Smith, T.J.

Paper	Title	Page
TUYPA02	High Precision SC Cavity Alignment Diagnostics with HOM Measurements	920
	J.C. Frisch, L. Hendrickson, J. May, D.J. McCormick, S. Molloy, M.C. Ross, T.J. Smith SLAC, Menlo Park, California N. Baboi, O. Hensler, L.M. Petrosyan DESY, Hamburg N.E. Eddy, S. Nagaitsev Fermilab, Batavia, Illinois O. Napoly, R. Paparella, C. Simon CEA, Gif-sur-Yvette
	Experiments at the TTF at DESY have demonstrated that the Higher Order Modes induced in Superconducting Cavities can be used to provide a variety of beam and cavity diagnostics. The centers of the cavities can be determined from the beam orbit which produces minimum power in the dipole HOM modes. The phase and amplitude of the dipole modes can be used as a high resolution beam position monitor, and the phase of the monopole modes to measure the beam phase relative to the accelerator RF. Beam orbit feedback which minimizes the dipole HOM power in a set of structures has been demonstrated. For most SC accelerators, the existing HOM couplers provide the necessary signals, and the downmix and digitizing electronics are straightforward, similar to those for a conventional BPM.
	Transparencies
TUPCH105	Performance of a Nanometer Resolution BPM System	1256
	S. Walston, C.C. Chung, P. Fitsos, J.G. Gronberg LLNL, Livermore, California S.T. Boogert Royal Holloway, University of London, Surrey J.C. Frisch, J. May, D.J. McCormick, M.C. Ross, S. Smith, T.J. Smith SLAC, Menlo Park, California H. Hayano, Y. Honda, N. Terunuma, J. Urakawa KEK, Ibaraki Y.K. Kolomensky, T. Orimoto UCB, Berkeley, California A. Lyapin, S. Malton, D.J. Miller UCL, London R. Meller Cornell University, Department of Physics, Ithaca, New York M. Slater, M.T. Thomson, D.R. Ward University of Cambridge, Cambridge V.V. Vogel DESY, Hamburg G.R. White OXFORDphysics, Oxford, Oxon
	International Linear Collider (ILC) interaction region beam sizes and component position stability requirements will be as small as a few nanometers. It is important to the ILC design effort to demonstrate that these tolerances can be achieved – ideally using beam-based stability measurements. It has been estimated that RF cavity beam position monitors (BPMs) could provide position measurement resolutions of less than one nanometer and could form the basis of the desired beam-based stability measurement. We have developed a high resolution RF cavity BPM system. A triplet of these BPMs has been installed in the extraction line of the KEK Accelerator Test Facility (ATF) for testing with its ultra-low emittance beam. The three BPMs are rigidly mounted inside an alignment frame on variable-length struts which allow movement in position and angle. We have developed novel methods for extracting the position and tilt information from the BPM signals including a calibration algorithm which is immune to beam jitter. To date, we have been able to demonstrate a resolution of approximately 20 nm over a dynamic range of ± 20 microns. We report on the progress of these ongoing tests.