Title : APF-enhanced hollow-core photonic fiber accelerator concept for tabletop X-ray systems
Abstract:
Laser-driven dielectric accelerators (LDDAs) based on hollow-core optical fibers present a promising platform for developing compact, cost-effective electron acceleration systems. In such structures, achieving sustained phase synchronization between the optical driving field and relativistic electrons remains a key challenge, particularly when aiming for stable longitudinal TM-like modes with high axial field intensity. In this work, we propose a novel design approach utilizing geometrically engineered hollow-core fibers combined with Alternating Phase Focusing (APF) to enhance phase locking, field confinement, and beam stability simultaneously. The study explores a family of hollow-core photonic crystal fibers (HC-PCFs) with modified cladding geometries-ranging from circular to anisotropic hexagonal and elliptic hole lattices-to tailor the propagation constant β(ω) for improved phase synchronism with accelerating electrons. Through full-wave Wave Optics simulations and mode analysis, we identify the topological dependencies between cladding symmetry, core-to-lattice spacing, and achievable longitudinal field enhancement Ez. This optimized geometry ensures robust guiding of TM-like modes with minimal field leakage, mitigating one of the critical efficiency losses encountered in dielectric accelerators.
Building upon this geometrical optimization, we incorporate an APF-based longitudinal phase modulation scheme, applied as a controlled variation of field phase along the propagation axis, enabling dynamic synchronization correction for velocity spread and minimizing phase slippage of the electron bunch. This dual approach-structural dispersion engineering and phase control-opens a pathway toward compact, fiber-based accelerator modules capable of producing quasi-monoenergetic electron beams suitable for portable hard X-ray generation. The implications of this integrated design are significant, offering a scalable route to tabletop X-ray imaging systems for medical diagnostics, material inspection, and ultrafast science applications. The proposed hollow-core APF-coupled accelerator concept thus bridges optical fiber photonics and accelerator physics, introducing a new paradigm in micro-structured, laser-synchronous acceleration technology.
