Doctoral Thesis, University of Southern California, Los Angeles, CA (2008)

Particle accelerators are the tools that physicists use today in order to probe the fundamental forces of Nature, by accelerating charged particles such as electrons and protons to high energies and then smashing them together. For the past 70 years the acceleration schemes have been based on the same technology, which is to place the particles onto radio-frequency electric fields inside metallic cavities. However, since the accelerating gradients cannot be increased arbitrarily due to limiting effects such as wall breakdown, in order to reach higher energies today’s accelerators require km-long structures that have become very expensive to built, and therefore novel accelerating techniques are needed to push the energy frontier further.
        Plasmas do not suffer from those limitations since they are gases that are already broken down into electrons and ions. In addition, the collective behavior of the particles in plasmas allows for generated accelerating electric fields that are orders of magnitude larger than those available in conventional accelerators. Such wakefields have been demonstrated experimentally, typically by feeding either single electron bunches or laser beams into high density plasmas. As such plasma acceleration technologies mature, one of the main future challenges is to monoenergetically accelerate a second trailing bunch by multiplying its energy in an efficient manner, so that it can potentially be used in a future particle collider.
        The work presented in this dissertation is a fruitful combination of theory, simulations and experiments that analyzes the use of multiple electron bunches in order to enhance certain plasma acceleration schemes. Specifically, the acceleration of a trailing electron bunch in a high-gradient wakefield driven by a preceding bunch is demonstrated experimentally for the first time by using bunches short enough to sample a small phase of the plasma wakes. Additionally, it is found through theoretical analysis and through simulations that by using multiple bunches to drive the wakefields, the energy of a trailing bunch could be efficiently multiplied in a single stage, thus possibly reducing the total length of the accelerator to a more manageable scale. Relevant proof-of-principle experimental results are also presented, along with suggested designs that could be tested in the near future. Furthermore, electron beam and plasma diagnostics are analyzed and presented, which are necessary for properly completing and understanding any plasma wakefield experiment. Finally, certain types of plasma sources that can be used in related experiments are designed, diagnosed and tested in detail.