| Ch. Magne, M. Jablonka, M. Lalot, V. Lethiers, M. Luong, O. Napoly, N. Baboi, P. Castro, A. Gössel, M. Hüning, G. Kreps, M. Liepe, M. Minty, S. Schreiber, D. Sertore, M. Wendt. |
This paper reports on recent beam measurements of higher order modes in the
TESLA Test Facility (TTF) accelerating modules. Using bunch trains of about
0.5 ms with 54 MHz bunch repetition and up to 90 % modulated intensity,
transverse higher order modes are resonantly excited when the beam is offset
and their frequency on resonance with the modulation frequency. With this
method, the trapped modes can be excited and their counteraction on the beam
observed on a wide-band BPM downstream of the module. Scanning the modulation
frequency from 0 to 27 MHz allows a systematic investigation of all possible
dangerous modes in the modules. |
