Wen, H.

Paper	Title	Page
THOAKI01	Advances in Large Grain/Single Crystal SC Resonators at DESY	2569
	W. Singer, A. Brinkmann, A. Ermakov, J. Iversen, G. Kreps, A. Matheisen, D. Proch, D. Reschke, X. Singer, M. Spiwek, H. Wen DESY, Hamburg P. Kneisel Jefferson Lab, Newport News, Virginia M. Pekeler ACCEL, Bergisch Gladbach
	The main aim of the DESY large grain R&D program is to check whether this option is reasonable to apply for fabrication of ca. 1'000 XFEL cavities. Two aspects are being pursued. On one hand the basic material investigation, on the other hand the material availability, fabrication and preparation procedure. Several single cell large grain cavities of TESLA shape have been fabricated and tested. The best accelerating gradients of 41 MV/m was measured on electropolished cavity. First large grain nine-cell cavities worldwide have been produced under contract of DESY with ACCEL Instruments Co. All three cavities fulfil the XFEL specification already in first RF test after only BCP (Buffered Chemical Polishing) treatment and 800 degrees C annealing. Accelerating gradient of 27 - 29 MV/m was reached. A fabrication method of single crystal cavity of ILC like shape was proposed. A single cell single crystal cavity was build at the company ACCEL. Accelerating gradient of 37.5 MV/m reached after only 112 microns BCP and in situ baking 120 degrees C for 6 hrs with the quality factor higher as 2x1010. The developed method can be extended on fabrication of multi cell single crystal cavities.
	Slides