Abstract
Within the SwissFEL project at the Paul Scherrer Institute (PSI), the hard X-ray line (Aramis) has been equipped with short-period in-vacuum undulators, known as the U15 series. The undulator design has been developed within the institute itself, while the prototyping and the series production have been implemented through a close collaboration with a Swiss industrial partner, Max Daetwyler AG, and several subcontractors. The magnetic measurement system has been built at PSI, together with all the data analysis tools. The Hall probe has been designed for PSI by the Swiss company SENIS. In this paper the general concepts of both the mechanical and the magnetic properties of the U15 series of undulators are presented. A description of the magnetic measurement equipment is given and the results of the magnetic measurement campaign are reported. Lastly, the data reduction methods and the associated models are presented and their actual implementation in the control system is detailed.
Highlights
As part of the general strategy of the Paul Scherrer Institute (PSI) regarding the development of light sources for research, a compact free-electron laser (FEL) called SwissFEL has been designed and constructed (Milne et al, 2017).SwissFEL consists of a low-emittance injector (Schietinger et al, 2016), a linac based on C-band accelerating technology and two beamlines: a soft X-ray beamline, Athos, which is under construction, covering the photon wavelength range between 0.6 and 4.9 nm, and a hard X-ray beamline, Aramis, which is under commissioning, covering the wavelength range between 1 and 7 A
The pole horizontal width can be reduced to a tip of only 15.0 mm, as opposed to, for instance, 40.0 mm as is used in the in-vacuum undulator found in the Swiss Light Source storage ring
The magnetic measurements start with the characterization of the single undulator magnets, continue in industry during different phases of undulator assembly and end in the PSI magnetic measurement laboratories, where the final optimization and characterization are performed before the installation of the undulator in the SwissFEL accelerator
Summary
Short-period in-vacuum undulators have been designed and installed within Aramis to achieve short emission wavelengths down to the interatomic scale with relatively low electron energies (see Table 1) Their magnetic structure has been designed only for on-axis operation, enough for a linac-driven FEL, reducing the magnetic forces while enhancing the field on the magnetic axis (see x2 for more details). The phase shifters will be discussed since they are essential to be able to operate the different modules together as a single long undulator as well as the active feed-forward orbit correction scheme based on the results of the magnetic measurements. This complex multi-system model is referred to as SUBLIME. (aramiS Undulator BeamLIne ModEl) and summarizes all the information that is required to operate the Aramis undulator from the control room
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