2,116 research outputs found
Is There a Significant Difference Between the Results of the Coulomb Dissociation of 8B and the Direct Capture 7Be(p,g)8B Reaction?
Recent claims of the Seattle group of evidence of "slope difference between
CD [Coulomb Dissociation] and direct [capture] results" are based on wrong and
selective data. When the RIKEN2 data are included correctly, and previously
published Direct Capture (DC) data are also included, we observe only a 1.9
sigma difference in the extracted so called "scale independent slope (b)",
considerably smaller than claimed by the Seattle group. The very
parameterization used by the Seattle group to extract the so called b-slope
parameter has no physical foundation. Considering the physical slope (S' =
dS/dE), we observe a 1.0 sigma agreement between slopes (S') measured in CD and
DC, refuting the need for new theoretical investigation. The claim that S17(0)
values extracted from CD data are approximately 10% lower than DC results, is
based on misunderstanding of the CD method. Considering all of the published CD
S17(0) results, with adding back an unconfirmed E2 correction of the MSU data,
yields very consistent S17(0) results that agree with recent DC measurements of
the Seattle and Weizmann groups. The recent correction of the b-slope parameter
(0.25 1/MeV) suggested by Esbensen, Bertsch and Snover was applied to the wrong
b-slope parameter calculated by the Seattle group. When considering the correct
slope of the RIKEN2 data, this correction in fact leads to a very small b-slope
parameter (0.14 1/MeV), less than half the central value observed for DC data,
refuting the need to correct the RIKEN2 data. In particular it confirms that
the E2 contribution in the RIKEN2 data is negligible. The dispersion of
measured S17(0) is mostly due to disagreement among individual DC experiments
and not due to either experimental or theoretical aspects of CD.Comment: Reference 12 amended with an important communication from Dr. Bertsc
Three-Dimensional Analysis of Wakefields Generated by Flat Electron Beams in Planar Dielectric-Loaded Structures
An electron bunch passing through dielectric-lined waveguide generates
erenkov radiation that can result in high-peak axial electric field
suitable for acceleration of a subsequent bunch. Axial field beyond
Gigavolt-per-meter are attainable in structures with sub-mm sizes depending on
the achievement of suitable electron bunch parameters. A promising
configuration consists of using planar dielectric structure driven by flat
electron bunches. In this paper we present a three-dimensional analysis of
wakefields produced by flat beams in planar dielectric structures thereby
extending the work of Reference [A. Tremaine, J. Rosenzweig, and P. Schoessow,
Phys. Rev. E 56, No. 6, 7204 (1997)] on the topic. We especially provide
closed-form expressions for the normal frequencies and field amplitudes of the
excited modes and benchmark these analytical results with finite-difference
time-domain particle-in-cell numerical simulations. Finally, we implement a
semi-analytical algorithm into a popular particle tracking program thereby
enabling start-to-end high-fidelity modeling of linear accelerators based on
dielectric-lined planar waveguides.Comment: 12 pages, 2 tables, 10 figure
Spatial Control of Photoemitted Electron Beams using a Micro-Lens-Array Transverse-Shaping Technique
A common issue encountered in photoemission electron sources used in electron
accelerators is the transverse inhomogeneity of the laser distribution
resulting from the laser-amplification process and often use of frequency up
conversion in nonlinear crystals. A inhomogeneous laser distribution on the
photocathode produces charged beams with lower beam quality. In this paper, we
explore the possible use of microlens arrays (fly-eye light condensers) to
dramatically improve the transverse uniformity of the drive laser pulse on UV
photocathodes. We also demonstrate the use of such microlens arrays to generate
transversely-modulated electron beams and present a possible application to
diagnose the properties of a magnetized beam.Comment: arXiv admin note: text overlap with arXiv:1609.0166
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Construction and testing of an 11.4 GHz dielectric structure based travelling wave accelerator
One major challenge in constructing a dielectric loaded traveling wave accelerator powered by an external rf power source is the difficulty in achieving efficient coupling. In this paper, we report that we have achieved high efficiency broadband coupling by using a combination of a tapered dielectric section and a carefully adjusted coupling slot. We are currently constructing an 11.4 GHz accelerator structure loaded with a permitivity=20 dielectric. Bench testing has demonstrated a coupling efficiency in excess of 95% with bandwidth of 600 MHz. The final setup will be tested at high power at SLAC using an X-band klystron rf source
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