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Buechner, A.

Paper Title Page
MOPCH161 Development of a Prototype Superconducting CW Cavity and Cryomodule for Energy Recovery 436
 
  • P.A. McIntosh, C.D. Beard, D.M. Dykes, B. Todd
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • S.A. Belomestnykh
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • A. Buechner, P. Michel, J. Teichert
    FZR, Dresden
  • J.M. Byrd, J.N. Corlett, D. Li
    LBNL, Berkeley, California
  • T. Kimura, T.I. Smith
    Stanford University, Stanford, Califormia
  • M. Liepe, V. Medjidzade, H. Padamsee, J. Sears, V.D. Shemelin
    Cornell University, Ithaca, New York
  • D. Proch
    DESY, Hamburg
 
  Energy Recovery LINAC (ERL) and LINAC-driven FEL proposals and developments are now widespread around the world. Superconducting RF (SRF) cavity advances made over the last 10 years for TESLA/TTF at 1.3 GHz, in reliably achieving accelerating gradients >20 MV/m, suggest their suitability for these ERL and FEL accelerators. Typically however, photon fluxes are maximised from the associated insertion devices when the electron bunch repetition rate is as high as possible, making CW-mode operation at high average current a fundamental requirement for these light sources. Challenges arise in controlling the substantial HOM power and in minimizing the power dissipated at cryogenic temperatures during acceleration and energy recovery, requiring novel techniques to be employed. This paper details a collaborative development for an advanced high-Qo cavity and cryomodule system, based on a modified TESLA cavity, housed in a Stanford/Rossendorf cryomodule. The cavity incorporates a Cornell developed resistive-wall HOM damping scheme, capable of providing the improved level of HOM damping and reduced thermal load required.  
MOPCH151 Pulsed RF System for the ELBE Superconducting Accelerator 411
 
  • A. Buechner, F.G. Gabriel
    FZR/FWFE, Dresden
  • H. Buettig, U. Lehnert, P. Michel, Ch. Schneider, R. Schurig
    FZR, Dresden
 
  The RF system for the ELBE accelerator was originally designed for CW mode. Although this works problem-free tests have shown that it is possible to reach higher gradients in the TESLA cavities with a pulsed RF system. The new RF system will be presented together with measurements of the achievable gradients. Roughly 30% higher gradients could now be used in pulsed mode. As positive side effects the radiation by field emission is reduced by the duty cycle and an easy in situ RF conditioning of cavities and coupler windows is possible.  
MOPCH152 A Pulsed-RF High-power Processing Effect of Superconducting Niobium Cavities observed at the ELBE Linear Accelerator 413
 
  • U. Lehnert, H. Buettig, P. Michel, Ch. Schneider, R. Schurig
    FZR, Dresden
  • A. Buechner, F.G. Gabriel
    FZR/FWFE, Dresden
 
  The driver LINAC of the ELBE radiation source is built for cw operation. However, in some cases a pulsed-mode operation was desired to extend the otherwise stringent gradient limits. The main restriction results from field emission that decreases the Q of the cavities which was evaluated from measurements of the liquid helium consumption. After pulsed-mode operation with gradients exceeding the maximum cw accelerating gradients by 30–40\% a significant reduction in the field emission was observed. This in turn allows higher accelerating gradients to be used in cw as well. We attribute this behaviour to an rf-processing of the cavity surface which burns off field emitters.