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Register a new userSimulation of Polarized Beams from Laser-Plasma Accelerators
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The generation of polarized particle beams still relies on conventional particle accelerators, which are typically very large in scale and budget. Concepts based on laser-driven wake-field acceleration have strongly been promoted during the last decades. Despite many advances in the understanding of fundamental physical phenomena, one largely unexplored issue is how the particle spins are influenced by the huge magnetic fields of plasma and, thus, how highly polarized beams can be produced. The realization of laser-plasma based accelerators for polarized beams is now being pursued as a joint effort of groups from Forschungszentrum Julich (Germany), University of Crete (Greece), and SIOM Shanghai (China) within the ATHENA consortium. As a first step, we have theoretically investigated and identified the mechanisms that influence the beam polarization in laser-plasma accelerators. We then carried out a set of Particle-in-cell simulations on the acceleration of electrons and proton beams from gaseous and foil targets. We could show that intense polarized beams may be produced if pre-polarized gas targets of high density are employed. In these proceedings we further present that the polarization of protons in HT and HCl gas targets is largely conserved during laser wake-field acceleration, even if the proton energies enter the multi-GeV regime. Such polarized sources for electrons, protons, deuterons and $^{3}$He ions are now being built in Julich. Proof-of-principle measurements at the (multi-)PW laser facilities PHELIX (GSI Darmstadt) and SULF (Shanghai) are in preparation.
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Plasma injection schemes are crucial for producing high-quality electron beams in laser-plasma accelerators. This article introduces the general concepts of plasma injection. First, a Hamiltonian model for particle trapping and acceleration in plasma waves is introduced; ionization injection and colliding-pulse injection are described in the framework of this Hamiltonian model. We then proceed to consider injection in plasma density gradients.
Laser-plasma accelerators (LPAs) outperform current radiofrequency technology in acceleration strength by orders of magnitude. Yet, enabling them to deliver competitive beam quality for demanding applications, particularly in terms of energy spread and stability, remains a major challenge. In this Letter, we propose to combine bunch decompression and active plasma dechirping for drastically improving the energy profile and stability of beams from LPAs. Start-to-end simulations demonstrate the efficacy of such post-acceleration phase-space manipulations and the potential to reduce current state-of-the-art energy spread and jitter from $1%$ to $0.10%$ and $0.024%$, respectively, closing the beam-quality gap to conventional acceleration schemes.
The acceleration of ions in the interaction of circular polarized laser pulses with overdense plasmas is investigated. For circular polarization laser pulses, the quasi-equilibrium for electrons is established due to the light pressure and the electrostatic field built up at the interacting front of the laser pulse. The ions located within the skin-depth of the laser pulse can be synchronously accelerated and bunched in the charge couple processes by the electrostatic field, and thereby monoenergetic and high intensity proton beam can be generated. The dynamics equations for accelerated ions are deduced and proved by particle-in-cell simulations.
The evolution of beam phase space in ionization-induced injection into plasma wakefields is studied using theory and particle-in-cell (PIC) simulations. The injection process causes special longitudinal and transverse phase mixing leading initially to a rapid emittance growth followed by oscillation, decay, and eventual slow growth to saturation. An analytic theory for this evolution is presented that includes the effects of injection distance (time), acceleration distance, wakefield structure, and nonlinear space charge forces. Formulas for the emittance in the low and high space charge regimes are presented. The theory is verified through PIC simulations and a good agreement is obtained. This work shows how ultra-low emittance beams can be produced using ionization-induced injection.
Plasma-based accelerators have achieved tremendous progress in the past few decades, thanks to the advances of high power lasers and the availability of high-energy and relativistic particle beams. However, the electrons (or positrons) accelerated in the plasma wakefields are subject to radiation losses, which generally suppress the final energy gains of the beams. In this paper, radiation reaction in plasma-based high-energy accelerators is investigated using test particle approach. Energy-frontier TeV colliders based on a multiple stage laser-driven plasma wakefield accelerator and a single-staged proton-driven plasma wakefield accelerator are studied in detail. The results show that the higher axial and transverse field gradients seen by an off-axis injected witness beam result in a stronger damping force on the accelerated particles. Proton-driven plasma wakefield accelerated electrons are shown to lose less energy compared to those accelerated in a multi-staged laser-driven plasma wakefield accelerator.
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