Minimization of the heat-induced deformation in the prefocusing mirror for the Elettra 2.0 nanoESCA/nanospectroscopy beamline

As part of the Elettra storage ring upgrade to 4th generation standards, the Nanospectroscopy/nanoESCA beamline is replacing its prefocusing mirror. The new mirror is a 100 mm x 40 mm x 40 mm monocristalline silicon piece, optimized for the maximum heatload produced by the 25 eV horizontal polarity of the beamline's undulators (100.4 mm period, kx = 7.3). This paper presents the layout and strategy followed to ensure a high quality photon delivery as well as and the calculations and the optimization process of the mirror geometry. To minimize the deformations, a notched, top-side cooling design was chosen, with an almost full-illumination of the top surface. The contact length between the cooling circuit and the mirror was optimized shorter than the mirror length, leading to slightly higher temperatures in the mirror extremities, but more preferable heatload-induced slope. Slits positioned before and after the mirror select only the center and least affected portion of the reflected radiation. Additional simulations confirmed that the optimized design performs equally well or better at higher photon energies.