Phase-Space Investigation of Laser-Driven Weakly Relativistic Electron Beams

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

This research project will measure some of the most important attributes of relativistic electron beams produced by interactions between a laser and a plasma. Novel laser-driven electron accelerators have the potential to become an essential part of future accelerator technology. In particular, laser-wakefield accelerators, which use laser-plasma interactions to produce high quality relativistic electron beams with an extremely short pulse duration of only a few femtoseconds (a few millionth of a billionth of a second) have shown tremendous progress. However, because of the exceptional challenge of characterizing these extremely short electron pulses that move with velocities close to the speed of light, their exact properties are still widely unknown. This investigation will be accomplished through the use of additional laser pulses that interact with the electron beam in such a way that the essential information about the temporal distribution of the electrons and their initial trajectory can be deduced. The experimental work will be supported by theoretical efforts. Low-emittance, few-femtosecond electron pulses with weakly relativistic beam energies are highly interesting as injectors for future electron accelerators or for ultrafast electron diffraction. It is possible to generate such pulses using laser-wakefield acceleration. However, the full time-resolved electron phase-space distribution of such pulses is still largely unknown. In this project, the injection process and properties of laser-wakefield accelerated electron beams with weakly relativistic beam energies of a few megaelectronvolts will be studied experimentally and theoretically. The comparably low beam energy allows the use of a temporal diagnostic that is incompatible with higher-energy beams. More specifically, ponderomotive scattering enhanced through a standing wave that has the potential to achieve a temporal resolution of 1 femtosecond will be used. This will be combined with a beam energy spectrometer to determine the energy-time correlation of the electron bunches and thus allow the temporally-resolved investigation of their 6D phase-space density. Because the bunches have not been subject to a significant net acceleration, this will also lead to invaluable information on the process of electron injection into the plasma accelerating structure. The properties of electron bunches generated via different electron injection mechanisms will be investigated using this diagnostic. These measurements are expected to lead to significant new insights into the physics behind laser-wakefield acceleration and in particular into the injection process. The experiments will be theoretically supported by particle-in-cell simulations.