36 research outputs found
Knife-edge based measurement of the 4D transverse phase space of electron beams with picometer-scale emittance
Precise manipulation of high brightness electron beams requires detailed
knowledge of the particle phase space shape and evolution. As ultrafast
electron pulses become brighter, new operational regimes become accessible with
emittance values in the picometer range, with enormous impact on potential
scientific applications. Here we present a new characterization method for such
beams and demonstrate experimentally its ability to reconstruct the 4D
transverse beam matrix of strongly correlated electron beams with sub-nanometer
emittance and sub-micrometer spot size, produced with the HiRES beamline at
LBNL. Our work extends the reach of ultrafast electron accelerator diagnostics
into picometer-range emittance values, opening the way to complex
nanometer-scale electron beam manipulation techniques
Accurate quantification of lattice temperature dynamics from ultrafast electron diffraction of single-crystal films using dynamical scattering simulations
In ultrafast electron diffraction (UED) experiments, accurate retrieval of
time-resolved structural parameters such as atomic coordinates and thermal
displacement parameters requires an accurate scattering model. Unfortunately,
kinematical models are often inaccurate even for relativistic electron probes,
especially for dense, oriented single crystals where strong channeling and
multiple scattering effects are present. This article introduces and
demonstrates dynamical scattering models tailored for quantitative analysis of
UED experiments performed on single-crystal films. As a case study, we examine
ultrafast laser heating of single-crystal gold films. Comparison of kinematical
and dynamical models reveals the strong effects of dynamical scattering within
nm-scale films and their dependence on sample topography and probe kinetic
energy. Applied to UED experiments on an 11 nm thick film using 750 keV
electron probe pulses, the dynamical models provide a tenfold improvement over
a comparable kinematical model in matching the measured UED patterns. Also, the
retrieved lattice temperature rise is in very good agreement with predictions
based on previously measured optical constants of gold, whereas fitting the
Debye-Waller factor retrieves values that are more than three times lower.
Altogether, these results show the importance of dynamical scattering theory
for quantitative analysis of UED, and demonstrate models that can be
practically applied to single-crystal materials and heterostructures.Comment: 12 pages, 7 figure
Ultrafast Relativistic Electron Nanoprobes
One of the frontiers in electron scattering is to couple ultrafast temporal
resolution with highly localized probes to investigate the role of
microstructure on material properties. Here, taking advantage of the
unprecedented average brightness of the APEX electron gun providing
relativistic electron pulses at high repetition rates, we demonstrate for the
first time the generation of ultrafast relativistic electron beams with
picometer-scale emittance and their ability to probe nanoscale features on
materials with complex microstructures. At the sample plane, the APEX beam is
tightly focused by a custom in-vacuum lens system based on permanent magnet
quadrupoles, and its evolution around the waist is tracked by a knife-edge
technique, allowing accurate reconstruction of the beam shape and local
density. We then use the focused beam to characterize a Ti-6 wt\% Al
polycrystalline sample by correlating the diffraction and imaging modality,
showcasing the capability to locate grain boundaries and map adjacent
crystallographic domains with sub-micron precision. This work provides a new
paradigm for ultrafast electron instrumentation, demonstrating the ability to
generate relativistic beams with ultrasmall transverse phase space volumes
enabling novel characterization techniques such as relativistic ultrafast
electron nano-diffraction and ultrafast scanning transmission electron
microscopy
ABSOLUTE BUNCH LENGTH MEASUREMENTS AT THE ALS BY INCOHERENTSYNCHROTRON RADIATION FLUCTUATION ANALYSIS
By analysing the pulse to pulse intensity fluctuations ofthe radiation emitted by a charge particle in the incoherent part of thespectrum, it is possible to extract information about the spatialdistribution of the beam. At the Advanced Light Source (ALS) of theLawrence Berkeley National Laboratory, we have developed and tested asimple scheme based on this principle that allows for the absolutemeasurement of the bunch length. A description of the method and theexperimental results are presented
The LCLS-II Gun & Buncher LLRF Controller Upgrade
LCLS-II is currently in its commissioning phase at SLAC. It is an X-ray FEL
driven by a CW superconducting LINAC. The beam injector plays a crucial role in
the overall performance of the accelerator, and is critical to the final
electron beam performance parameters. The LCLS-II injector comprises of a 185.7
MHz VHF copper gun cavity, and a 1.3 GHz two-cell L-band copper buncher cavity.
The FPGA-based controller employs feedback and Self-Excited Loop logic in order
to regulate the cavity fields. It also features several other functionalities,
such as live detune computation, active frequency tracking, and waveform
recording. The LLRF system drives the cavities via two 60 kW SSAs through two
power couplers, and thus stabilizes the fields inside the plant. This paper
provides an outline of the general functionalities of the system, alongside a
description of its hardware, firmware and software architecture, before
finalizing with the current status of the project and its future goals.Comment: Poster presented at LLRF Workshop 2022 (LLRF2022, arXiv:2208.13680
Electron Sources for Accelerators
Electron sources are essential to an array of electron accelerator supporting
research in high-energy physics and beyond. This report summarizes the
"Snowmass 2021 Electron Source Workshop" which reviewed the current
state-of-the art research and identified some possible research directions