| Paper |
Title |
Page |
| MOPC019 |
Velocity Bunching at FLASH
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112 |
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- T. Limberg, B. Beutner, W. Decking, M. Huening, M. Krasilnikov, M. Vogt
DESY, Hamburg
- O. Grimm
Uni HH, Hamburg
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The vacuum-ultra-violet free electron laser in Hamburg (FLASH) is a linac driven SASE-FEL. High peak currents are, in routine operation, produced using magnetic bunch compression chicanes. Longitudinal dispersion in these chicanes allow bunch length changes of relativistic electron beams. For low energy electron beams (~5 MeV), the velocity dependence on electron energy can be utilized for bunch compression. Since strong bunch compression at low beam energies gives rise to strong space charge interactions which has an impact on, for instance, beam emittance and is therefore not suitable for full compression to the kA peak currents needed for SASE operation. Moderate velocity bunching, however, might be used to optimize the total bunch compression system of FLASH or the European XFEL. Experiments on the velocity bunching process at FLASH are presented here. Results on bunch length and transverse emittance measurements are discussed and compared with numerical tracking calculations.
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| TUPC030 |
Transverse Electron Beam Size Effect on the Bunch Profile Determination with Coherent Radiation Diagnostics
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1113 |
| |
- O. Grimm, H. Delsim-Hashemi, J. Rossbach
Uni HH, Hamburg
- V. Balandin, N. Golubeva
DESY, Hamburg
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Longitudinal diagnostics of electron bunches can be done by measurement of coherent radiation (e.g., in the form of transition radiation) and subsequent extraction of the form factor. By measuring short wavelengths, fine structures in the bunch can be resolved. However, the form factor depends on the three-dimensional charge density distribution, and the usual practice of considering only a one-dimensional line charge in interpreting the radiation spectra is questionable, as the finite transverse extend of the electron bunch can reduce the form factor magnitude at short wavelengths. An experimental study of this issue using a two stage single shot spectrometer has been carried out at the FLASH free-electron laser at DESY, Hamburg. The coherent transition radiation spectra for two beam optics settings were recorded and compared. In one setting the transverse beam size at the transition radiation target screen has been blown up by a factor of about 3.5 compared to the second setting. The ratio of these two spectra shows a suppression of radiation intensity at short wavelengths, as expected from a theoretical calculation. In this paper the result of this study is presented.
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| TUPC031 |
Longitudinal Beam Diagnostics Application of Synchrotron Radiation at FLASH
|
1116 |
| |
- O. Grimm, J. Rossbach
Uni HH, Hamburg
- C. Behrens, B. Schmidt
DESY, Hamburg
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For the operation of the FLASH free electron laser at DESY, Hamburg, tools to measure the longitudinal charge distribution and especially its stability over time are important for efficient machine running. Several techniques using both coherent far-infrared and incoherent visible synchrotron radiation from the two bunch compressor chicanes are summarized and compared in this paper. The experimental setups used are - a Martin-Puplett interferometer with both a room-temperature pyroelectric and a liquid-Helium cooled bolometer as detector,
- a streak camera to directly measure the time profile,
- the analysis of intensity fluctuations of the optical synchrotron radiation measured (with a photomultiplier) through a narrow filter,
- a single shot grating spectrometer covering the spectral range from 5 μm to 150 μm.
Data from the various and complementary experimental methods will be presented and compared.
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| TUPC110 |
Bunch Diagnostics with Coherent Infrared Undulator Radiation at FLASH
|
1320 |
| |
- A. Willner, H. Delsim-Hashemi, O. Grimm, J. Rossbach
Uni HH, Hamburg
- B. Schmidt
DESY, Hamburg
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The operation of the FLASH free electron laser at DESY, Hamburg, requires a high electron beam quality, one important parameter being the longitudinal charge distribution. As a new tool for investigations using coherent radiation techniques, FLASH has been equipped with an electromagnetic undulator. The device is tunable up to a maximum K-Value of 44, corresponding to 200 um wavelength at an electron energy of 500 MeV. The emitted radiation has been characterized in a first measurement campaign using a dispersive spectrometer based on reflective blazed gratings and a pyroelectric detector, operated in a Nitrogen-purged atmosphere. This paper will summarize the measurements and the results obtained from a longitudinal diagnostics analysis.
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