Tailored plasma-density profiles for enhanced energy extraction in passive plasma beam dumps. Plasma Physics and Controlled Fusion.

Proton-driven plasma wakefield acceleration has been demonstrated in simulations to be capable of accelerating particles to the energy frontier in a single stage, but its potential is hindered by the fact that currently available proton bunches are orders of magnitude longer than the plasma wavelength. Fortunately, proton micro-bunching allows driving plasma waves resonantly. In this paper, we propose using a hollow plasma channel for multiple proton bunch driven plasma wakefield acceleration and demonstrate that it enables the operation in the nonlinear regime and resonant excitation of strong plasma waves. This new regime also involves beneficial features of hollow channels for the accelerated beam (such as emittance preservation and uniform accelerating field) and long buckets of stable deceleration for the drive beam. The regime is attained at a proper ratio among plasma skin depth, driver radius, hollow channel radius, and micro-bunch period.

By using intense laser irradiating a micro plane target obliquely, an enhanced γ-ray source is generated. Due to the superposition of the incident and the reflected laser pulses, electron bunches with density of ∼ 300n c are extracted and accelerated. When these electron bunches separate from the edge of the target that the laser is leaving, they co-propagate with the laser field and emit dense γ-rays simultaneously. Simulation results show that the emitted γ photons are 253n c dense with an averaged energy of ∼ 12 MeV. The yield of γ photons is ∼ 7 × 10 12 , achieving a high brightness of ∼ 4 × 10 23 photons/s/mm 2 /mrad 2 /0.1%BW. Influences of the laser intensity and the incident angle on the γ-rays emission are discussed. The γ-ray yield, the conversion efficiency from the laser to the γ-rays and the averaged γ-ray energy are increasing when irradiating a higher intensity laser. With the increasing of the incident angle, the peak photon density increases when the angle is smaller than 20 • and then drops to a stable value, while the divergence decreases when the incident angle is smaller than ∼ 16 • and then increases.

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