Status of a Prototype HTS Helical Undulator Coil for Compact FELs

A superconducting helical undulator is not only very compact but also more effective in terms of synchrotron radiation production and free-electron laser (FEL) amplification compared to other undulator geometries. Furthermore, the superconductor is used very efficiently in a helical geometry with respect to the undulator field generation and the produced circular polarized photons are suitable for the majority of experiments performed at FEL facilities. To realize more compact FELs, a combination of short-period and high-field undulators are required. We investigate the application of high-temperature superconductors (HTS) to reach higher magnetic fields at 4.2 K and larger operating margins as compared to low-temperature superconductors. This contribution discusses the development work done on a superconducting helical undulator prototype with a period length of 13 mm, wound in a bifilar winding scheme from coated REBCO tape conductor. Electromagnetic simulations predict a peak field amplitude of up to 2.8 T for a 5 mm gap at 4.2 K. The status of a prototype coil is presented and discussed.