Abstract
Laser and beam driven wakefields promise orders of magnitude increases in electric field gradients for particle accelerators for future applications. Key areas to explore include the emittance properties of the generated beams and overcoming the dephasing limit in the plasma. In this paper, the first in-depth study of the self-injection mechanism into wakefield structures from non-homogeneous cluster plasmas is provided using high-resolution two dimensional particle-in-cell simulations. The clusters which are typical structures caused by ejection of gases from a high-pressure gas jet have a diameter much smaller than the laser wavelength. Conclusive evidence is provided for the underlying mechanism that leads to particle trapping, comparing uniform and cluster plasma cases. The accelerated electron beam properties are found to be tunable by changing the cluster parameters. The mechanism explains enhanced beam charge paired with large transverse momentum and energy which has implications for the betatron x-ray flux. Finally, the impact of clusters on the high-power laser propagation behavior is discussed.
Highlights
A cluster plasma is a collection of ionized atomic clusters of various sizes which are usually randomly distributed
We investigate how different cluster parameters might be able to increase the dephasing length through the clusters’ impact on the group velocity of the short laser pulse propagating through the plasma
We presented the first high-resolution numerical study of the interaction of a high-power laser pulse with a cluster plasma in which it was shown that it is important to simulate cluster plasmas with random cluster positions rather than periodically aligned positions
Summary
A cluster plasma is a collection of ionized atomic clusters of various sizes which are usually randomly distributed. Wakefields are electron plasma waves driven by a high power laser pulse or a relativistic particle bunch. They are able to generate accelerating (and focussing) electric fields of up to 100 GV m−1. Laser-driven wakefields have proven to be able to accelerate high-charge electron beams of high quality in [32,33,34,35] Following these milestone experiments the race for higher particle energies and better beam quality has produced promising results [36,37,38,39,40,41]. This is followed by a discussion of the results presented
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