Title: Unexpected Results on Microwave Waveguide Mode Transmission
Measurements in the SPS Beam-pipe
Last_Name: Kroyer
First_Name: Thomas
Institute: CERN
email: tom.kroyer@cern.ch
F. Caspers, CERN, T. Kroyer, TU Vienna and CERN
In order to measure the electron cloud density, a microwave transmission measurement was set up over 30m in the SPS beam-pipe. The use of TE waveguide modes eliminates direct interaction with the highly relativistic beam. An electron cloud present in the beam-pipe should lead to a small phase shift of the CW microwave signal. Since this phase shift is modulated by the bunch revolution frequency it translates to a phase modulation which can be measured. However, defying all expectations, a huge beam-induced signal attenuation was found which cannot be understood by current electron cloud models. This attenuation showed strongly fluctuating memory effects of the order of microseconds after the passage of a batch or single bunch. Both effects are present for a wide range of microwave signal frequencies and beam parameters. Models to possibly explain this effect are discussed.
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