Evaluation of the Horizontal to Vertical Transverse Impedance Ratio for LHC Beam Screen Using a 2D Electrostatic Code

The classical 2 wire method is not suitable for high precision transverse impedance measurements on a homogeneous copper beampipe with non-circular cross-section due to measurement noise limitations in case of narrow wire spacing. Thus we tackled the problem by simulating the 2D electrostatic field and image charge distribution of that setup and subsequently calculating the corresponding surface current for a TEM wave excitation. In this computer simulation the 2 wires can be assumed lossless, which is not possible in a practical bench setup. The theoretical justification for the method and certain limitations are discussed. The results obtained compare very well to several independent numerical and analytical results.