Teichert, J.

Paper	Title	Page
MOPPH016	Gain Deterioration at Particular Wavelengths in a Partially Waveguided FEL	36
	U. Lehnert, P. Michel, G. Staats, J. Teichert, R. Wuensch FZD, Dresden V. B. Asgegar University of Pune, Pune
	At ELBE certain wavelengths within the working range of the FIR-FEL have been found to be inaccessible. The FEL either completely stops lasing or shows marked drop-outs in the observed optical spectra. The reason of this behaviour is sought in the use of a partial waveguide through the undulator to the downstream mirror combined with free optical propagation to the upstream mirror. The light pulse from the upstream mirror couples into the lowest transverse mode of the waveguide with minor contributions of other modes. The light generated in the gain process, however, is distributed over some of these modes and experiences dispersion over the waveguided propagation length. At the exit of the waveguide the different modes recombine with certain phase shifts. Depending on the amount of phase shift and the mode composition of the light a gain drop or even inversion is possible if a major part of the stimulated emission is out of phase to the primary beam. This work attempts to compute the mode distribution of the stimulated light emission and to translate this into a prediction of those wavelengths where the gain is markedly reduced by destructive interference of different modes.
THAAU02	Initial Commissioning Experience with the Superconducting RF Photoinjector at ELBE	467
	J. Teichert, A. Arnold, H. Buettig, D. Janssen, M. Justus, U. Lehnert, P. Michel, P. Murcek, A. Schamlott, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang FZD, Dresden T. Kamps, J. Rudolph, M. Schenk BESSY GmbH, Berlin G. Klemz, I. Will MBI, Berlin
	A radio frequency photo injector with a superconducting acceleration cavity (SRF gun) for installation at the Radiation Source ELBE was developed within a collaboration of BESSY, DESY, FZD, and MBI. The aim of the project is to improve the electron beam quality and to extend the parameter range of the ELBE accelerator. Especially the bunch charge will be increased up to 1 nC and the transverse emittance will be reduced to 1 - 3 mm mrad. At present, the thermionic injector at ELBE delivers bunches of 77 pC at about 8 mm mrad. Furthermore, the SRF gun together with its diagnostic beam line is an excellent test bench for extended studies and improvements of this new and promising injector type. The gun cryostat, the electron diagnostic beamline, and the driver laser with optical beamline were installed in summer and fall 2007. In November the first beam was produced. It will be reported on the experience gained at the first phase of commissioning. Results of rf and beam parameter measurements with Cu and Cs2Te photo cathodes will be presented.
	Slides
FRAAU03	Investigation and Improvement of Beam Stability at the ELBE FELs	543
	P. Michel, M. Justus, U. Lehnert, P. Michel, D. Proehl, R. Schurig, W. Seidel, J. Teichert FZD, Dresden
	At the radiation source ELBE in the Forschungszentrum Dresden-Rossendorf two free electron lasers (4-20 μm and 20-230 μm) are in routine user operation for a wide range of IR experiments for some years. The lasers are driven by a superconducting RF Linac which permits the generation of a cw-beam with high average beam power. For many experiments the frequency and power stability of the laser beam is of outstanding importance. Therefore studies on fluctuations and drifts in different time scales (from μs to hours) were accomplished and possible causes for these instabilities were investigated. To improve the long and short term stability we developed and implemented active feed back controls for electron energy and thus laser wavelength and out-coupled IR-beam power at ELBE.