The world’s first elliptical in-vacuum undulator, IVUE32, is currently being developed at Helmholtz-Zentrum Berlin. IVUE32 is an APPL-II–type device that enables longitudinal shifting of the upper and lower magnet arrays in order to tune the polarization of the emitted radiation. Implementing this shifting motion in the conical transition sections at the entrance and exit of the in-vacuum undulator is challenging. In particular, wakefield effects are of critical importance, so the impedance characteristics of the devices must be understood. Because of the electrical dimensions, simplifications are employed in the simulations, which makes measurements necessary to validate the simulations.

To this end, Helmholtz-Zentrum Berlin is establishing a new measurement technique based on the Goubau line. A surface wave is used to emulate the wakefield. While the initial results are promising, the applicability of the method is limited by unwanted reflections, and it has not been possible to fully remove these reflections from the recorded signal using suitable calibration strategies. It is therefore necessary to find strategies for (computational) reflection removal.

In this project, we will (i) develop an ad hoc numerical solver based on the boundary element method that exceeds the computational speed of standard algorithms in commercial software, and (ii) use the established solver to derive an advanced impedance measurement setup. For this setup, we will, on the one hand, derive an optimized horn antenna; measurements at Helmholtz-Zentrum Berlin will be used to verify our design. On the other hand, we will use our solver to assess the feasibility of a novel concept in which the Goubau line is coated with a time-varying medium, so that backward-traveling waves can be separated (algorithmically) through appropriate manipulation.