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Damping Test of the Higher-Order Modes of the Re-Entrant Accelerating Cavity

1981; Institute of Electrical and Electronics Engineers; Volume: 28; Issue: 3 Linguagem: Inglês

10.1109/tns.1981.4331958

1558-1578

Y. Yamazaki, K. Takata, S. Tokumoto,

Gyrotron and Vacuum Electronics Research

Higher-order modes were studied in a model cavity (500 MHz re-entrant single cell cavity) which was designed for the KEK-PF 2.5 GeV electron storage ring. The longitudinal electric field and the transverse electric and magnetic fields were measured near the beam axis for the higher-order modes. The observed parameters of the TMO-mode resonances were in reasonable agreement with the SUPERFISH calculation. The TM011-like resonance at 758 MHz has the highest shunt impedance of 3.0 MΩ. The observed transverse coupling impedances of the HEMl modes at 829 MHz (TM110-like) and 1071 MHz (TM111-like) were 12 NΩ/m and 27 MΩ/m, respectively. Damping couplers are being developed to prevent the cavities from driving the coupled-bunch instabilities. The impedances were reduced to less than 0.01 MΩ and 0.2 MΩ/m for almost all of the TM0- and HEMl-mode resonances, respectively, in a low power test.