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Characterization of fields and radiation

Characterization of fields and radiation
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Axel Bernhard

Characterisation of superconductive undulators

The characterisation of superconductive undulators has three main aspects

  • characterisation of the magnetic field

  • interactions with the electron beam

  • characterisation of the undulator radiation

     

Characterisation of the undulator field

Undulator fields are characterised both by spacial maps of the on-axis field and by the first and second field integral. Field maps are normally measured by means of hall-probe scans. Field integrals can be measured by the stretched-wire or the rotating-coil method. Moreover it is possible to determine the electron trajectory through an undulator by the pulsed-wire technique. In the particular case of superconductive undulators these techniques are complicated by the fact that the measurements have to be performed at cryogenic temperature. The field maps of the first undulator coils built for ANKA were taken by the supplier (ACCEL Instruments, Germany). In 2007 a magnetic field measurement setup for short superconductive undulator test coils was built up at the Forschungszentrum Karlsruhe. A second setup layed out for full-scale superconductive undulator coils is under construction. The conception of this setup is a joint project of Forschungszentrum, University of Erlangen and LAS.

Carrying out and analysing magnetic field measurements on test devices is part of the development projects conducted by the workgroup Superconductive Undulator Technologies at the LAS. The sofware for data analysis is developed in-house.

 

Interactions with the electron beam

There are two main aspects of the mutual interactions between the electron beam and a superconductive undulator. On the one hand, the high-energy electron beam introduces heat into the cold superconducting coils. On the other hand, non-vanishing integrals of the undulator field perturb the electron orbit. The investigation of these orbit perturbations, especially taking into account hysterese and transient effects, is one of the fields in which LAS is active. The goal of these investigations is a physical understanding of these perturbing effects as well as the development of effective compensation schemes.

 

Characterisation of the undulator radiation

For the spectral and spacial characterisation of the radiation emitted by the SCU14 demonstrator at ANKA (the first superconductive undulator ever installed in a storage ring) a diagnostic beamline is operated, equipped with an energy dispersive detector (Roentec Xflash, 0-20keV, 120eV resolution) and a Si-111-channelcut monochromator (University of Wuppertal, 2.3-20keV). LAS is routinely performing measurements at this beamline. One of the aims of these measurements is to correlate spectral properties with types of errors exhibited by the measured magnetic field.