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TY - CONF AU - Cahill, A.D. AU - Dal Forno, M. AU - Dolgashev, V.A. ED - Petit-Jean-Genaz, Christine ED - Kim, Dong Eon ED - Kim, Kyung Sook ED - Ko, In Soo ED - Schaa, Volker RW TI - TM01 Mode Launcher for Use in High Brightness Photoguns J2 - Proc. of IPAC2016, Busan, Korea, May 8-13, 2016 C1 - Busan, Korea T2 - International Particle Accelerator Conference T3 - 7 LA - english AB - Photo rf guns are a source of electron beams for X-ray FELs such as LCLS and European XFEL. In existing photoguns power is coupled into the cavity by waveguides through the cell walls, like LCLS, or through coaxial coupling, at the European XFEL. We are considering feeding a gun using a circular waveguide with the TM01 mode. To do that we need a mode launcher, a matched device that couples the rectangular TE01 mode waveguide to a TM01 mode in a circular waveguide. Use of the mode launcher reduces complexity of the gun cavity and increases flexibility of positioning the input waveguide relative to the gun body. Mode launchers have been successfully used at SLAC and elsewhere for X-band high gradient tests. Because the existing mode launchers were not built for high brightness guns, they have a significant quadrupole field component. High brightness rf guns have tight requirements on output beam properties, and this quadrupole component adversely affects the beam. We have designed a mode launcher free of this disadvantage. We present design considerations, methodology, and an example S-band mode launcher. PB - JACoW CP - Geneva, Switzerland SP - 491 EP - 493 KW - quadrupole KW - gun KW - electron KW - impedance KW - cavity DA - 2016/06 PY - 2016 SN - 978-3-95450-147-2 DO - 10.18429/JACoW-IPAC2016-MOPMW039 UR - http://jacow.org/ipac2016/papers/mopmw039.pdf ER -