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abstract:
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Plasma based electron beam sources, which are now
under development, will produce beams with much higher particle
densities than are currently available. Plasma sources can create
beams with brightness (the measure of achievable beam density)
orders of magnitude greater than radio frequency photoinjectors,
the current state-of-the-art. Plasma density transition trapping
is one example of the many plasma electron beam source schemes
under development. Plasma density transition trapping is a
recently proposed self-injection mechanism for plasma wake field
accelerators. The technique uses a sharp downward plasma density
transition to trap and accelerate background plasma electrons in a
plasma wake field.
This dissertation examines the different regimes in which plasma
density transition trapping can operate and the quality of the
electron beams captured in terms of emittance, energy spread, and
brightness. This is accomplished using two-dimensional
Particle-In-Cell (PIC) simulations which show that the captured
beam parameters can be optimized by manipulating the overall
plasma density, as well as the density profile. A general set of
scaling laws is developed that predicts how the brightness of
transition trapping beams, or the beams produced by any plasma
system, scales with the plasma density. These scaling laws
predict that beam brightness increases linearly with the plasma
density of the source.
The design and execution of the first plasma density transition
trapping experiment is also documented in this dissertation.
Plasma with density on the order of 10E-13 / cm^-3 was used
in the experiment. Plasma density transitions steep enough to
produce trapping at this density were created and measured.
Interaction between the plasma transition and a driving electron
beam pulse did not, however, produce trapped electrons. Detailed
measurements of the drive beam parameters revealed that it did not
meet the trapping experiment design criteria. Simulations using
the measured plasma and beam parameters predict zero captured
charge in agreement with observations.
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