Simulation of the low-frequency collimator impedance

The low-frequency transverse collimator impedance constitutes a major part of the LHC impedance budget. In this paper numerical simulations for frequencies below 1 MHz using a commercial package are presented. From the 3D field solution of the two-wire simulations the transverse impedance is directly calculated. After a cross-check with theory for rotationally symmetric structures a geometry with two jaws and an LHC graphite collimator is examined. Furthermore, a simple physics picture that explains the principal characteristics of the impedance at high and low frequencies is given.