ERL RELATED HOM MEASUREMENTS AT ELBE.

Higher order mode (HOM) wakefields building up in the SCRF cavities are likely to be a major factor in 4GLS. A series of measurements of the HOMs of the SCRF cavities at the ELBE light source has been performed. The power extracted by the HOM couplers over a wide band-width (1.7GHz-2.9GHz) has been measured using a spectrum analyser, for various bunch trajectories through the cavities. Network analysers have also been used to determine the external Q of these modes. These meas-urements will be used to estimate the dominant modes which will require significant damping for 4GLS