Bench measurements of the LHC injection kicker low frequency impedance properties

The LHC injection kicker contains a ceramic tube with inside printed metallic strips as a RF bypass in order to minimise the beam coupling impedance. These strips are capacitively coupled at one side to avoid eddy current during kicker transients. Experimentally it was found already earlier, using bench techniques, that in the region between 10 and 30 MHz certain resonances and thus peaks in the coupling impedance occur, related to the transition of the image current from the “cold conductor" to the bypass strips. The presence of these resonances has been reconfirmed as well as their properties. A practical method for reducing their influence by attaching lossy ferrite rings to the ends of the ceramic pipe is proposed and has partly been tested. As the present measurements were done on a mock-up for this RF bypass, which has limited validity towards higher frequencies, a full scale test should be repeated, once the first prototype of the 3 meter long ceramic chamber with printed bypass strips is available.