Nano-Fabricated Free-Standing Wire-Scanners with Sub-Micrometer Resolution

TL;DR

This paper presents the development and testing of nano-fabricated free-standing wire scanners with sub-micrometer resolution for advanced beam diagnostics in free-electron lasers, achieving significantly improved spatial resolution and resilience.

Contribution

It introduces a novel nano-lithography fabrication technique for free-standing wire scanners with sub-micrometer resolution, enhancing beam diagnostic capabilities in FELs.

Findings

Achieved a geometrical resolution of about 250 nm.

Successfully tested resilience to heat-loading at SwissFEL.

Characterized low charge electron beams with a vertical size of 400-500 nm.

Abstract

Diagnostics of the beam transverse profile with ever more demanding spatial resolution is required by the progress on novel particle accelerators - such as laser and plasma driven accelerators - and by the stringent beam specifications of the new generation of X-ray facilities. In a linac driven Free-Electron-Laser (FEL), the spatial resolution constraint joins with the further requirement for the diagnostics to be minimally invasive in order to protect radiation sensitive components - such as the undulators - and to preserve the lasing mechanism. As for high resolution measurements of the beam transverse profile in a FEL, wire-scanners (WS) are the top-ranked diagnostics. Nevertheless, conventional WS consisting of a metallic wire (beam-probe) stretched onto a frame (fork) can provide at best a rms spatial resolution at the micrometer scale along with an equivalent surface of impact on the electron beam. In order to improve the spatial resolution of a WS beyond the micrometer scale along with the transparency to the lasing, PSI and FERMI are independently pursuing the technique of the nano-lithography to fabricate a free-standing and sub-micrometer wide WS beam-probe fully integrated into a fork. Free-standing WS with a geometrical resolution of about 250 nm have been successfully tested at SwissFEL where low charge electron beams with a vertical size of 400-500 nm have been characterized. Further experimental tests carried out at SwissFEL at the nominal beam charge of 200 pC confirmed the resilience to the heat-loading of the nano-fabricated WS. In this work, details on the nano-fabrication of free-standing WS as well as results of the electron-beam characterization are presented.