A compact accelerator for MHz high repetition rate soft x-ray free electron laser

TL;DR

This paper introduces a compact, high-repetition-rate soft X-ray FEL accelerator design that fits within a 100-meter footprint, utilizing superconducting technology and advanced lattice configurations to reduce costs and expand access.

Contribution

It presents a novel compact accelerator layout for MHz soft X-ray FELs, integrating superconducting technology and diffraction-limited storage rings, with detailed analysis of radiation effects and beam quality.

Findings

Horizontal emittance growth below 10% with 11-bending magnets

High beam quality maintained at 60A peak current

Potential upgrade path for hard X-ray generation

Abstract

High-brightness X-ray Free Electron Lasers (FELs) produce spatially and temporally coherent pulses on attosecond to femtosecond timescales, providing a transformative tool for discovery across biology, chemistry, physics, and materials science. This paper proposes a compact accelerator that enables a high-repetition-rate (MHz) 1 nm soft X-ray FEL with a footprint of less than 100 meters. Such an FEL is suitable for installation within research institution settings where space is limited. The accelerator leverages a multi-turn recirculating linear accelerator that integrates state-of-theart superconducting accelerator technology with recent advances in diffraction-limited storage rings. We present the conceptual layout and analyze the impact of two most challenging factors for such a compact accelerator, incoherent and coherent synchrotron radiation. We have systematically studied both effects for different multi-bend achromat lattices and electron beam peak currents. For a peak current of 60 Ampere before final compression and using 11-bending magnets, the horizontal emittance growth after the 90-degree arc can be kept below 10%, demonstrating that these effects are not limiting factors for achieving high-quality electron beams. Such a compact X-ray FEL facility would substantially reduce both construction and operational costs, greatly expanding access to these powerful research tools. Furthermore, this concept provides a potential upgrade path to generating hard X-ray radiation by incorporating high accelerating gradient structures to further accelerate a portion of the MHz electron beam.