The development of compact accelerator facilities providing high-brightness beams is one of the most challenging tasks in the field of next-generation compact and cost affordable particle accelerators, to be used in many fields for industrial, medical, and research applications. The ability to shape the beam longitudinal phase space, in particular, plays a key role in achieving high-peak brightness. Here we present a new approach that allows us to tune the longitudinal phase space of a high-brightness beam by means of plasma wakefields. The electron beam passing through the plasma drives large wakefields that are used to manipulate the time-energy correlation of particles along the beam itself. We experimentally demonstrate that such a solution is highly tunable by simply adjusting the density of the plasma and can be used to imprint or remove any correlation onto the beam. This is a fundamental requirement when dealing with largely time-energy correlated beams coming from future plasma accelerators.

Poincaré covariant definitions for the spin-dependent spectral function and for the momentum distributions within the light-front Hamiltonian dynamics are proposed for a three-fermion bound system, starting from the light-front wave function of the system. The adopted approach is based on the Bakamjian–Thomas construction of the Poincaré generators, which allows one to easily import the familiar and wide knowledge on the nuclear interaction into a light-front framework. The proposed formalism can find useful applications in refined nuclear calculations, such as those needed for evaluating the European Muon Collaboration effect or the semi-inclusive deep inelastic cross sections with polarized nuclear targets, since remarkably the light-front unpolarized momentum distribution by definition fulfills both normalization and momentum sum rules. Also shown is a straightforward generalization of the definition of the light-front spectral function to an $A$-nucleon system.

The distorted spin-dependent spectral function of a nucleon inside an $A=3$ nucleus is introduced as a novel tool for investigating the polarized electron scattering off polarized $^{3}\mathrm{He}$ in the semi-inclusive DIS regime (SiDIS), going beyond the standard plane-wave impulse approximation. This distribution function is applied to the study of the spectator SiDIS, $\stackrel{P\vec}{^{3}\mathrm{He}}(\stackrel{P\vec}{e},{e}^{$'${}}^{2}\mathrm{H})X$, to properly take into account the final-state interaction between the hadronizing quark and the detected deuteron, with the final goal of a more reliable extraction of the polarized parton distribution ${g}_{1}(x)$ inside a bound proton. Our analysis allows one to single out two well-defined kinematical regions where the experimental asymmetries could yield very interesting information: the region where the final-state effects can be minimized, and therefore the direct access to the parton distributions in the proton is feasible, and the one where the final-state interaction dominates, and the spectator SiDIS reactions can elucidate the mechanism of the quark hadronization itself. The perspectives of extending our approach (i) to the mirror nucleus, $^{3}\mathrm{H}$, for achieving a less model-dependent flavor decomposition and (ii) to the asymmetries measured in the standard SiDIS reactions, $\stackrel{P\vec}{e}+\stackrel{P\vec}{^{3}\mathrm{He}}$\rightarrow${}{e}^{$'${}}+h+X$, with $h$ a detected fast hadron, with the aim of extracting the neutron transversity, are discussed.