Magnetic Field Correction Concepts for Superconducting Undulators

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.