Experimental demonstration of the induction-shimming concept in superconductive undulators

Abstract

In an undulator, magnetic field errors limit the quality of the emitted photon beam. In an ideal undulator, the sinusoidal motion of the electron beam and the emitted photons are in phase along the whole trajectory. Small variations in the magnetic field from period to period can produce phase errors and have to be corrected. This procedure is called shimming. Recently, a new scheme for superconductive undulators based on Faraday's law of induction in a type-II superconductor was proposed in which these errors are automatically minimized. The field errors create currents and therefore magnetic fields in an array of coupled high temperature superconductor loops which minimize the field errors. In this paper the first experimental results of a test of this new concept are described.

Shaping Photon Beams with Undulators and Wigglers

“…Specific shimming techniques like the induction shimming have been proposed and successfully been tested (Wollmann et al 2008(Wollmann et al , 2009). Another approach is based on high-temperature superconducting tapes with lithographically imprinted correction loops for local shimming (Arbelaez et al 2013;Rochepault et al 2014).…”

Development trends for insertion devices of future synchrotron light sources

“…The other critical issue of a superconducting undulator is field shimming. Shimming methods were developed at ANKA [50] and NSRRC [51]. The SU at NSRRC was shimmed using iron-shim pieces and a low-temperature trim coil; the maximum field correction achieved using iron-shim pieces or a trim coil is approximately 2%.…”

“…The method based on trim-iron pieces is more cost effective in terms of testing procedure, and no heat loss is caused by the additional current leads of the trim-coil method. A SU mockup with one undulator coil [50] was developed to test the field shimming in ANKA; an array of coupled HTS loops was attached to the surface of the SU. The maximum field correction obtained with this shimming method was approximately 1%.…”

Error Analysis and Field Correction Methods in Superconducting Undulators

“…Several correction concepts have already been proposed. Some are passive, such as magnetic shims [7], inductive shimming coils [8], or indentations into the poles Fig. 1.…”