Lilje, L.

Paper	Title	Page
TUP89	Static Absolute Force Measurement for Preloaded Piezoelements Used for Active Lorentz Force Detuning System	486
	S. P. Sekalski, A. Napieralski, S. P. Sekalski TUL, Lodz A. Bosotti INFN/LASA, Segrate (MI) M. Fouaidy IPN, Orsay L. Lilje, S. Simrock DESY, Hamburg R. Paparella, P.F. Puricelli INFN Milano, Milano
	To reach high gradients in pulsed operation of superconducting (SC) cavities an active Lorentz force detuning compensation system is needed. For this system a piezoelement can be used as an actuator (other option is a magnetostrictive device). To guarantee the demanded lifetime of the active element, the proper preload force adjustment is necessary. To determine this parameter an absolute force sensor is needed which will be able to operate at cryogenic temperatures. Currently, there is no calibrated commercial available sensor, which will be able to measure the static force in such an environment. The authors propose to use a discovered phenomenon to estimate the preload force applied to the piezoelement. The principle of the proposed solution based on a shape of impedance curve, which changes with the value of applied force. Especially, the position of resonances are monitored. No need of specialized force sensor and measurement in-situ are additional advantages of proposed method.
WE102	State of the Art SRF Cavity Performance	518
	L. Lilje DESY, Hamburg
	The paper will review superconducting RF cavity performance for β=1 cavities used in both linear and circular accelerators. These superconducting cavities are used in two kinds of applications: High current storage rings and efficient high duty cycle linacs. In recent years the performance of those cavities has been improving steadily. High accelerating gradients have been achieved using advanced surface preparation techniques like electropolishing and surface cleaning methods like high pressure water rinsing. High intensity beams can be handled with advanced higher-order-mode damping schemes.
	Transparencies
THP95	Electro Polishing of Niobium Cavities at DESY	824
	A. Matheisen, L. Lilje, H. Morales, B. Petersen, M. Schmoekel, N. Steinhau-Kühl DESY, Hamburg
	At DESY a facility for electro polishing (EP) of the super conducting (s.c.) TESLA/TTF cavities have been built and is operational since summer 2003. The EP infrastructure is capable to handle single-cell structures and the standard TESLA/ TTF nine-cell cavities. Several electro polishing processes have been made since and acceleration voltage up to 40 MV/m have been reached in nine cell structures. We report on measurements and experiences gained since 2003 as well as on handling procedures developed for the preparation of electro polished resonators. Specific data like heat production, variation of current density and bath aging will be presented. Another important point for reproducible results is the quality control of the electro polishing process. First quality control steps to be implanted in the EP procedure for large-scale production will be described.