The beam transport to the FELs has to perform a bunch compression and for that a chicane was planned between LINAC 1 and the S-arc. To design it the required transport matrix element R₅₆ should be determined. This value depends on the longitudinal phase space after LINAC 1 and the desired longitudinal phase space in the FELs. Due to the complexity of the problem no exact values could be obtained from numerical simulations. As an estimate of the maximum required R₅₆ a value of 450 mm was fixed. A variable chicane is planned which allows to vary R₅₆ from 0 to this maximum. This gives an enormous flexibility in connection with LINAC 2, which for instance makes it possible to measure the longitudinal phase space.
To allow two-colour experiments at ELBE  with two FELs running synchronously in the future the beam transport has to be suitably designed. Even if these steps are not realized now the needed place for them has to be reserved. Because of tight space there is no other possibility than to combine the variable chicane with the beam separation for two-colour experiments and the beam transport to the nuclear physics experiments. A side effect of such a combination is the saving of extra dipoles for these tasks. As a consequence the size of the chicane is completely determined by the geometry resulting from the deflection angles of both energies at two-colour experiments. These angles were set to 30 and 45 degrees corresponding to a RF induced energy modulation of ± 5.23 MeV for a 30 MeV beam. This results in an even higher maximum R₅₆ of the chicane of 633 mm with a maximum beam offset of 513 mm in its center. In Fig. 1 an overview of the chicane with the combined beam separation is given.

There exist five different beam paths in this design:

Fig. 1: Design of beam separation combined with variable chicane

1 - Straight through to the radiation physics and neutron physics caves (all dipoles off). 2 - A separate path for the beams with sufficiently low energy. 3 - A path for the higher energy beam back to the continuation of line 1. For two-colour experiments this path and path 2 are used alternatively by sub- sequent pulses. 4 - A beam path to the nuclear physics cave (only dipole 4 switched on). 5 - A variable beam path for normal chicane operation.

Beam transport calculations for all five beam paths were performed and it is possible to match the beam to the different requirements. The position of the viewscreens and beam adjustment rules are defined.
 FWF 05/18/01 © A. Büchner