Rf impedance calculations for three-dimensional devices for HERA

On account of the high beam current on both of the HERA rings once must be specially careful that the parasitic shunt impedances remain small. High impedance both affects the stability of the beam and causes heating of the cavity walls. The 3-dimensional code URMEL of the MAFIA-family was used to perform the calculation of the shunt impedance and obtain the field plots. In this paper the design and function of several proposed HERA kickers and diagnostic tanks are described. The final structures shown are a result of several redesign stages using these codes. The a priori calculation has proven to be an invaluable tool for keeping all parasitic side effects below the tolerable tight limit