• V. B. Asgekar
  University of Pune, Pune
• U. Lehnert, P. Michel
  FZD, Dresden

A tapered undulator experiment was carried out at the Forschungszentrum Dresden-Rossendorf (ELBE) far-infrared FEL. The main motivation was to see whether the presence of a dispersive medium due to the partially waveguided resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering (i.e. a decrease of undulator field amplitude over the beam path) proves beneficial for the output power we observe an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicates a maximum small-signal gain for zero taper while the output peak power is highest for negative taper. Whereas the saturated power output and the detuning curve characteristics agree with the known theoretical predictions, the wavelength shifts showed deviations from the expected values. Details of the experiment are presented.

• U. Lehnert, M. Helm, P. Michel, H. Schneider, W. Seidel, S. Winnerl
  FZD, Dresden
• A. Aksoy
  Ankara University, Faculty of Engineering, Tandogan, Ankara

To extend the wavelength range of possible experiments from the FIR into the THz region a dedicated beamline is planned at the ELBE Radiation Source. The beamline will deliver coherent transition radiation and coherent synchrotron radiation as broad-band (essentially single-cycle) radiation. Superradiant undulator radiation will be produced for a tunable narrow-band radiation source in the 100GHz to 3THz range. This requires a compression of the ELBE electron beam down to 150fs bunchlength. The beam transport and bunch compression scheme as well as the properties of the produced radiation are presented in detail.

• H. Bluem, V. Christina, D. Dowell, J.H. Park, J. Rathke, A.M.M. Todd, L.M. Young
  AES, Medford, NY
• L.R. Dalesio
  EPIC Consulting, Medford, New York
• D. Douglas
  Douglas Consulting, York, Virginia
• S. Gewinner, H. Junkes, G. Meijer, W. Schöllkopf, W.Q. Zhang, G. von Helden
  FHI, Berlin
• S.C. Gottschalk, R.N. Kelly
  STI, Washington
• K. Jordan
  Kevin Jordan PE, Newport News, Virginia
• U. Lehnert, P. Michel
  HZDR, Dresden
• W. Seidel, R. Wünsch
  FZD, Dresden

The Fritz Haber Institute of the Max Planck Society in Berlin, Germany will celebrate its Centennial in 2011. Coincident with this event, they will christen a THz Free Electron Laser (FEL) that will operate from 3 to 300 microns. A linac with a gridded thermionic gun is required to operate from 15 to 50 MeV at 200 pC while delivering a transverse rms emittance of 20 mm-mrad in a 1 psec rms, 50 keV rms energy spread bunch at the wigglers. Mid-IR and far-IR wigglers enable this electron beam to deliver the required radiation spectrum. In addition to the longitudinal emittance, a key design requirement is the minimization of the micropulse and macropulse jitter to ensure radiation wavelength stability and timing consistency for pump probe experiments. We present the completed physics and engineering design that delivers the required performance for this device. Shipment is scheduled for the end of the calendar year and the status of fabrication will be summarized.

• R. Xiang, A. Arnold, P. Michel, P. Murcek, J. Teichert
  HZDR, Dresden

The thermal emittance of the photocathode is an interesting physical property for the photoinjector, because it decides the minimum emittance the photoinjector can finally achieve. In this paper we will report the latest results of the thermal emittance of the Cs2Te photocathode in FZD Superconducting RF gun. The measurement is performed with solenoid scan method with very low bunch charge and relative large laser spot on cathode, in order to reduce the space charge effect as much as possible, and meanwhile to eliminate the wake fields and the effect from beam halos.

• J. Teichert, A. Arnold, H. Büttig, D. Janssen, M. Justus, U. Lehnert, P. Michel, P. Murcek, Ch. Schneider, R. Schurig, R. Xiang
  HZDR, Dresden
• T. Kamps, J. Rudolph, M. Schenk, F. Staufenbiel
  HZB, Berlin
• G. Klemz, I. Will
  MBI, Berlin

The superconducting RF photo-injector (SRF gun) at FZD is the first operating electron injector of its kind. The gun with a 3½-cell cavity and a frequency of 1.3 GHz produces an electron beam of 3 MeV with a maximum bunch charge of about 400 pC. Also the design values for the acceleration gradient could not be reached with the cavity which is in use at present the SRF gun will improve the beam quality for ELBE users. End of 2009 the beamline was installed which connects the SRF gun with the ELBE accelerator. We will report on the first test and on the progress in applying the SRF gun for user operation.