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TY - CONF AU - Pande, S.A. AU - Burt, G. AU - Christou, C. AU - Gu, P. ED - Petit-Jean-Genaz, Christine ED - Kim, Dong Eon ED - Kim, Kyung Sook ED - Ko, In Soo ED - Schaa, Volker RW TI - Modifications to the Pump Out Box to Lower the Qext of Diamond SCRF Cavities J2 - Proc. of IPAC2016, Busan, Korea, May 8-13, 2016 C1 - Busan, Korea T2 - International Particle Accelerator Conference T3 - 7 LA - english AB - Diamond's CESR-B cavities are iris coupled and have fixed Qext. For reliability, the cavities are operated at lower voltages. This results in the optimum condition for beam loading being satisfied at a much lower power typically about 100 kW. For operation at 300 mA with two cavities, the RF power needed per system exceeds 200 kW. Consequently, the cavities need to be operated under-coupled. To lower the Qext and move the optimum operating point nearer to 200kW, 3 stub tuners are used in the waveguide feed line. The difference in the height of the coupling waveguide on cavity and that of the vacuum side waveguide on the window assembly results in a step transition which affects the Qext. The present window/step location results in Qext higher than that without the window. The Qext can be lowered by re-locating the RF window or by shifting the step change in the waveguide cross-section from its present location. This needs modification to the Pump Out box. The pros and cons of the proposed modification to the pump out box in terms of standing waves and multipacting characteristics studied with CST Studio are discussed in this paper. PB - JACoW CP - Geneva, Switzerland SP - 2251 EP - 2253 KW - cavity KW - coupling KW - operation KW - simulation KW - electron DA - 2016/06 PY - 2016 SN - 978-3-95450-147-2 DO - 10.18429/JACoW-IPAC2016-WEPMB060 UR - http://jacow.org/ipac2016/papers/wepmb060.pdf ER -