OPTIMISATION OF BEAM INJECTION INTO THE FIRST ACCELERATING MODULE AT TTF2 WITH CAVITY DIPOLE MODE SIGNALS N. Baboi, H. Schlarb, M. Wendt, G. Kreps, DESY, Hamburg; O. Napoly, R.G. Paparella, CEA/Saclay, DSM/DAPNIA, Gif-sur-Yvette; M. Ross, J. Frisch, T. Smith, D. McCormick, SLAC, Menlo Park, CA OPTIMISATION OF BEAM INJECTION INTO THE FIRST ACCELERATING MODULE AT TTF2 WITH CAVITY DIPOLE MODE SIGNALS N. Baboi, H. Schlarb, M. Wendt, G. Kreps, DESY, Hamburg; O. Napoly, R.G. Paparella, CEA/Saclay, DSM/DAPNIA, Gif-sur-Yvette; M. Ross, J. Frisch, T. Smith, D. McCormick, SLAC, Menlo Park, CA DIPAC 2005, Lyon, France, June 6-8, 2005 POM019 The TESLA TEST FACILITY at DESY BEAM ALIGNMENT IN THE FIRST CAVITY OF THE MODULE ACC1 HOM - ELECTRONICS Dipole passband Mode # Frequency (simulation) [MHz] R/Q [MW/m 2 ] 1 (TE-like) (TM-like) The interaction of the beam with the higher order modes (HOM) in the TESLA cavities has been studied in the past at the TESLA Test Facility (TTF) in order to determine whether the dipole modes with the highest loss factor are sufficiently damped. The same modes can be used actively for beam alignment. Table: Dipole modes with highest R/Q used for beam monitoring Dipole mode: a. spectrum and b. time domain signal for various beam positions a b Previously it has been shown that by moving the beam with a single horizontal and one vertical magnetic-steerer, the beam can be send through the center of single cavities. Here we have two pairs of steerers for full freedom of beam movement. We moved the beam such that the angle of the beam in the middle of a given cavity is kept constant. This way one can find the center of the cavity where the dipole mode amplitude (measured at HOM couplers) is minimum. Then by moving the beam such that the position of the beam stays constant, one can find the axis of the cavity. Install HOM-electronics at all couplers (single mode, 1.73 GHz) Study beam alignment with multi-cavity signals Measure cavity misalignment in the module Study polarization of modes FUTURE PLANS Find center of cavity: - move beam such that the beam angle is kept constant in middle of the cavity - make alternative x an y scans; for each scan keep as reference the result of previous scan Find axis of cavity: - move beam such that the position is kept fixed in the middle of the cavity - make alternative x and y scans Alignment on axis of cavity 1 should be close to alignment in whole module Schematic view of the HOM-based alignment setup rf gun2 steerer pairsaccelerating module - ACC1 4.5MeV 12…19 MV/m from HOM-couplers Spectrum Analyzer Multiplexer Steering Has been measured short after the HOM beam alignment. Lowest steering has been found at this position for the x plane, but further away in the y plane. This could be explained by high misalignment and tilt in vertical plane of cavity 1 with respect to the module axis. A better beam alignment should be based on information from several cavities: - center beam in cavity 1 and 8, or - minimize overall wakefield in the module Note: the module is steering the beam through: 1. wakefields, 2. coupler kicks, and 3. focusing of accelerating field module ACC4 Down-converts the dipole bands. Provides phase as well, it’s faster, more modes and cavities can be measured in parallel. Can give beam offset and angle. Calibrate signals by help of beam steerers. Then can provide on-line information about beam position and angle in all cavities. Resolution for single cavity, single mode measurement approximately 5  m RMS. Theoretical resolution is sub- micron.