would be present toward the end of a pulse longer than 1500-ns. The 1600-ns pulse experiments are designed to resolve these and other beam-dynamics issues with a long-pulse beam.
Pulsed Power Conference, 2005 IEEE; 07/2005
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C. Ekdahl,
E.O. Abeyta,
R. Bartsch,
L. Caudill,
K.C.D. Chan,
D. Dalmas,
S. Eversole,
R. Gallegos,
J. Harrison,
M. Holzscheiter, [......],
A. Meidinger,
K. Moy,
R. Sturgess,
A. Tipton,
C.Y. Tom,
M. Schulze,
T. Hughes,
C. Mostrom,
Y. Tang,
R. Briggs
[show abstract]
[hide abstract]
ABSTRACT: When completed, the DARHT-II linear induction accelerator (LIA) will produce a 2 kA, 18 MeV electron beam with more than 1500 ns current/energy “flat-top.” In initial tests DARHT-II has already accelerated beams with current pulse lengths from 500 ns to 1200 ns full-width at half maximum (FWHM) with more than 1.2 kA peak current and 12.5 MeV peak energy. Experiments will soon begin with a ∼ 1600 ns flat-top pulse, but with reduced current and energy. These pulse lengths are all significantly longer than any other multi-MeV LIA, and they define a novel regime for high-current beam dynamics, especially with regard to beam stability. Although the initial tests demonstrated the robustness of the DARHT-II LIA to BBU, the < 1200 ns FWHM pulse lengths were too short to test the predicted protection against ion-hose instability. The present experiments are designed to resolve these and other beam-dynamics issues with a ∼ 1600 ns pulse length beam.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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C. Ekdahl,
E.O. Abeyta,
H. Bender,
W. Broste,
C. Carlson,
L. Caudill,
K.C.D. Chan,
Y.J. Chen,
D. Dalmas,
G. Durtschi, [......],
M. Schauer,
D. Simmons,
H.V. Smith,
J. Studebaker,
R. Sturgess,
G. Sullivan,
C. Swinney,
R. Temple,
C.Y. Tom,
S.S. Yu
[show abstract]
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ABSTRACT: The DARHT-II linear-induction accelerator has been successfully operated at 1.2-1.3 kA and 12.5-12.7 MeV to demonstrate the production and acceleration of an electron beam. Beam pulse lengths for these experiments were varied from 0.5 μs to 1.2 μs full-width half-maximum. A low-frequency inductance-capacitance (LC) oscillation of diode voltage and current resulted in an oscillation of the beam position through interaction with an accidental (static) magnetic dipole in the diode region. There was no growth in the amplitude of this oscillation after propagating more than 44 m through the accelerator, and there was no loss of beam current that could be measured. The results of these initial experiments are presented in this paper.
IEEE Transactions on Plasma Science 05/2005; · 1.17 Impact Factor
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B.T. McCuistian,
O. Abeyta,
P. Aragon,
L. Caudill,
C. Ekdahl,
S. Eversole,
D. Dalmans,
J. Harrison,
E. Jacquez, J. Johnson, [......],
M. Sanchez,
J. Schwaegel,
D. Simmons,
J. Studebaker,
G. Sulliva,
C. Swinney,
R. Temple,
S. Eylon,
T. Houck,
R. Sturges
[show abstract]
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ABSTRACT: The dual axis radiographic hydrotest facility (DARHT) at Los Alamos National Laboratory produces flash radiographs of hydrodynamic experiments using two linear induction accelerators situated on orthogonal axes. The first axis accelerator is operational and has produced radiographs of hydrodynamic experiments. The second axis accelerator, which is in the commissioning stage, will generate an 18-MeV, 2-kA, 2-μs electron beam. These parameters are reduced during the initial phase of commissioning to ≥12-MeV, ≥1-kA, and ≥350-ns. These reduced parameters allow lower voltages and fewer components than what will be necessary for the final machine. This paper presents experimental results of commissioning the second axis DARHT accelerator, including an overview of the pulsed power system plus electrical performance data from the 3-MV injector Marx generator and the 200-kV, 2-μs induction accelerator cells. Beam transport data will also be presented.
Pulsed Power Conference, 2003. Digest of Technical Papers. PPC-2003. 14th IEEE International; 07/2003
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ABSTRACT: It is shown that the Landau-Lifshitz-Gilbert equation can be used
in conjunction with Maxwell's equations to model the magnetization
reversal process in those situations in which the nonmagnetic
interactions in the material are negligible. It is seen that the
resulting behavior, called uniform rotation, is characterized by
intermediate magnetization states for which
Δ× M &oarr;≈0, and may be described as a
procession of the magnetization vector about the small demagnetizing
field that is induced during the switch. The work presented is part of a
broader attempt to simulate the magnetization reversal process in
induction linacs. The results of a numerical simulation of the flux
reversal process in an infinite cylinder with idealized boundary
conditions are presented
Particle Accelerator Conference, 1989. Accelerator Science and Technology., Proceedings of the 1989 IEEE; 04/1989
