22 research outputs found
Photodissociation of NO2 by pulsed laser light at 6943 A
Two photon absorption in photodissociation of nitrogen dioxide using pulsed laser at 6943
Generation of meter-scale hydrogen plasmas and efficient, pump-depletion-limited wakefield excitation using 10 GeV electron bunches
High repetition rates and efficient energy transfer to the accelerating beam
are important for a future linear collider based on the beam-driven plasma
wakefield acceleration scheme (PWFA-LC). This paper reports the first results
from the Plasma Wakefield Acceleration Collaboration (E300) that are beginning
to address both of these issues using the recently commissioned FACET-II
facility at SLAC. We have generated meter-scale hydrogen plasmas using
time-structured 10 GeV electron bunches from FACET-II, which hold the promise
of dramatically increasing the repetition rate of PWFA by rapidly replenishing
the gas between each shot compared to the hitherto used lithium plasmas that
operate at 1-10 Hz. Furthermore, we have excited wakes in such plasmas that are
suitable for high gradient particle acceleration with high drive-bunch to wake
energy transfer efficiency -- a first step in achieving a high overall energy
transfer efficiency. We have done this by using time-structured electron drive
bunches that typically have one or more ultra-high current (>30 kA) femtosecond
spike(s) superimposed on a longer (~0.4 ps) lower current (<10 kA) bunch
structure. The first spike effectively field-ionizes the gas and produces a
meter-scale (30-160 cm) plasma, whereas the subsequent beam charge creates a
wake. The length and amplitude of the wake depends on the longitudinal current
profile of the bunch and plasma density. We find that the onset of pump
depletion, when some of the drive beam electrons are nearly fully depleted of
their energy, occurs for hydrogen pressure >1.5 Torr. We also show that some
electrons in the rear of the bunch can gain several GeV energies from the wake.
These results are reproduced by particle-in-cell simulations using the QPAD
code. At a pressure of ~2 Torr, simulations results and experimental data show
that the beam transfers about 60% of its energy to the wake
Wakefield Generation in Hydrogen and Lithium Plasmas at FACET-II: Diagnostics and First Beam-Plasma Interaction Results
Plasma Wakefield Acceleration (PWFA) provides ultrahigh acceleration
gradients of 10s of GeV/m, providing a novel path towards efficient, compact,
TeV-scale linear colliders and high brightness free electron lasers. Critical
to the success of these applications is demonstrating simultaneously high
gradient acceleration, high energy transfer efficiency, and preservation of
emittance, charge, and energy spread. Experiments at the FACET-II National User
Facility at SLAC National Accelerator Laboratory aim to achieve all of these
milestones in a single stage plasma wakefield accelerator, providing a 10 GeV
energy gain in a <1 m plasma with high energy transfer efficiency. Such a
demonstration depends critically on diagnostics able to measure emittance with
mm-mrad accuracy, energy spectra to determine both %-level energy spread and
broadband energy gain and loss, incoming longitudinal phase space, and matching
dynamics. This paper discusses the experimental setup at FACET-II, including
the incoming beam parameters from the FACET-II linac, plasma sources, and
diagnostics developed to meet this challenge. Initial progress on the
generation of beam ionized wakes in meter-scale hydrogen gas is discussed, as
well as commissioning of the plasma sources and diagnostics