title: Phase-locked MHz pulse selector for x-ray sources.
abstract: Picosecond x-ray pulses are extracted with a phase-locked x-ray pulse selector at 1.25 MHz repetition rate from the pulse trains of the accelerator-driven multiuser x-ray source BESSY II preserving the peak brilliance at high pulse purity. The system consists of a specially designed in-vacuum chopper wheel rotating with ≈1  kHz angular frequency. The wheel is driven in an ultrahigh vacuum and is levitated on magnetic bearings being capable of withstanding high centrifugal forces. Pulses are picked by 1252 high-precision slits of 70 μm width on the outer rim of the wheel corresponding to a temporal opening window of the chopper of 70 ns. We demonstrate how the electronic phase stabilization of ±2  ns together with an arrival time jitter of the individual slits of the same order of magnitude allows us to pick short single bunch x-ray pulses out of a 200 ns ion clearing gap in a multibunch pulse train as emitted from a synchrotron facility at 1.25 MHz repetition rate with a pulse purity below the shot noise detection limit. The approach is applicable to any high-repetition pulsed radiation source, in particular in the x-ray spectral range up to 10 keV. The opening window in a real x-ray beamline, its stability, as well as the limits of mechanical pulse picking techniques in the MHz range are discussed.
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Förster
authors.forename: Bernd
authors.initials: B
authors.lastname: Lindenau
authors.forename: Marko
authors.initials: M
authors.lastname: Leyendecker
authors.forename: Franz
authors.initials: F
authors.lastname: Janssen
authors.forename: Carsten
authors.initials: C
authors.lastname: Winkler
authors.forename: Frank O
authors.initials: FO
authors.lastname: Schumann
authors.forename: Jürgen
authors.initials: J
authors.lastname: Kirschner
authors.forename: Karsten
authors.initials: K
authors.lastname: Holldack
authors.forename: Alexander
authors.initials: A
authors.lastname: Föhlisch