Plasma-based accelerating structures

Plasma-based accelerators have the ability to sustain extremely large accelerating gradients, with possible high-energy physics applications. This dissertation further develops the theory of plasma-based accelerators by addressing three topics: the performance of a hollow plasma channel as an accelerating structure, the generation of ultrashort electron bunches, and the propagation of laser pulses in underdense plasmas.; The excitation of plasma waves in a hollow plasma channel by a laser pulse or relativistic charged particle beam is analyzed. The mode frequencies and loss factors of the excited channel modes are calculated. The effects of non-ideal hollow plasma channels are discussed. Particle beam stability in a hollow plasma channel is examined. The dipole wakefield couples to the transverse displacement of the particle beam, which results in beam breakup. Single-bunch beam breakup growth lengths are derived for particle beam propagation in the weak-focusing and strong-focusing regimes. The effects of longitudinal wakefields on the beam energy spread is examined. Multi-bunch beam breakup is discussed and methods for reducing beam breakup are proposed and evaluated.; The production of ultrashort electron bunches by dephasing and trapping background plasma electrons undergoing fluid oscillations in a plasma wave is studied. The plasma electrons are dephased by colliding two counter-propagating laser pulses which generate a slow phase velocity beat wave. The threshold laser pulse amplitudes, the optimal injection phase for trapping, and the trapping volume are calculated. The dynamics and quality of the generated electron bunches are examined. The analysis indicates that this optical injection scheme has the capability to produce relativistic femtosecond electron bunches with fractional energy spread of a few percent and normalized transverse emittance less than 1 mm mrad using 1 terawatt injection laser pulses.; The propagation of ultrashort high-power laser pulses in underdense plasmas is studied. Envelope equations are derived for optical beam parameters which include finite-radius and finite pulse length effects. Solutions of the envelope equations are presented for an adiabatic plasma response. For the general non-adiabatic plasma response, laser-plasma instabilities are examined and asymptotic instability growth rates are derived.