Abstract
High gain free electron lasers (FELs) driven by high repetition rate recirculating accelerators have received considerable attention in the scientific and industrial communities in recent years. Cost-performance optimization of such facilities encourages limiting machine size and complexity, and a compact machine can be realized by combining bending and bunch length compression during the last stage of recirculation, just before lasing. The impact of coherent synchrotron radiation (CSR) on electron beam quality during compression can, however, limit FEL output power. When methods to counteract CSR are implemented, appropriate beam diagnostics become critical to ensure that the target beam parameters are met before lasing, as well as to guarantee reliable, predictable performance and rapid machine setup and recovery. This article describes a beam line for bunch compression and recirculation, and beam switchyard accessing a diagnostic line for EUV lasing at 1 GeV beam energy. The footprint is modest, with 12 m compressive arc diameter and $\ensuremath{\sim}20\text{ }\text{ }\mathrm{m}$ diagnostic line length. The design limits beam quality degradation due to CSR both in the compressor and in the switchyard. Advantages and drawbacks of two switchyard lines providing, respectively, off-line and on-line measurements are discussed. The entire design is scalable to different beam energies and charges.
Highlights
Soon after the advent of high gain free electron lasers (FELs) in the infrared (IR) and ultraviolet (UV) [1], scientific and industrial communities began considering the production of high average FEL power at tens of nm wavelength [2]
A 100 pC charge bunch is compressed in length by a factor ∼60, reaching the final peak current of 1 kA at an energy of 1 GeV. This electron beam brightness is consistent with requirements for GW-peak power single-pulse lasing, and for providing several tens of kW-average FEL power from a MHz-level bunch repetition rate superconducting linac— thereby demonstrating the feasibility of an energyrecovery linac (ERL)-driven spontaneous emission (SASE) FEL devoted to EUV lithography in a cost-effective and industrially compatible footprint
As discussed in the Introduction, diagnostic lines are to be installed between the compressive arc (CA) and the undulator; we have developed designs that are parallel to the FEL production beam line
Summary
Soon after the advent of high gain free electron lasers (FELs) in the infrared (IR) and ultraviolet (UV) [1], scientific and industrial communities began considering the production of high average FEL power at tens of nm wavelength [2]. In order to reduce machine size and complexity, bunch length compression in the compressive arc (CA) is performed during the very last stage of recirculation (Fig. 1) This scheme avoids any need for additional space in the layout for magnetic compressors, minimizes potential for beam quality degradation introduced by compression at lower energies, and maximizes available length for beam acceleration up to the undulator. A 100 pC charge bunch is compressed in length by a factor ∼60, reaching the final peak current of 1 kA at an energy of 1 GeV This electron beam brightness is consistent with requirements for GW-peak power single-pulse lasing, and for providing several tens of kW-average FEL power from a MHz-level bunch repetition rate superconducting linac— thereby demonstrating the feasibility of an ERL-driven SASE FEL devoted to EUV lithography in a cost-effective and industrially compatible footprint.
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