Fabrication, measurement, and tuning of the two-mode transverse deflecting structure

Shanghai Synchrotron Radiation Facility (SSRF)/Shanghai soft X-ray FEL facility (SXFEL) has developed an advanced transverse deflecting structure two-mode transverse deflecting structure (TTDS) to deflect beams at any angle. The rf design of the TTDS uses a two-mode structure utilizing both the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mrow><a:mi mathvariant="normal">H</a:mi><a:mi mathvariant="normal">E</a:mi><a:mi mathvariant="normal">M</a:mi></a:mrow><a:mn>11</a:mn></a:msub></a:math> and <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"><f:msub><f:mrow><f:mi mathvariant="normal">H</f:mi><f:mi mathvariant="normal">E</f:mi><f:mi mathvariant="normal">M</f:mi></f:mrow><f:mn>12</f:mn></f:msub></f:math> modes for simultaneous vertical and horizontal deflections, operating at 2856 and 5712 MHz, respectively. The design was published in Physical Review Accelerators and Beams in April 2024. A TTDS prototype with 14 regular cells and 2 coupler cells was fabricated at SSRF/SXFEL. Because of the differences in electromagnetic field distributions between the two modes of the TTDS, the nonresonant perturbation measurement was studied by taking the coexisting two modes in mind. Based on an independent tuning process between the modes, a sequential tuning process was designed and established. Using the existing measurement system in the Microwave Laboratory at SSRF, all necessary measurements and tuning have been completed, and the TTDS prototype is ready for high-power tests.