[Paper Review] Laser-Driven Structure-Based Accelerators

R. J. England, D. Filippetto+18 more|arXiv (Cornell University)|Mar 16, 2022

Laser-Plasma Interactions and Diagnostics4 citations

TL;DR

This paper proposes laser-driven structure-based accelerators (LSA) as a compact, high-gradient alternative to conventional RF accelerators, using dielectric, photonic crystal, or plasmonic microstructures to accelerate electrons and positrons via laser fields. It demonstrates GV/m accelerating gradients, low beamstrahlung losses (~few percent), and feasibility for multi-TeV colliders with scalable, CMOS-compatible fabrication and high-repetition-rate operation.

ABSTRACT

Particle acceleration in microstructures driven by ultrafast solid state lasers is a rapidly evolving area of advanced accelerator research, leading to a variety of concepts based on planar-symmetric dielectric gratings, hollow core fibers, photonic crystals, and plasmonic meta-surfaces. This approach leverages well-established industrial fabrication capabilities and the commercial availability of tabletop lasers to reduce cost, with demonstrated axial accelerating fields in the GV/m range. Wide-ranging international efforts have significantly improved understanding of gradient limits, structure design, particle focusing and transport, staging, and development of compatible low-emittance electron sources. With a near-term focus on low-current MeV-scale applications for compact scientific and medical instruments, as well as novel diagnostics capabilities, structure-based laser-driven accelerators have several key benefits that warrant consideration for future high-energy physics machines, including low beamstrahlung energy loss, modest power requirements, stability, and readiness of supporting technologies.

Motivation & Objective

• To establish laser-driven structure-based accelerators (LSA) as a credible alternative to conventional RF accelerators for future high-energy physics applications.
• To address the technological gap in funding and development for LSA, particularly for multi-TeV linear collider applications.
• To demonstrate near-term feasibility of LSA through integrated, wafer-scale prototypes combining high-gradient structures, beam control, and laser phasing.
• To enable low-cost, high-efficiency acceleration by leveraging commercial CMOS and telecommunications fabrication and laser technologies.
• To validate the path toward a multi-GeV-scale prototype as a stepping stone to a full TeV-scale collider.

Proposed method

• Utilizes dielectric laser acceleration (DLA), plasmonically-enhanced metasurfaces (MLA), and photonic crystal structures to confine and phase laser fields for linear acceleration in vacuum.
• Employs carrier-envelope phase-locked solid-state fiber lasers at 20 MHz repetition rate to drive synchronized, high-precision laser fields across integrated chip-scale structures.
• Integrates on-chip photonic waveguides and power splitters to distribute laser energy across multiple accelerating sections on 6-inch wafers.
• Applies active thermal and mechanical feedback systems to stabilize alignment and maintain phase coherence across multi-stage modules.
• Uses interferometric beam alignment and feedback to maintain beam quality and minimize emittance growth over long distances.
• Employs optical diagnostics and real-time feedback to monitor laser illumination, beam position, and performance across accelerating stages.

Experimental results

Research questions

• RQ1 Can laser-driven structure-based accelerators achieve GV/m accelerating gradients with stable, high-brightness electron beams?
• RQ2 What are the critical technical barriers to scaling LSA to multi-TeV linear collider energies, particularly regarding thermal management and wakefield effects?
• RQ3 Can sub-cycle phase and timing control of high-power drive lasers enable efficient, synchronized acceleration across multiple parallel channels?
• RQ4 To what extent can wall-plug efficiency and cost per GeV be reduced by leveraging commercial CMOS and fiber laser technologies?
• RQ5 Can a multi-stage, wafer-scale LSA prototype demonstrate beam control, emittance preservation, and efficient energy transfer at GeV-scale energies?

Key findings

• GV/m accelerating gradients have been experimentally demonstrated, with energy gains exceeding 0.3 MeV for few-femtocoulomb (fC) beams.
• Beamstrahlung energy loss in a multi-TeV collider scenario is projected to be in the few percent range, significantly lower than the tens of percent seen in conventional RF accelerators.
• Wall plug efficiencies comparable to or better than conventional RF accelerators are considered feasible using high-efficiency solid-state lasers and nanofabricated structures.
• Thermal conductivity and wakefield control in dielectric structures are identified as key near-term technology gaps requiring resolution.
• High-gradient focusing schemes that preserve beam quality while minimizing interception are essential and under active development.
• A multi-stage, wafer-scale prototype incorporating synchronized laser delivery, beam steering, and diagnostics is proposed as a critical milestone for validating the LSA path to a TeV-scale collider.