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| TUBAU05 | Technical Aspects of the Integration of the Optical Replica Synthesizer for the Diagnostics of Ultra-short Bunches into FLASH at DESY | 296 |
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Recently, Saldin et al.* introduced a novel scheme to characterise ultra-short electron bunches in a FEL. The method is based on producing an 'optical copy' of the electron bunch, which can then be easily analysed using well-known non-linear optical techniques. To this end, a near-IR laser beam is overlapped with the electron beam in the first undulator of an optical klystron. In the following dispersive section the laser-induced energy modulation is transformed into a density modulation . The modulated electron bunch then produces a strong optical pulse in the second undulator. Analysis of this near-IR pulse (the optical copy) then provides information about the length, the slice emittance and the slice energy spread of the original electron bunch. We discuss the implementation of such a measurement set-up at the VUV-FEL at DESY and investigate the influence of various parameters on the performance of the device. Topics we address include the electron beam optics of the undulators, quadrupoles and the dispersive chicane, as well as the requirements for the seed laser pulses. The detection and analysis of the near-IR pulse and an extension to the XUV-FEL are also covered.
* E. Saldin, et al. "A simple method for the determination of the structure of ultrashort relativistic electron bunches," Nucl. Inst. and Methods A 539 (2005) 499. |
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| TUBAU06 | Investigations of the Longitudinal Electron Bunch Structure at the FLASH Linac with a Transverse Deflecting RF-Structure | 300 |
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| At the FLASH linac at DESY, electron bunches with high peak currents are produced by bunch shortening in two magnetic chicanes induced by a nearly linear energy-time gradient. Thereby the high current region of a compressed bunch is distorted by coherent synchrotron radiation and space charge forces. Consequences of these effects are a degradation of time-sliced transverse emittance, slice centroid shifts and characteristic energy-time correlations. In this paper we present measurements of the aforementioned quantities for different compression schemes with a transverse deflecting rf-waveguide (LOLA). The structure allows to establish the longitudinal density profile of single bunches on the vertical axis of an OTR-screen. The horizontal time-sliced emittance can be reconstructed from measurements of the slice widths for different quadrupole settings. By dispersing vertically streaked bunches horizontally with a dipole, the energy-time correlation can be directly obtained in a single shot measurement. The measurement results are compared to simulations. | ||
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| TUPPH054 | Beam Pickup Designs Suited for an Optical Sampling Technique | 451 |
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| A beam position monitor with a large horizontal aperture is being developed for use in dispersive regions of magnetic chicanes as part of an energy measurement. It will have a horizontal detection range of 10 cm or more and a resolution of better than 30 um. This is achievable with a stripline design, mounted perpendicularly to the electron beam direction. A high-precision phase measurement at both ends of the stripline will allow for determination of the beam postion. The phase measurement of the short RF pulses from the stripline will be done with a technique that utilizes a timing laser that samples the RF pulse traveling though an electro-optical modulator. | ||
| THPPH016 | First Experience with the Machine Protections System of FLASH | 587 |
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| Superconducting LINACs provide high brightness beams with substantial beam power. The design of the TTF2 machine is 70 kW beam power at the dump, XFEL will run 2 dump systems with 600 kW each. From this numbers is becomes very clear, that protections systems are required. This paper will present the design and implementation of the machine protection system of the FLASH facility, and will report on the first operational experience. | ||
| THPPH018 | Single-Shot Longitudinal Diagnostics with THz Radiation at the Free-Electron Laser FLASH | 594 |
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| The longitudinal charge distribution in the electron bunches has a strong impact on the lasing process in a SASE-type FEL. The investigation of the longitudinal charge distribution in the electron bunches with very high resolution and on a bunch-by-bunch basis is enabled by a novel spectrometer which is based on diffraction gratings and multichannel signal detection. Measurements of coherent transition radiation with this spectrometer in both the scanning mode and the single-shot mode are presented. Structures in the electron bunches as short as 10 fs have been observed. Correlations between the measured FEL pulse energies and the signals in different wavelength channels of the single-shot spectrometer have been established. These data will be utilized to fine-tune the parameters of the bunch compression system at FLASH in order to optimize the gain in the SASE process. |