1,710 research outputs found
Single-shot electro-optic sampling of coherent transition radiation at the A0 Photoinjector
Future collider applications and present high-gradient laser plasma wakefield
accelerators operating with picosecond bunch durations place a higher demand on
the time resolution of bunch distribution diagnostics. This demand has led to
significant advancements in the field of electro-optic sampling over the past
ten years. These methods allow the probing of diagnostic light such as coherent
transition radiation or the bunch wakefields with sub-picosecond time
resolution. Potential applications in shot-to-shot, non-interceptive
diagnostics continue to be pursued for live beam monitoring of collider and
pump-probe experiments. Related to our developing work with electro-optic
imaging, we present results on single-shot electro-optic sampling of the
coherent transition radiation from bunches generated at the A0 photoinjector.Comment: 3 p
Formation of Compressed Flat Electron Beams with High Transverse-Emittance Ratios
Flat beams -- beams with asymmetric transverse emittances -- have important
applications in novel light-source concepts, advanced-acceleration schemes and
could possibly alleviate the need for damping rings in lepton colliders. Over
the last decade, a flat-beam-generation technique based on the conversion of an
angular-momentum-dominated beam was proposed and experimentally tested. In this
paper we explore the production of compressed flat beams. We especially
investigate and optimize the flat-beam transformation for beams with
substantial fractional energy spread. We use as a simulation example the
photoinjector of the Fermilab's Advanced Superconducting Test Accelerator
(ASTA). The optimizations of the flat beam generation and compression at ASTA
were done via start-to-end numerical simulations for bunch charges of 3.2 nC,
1.0 nC and 20 pC at ~37 MeV. The optimized emittances of flat beams with
different bunch charges were found to be 0.25 {\mu}m (emittance ratio is ~400),
0.13 {\mu}m, 15 nm before compression, and 0.41 {\mu}m, 0.20 {\mu}m, 16 nm
after full compression, respectively with peak currents as high as 5.5 kA for a
3.2-nC flat beam. These parameters are consistent with requirements needed to
excite wakefields in asymmetric dielectric-lined waveguides or produce
significant photon flux using small-gap micro-undulators.Comment: 17
Formation and Acceleration of Uniformly-Filled Ellipsoidal Electron Bunches Obtained via Space-Charge-Driven Expansion from a Cesium-Telluride Photocathode
We report the experimental generation, acceleration and characterization of a
uniformly-filled electron bunch obtained via space-charge-driven expansion
(often referred to as "blow-out regime") in an L-band (1.3-GHz) radiofrequency
photoinjector. The beam is photoemitted from a Cesium-Telluride semiconductor
photocathode using a short ( fs) ultraviolet laser pulse. The produced
electron bunches are characterized with conventional diagnostics and the
signatures of their ellipsoidal character is observed. We especially
demonstrate the production of ellipsoidal bunches with charges up to
nC corresponding to a -fold increase compared to previous experiments
with metallic photocathodes.Comment: 9, pages, 13 figure
Using the de Haas-van Alphen effect to map out the closed three-dimensional Fermi surface of natural graphite
The Fermi surface of graphite has been mapped out using de Haas van Alphen
(dHvA) measurements at low temperature with in-situ rotation. For tilt angles
between the magnetic field and the c-axis, the majority
electron and hole dHvA periods no longer follow the behavior
demonstrating that graphite has a 3 dimensional closed Fermi surface. The Fermi
surface of graphite is accurately described by highly elongated ellipsoids. A
comparison with the calculated Fermi surface suggests that the SWM trigonal
warping parameter is significantly larger than previously thought
Conversion of a transverse density modulation into a longitudinal phase space modulation using an emittance exchange technique
We report on an experiment to produce a train of sub-picosecond microbunches
using a transverse-to-longitudinal emittance exchange technique. The generation
of a modulation on the longitudinal phase space is done by converting an
initial horizontal modulation produced using a multislits mask. The preliminary
experimental data clearly demonstrate the conversion process. To date only the
final energy modulation has been measured. However numerical simulations, in
qualitative agreement with the measurements, indicate that the conversion
process should also introduce a temporal modulation.Comment: 4 pages, 6 figures. Submitted to the proceedings of the Physics and
Applications of High-Brightness Electron Beams (HBEB09), Nov. 16-19, 2009,
Maui H
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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