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shielding

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TUP71 Highly Sensitive Measurements of the Dark Current of Superconducting Cavities for TESLA Using a SQUID Based Cryogenic Current Comparator pick-up, electron, feedback, cryogenics 432
 
  • W. Vodel, R. Neubert, S. Nietzsche
    FSU, Jena
  • K. Knaack, M. Wendt, K. Wittenburg
    DESY, Hamburg
  • A. Peters
    GSI, Darmstadt
  This contribution presents a Cryogenic Current Comparator (CCC) as an excellent tool for detecting dark currents generated, e.g. by superconducting cavities for the upcoming TESLA project (X-FEL) at DESY. To achieve the maximum possible energy the gradient of the superconducting RF cavities should be pushed close to the physical limit of 50 MV/m. The undesired field emission of electrons (so-called dark current) of the superconducting RF cavities at strong fields may limit the maximum gradient. The absolute measurement of the dark current in correlation with the gradient will give a proper value to compare and classify the cavities. The main component of the CCC is a highly sensitive LTS-DC SQUID system which is able to measure extremely low magnetic fields, e.g. caused by the dark current. For this reason the input coil of the SQUID is connected across a special designed toroidal niobium pick-up coil for the passing electron beam. A noise limited current resolution of nearly 2 pA/√(Hz) with a measurement bandwidth of up to 70 kHz was achieved in the laboratory. Design issues of the CCC and the application in the CHECHIA cavity test stand at DESY as well as experimental results will be discussed.  
 
THP07 Performance Improvement of the Multicell Cavity Prototype for Proton LINAC Projects proton, linac, electron, target 611
 
  • B. Visentin, D. Braud, J.P. Charrier, B. Coadou, Y. Gasser, J.P. Poupeau, P. Sahuquet
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  • S. Bousson, H. Gassot, H. Saugnac, P. Szott
    IPN, Orsay
  • G. Devanz
    CEA/DAPNIA-SACM, Gif-sur-Yvette Cedex
  The CEA-Saclay/IPN-Orsay collaboration allowed to develop a multicell superconducting cavity prototype (704 MHz, β=0.65). Since the first experimental results[*], achieved in a vertical cryostat and the horizontal one "CryHoLab", the accelerating field Eacc has been recently improved up to 19 MV/m (Epeak = 43 MV/m, Bpeak = 83 mT, Q0 = 9.109). Eacc is now limited by quench. The previous one limitation, due to a non understood phenomenon, disappeared . The excellent performances of this 5-cell proton cavity validate the design, the technological choices, the manufacturing and the cavity preparation process. These results augur well for our future R&D program on multicell superconducting cavities within the European CARE/HIPPI framework.

[*] Proceedings of PAC2003, Portland, USA, TAB047, p.1303