Circumventing the Dephasing and Depletion Limits of Laser-Wakefield Acceleration

Abstract

Compact electron accelerators are paramount to next-generation synchrotron light sources and freeelectron lasers, as well as for advanced accelerators at the TeV energy frontier. Recent progress in laserplasma driven accelerators (LPA) has extended their electron energies to the multi-GeV range and improved beam stability for insertion devices. However, the subluminal group velocity of plasma waves limits the final electron energy that can be achieved in a single LPA accelerator stage, also known as the dephasing limit. Here, we present the first laser-plasma driven electron accelerator concept providing constant acceleration without electrons outrunning the wakefield. The laser driver is provided by an overlap region of two obliquely incident, ultrashort laser pulses with tilted pulse fronts in the line foci of two cylindrical mirrors, aligned to coincide with the trajectory of the accelerated electrons. Such a geometry of laterally coupling the laser into a plasma allows for the overlap region to move with the vacuum speed of light, while the laser fields in the plasma are continuously being replenished by the successive parts of the laser pulses. Our scheme is robust against parasitic self-injection and self-phase modulation as well as drive-laser depletion and defocusing along the accelerated electron beam. It works for a broad range of plasma densities in gas targets. This method opens the way for scaling up electron energies beyond 10 GeV, possibly towards TeV-scale electron beams, without the need for multiple laser-accelerator stages.

Dephasingless Laser Wakefield Acceleration

“…This concept improves upon the chromatic flying focus [19] by providing the original features of a small focal spot that can propagate at any velocity over any distance, while using an achromatic focusing system to maintain a transformlimited pulse duration ideal for LWFA. The concept does not require (1) the plasma to be colocated with an active lasing media [26], (2) a structured plasma [27], or (3) multiple intersecting laser pulses [28]. In contrast to the pair of laser pulses with tilted pulse fronts employed in the traveling wave electron acceleration described by Debus et al [28], the axiparabola-echelon pair delivers a single laser pulse that can drive a cylindrically symmetric wakefield, preserving the favorable focusing fields and maintaining the strong electrostatic fields resulting from near spherical expulsion of electrons in the bubble regime.…”

“…The concept does not require (1) the plasma to be colocated with an active lasing media [26], (2) a structured plasma [27], or (3) multiple intersecting laser pulses [28]. In contrast to the pair of laser pulses with tilted pulse fronts employed in the traveling wave electron acceleration described by Debus et al [28], the axiparabola-echelon pair delivers a single laser pulse that can drive a cylindrically symmetric wakefield, preserving the favorable focusing fields and maintaining the strong electrostatic fields resulting from near spherical expulsion of electrons in the bubble regime. Further, by adjusting the profile of the echelon, the ponderomotive force can be made to follow a dynamic trajectory, with either accelerations or decelerations to control trapping and reduce dark current.…”

Metrics and Design of an Instruction Roofline Model for AMD GPUs

“…Figure 2 In this work, we run PIConGPU's Traveling Wave Electron Acceleration (TWEAC) and Laser Wakefield Acceleration (LWFA) simulations. A deeper dive into the science of the TWEAC and LWFA simulations is explained by Debus et al [13]. We profile the simulations using various state-of-the-art profiling tools and micro-kernel benchmarking suites.…”

Optimization of Electron Beams Based on Plasma-Density Modulation in a Laser-Driven Wakefield Accelerator

“…However, some of these methods demand sophisticated configurations, and the produced e beams are deficient in charge, energy spread, or peak energy, which hinder their practical applications. Recently, some significant studies have been reported to improve the specific qualities of e beams, including the peak energy [16][17][18][19][20], the energy spread [21][22][23][24][25][26], the brightness [24,27,28], the reproducibility [29][30][31], etc. More considerable research efforts, however, are still needed to focus on generating reproducible high-quality electrons for table-top light sources, which should have a broad-ranging impact across multiple scientific fields.…”