Institut de recherche sur les lois fondamentales de l'Univers

Each nine cell superconducting (SC) accelerator cavity in the TESLA Test Facility (TTF) at DESY has two higher order mode (HOM) couplers that efficiently remove the HOM power. They can also provide useful diagnostic signals. The most interesting modes are in the first 2 cavity dipole passbands. They are easy to identify
and their amplitude depends linearly on the beam offset from the cavity axis making them excellent beam position monitors (BPM). By steering the beam through an eightcavity
cryomodule, we can use the HOM signals to
estimate internal residual alignment errors and minimize wakefield related beam emittance growth. We built and tested a time-domain based waveform recorder system that captures information from each mode in these two bands on each beam pulse. In this paper we present a preliminary experimental study of the single-bunch generated HOM signals at the TTF linac including estimates of cavity alignment precision and HOM BPM resolution.