254 research outputs found
Optimal positron-beam excited plasma wakefields in Hollow and Ion-Wake channels
A positron-beam interacting with the plasma electrons drives radial suck-in,
in contrast to an electron-beam driven blow-out in the over-dense regime,
. In a homogeneous plasma, the electrons are radially sucked-in from
all the different radii. The electrons collapsing from different radii do not
simultaneously compress on-axis driving weak fields. A hollow-channel allows
electrons from its channel-radius to collapse simultaneously exciting coherent
fields. We analyze the optimal channel radius. Additionally, the low ion
density in the hollow allows a larger region with focusing phase which we show
is linearly focusing. We have shown the formation of an ion-wake channel behind
a blow-out electron bubble-wake. Here we explore positron acceleration in the
over-dense regime comparing an optimal hollow-plasma channel to the ion-wake
channel. The condition for optimal hollow-channel radius is also compared. We
also address the effects of a non-ideal ion-wake channel on positron-beam
excited fields.Comment: Proceedings of IPAC2015, Richmond, VA, USA 3: Alternative Particle
Sources and Acceleration Techniques A22 - Plasma Wake eld Acceleration
http://accelconf.web.cern.ch/AccelConf/IPAC2015/papers/wepje001.pdf, 2015
(ISBN 978-3-95450-168-7) pp 2674-267
Beam loading in the nonlinear regime of plasma-based acceleration
A theory that describes how to load negative charge into a nonlinear,
three-dimensional plasma wakefield is presented. In this regime, a laser or an
electron beam blows out the plasma electrons and creates a nearly spherical ion
channel, which is modified by the presence of the beam load. Analytical
solutions for the fields and the shape of the ion channel are derived. It is
shown that very high beam-loading efficiency can be achieved, while the energy
spread of the bunch is conserved. The theoretical results are verified with the
Particle-In-Cell code OSIRIS.Comment: 5 pages, 2 figures, to appear in Physical Review Letter
Natural noise and external wake field seeding in a proton-driven plasma accelerator
We discuss the level of natural shot noise in a proton bunch-driven plasma
accelerator. The required seeding for the plasma wake field must be larger than
the cumulative shot noise. This is the necessary condition for the axial
symmetry of the generated wake and the acceleration quality. We develop an
analytical theory of the noise field and compare it with multi-dimensional
simulations. It appears that the natural noise wake field generated in plasma
by the available at CERN super-protons-synchrotron (SPS) bunches is very low,
at the level of a few 10 kV/m. This fortunate fact eases the requirements on
the seed. Our three dimensional simulations show that even a few tens MeV
electron bunch precursor of a very moderate intensity is sufficient to seed the
proton bunch self-modulation in plasma.Comment: 5 pages, 5 figure
Radiative Losses in Plasma Accelerators
We investigate the dynamics of a relativistic electron in a strongly
nonlinear plasma wave in terms of classical mechanics by taking into account
the action of the radiative reaction force. The two limiting cases are
considered. In the first case where the energy of the accelerated electrons is
low, the electron makes many betatron oscillations during the acceleration. In
the second case where the energy of the accelerated electrons is high, the
betatron oscillation period is longer than the electron residence time in the
accelerating phase. We show that the force of radiative friction can severely
limit the rate of electron acceleration in a plasma accelerator.Comment: 17 pages, 5 figure
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