84 research outputs found
Seeding of the Self-Modulation in a Long Proton Bunch by Charge Cancellation with a Short Electron Bunch
In plasma wakefield accelerators (e.g. AWAKE) the proton bunch
self-modulation is seeded by the ionization front of a high-power laser pulse
ionizing a vapour and by the resulting steep edge of the driving bunch profile
inside the created plasma. In this paper, we present calculations in 2D linear
theory for a concept of a different self-modulation seeding mechanism based on
electron injection. The whole proton bunch propagates through a preformed
plasma and the effective beam current is modulated by the external injection of
a short electron bunch at the centre of the proton beam. The resulting sharp
edge in the effective beam current in the trailing part of the proton bunch is
driving large wakefields that can lead to a growth of the seeded
self-modulation (SSM). Furthermore, we discuss the feasibility for applications
in AWAKE Run 2
A Method to Determine the Maximum Radius of Defocused Protons after Self-Modulation in AWAKE
The AWAKE experiment at CERN aims to drive GV/m plasma wakefields with a
self-modulated proton drive bunch, and to use them for electron acceleration.
During the self-modulation process, protons are defocused by the transverse
plasma wakefields and form a halo around the focused bunch core. The two-screen
setup integrated in AWAKE measures the transverse, time-integrated proton bunch
distribution downstream the \unit[10]{m} long plasma to detect defocused
protons. By measuring the maximum radius of the defocused protons we attempt
calculate properties of the self-modulation. In this article, we develop a
routine to identify the maximum radius of the defocused protons, based on a
standard contour method. We compare the maximum radius obtained from the
contour to the logarithmic lineouts of the image to show that the determined
radius identifies the edge of the distribution.Comment: 3 pages, 4 figures, EAAC 2017 NIMA proceeding
Influence of proton bunch parameters on a proton-driven plasma wakefield acceleration experiment
We use particle-in-cell (PIC) simulations to study the effects of variations
of the incoming 400 GeV proton bunch parameters on the amplitude and phase of
the wakefields resulting from a seeded self-modulation (SSM) process. We find
that these effects are largest during the growth of the SSM, i.e. over the
first five to six meters of plasma with an electron density of cm. However, for variations of any single parameter by
5%, effects after the SSM saturation point are small. In particular, the
phase variations correspond to much less than a quarter wakefield period,
making deterministic injection of electrons (or positrons) into the
accelerating and focusing phase of the wakefields in principle possible. We use
the wakefields from the simulations and a simple test electron model to
estimate the same effects on the maximum final energies of electrons injected
along the plasma, which are found to be below the initial variations of
5%. This analysis includes the dephasing of the electrons with respect to
the wakefields that is expected during the growth of the SSM. Based on a PIC
simulation, we also determine the injection position along the bunch and along
the plasma leading to the largest energy gain. For the parameters taken here
(ratio of peak beam density to plasma density ), we
find that the optimum position along the proton bunch is at , and that the optimal range for injection along the plasma (for
a highest final energy of 1.6 GeV after 10 m) is 5-6 m.Comment: 9 pages, 12 figure
Emittance preservation of an electron beam in a loaded quasi-linear plasma wakefield
We investigate beam loading and emittance preservation for a high-charge
electron beam being accelerated in quasi-linear plasma wakefields driven by a
short proton beam. The structure of the studied wakefields are similar to those
of a long, modulated proton beam, such as the AWAKE proton driver. We show that
by properly choosing the electron beam parameters and exploiting two well known
effects, beam loading of the wakefield and full blow out of plasma electrons by
the accelerated beam, the electron beam can gain large amounts of energy with a
narrow final energy spread (%-level) and without significant emittance growth.Comment: 8 pages, 10 figure
Simulation Study of an LWFA-based Electron Injector for AWAKE Run 2
The AWAKE experiment aims to demonstrate preservation of injected electron
beam quality during acceleration in proton-driven plasma waves. The short bunch
duration required to correctly load the wakefield is challenging to meet with
the current electron injector system, given the space available to the
beamline. An LWFA readily provides short-duration electron beams with
sufficient charge from a compact design, and provides a scalable option for
future electron acceleration experiments at AWAKE. Simulations of a shock-front
injected LWFA demonstrate a 43 TW laser system would be sufficient to produce
the required charge over a range of energies beyond 100 MeV. LWFA beams
typically have high peak current and large divergence on exiting their native
plasmas, and optimisation of bunch parameters before injection into the
proton-driven wakefields is required. Compact beam transport solutions are
discussed.Comment: Paper submitted to NIMA proceedings for the 3rd European Advanced
Accelerator Concepts Workshop. 4 pages, 3 figures, 1 table Changes after
revision: Figure 2: figures 2 and 3 of the previous version collated with
plots of longitudinal electric field Line 45: E_0 = 96 GV/m Lines 147- 159:
evaluation of beam loading made more accurate Lines 107 - 124: discussion of
simulation geometry move
Future colliders based on a modulated proton bunch driven plasma wakefield acceleration
Recent simulation shows that a self-modulated high energy proton bunch can
excite a large amplitude plasma wakefield and accelerate an externally injected
electron bunch to the energy frontier in a single stage acceleration through a
long plasma channel. Based on this scheme, future colliders, either an
electron-positron linear collider (e+-e- collider) or an electron-hadron
collider (e-p collider) can be conceived. In this paper, we discuss some key
design issues for an e+-e- collider and a high energy e-p collider, based on
the existing infrastructure of the CERN accelerator complex.Comment: Proceedings of IPAC1
Laser pulse propagation in a meter scale rubidium vapor/plasma cell in AWAKE experiment
We present the results of numerical studies of laser pulse propagating in a
3.5 cm Rb vapor cell in the linear dispersion regime by using a 1D model and a
2D code that has been modified for our special case. The 2D simulation finally
aimed at finding laser beam parameters suitable to make the Rb vapor fully
ionized to obtain a uniform, 10 m-long, at least 1 mm in radius plasma in the
next step for the AWAKE experiment.Comment: Conference proceeding ,NIMA_EAAC 2015, 6 pages, 7 figure
Self-injection by trapping of plasma electrons oscillating in rising density gradient at the vacuum-plasma interface
We model the trapping of plasma within the density structures excited
by a propagating energy source () in a rising plasma density
gradient. Rising density gradient leads to spatially contiguous coupled
up-chirped plasmons (). Therefore phase mixing
between plasmons can lead to trapping until the plasmon field is high enough
such that trajectories returning towards a longer wavelength see a
trapping potential. Rising plasma density gradients are ubiquitous for
confining the plasma within sources at the vacuum-plasma interfaces. Therefore
trapping of plasma- in a rising ramp is important for acceleration
diagnostics and to understand the energy dissipation from the excited plasmon
train \cite{LTE-2013}. Down-ramp in density \cite{density-transition-2001} has
been used for plasma- trapping within the first bucket behind the driver.
Here, in rising density gradient the trapping does not occur in the first
plasmon bucket but in subsequent plasmon buckets behind the driver. Trapping
reduces the Hamiltonian of each bucket where are trapped, so it is a
wakefield-decay probe. Preliminary computational results for beam and
laser-driven wakefield are shown.Comment: Proceedings of International Particle Accelerator Conference, IPAC
2014, Dresden, Germany, June 2014,
http://accelconf.web.cern.ch/AccelConf/IPAC2014/papers/tupme051.pd
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