• P. Michel, P. Evtushenko, U. Lehnert, Ch. Schneider, R. Schurig, W. Seidel, J. Teichert, D. Wohlfarth
  FZR, Dresden

A FEL in the mid infrared range is one of the applications of the ELBE cw-electron accelerator. The successful operation of the lasing process for the different wavelength is mainly determined by the alignment of the optical cavities, the bunch length and the energy spread of the electron beam so as the transversal adjustment of the beam through the FEL. The energy spread and the bunch length of the electron beam have their minima at different phase conditions of the accelerator. For various energy settings of the accelerator a special adjustment of both parameters has to be found for the lasing process. The presentation describes the diagnostic tools used at ELBE for the correct alignment of the optical cavity, the steering of the electron beam through the FEL and the adjustment of the electron beam parameters with respect to energy spread and bunch length.

• U. Lehnert, P. Michel, W. Seidel, D. Stehr, J. Teichert, D. Wohlfarth, R. Wuensch
  FZR, Dresden

First lasing of the mid-infrared free-electron laser at ELBE was achieved on May 7, 2004. Since then stable lasing has been achieved in the IR range from 4 to 22~μm using electron beam energies from 15 to 35~MeV. At all wavelengths below 20~μm a cw optical power higher than 1~W can be produced with an electron beam of 50~pC bunch charge or less. The optical pulse width at its minimum (2.2~ps measured at 17~μm) resembles the typical electron bunch length of 2~ps without bunch compression but can be increased by detuning the optical cavity. The optical bandwidth was in all cases close to the fourier limit.

• W. Seidel, E. Grosse, U. Lehnert, P. Michel, R. Schlenk, U. Willkommen, D. Wohlfarth, R. Wuensch
  FZR, Dresden
• A. Wolf
  MPI-K, Heidelberg

After successfully commissioning the mid-infrared FEL (U27) and adjoining a second accelerator unit (up to 35 MeV) at ELBE we have modified our plan how to produce radiation in the far infrared.To ensure the continuous variation of the wavelength up to 150 microns we want to complement the U27 undulator by a permanent magnet undulator with a period of 100 mm (U100). The minimum gap of 24 mm and the hybrid construction consisting of Sm/Co magnets and soft iron poles ensures sufficient radiation resistance and allows rms undulator parameters up to 2.7. The large field variation allows us to cover the whole wavelength range by only two different electron energies (e.g. 20 and 35 MeV). To reduce the transverse beam size we use a partial waveguide which is 10 mm high and wide enough to allow free propagation in horizontal direction. It spans from the last quadrupole in front of the undulator up to the downstream mirror and is somewhat longer than 8 m. To minimize the coupling losses between free propagation and the waveguide mode appropriate bifocal resonator mirrors will be used. Detailed calculations and computer simulations predict an outcoupled laser power of roughly 35 W around 40 microns and 20 W at 150 microns.

• T.  Kamps, V. Duerr, K. Goldammer, D. Kraemer, P. Kuske, J. Kuszynski, D. Lipka, F. Marhauser, T. Quast, R. Richter
  BESSY GmbH, Berlin
• P. Evtushenko
  Jefferson Lab, Newport News, Virginia
• U. Lehnert, P. Michel, J. Teichert
  FZR, Dresden
• I. Will
  MBI, Berlin

Funding: Funded by the Bundesministerium für Bildung und Forschung, the State of Berlin and the Zukunftsfonds Berlin

A superconducting rf photo electron injector (SRF gun) is currently under construction by a collaboration between BESSY, DESY, FZR and MBI. The project aims at the design and setup of an CW SRF gun including a diagnostics beamline for the ELBE FEL and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development serving a multitude of operation settings ranging from low-charge (77pC), low-emittance (1 pi mm mrad) mode to high-charge (2.5nC) operation of the gun. For these operation modes beam dynamics simulations are resulting in boundary conditions for the beam instrumentation. Proven and mature technology is projected wherever possible, for example for current and beam position monitoring. The layout of the beam profile and emittance measurement systems is described. For the bunch length, which varies between 5 and 50 ps, two schemes using Electro-optical sampling and Cherenkov radiation are detailed. The beam energy and energy spread is measured with an especially designed 180 degree spectrometer.

• J. Teichert, A. Arnold, H. Buettig, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang
  FZR, Dresden
• T.  Kamps, D. Lipka, F. Marhauser
  BESSY GmbH, Berlin
• W.-D. Lehmann
  IfE, Dresden
• J. Stephan
  IKST, Drsden
• V. Volkov
  BINP SB RAS, Novosibirsk
• I. Will
  MBI, Berlin

A superconducting rf photo electron injector (SRF gun) is under development at the Forschungszentrum Rossendorf. The project aims at several issues: improvement of the beam quality for the ELBE superconducting electron linac, demonstration of feasibility of this gun type, investigation of critical components, and parameter studies for future application (BESSY-FEL, 4GLS). In 2005, a substantial progress has been made. The two 3.5-cell niobium cavities for the gun have been delivered from the company ACCEL. The main parts for gun cryostat like vacuum vessel, cryogenic and magnetic shields are ready. Test benches for the cathode cooling system and the cavity tuner are being assembled. The photo cathode preparation lab has been arranged, and the diagnostic beam line has been designed (see T. Kamps et al., this conference). After delivering the gun cavities, their rf properties are being measured at room temperature and the warm tuning is being carried out. The set-up for this treatment and measurement as well as the results will be presented.