| Paper | Title | Page |
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| TUPPH056 | The Impact of the Space Charge on the STARS Performance | 374 |
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| BESSY is proposing a two-stage high-gain harmonic generation (HGHG) FEL, STARS, to demonstrate and investigate the cascading proposed for the BESSY Soft X-ray FEL. STARS will have a target wavelength range from 70 nm to 40 nm with peak powers up to a few hundred MWs and pulse lengths less than 20 fs (rms). In an HGHG stage an energy modulation is imprinted to the electron beam by a seeding radiation. A dispersive section converts this energy modulation to a spatial modulation which is optimized for a particular harmonic. The subsequent radiator is optimized for this harmonics and generates radiation with high power which is used as seeding radiation for the next stage. During the passage through the Dispersive section, subsequent drifts and the radiator, space charge effects can reduce the generated bunching and degrade the FEL Performance. We present simulation studies for the impact of the space charge forces in the undulator section on STARS performance. | ||
| TUPPH058 | Developments in Cascaded HGHG-FELs | 378 |
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Seeding in combination with frequency up conversion is widely recognized as a method to provide FEL radiation with properties superior to the SASE output. In addition to High Gain Harmonic Generation (HGHG) scheme, successfully demonstrated in Brookhaven* and proposed for the BESSY soft X-ray FEL, several alternative schemes have been proposed during the last years. This paper discusses and compares these proposals to the original cascading of HGHG-stages which includes the fresh bunch technique.
* L. H. Yu, Phys. Rev. Letters, 91, 074801, 2003 |
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| TUPPH072 | sFLASH: An Experiment for Seeding VUV Radiation at FLASH | 405 |
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| The paper describes an FEL seeding experiment at VUV wavelengths,to be installed at the existing SASE FEL user facility FLASH. Beyond a proof-of-principle demonstration in the VUV, the emphasis will be on high stability in terms of intensity and timing thus providing a future alternative operation mode of FLASH for users. The seed laser generates high harmonics (HHG) by focusing a near-infrared laser into a noble gas jet. The efficient transport of the short wavelength (30nm) radiation and the spatial and temporal overlap with the electron beam are among the challenging tasks. The interaction of the seed laser and the electron beam takes place in a new undulator section to be installed in front of the existing FLASH undulator. Four hybrid variable-gap undulators are foreseen with a total length of 10 meters. In the space between undulator sections there are diagnostics devices for both the electron beam and the seed laser. After the undulators there is a weak magnetic chicane as a separator of the electron beam and the seeded FEL radiation. Finally a VUV beamline transports the radiation to an experimental hutch where the temporal characterization of the amplified pulses takes place. | ||
| THBAU04 | Results from the Optical Replica Experiments at FLASH | 497 |
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| We present experimental results from the optical replica synthesizer,a novel device to diagnose sub-ps electron bunches by creating a coherent optical pulse in the infrared that has the envelope of the electron bunch and analyzing the latter by frequency resolved optical gating methods. Such a device was recently installed in FLASH at DESY. During an experiment period the spatial and temporal overlap of a several ps long electron bunch and a 200 fs laser pulse were achieved within an undulator. Coherent transition radiation due to the induced micro-bunching was observed on a silver-coated silicon screen and varying the timing between electrons and laser pulse produced two-dimensional images of the slices as a function of the longitudinal position within the electron bunch. In a second experiment the strongly compressed electron bunch is modulated by the laser pulse and replica pulses that are emitted from a second undulator are observed and diagnosed by frequency resolved optical gating methods. | ||
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