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Magnet design for superconductive undulators

Magnet design for superconductive undulators
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Axel Bernhard

Magnet design for superconductive undulators

Undulators are advanced devices for the generation of synchrotron radiation installed in the straight sections of synchrotron radiation sources. They typically consist of two periodic arrangements of permanent or electromagnets facing each other and sepatated by the so-called undulator gap. Electrons passing this gap are forced onto an undulating track by the Lorentz force. The transverse acceleration causes them to emit synchrotron radiation. In undulators the deflection of the electons is relatively weak. Therefore the photons emitted by an individual electron along its trajectory through the undulator can interfere, resulting in a sharply peaked line spectrum of the undulator radiation.

The undulator spectrum, its tunability range and intensity are determined by the undulator's magnetic field strength and period length. At the same time the achievable field strength is detemined by the properties of the magnetic field sources and their geometry – in particular by the period length and the undulator gap width. Compared to permanent magnet or normal conducting undulators superconductive undulators stand out due to a significantly higher achievable magnetic field strength for a given gap width and period length. Moreover, special designs capable of electrically variable period length or generation of helical field with switchable helicity are possible.

The workgroup Superconductive Undulator Technologies works on design and optimisation of superconductive undulatos according to the experimental requirements and the basic conditions posed by their operation in a particular particle accelerator (storage ring, linear accelerator, wakefield accelerator). This work is mainly based on numerical simulations performed with the commercial finite element software Vectorfields OPERA, the ESRF-code RADIA and in-house developed software.