Magnetic Field Correction Concepts for Superconducting Undulators

Abstract

The ability to correct magnetic field errors in a superconducting undulator is critical for the successful application of these devices in future and existing light sources. These field errors, which can emanate from sources such as machining and coil winding imperfections, can lead to reduced light source performance by introducing errors in both the electron trajectory and the relative phase relationship between the oscillating electrons and the emitted photons. In this work, correction schemes are presented, which use a single power supply along with a superconducting switch network to define the path for the current during undulator tuning. The basic switching concept was previously designed and successfully tested at Lawrence Berkeley National Laboratory; the approach presented here is a significant advancement in generalizing and scaling that core concept. A new fabrication method is presented here, which uses lithographic methods to produce current paths and switch heaters on a superconducting film. The effect of an example corrector current path design on the magnetic field is investigated using the Finite Element Method, and the results at various undulator and corrector energization levels are presented. Experimental results from the heater switch concept are also presented.

Review and prospects of world-wide superconducting undulator development for synchrotrons and FELs

“…Taking ANL 1.1 m long NbTi planar SCU18-1 for example [27]: correction coils are added at both coil ends to compensate the kick induced by the first field integral, as shown in figure 29(a); a long Helmholtz-like coil wound with ten turns of ∅0.7 NbTi wire is placed above and below the superconducting coil assembly for compensating the undesired dipole field along the undulator length, as shown in figure 29(b); a pair of dipole coils are installed upstream and downstream of the SCU coil assembly inside the cryostat for compensating the 2nd field integral, as shown in figure 29(c). Similar correction approaches are also applied for the SCUs developed at KIT and LBNL [41,175]. In conclusion, using these auxiliary coils is a conventional method for correcting the 1st and 2nd field integrals in both PM and SCUs.…”

Error Analysis and Field Correction Methods in Superconducting Undulators

“…The concept of line current correctors proposed in [12] is used. However, the correction scheme proposed here considers correctors with an unidirectional current and no heater.…”

“…Other are active, such as superconducting coils [5], [10] and a superconducting switch network [11]. The concept of correction with line current pairs has been proposed in [12]. The switching device has been successfully tested, but a full correction network has not been fabricated yet.…”

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). Only recently, the question arose whether geometric errors can be kept at a low level already during fabrication and assembly such that the tedious SCU shimming can completely be avoided.…”