Technology Challenges for SRF Guns as ERL Sources in View of Rossendorf work


Technology Challenges for SRF Guns as ERL Sources in View of Rossendorf work

Janssen, D.; Büttig, H.; Evtushenko, P.; Lehnert, U.; Michel, P.; Möller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Xiang, R.; Stephan, J.; Lehmann, W.-D.; Kamps, T.; Lipka, D.; Volkov, V.; Will, I.

After discussing the demands on ERL injectors for different projects, we will discuss the technological challenges and the obtained solutions for different parts of the SRF gun. The first point is the shape of the gun cavity and the tuning system. An essential parameter is the length of the first cell, which is determined by the condition, that the field strength at the cathode has a maximal value at the moment of electron emission. If the cavity consists of different cells, as the 3 ½ cell cavity of the Rossendorf gun, two independent tuning systems are necessary. An essential point is the installation of a normal conducting cathode inside a superconducting cavity. The cathode must be isolated by a vacuum gap, it must be alignable and exchangeable from outside of the cryostat and on has to cool down it to LN2 temperature. The next point of discussion is the RF choke filter, which prevents the leakage of RF power, caused by the coaxial between the cathode and the cavity. Different solutions will be shown. In order to focus the beam and to avoid the increasing of transverse emittance a static magnetic field is applied immediately after the cathode in normal conducting RF guns. For a superconducting cavity three possibilities exist to reach the same effect: The first is to put a solenoid after the cavity and outside the cryostat. The second one is the so called RF focussing, where near the cathode a radial component of the RF field is created, which focus the beam. The most elegant way is to put an additional magnetic RF mode into the cavity. It is shown, that for emittance compensation the phase of this mode is not relevant and the amplitude is inside the limit, given by the maximal surface field strength. Especially for high current guns the input of RF power could be a problem. We will show the limits of the RF coupler in the current Rossendorf project and discuss the idea of a coaxial input of RF power from the cathode side of the gun, where the coaxial between the cathode and the cavity is the main part of the RF input coupler. In the last point we discuss the experimental results obtained in Rossendorf and present the status of the current project.

  • Nuclear Instruments and Methods in Physics Research A 557(2006), 80-86
    DOI: 10.1016/j.nima.2005.10.120
    ISSN: 0168-9002
    Cited 5 times in Scopus
  • Invited lecture (Conferences)
    32nd Advanced ICFA Beam Dynamics Workshop on Energy Recovering Linacs ERL 2005, 19.-23.03.2005, Newport News, USA

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