  Espresso is a novel acceleration model for Ultra-High-Energy Cosmic Rays
(UHECRs), where lower-energy CRs produced in supernova remnants experience a
one-shot reacceleration in the relativistic jets of powerful Active Galactic
Nuclei (AGNs) to reach energies up to $10^{20}$ eV. To test the espresso
framework, we follow UHECR acceleration bottom-up from injection to the highest
energies by propagating 100,000 particles in realistic 3D magneto-hydrodynamic
(MHD) simulations of ultra-relativistic jets. We find that simulations agree
well with analytical expectations in terms of trajectories of individual
particles. We also quantify that $\sim 10\%$ of CR seeds gain a factor of
$\sim\Gamma^2$ in energy, where $\Gamma$ is the jet's effective Lorentz factor;
moreover, about $0.1\%$ of the particles undergo two or more shots to achieve
gains in excess of $\Gamma^2$. Particles are generally accelerated up to the
jet's Hillas limit, indicating that the espresso mechanism should boost
galactic CRs to UHECRs in typical AGN jets. Finally, we discuss how espresso
acceleration in AGN jets is consistent with UHECR spectra and chemical
composition, and also with the UHECR arrival directions measured by Auger and
Telescope Array.
