Singer W.

Paper	Title	Page
TUP74	Progress of the Test Cavity Program for the European XFEL	327
	A. Brinkmann, J. Iversen, D. Reschke, W. Singer, X. Singer, K. Twarowski, J. Ziegler DESY Hamburg
	Two main goals of the test cavity program for the European XFEL are the qualification of alternative niobium vendors and the investigation of the capabilities of large grain niobium for large-scale nine-cell cavity production. About 25 1.3 GHz single-cell cavities of TESLA shape have been completed at Accel Instruments and DESY. Alternative vendors for high purity fine-grain niobium are ITEP Giredmet, Cabot, Ningxia and Plansee. The in-house fabricated cavities have been tested after 800C firing and final electropolishing (EP) treatment. All cavities exceed gradients of 35 MV/m at high Q-values. For the large grain cavities of high RRR Heraeus niobium gradients up to 41 MV/m have been achieved. The performance after final chemical etching (BCP) is compared to EP for several cavities.
WE301	Progress in Seamless RF Cavities
	W. Singer DESY
	In connection with the ILC activities the interest to fabrication of seamless cavities is increased. Seamless technique has potentially an advantage over the standard cavity fabrication by deep drawing and electron beam welding. Seamless technique allows avoiding the risk of performance degradation at the welding area. Last progress in development of the superconducting connection between adjacent cavities opens the way to manufacture the accelerating cavities as a rotationally symmetric cells part by seamless fabrication technology and extra an asymmetric end groups. Lower cost of fabrication especially for a large series and better statistic in RF-performance can be expected. Problems of the fabrication of seamless tubes and cavities from bulk niobium and clad NbCu are mainly solved on laboratory level. Fabrication of multi cell cavities was recently proven. First 9- cell cavities of TESLA shape are produced. For the preparation of seamless cavities the combination of the centrifugal barrel polishing CBP with electropolishing seams to be reasonable. CBP allows reaching more uniform material removal and smooth off the surface for the next treatment steps. The highest achieved accelerating gradient for bulk niobium cavities is up to now the same for both seamless and welded versions (ca. 40 MV/m). The NbCu clad cavities demonstrated an accelerating gradient up to 40 MV/m too. The still remaining draw back of NbCu cavities is the frozen-in magnetic flux, caused by introduced thermo-currents.
	Slides(PDF)
WEP17	Considerations on the third harmonic RF of the European XFEL	481
	E. Vogel, M. Dohlus, M. Huening, K. Jensch, A. Matheisen, W. -D. Moeller, A. Schmidt, W. Singer DESY Hamburg H. Edwards, E. Harms, T. Khabiboulline Fermilab
	Ultra short bunches with high peak current are required for the creation of high brilliance coherent light in the x-ray range in undulators. At the European x-ray free electron laser (XFEL) they will be obtained by a two stage bunch compression scheme based on off the rf field crest acceleration and transverse magnetic chicanes. The deviation of the rf field's sine shape from a straight line leads to long bunch tails and reduce peak current. This effect will be eliminated by adding a third harmonic rf system. The paper surveys the basic principle for the third harmonic rf, the most relevant design parameters, the actual status of beam physical examinations and potential concepts for the technical realization.