| Paper | Title | Page |
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| MOPKF012 | A 7T Multipole Wiggler in BESSY II: Implementation and Commissioning Results | 324 |
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| To generate hard X-ray beams for residual stress analysis and for magnetic scattering with the BESSY II SR source, a 7T wiggler with 17 poles has been implemented. Several problems had to be solved. Wake fields induced by smaller steps in the geometry of the radiation shield inside the beam chamber led to intolerable LHe consumption, which have been analysed numerically and then cured by improving the shield geometry. Much of the routine operation procedures are influenced by the unusually high radiation power level of max. 55 kW. For system protection an interlock system dumps the electron beam automatically in case of relevant error events. This wiggler is by far the strongest perturbation of the linear beam optics, breaking seriously the symmetry of the ring. Beam optical parameters including tune shift and beta beat have been measured to quantify these perturbations and develop efficient cures to limit the negative effects on beam lifetime and dynamic aperture. So far the wiggler is operated at 2.8 T and max. currents up to 250 mA in normal user shifts. | ||
| WEPKF026 | Kicker Pulser with High Stability for the BESSY FEL | 1654 |
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| In the BESSY FEL design a kicker system is forseen to extract electron bunches from the main LINAC into two FEL beam lines, beside the straigth main beamline. Sine half wave pulsers with a repetion rate of up to 1 kHz and modest pulse currents of 120A will be used. To receive the maximum FEL gain, it is crucial, that the extracted bunches enter well centered into the undulators. Hence, the extraction demands for very high short-term stability of the magnetic field (shot to shot). A kicker pulse amplitude with a relative amplitude jitter smaller than 5* 10-5 would be tolerable ?more than one order smaller than the jitter of conventional BESSY II kicker systems in use. A new highly stable semiconductor based kicker pulser prototype was designed, built and tested at BESSY. It was shown that the stability of the pulse current fulfills the FEL requirements. The pulser design, its layout and the corresponding pulse current jitter measurements are presented. | ||
| WEPLT051 | Sub-Picosecond Electron Bunches in the BESSY Storage Ring | 1951 |
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BESSY is a low emittance, 1.7 Gev electron storage ring. A dedicated, low alpha optics is applied to produce short electron bunches for coherent synchrotron radiation (CSR) in the THz range[*]. By a further detuning of the optics, stable pulses as short as 0.7 ps rms length were produced. The sub-ps pulse shape is analysed by an auto-correlation method of the emitted CSR. The CSR-bursting instability is measured and compared with theory to estimate the current for stable, sub-ps pulses. Present limits of the low alpha optics are discussed.
* M. Abo-Bakr et al., Phys. Rev. Lett. 88, 254801 (2002). |
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| THPKF015 | Compressed Electron Bunches for THz-Generation - Operating BESSY II in a Dedicated Low Alpha Mode | 2287 |
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For the first time an electron storage ring was operated during regular user shifts in a dedicated 'low alpha' mode, where electron bunches are compressed to 5 times shorter length for THz [*] and short X-ray pulses experiments. The 1 mm rms-long bunches emit powerfull, coherent THz waves, up to 107 times stronger than incoherent radiation. We report on machine set up and operating experience.
* M. Abo-Bakr et al., Phys. Rev. Lett. 88, 254801 (2002) |