FLASH II ist eine Kooperation von DESY und HZB

FLASH II Proposal

Sketch of the new tunnel and experimental hall for the FLASH II extension, along with a footprint of the existing FLASH accelerator tunnel and experimental hall.


In order to keep and extend further Germanys leading role in designing, constructing and operating FEL based radiation sources, DESY in close collaboration with HZB/BESSY proposes the construction of a second FEL undulator line (called FLASH II) in a separate tunnel and a second experimental hall to enhance significantly the user capacity and to allow implementation of seeding schemes which promise radiation properties superior to SASE. The two seeding approaches envisaged for FLASH II are HGHG and HHG.  FLASH II will consist of the following elements:

  • A fast electron beam switch to be installed immediately behind the last superconducting accelerator module, enabling distribution of the accelerated and compressed electron beam to both FEL undulator lines (i.e. the existing FLASH undulator and the new FLASH II undulator chain) without compromising the electron beam quality. This proceeds in a similar manner as foreseen for the European X-ray Laser Project XFEL.
  • A new tunnel housing a magnet system for electron beam optics, a new FEL undulator line incorporating a two-stage HGHG cascade with variable gap in order to generate photon pulses of variable femtosecond duration, gigawatt peak power, full shot-to-shot pulse reproducibility and full transverse and longitudinal coherence and a new electron beam dump. Another approach making use of the same undulator system is aiming for very short seeding wavelengths using the High-Harmonic Generation (HHG) in gas to provide the initial seeding radiation. While it is foreseen that the first HGHG experiments will be performed using the fourth harmonics of a 10 Hz Ti:Sa Laser as seed, in parallel the development of seed lasers will be pushed forward, enabling  HGHG with higher repetition rate and an HHG seed.
  • A new tunable laser system and laser beam line to generate and transport the seeding radiation to the FLASH II tunnel.
  • A new experimental hall providing space and basic infrastructure for approximately six new photon beamlines and the corresponding experimental station.
  • One user beamline comprising the photon diagnostics and photon beam manipulation tools required for typical users.

Sketch of the cascaded HGHG scheme proposed for FLASH II (the electron beam comes from the right). This same system can also be used for direct HHG seeding and for SASE, e.g. lasing without seed.