• D. Lipka, D. Nölle, M. Siemens, S. Vilcins
  DESY, Hamburg
• F. Caspers
  CERN, Geneva
• H. Maesaka, T. Shintake
  RIKEN/SPring-8, Hyogo
• M. Stadler, D.M. Treyer
  PSI, Villigen

XFELs require high precision orbit control in the long undulator sections. Due to the pulsed operation of these systems the high precision has to be reached by single bunch measurements. So far cavity BPMs achieve the required performance and will be used at the European XFEL between each of the 116 undulators. Coupling between the orthogonal planes limits the precision of beam position measurements. A first prototype build at DESY shows a coupling between orthogonal planes of about -20 dB, but the requirement is lower than -40 dB (1%). The next generation Cavity BPM was build with tighter tolerances and mechanical changes, the orthogonal coupling is measured to be lower than -43 dB. This report discusses the various observations, measurements and improvements which were done.

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

The resonant stripline pickup was chosen for a Beam Position Monitor (BPM) developed for the 250 MeV PSI XFEL Injector to reach the desired sensitivity of 10 micrometers in beam position. The electromagnetic design of this cavity, performed with Microwave Studio, was optimized in terms of the main radiofrequency characteristics - frequency, shunt impedance, Q value - of the resonant modes of interest, in order to obtain the pickup sensitivity required by the electronics (direct sampling, [*]). Also mechanical aspects of the design are presented, with particular attention to the solution adopted for the stripline alignment. Based on the simulated geometry, a pickup prototype was carried out and tested, allowing to verify the correct characteristics of the resonant modes and to state the present resonant stripline pickup design as one possible candidate for the standard (non-undulator) BPM system of the PSI XFEL and also for other linear accelerators or storage ring transfer lines.

[*]: B. Keil, S. Lehner. S. Ritt, "Application of a 5 GSPS Analogue Ring Sampling Chip For Low-cost Single-shot BPM Systems", Proc. EPAC 2008, Genoa, Italy, 1167 (2008).

• F. Müller, S. Hunziker, V. Schlott, B. Steffen, D.M. Treyer
  PSI, Villigen
• T. Feurer, F. Müller
  IAP Univ. Bern, Bern

Pulsed Yb fiber lasers emit at 1030 nm which provides a better phase matching in standard EO crystals (GaP, ZnTe) than Ti:Sa lasers (800nm). We present a mode locked ytterbium fiber laser which is phase locked to the RF. A subsequent fiber amplifier is used to boost the power and to broaden the spectrum due to nonlinear effects. The produced pulses have a spectral width of up to 100 nm and are therefore suitable for EO bunch length measurements, especially for spectral decoding. The laser delivers a chirped pulse of some ps, the fourier limited pulse duration of ~30 fs can be almost reached by an additional shaper setup with a spatial light modulator in the Fourier plane.