31,772 research outputs found
Three-Dimensional Analysis of Wakefields Generated by Flat Electron Beams in Planar Dielectric-Loaded Structures
An electron bunch passing through dielectric-lined waveguide generates
erenkov radiation that can result in high-peak axial electric field
suitable for acceleration of a subsequent bunch. Axial field beyond
Gigavolt-per-meter are attainable in structures with sub-mm sizes depending on
the achievement of suitable electron bunch parameters. A promising
configuration consists of using planar dielectric structure driven by flat
electron bunches. In this paper we present a three-dimensional analysis of
wakefields produced by flat beams in planar dielectric structures thereby
extending the work of Reference [A. Tremaine, J. Rosenzweig, and P. Schoessow,
Phys. Rev. E 56, No. 6, 7204 (1997)] on the topic. We especially provide
closed-form expressions for the normal frequencies and field amplitudes of the
excited modes and benchmark these analytical results with finite-difference
time-domain particle-in-cell numerical simulations. Finally, we implement a
semi-analytical algorithm into a popular particle tracking program thereby
enabling start-to-end high-fidelity modeling of linear accelerators based on
dielectric-lined planar waveguides.Comment: 12 pages, 2 tables, 10 figure
First-passage theory of exciton population loss in single-walled carbon nanotubes reveals micron-scale intrinsic diffusion lengths
One-dimensional crystals have long range translational invariance which
manifests as long exciton diffusion lengths, but such intrinsic properties are
often obscured by environmental perturbations. We use a first-passage approach
to model single-walled carbon nanotube (SWCNT) exciton dynamics (including
exciton-exciton annihilation and end effects) and compare it to results from
both continuous-wave and multi-pulse ultrafast excitation experiments to
extract intrinsic SWCNT properties. Excitons in suspended SWCNTs experience
macroscopic diffusion lengths, on the order of the SWCNT length, (1.3-4.7 um)
in sharp contrast to encapsulated samples. For these pristine samples, our
model reveals intrinsic lifetimes (350-750 ps), diffusion constants (130-350
cm^2/s), and absorption cross-sections (2.1-3.6 X 10^-17 cm^2/atom) among the
highest previously reported.and diffusion lengths for SWCNTs.Comment: 6 pages, 3 figure
Transverse self-modulation of ultra-relativistic lepton beams in the plasma wakefield accelerator
The transverse self-modulation of ultra-relativistic, long lepton bunches in
high-density plasmas is explored through full-scale particle-in-cell
simulations. We demonstrate that long SLAC-type electron and positron bunches
can become strongly self-modulated over centimeter distances, leading to wake
excitation in the blowout regime with accelerating fields in excess of 20 GV/m.
We show that particles energy variations exceeding 10 GeV can occur in
meter-long plasmas. We find that the self-modulation of positively and
negatively charged bunches differ when the blowout is reached. Seeding the
self-modulation instability suppresses the competing hosing instability. This
work reveals that a proof-of-principle experiment to test the physics of bunch
self-modulation can be performed with available lepton bunches and with
existing experimental apparatus and diagnostics.Comment: 8 pages, 8 figures, accepted for publication in Physics of Plasma
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