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Title |
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| MOPPH008 |
A Beam Shaper for the Optical Beamline of RF Photoinjectors
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53 |
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- G. Klemz
MBI, Berlin
- I. Will
FZR, Dresden
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The transversal beam profile of a laser beam irradiating the photocathode has a significant influence on the emittance of the generated electron beam. Achieving the lowest emittance requires a flat-top beam profile. A typical laser, however, produces an intensity profile which is close to a Gaussian. That is why a special optical element, the so-called beam shaper, is required. We compare different technical solutions for the critical beam-shaping element. The demands on the design of the beamline resulting from the insertion of the beam shaper will be outlined. An aspherical lens pair of the Galilean type seems to be a favourable solution. It permits to precisely control the final intensity profile, it maintains both the temporal shape of the pulse and the coherence of the laser beam. Simulation of the propagation of the beam profile are presented. The described refractive beam-shaper significantly improves the energy efficiency of the complete beamline. It therefore allows to reduce the requirements regarding the energy of the laser pulses. Consequently, the application of an appropriately designed beam shaper can lead to a significant reduction of the overall costs of the laser.
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| THPPH006 |
Photocathode Laser for the Superconducting Photo Injector at the Forschungszentrum Rossendorf
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564 |
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- I. Will, G. Klemz
MBI, Berlin
- F. Staufenbiel, J. Teichert
FZR, Dresden
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We report on the design of the photocathode laser for a superconducting RF gun under development at the Forschungszentrum Rossendorf. The laser consists of a short-pulse oscillator, a pulse-picking Pockels cell, a linear amplifier chain and a frequency conversion stage. It generates pulses of about 5 ps duration with 13 MHz repetition rate and 1 W average power at 263 nm wavelength. Both the oscillator and the amplifiers are pumped by fiber-coupled semiconductor diodes. Nd:YLF is used as the gain medium of this laser. It introduces only small distortions on the optical wavefront of the laser beam and supports pulses of a few picoseconds duration. The beamline which transfers the laser beam to the photocathode of the RF gun has a large impact on the final beam profile. One can optimize the emittance of the electron beam by illuminating the cathode with a nearly flat-top beam profile. This is achieved by a pair of aspheric lenses and appropriate imaging optics in the beamline. Simulation of the beamline and its effect on the laser profile at the photocathode of the RF gun are also presented.
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| THPPH017 |
Experience with the Photoinjector Laser at FLASH
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590 |
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- S. Schreiber, M. Görler, K. Klose, M. Staack
DESY, Hamburg
- L. Fröhlich
Uni HH, Hamburg
- I. H. Templin, I. Will
MBI, Berlin
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The photoinjector laser system of FLASH is a key element for the generation of high quality electron beams required for a stable and reliable operation of the facility. FLASH is the VUV and soft X-ray FEL user facilitry at DESY. FLASH is based on superconducting accelerating structures allowing to accelerate electron bunch trains of a length of up to 800 us with a repetition rate of 10 Hz. Based on the standard 1 MHz pattern, the laser provides to some extend a flexible bunch train structure. We report on operational issues and on the performance of the laser system with emphasis on its transverse and longitudinal properties, energy and timing stability.
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| THPPH007 |
First RF-Measurements at the 3.5-Cell SRF-Photo-Gun Cavity in Rossendorf
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567 |
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- A. Arnold, H. Buettig, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, J. Teichert, R. Xiang
FZR, Dresden
- T. Kamps, D. Lipka, F. Marhauser
BESSY GmbH, Berlin
- G. Klemz
DESY Zeuthen, Zeuthen
- W.-D. Lehmann
IfE, Dresden
- A. Matheisen, B. van der Horst
DESY, Hamburg
- J. Stephan
IKST, Drsden
- V. Volkov
BINP SB RAS, Novosibirsk
- I. Will
MBI, Berlin
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At the Forschungszentrum Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF-Photo-Gun) is nearly finished. One of the main attention was focussed at the treatment of the cavity. Their RF properties were measured at room temperature. The warm tuning was carried out considering pre-stressing and tuning range of both tuners (half cell and full cells). The adjusted field profiles and pass band frequencies of the four fundamental modes met the requirements. An external Q study of the main coupler yielded to an optimal antenna length and showed very good agreement between simulation and measurement. Furthermore the characteristics of the choke filter and both HOM filters were simulated, measured and tuned at the pi-mode frequency. The preparation (etching and rinsing) and the cold test were successfully done at DESY. The poster presents the setup for the measurements as well as a comparison of the simulated and measured results. Submitted as poster to the 2006 FEL conference
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| THPPH009 |
Cryomodule and Tuning System of the Superconducting RF Photo-Injector
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575 |
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- J. Teichert, A. Arnold, H. Buettig, R. Hempel, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang
FZR, Dresden
- T. Kamps, D. Lipka
BESSY GmbH, Berlin
- G. Klemz
DESY Zeuthen, Zeuthen
- W.-D. Lehmann
IfE, Dresden
- J. Stephan
IKST, Drsden
- I. Will
MBI, Berlin
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We present the designs and report on the progress in construction and testing of the cryomodule and the tuning system for the SRF gun. The SRF gun project, a collaboration of BESSY, DESY, MBI and FZR, aims at the installation of a high average current CW photo injector at the ELBE linac with a Nb cavity. The cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid N cooled thermal shield, and a He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10 kW power coupler is adopted from ELBE module. A cooling and support system for the NC photo cathode has been developed and tested. It allows the adjustment of the cathode with respect to the cavity from outside. The cryomodule will be connected with the 220 W He refrigerator of ELBE and will operate at 1.8 to 2 K. The static thermal loss is expected to be less than 20 W. Two tuners will be installed for separate tuning of the three TESLA cells and the half-cell. The tuners are dual spindle-lever systems with step motors and low-vibration gears outside the cryostat. Functionality, tuning range and accuracy have been tested in cryogenic environment.
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