Design and Fabrication Concepts of a Compact Undulator With Laser- Structured 2g-HTS Tapes

To produce small-scale high-field undulators for table-top free electron lasers (FELs), compact designs have been proposed using high temperature superconducting (HTS) tapes, which show both large critical current densities and high critical magnetic fields with a total tape thickness of about 50 $\mu$m and a width of up to 12 mm. Instead of winding coils, a meander structure can be laser-scribed directly into the superconductor layer, guiding the current path on a quasi-sinusoidal trajectory. Stacking pairs of such scribed tapes allows the generation of the desired sinusoidal magnetic fields above the tape plane, along the tape axis. Two practically feasible designs are presented, which are currently under construction at KIT: A coil concept wound from a single structured tape with a length of 15 m, which is a progression of a design that has been presented already in the past, as well as a novel stacked and soldered design, made from 25 cm long structured tapes, soldered in a zig-zag-pattern. In this contribution the designs are briefly recapped and the experimental progress is presented.