Figure 1: Schematic layout of the FLASH facility. The electron gun is on the left, the experimental hall on the right. Behind the last accelerating module, the beam is switched between FLASH I, which is the present undulator line, and FLASH II, which is the upgrade. Behind the extraction point, space is reserved for an additional laser system for seeding.

A major extension of the FLASH facility is FLASH II which was a combined proposal by DESY and HZB. It includes a new experimental Hall to double the number of user stations and an additional variable-gap undulator in a separate tunnel to be able to deliver two largely independent wavelengths to two different user stations simultaneously. The electron beam is switched between the present fixed-gap undulator line of FLASH (now referred to as FLASH I) and the new variable gap undulator FLASH II (see Fig. 1). The modification needed to the present facility is minor. Space for a total of at least five experimental stations is foreseen. The angle of the first deflecting mirror for FLASH II is 1 degree. As a consequence, at least for one beamline the 5th harmonic of 0.8 nm will be delivered with a minimal amount of loss at the optical components.

In addition to the SASE mode used in FLASH I, HHG seeding is foreseen for wavelengths between 10 nm and 40 nm. It uses a Ti:Sa laser at a repetition rate of 100 kHz, which is under development at DESY. For long wavelengths, SASE has to be used. At the smaller wavelength end, down to 10 nm, the seed power expected is still enough for sufficient seeding. Further decrease in wavelength is possible by employing a classical HGHG scheme, where we go to a higher harmonic before saturation, thus avoiding a large energy spread which decreases the saturation power.
A study to extend the wavelength range down to 2 nm is in progress. The idea is to use a short afterburner optimized for this short wavelength at an energy of 1.25 GeV. In order to allow a variable polarization of the radiation pulses, this afterburner will be an APPLE III undulator. However, this wavelength can only be reached at reduced power, typically a few percent of the fundamental.

Download [0 MB, 2592 x 1552]