Abstract
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.
Highlights
Short-period alternatives to traditional permanent magnet undulators are in-vacuum and superconducting magnetbased undulators [1,2,3], short-period electromagnet-based undulators [4], microfabricated permanent magnet undulators [5], and microfabricated electromagnet undulators [6,7]
The most extreme case is using this rf undulator in compact x-ray free electron lasers (FELs) and the bunches of interest are extremely short, much smaller than 100 fs rms, and their bandwidth extends to several tens of THz
In this work we reported the design of a short-period rf undulator at 91.392 GHz
Summary
Short-period alternatives to traditional permanent magnet undulators are in-vacuum and superconducting magnetbased undulators [1,2,3], short-period electromagnet-based undulators [4], microfabricated permanent magnet undulators [5], and microfabricated electromagnet undulators [6,7]. Another approach to produce short-period undulators is to use oscillating electromagnetic (EM) fields where the electron beam is wiggled by both the electric and magnetic fields This approach includes inverse Compton scattering sources [9,10], laser-driven dielectric undulators [11,12,13,14], and rf or microwave undulators [15,16,17,18,19,20,21,22,23]. Other methods of producing polarized soft x-rays include high harmonic generation sources [45], which are not efficient in the x-ray regime, and magnetized films [46,47], which are limited to specific wavelengths, low intensity, and achieve only 60% circular polarization Axisymmetric rf undulators, such as the rf undulator of Tantawi et al [20] and the one presented in this work, can produce any polarization by the user modifying the rf excitation of the undulator cavity. Parts of this work have been reported in conference format in Toufexis et al [22,23,31]
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