• F. Müller, P. Peier, V. Schlott
  PSI, Villigen
• B. Steffen
  DESY, Hamburg

Electro Optical (EO) sampling is a promising non-destructive method for measuring ultra short (sub picosecond) electron bunches. A prototype of a compact EO bunch length monitor system for the future SwissFEL facility was designed and built at PSI. Its core components are an optical setup including the electro optically active crystal and an Ytterbium fiber laser system which emits broadband pulses at 1050nm. The new monitoring system is described in detail and first experimental results from the SLS injector are presented.

• B. Steffen
  DESY, Hamburg
• F. Müller, P. Peier, V. Schlott
  PSI, Villigen

Electro Optical (EO) sampling is a promising non-destructive method for measuring ultra short (sub-ps) electron bunches. The FEMTO slicing experiment at the Swiss Light Source modulates about 3 pC of the 5 nC electron bunch longitudinally. The coherent synchrotron radiation (CSR) emitted by this substructure was measured in a single shot EO technique in gallium phosphide (GaP) using pulses from an Yb fiber laser. The arrival time jitter and the broadening of this ps long structure over several turns of the synchrotron could be measured with sub-ps resolution.

• B. Keil, A. Citterio, M.M. Dehler, R. Ditter, V. Schlott, L. Schulz, D.M. Treyer
  PSI, Villigen

This paper introduces the architecture and first beam commissioning results of the standard BPM system for the SwissFEL test injector, a 250MeV linac that is progressively being commissioned in order to perform R&D for the "SwissFEL" 5.8GeV hard-X-ray FEL facility proposed at PSI. Since the SwissFEL has a nominal bunch charge range of 10-200pC, the test injector is equipped with 500MHz resonant stripline BPMs that are optimized for high dynamic range and sensitivity, to support machine operation well below 10pC. Beam tests with a 5 GSa/s direct sampling electronics designed at PSI showed a single-bunch resolution of <20um RMS at 2pC and typically 7um RMS for charges >10pC. The BPMs also measure bunch charge, insensitively to dark current, with <30fC RMS resolution at 2pC.

• G.L. Orlandi, R. Ischebeck, V. Schlott
  PSI, Villigen
• B. Steffen
  DESY, Hamburg

The spectral and angular distribution of the radiation intensity by a single and individually radiating electron is in principle different from what expected from a high density electron beam. For a given wavelength, the beam particle density modifies via a charge form factor the angular and spectral distributions characterizing the radiation emission by a single electron. In particular, under high energy and high particle density conditions, the Transition Radiation (TR) energy spectrum by an electron beam is expected to be affected by the electron-transverse-density that, at very short wavelength – even in the visible, in principle - can influence the number of photons emitted at a given wavelength and their angular distribution (brightness increase with density). The investigation of such a phenomenon is relevant to beam diagnostics and to understand the bunch collective effects influencing TR emission. The status of the experimental investigation of the beam-transverse-size effects in the Optical Transition Radiation (OTR) at SLS and, in perspective, at the SwissFEL will be presented and the main formal aspects of the model predicting them will be described.

• M. Aiba, H.-H. Braun, M. Böge, C. Calvi, T. Garvey, B. Keil, S. Reiche, V. Schlott, T. Schmidt
  PSI, Villigen

Transverse beam trajectory control is of great importance for SwissFEL as the lasing strategy is based on a relatively low energy and low emittance beam compared with other X-FEL facilities, thus aiming at a reasonable construction cost and size of the facility. A study of beam based alignment and orbit feedback has been performed, and a trajectory correction scenario, which would fulfill the beam requirements as well as the hardware constraints, has been set up. The beam based alignment will be discussed for the linac and the undulator section separately because of the much tighter tolerance in the latter. Several correction algorithms are examined using numerical simulations. BPM requirements and orbit feedback concept will be discussed, with reference to some available data on dynamic disturbances such as ground motion at the PSI site, e.g. at the SwissFEL injector test facility currently under commissioning.