PSI, Villigen
ELETTRA, Basovizza
CERN, Geneva
Currently a X band traveling wave accelerator structure is fabricated in a collaboration between CERN and PSI. It will compensate nonlinearities in the longitudinal phase space at the injector prototype of the PSI-XFEL, whereas CERN will use it to test break down limits and rates in the high gradient regime. Due to the modest beam energies, the operation in the PSI-XFEL injector is quite sensitive to transverse wakes destroying the beam emittance. In that respect, the structure will use an active monitoring of the beam to structure alignment and include two wake field monitors coupling to the transverse higher order modes. These allow steering the beam to the structure axis giving a higher precision than mechanical alignment strategies. Localized offsets due to bends or tilts have individual signatures in the frequency spectrum, which in turn are correlated with different delays in the signal envelope. By taking advantage of this combined with the single bunch mode at the PSI-XFEL, the use of a relatively simple detector type RF front end should be possible, which will not only show beam offsets, but also higher order misalignments as tilts in the structure.
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).
PSI, Villigen
In this paper, we describe four very different operating modes of the SwissFEL facility, the requirements of the challenging beam diagnostics and ultra-stable RF systems needed for two special operating modes with 10 pC, and the present status of developing beam diagnostics and RF systems for the PSI 250 MeV injector test facility, which is under construction.
