Abstract
SwissFEL is a x-rays free electron laser (FEL) driven by a 5.8 GeV linac under construction at Paul Scherrer Institut. In SwissFEL, wire scanners (WSCs) will be complementary to view-screens for emittance measurements and routinely used to monitor the transverse profile of the electron beam during FEL operations. The SwissFEL WSC is composed of an in-vacuum beam-probe---motorized by a stepper motor---and an out-vacuum pick-up of the wire signal. The mechanical stability of the WSC in-vacuum hardware has been characterized on a test bench. In particular, the motor induced vibrations of the wire have been measured and mapped for different motor speeds. Electron-beam tests of the entire WSC setup together with different wire materials have been carried out at the 250 MeV SwissFEL Injector Test Facility (SITF, Paul Scherrer Institut, CH) and at FERMI (Elettra-Sincrotrone Trieste, Italy). In particular, a comparative study of the relative measurement accuracy and the radiation-dose release of $\mathrm{Al}(99)\ensuremath{\mathbin:}\mathrm{Si}(1)$ and tungsten (W) wires has been carried out. On the basis of the outcome of the bench and electron-beam tests, the SwissFEL WSC can be qualified as a high resolution and machine-saving diagnostic tool in consideration of the mechanical stability of the scanning wire at the micrometer level and the choice of the wire material ensuring a drastic reduction of the radiation-dose release with respect to conventional metallic wires. The main aspects of the design, laboratory characterization and electron beam tests of the SwissFEL WSCs are presented.
Highlights
SwissFEL will provide coherent x-rays light in the wavelength region 7 − 0.7 nm and 0.7 − 0.1 nm [1]
Laboratory tests aimed at determining the mechanical stability of the in-vacuum hardware of the wire scanners (WSCs) and, in particular, the stepper-motor induced vibration of the wire in the speed range of interest of SwissFEL were carried out. e-beam tests of a prototype of the SwissFEL WSC—in-vacuum and out-vacuum components—were performed: (1) at low charge and energy— 10 pC and 250 MeV—at SITF [17] and (2) at high charge and energy—700 pC and 1.5 GeV—at FERMI; S. Grulja (FERMI) [18,19]
The possibility to use for the SwissFEL WSC—as an alternative to tungsten—a different metallic wire was investigated keeping in mind the constraint to reduce as much as possible the release of the radiation-dose along the machine during a WSC measurement
Summary
SwissFEL will provide coherent x-rays light in the wavelength region 7 − 0.7 nm and 0.7 − 0.1 nm [1]. In SwissFEL, WSCs will be complementary to view-screens for emittance measurements and, thanks to the barely invasive feature, used for routine monitoring of the transverse profile of the electron beam during FEL operations. In SwissFEL, the wire-scanned profile of the electron beam will be reconstructed thanks to the beam-synchronous acquisition (BSDAQ) of the encoder read-out of the wire-position and of the signal read-out of the BLM at every rf shot. Laboratory tests aimed at determining the mechanical stability of the in-vacuum hardware of the WSC and, in particular, the stepper-motor induced vibration of the wire in the speed range of interest of SwissFEL were carried out. A comparative study of the scanning performances—relative measurement accuracy and radiation-dose release—of a Alð99Þ∶Sið1Þ wire with a diameter of 12.5 μm and a tungsten (W) wire with a diameter of 5 μm was carried out at FERMI at a beam energy of 1.325 GeV and at a charge of 700 pC
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