We present the design of a rf undulator at 91.392 GHz that has a period of 1.75 mm, while the minimum beam aperture seen by the beam is 2.375 mm. To confine the fields inside the undulator a corrugated waveguide is connected through a matching section to a linear taper and a mirror. After the mirror, a Bragg reflector and a matching section are used to reflect back all the fields leaking out of the mirror opening. This undulator requires approximately 1.4 MW for submicrosecond pulses to generate an equivalent K value of 0.1. Transferring such amounts of power at mm-wave frequencies requires overmoded corrugated waveguides, and coupling through irises creates excessive pulsed heating. We have designed a coupling scheme that allows coupling power from a highly overmoded corrugated waveguide to the undulator cavity through the beam pipe without disturbing the undulator fields. This system of the rf undulator and its coupling scheme allows for fast dynamic control of the polarization of the emitted light.

• Received 26 July 2019

DOI:https://doi.org/10.1103/PhysRevAccelBeams.22.120701

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Published by the American Physical Society