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Design of a third harmonic Landau cavity for the SRRC storage ring

We present here our design of the SRRC third-harmonic Landau cavity to be operated on the first stage in a passive mode for bunch lengthening so as to increase the Touschek life-time. Its implementation will also be helpful for suppression of the longitudinal coupled-bunch instabilities observed in the storage ring of SRRC. The cavity profile was optimized with the 2D code URMEL with the following criteria: (1) maximization of the shunt impedance; (2) minimization of the maximal power flow density on the cavity surface; (3) feasibility of the mechanical constructions. A prototype is now under construction.