Elevating electron energy gain and betatron X-ray emission in proton-driven wakefield acceleration

TL;DR

This study uses particle-in-cell simulations to explore how plasma density affects wakefield excitation, witness electron acceleration, and betatron X-ray emission in proton-driven plasma wakefield acceleration, revealing enhanced energy gain and radiation at high densities.

Contribution

It provides new insights into the influence of plasma density on wakefield dynamics and radiation emission, highlighting nonlinear saturation effects and potential for high-energy photon generation.

Findings

Higher plasma density increases microbunch formation and wakefield strength.

Elevated densities lead to broadband X-ray and gamma-ray emission.

Witness electron energy gain is significantly enhanced at high plasma densities.

Abstract

The long proton beams present at CERN have the potential to evolve into a train of microbunches through the self-modulation instability process. The resonant wakefield generated by a periodic train of proton microbunches can establish a high acceleration field within the plasma, facilitating electron acceleration. This paper investigates the impact of plasma density on resonant wakefield excitation, thus influencing acceleration of a witness electron bunch and its corresponding betatron radiation within the wakefield. Various scenarios involving different plasma densities are explored through particle-in-cell simulations. The peak wakefield in each scenario is calculated by considering a long pre-modulated proton driver with a fixed peak current. Subsequently, the study delves into the witness beam acceleration in the wakefield and its radiation emission. Elevated plasma density increases both the number of microbunches and the accelerating gradient of each microbunch, consequently resulting in heightened resonant wakefield. Nevertheless, the scaling is disrupted by the saturation of the resonant wakefield due to the nonlinearities. The simulation results reveal that at high plasma densities an intense and broadband radiation spectrum extending into the domain of the hard X-rays and gamma rays is generated. Furthermore, in such instances, the energy gain of the witness beam is significantly enhanced. The impact of wakefield on the witness energy gain and the corresponding radiation spectrum is clearly evident at extremely elevated densities.