Magnetic Field Test Facility for Superconductive Undulator Coils

Abstract

Superconducting undulators and wigglers are developed for synchrotron light sources, damping rings for linear colliders and polarized positron sources. In an undulator the emitted photons along the trajectory have to interfere. In order to do so the magnetic field in all periods has to be almost identical. The field strength over one or several hundred periods is not allowed to deviate by more than 1%. Translated into mechanical accuracy the position of the wire and the poles has to be more accurate than about 5 m over 1 to 2 m. High quality measurement of the field is an essential requirement. In this paper we present two field measuring systems, one is under construction and another one is under design phase at the Forschungszentrum Karlsruhe.

Novel correction procedure for compensating thermal contraction errors in the measurement of the magnetic field of superconducting undulator coils in a liquid helium cryostat

“…The operation of the magnet increases the heat load in the cryostat. In vertical cryostats the helium level can be guaranteed by manual refill (Mashkina et al, 2008), interface with a dewar (Bertucci et al, 2019) or a cryogenic plant Sketch of the geometry used for modelling the magnetic field measurement. The baseline figure represents the cryostat and it is modified from Marchetti et al (2022b).…”

“…That is why the implementation of SCUs is being considered by several FEL projects world-wide (SLAC, 2020;Tang et al, 2020). Research and development of superconducting undulator coils requires building up test stands for characterization of the coils (Mashkina et al, 2008;Harder et al, 2005;Grau et al, 2016;Kasa et al, 2019). Increasing stringent mechanical requirements on the coils' precision calls for development of high-precision diagnostics for their characterization (Zhang & Calvi, 2022).…”

Magnetic field measurement system in vertical status for superconducting undulator cooled in Dewar

“…This system can meet the measurement requirements of over 1.5 m SCU, and is also suitable for the validation trials of short-period SCU prototypes (20 and 30.5 periods). Vertical measurement can provide a reference experience for horizontal measurement of the SCU's magnetic field under normal operating conditions without cryogenic immersion [6,7]. Specifically, the vertical measurement can verify whether the SCU can be successfully excited to the design current, and local shimming or adjustment can be performed on the magnetic poles according to the magnetic field measurement results to offset various errors in manufacturing.…”

Conceptual Design of a Liquid Helium Vertical Test-Stand for 2m long Superconducting Undulator Coils

“…Numerical simulations [10,11] show that ensuring high precision manufacturing of the coils and their relative alignment are important aspects for the development of the prototype module. An early and fast characterization of the stand alone coil, before installation in the final cryostat, would allow a prompt evaluation of the magnet properties, as routinely pursued in other facilities world-wide [12,13]. Magnetic correction procedures, such as shimming [14] or discard of the coil could possibly be applied early enough to guarantee proper performances of the final cryomodule.…”