This element defines the acceptance angle of the incoming photon beam. Due to the very high peak power (or fluence) characterizing the FEL photon beam impinging on this element (about 40 mJ/cm2 for FEL1 at 20 nm, and about 400 mJ/cm2 for FEL2 at 5 nm), particular care has been used in designing it. The radiation incidence angle on the BDA is 7.6º. This value is the minimum possible according to mechanical constrains, and it increases the illuminated area by a factor of ~8, decreasing the fluence of the same amount. Mechanically, the BDA is formed by two trunks of pyramid as shown in  the figure below . The central aperture of each trunk is 20x20 mm2, and they are moved one respect to the other in order to select the effective aperture. A complete closure of the total aperture is possible, and the central aperture itself can be moved ±12.5 mm around the ideal axis (equivalent to about ±0.6 mrad).

Ultima modifica il Venerdì, 15 Novembre 2019 12:07