A. Crisol, F. Bisti, C. Colldelram, M.L. Llonch, B. Molas, R. Monge, J. Nicolás, L. Nikitina, M. Quispe, L. Ribó, M. Tallarida
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
LOREA beamline (BL20) at ALBA Synchrotron is a new soft X-Ray beamline dedicated to investigate electronic structure of solids by means ARPES technique. Optical design has been developed in-house so as most of beamline core opto-mechanics like Monochromator. The design made for LOREA is based on a Hettrick-Underwood grating type that operates without entrance slit. Experience cumulated over years allowed to face the challenge of designing and building UHV Monochromator. The large energy range of LOREA (10-100 eV) requires a device with 3 mirrors and 4 gratings with variable line spacing to reduce aberrations. Monochromator most important part, gratings system, has been carefully designed to be isolated from external disturbances as cooling water, and at the same time having high performances. Deep analytical calculations and FEA simulations have been carried out, as well as testing prototypes. The most innovative part of Monochromator is gratings cooling with no vacuum guards or double piping that are well-known source of troubles. Heat load is removed by copper straps in contact with a temperature controller device connected to fixed water lines. In addition, motion mechanics and services (cabling, cooling) are independent systems. Designs involved give high stability (resonance modes over 60Hz) and angular resolution below 0.1 µrad over 11° range. On mirrors side, it has been used gonio mechanics from MIRAS* plus an eutectic InGa interface between cooling and optics to decouple them. Grating and mirror holders are fully removable from main mechanics to be able to assembled at lab measuring to achieve the best fit. Instrument has been already assembled and motions characterization or stability measurements are giving expected results matching with specifications. * L. Ribó et al., "MECHANICAL DESIGN OF MIRAS, INFRARED MICROSPECTROSCOPY BEAM LINE AT ALBA SYNCHROTRON", presented at MEDSI’16, Barcelona, Spain, September 2016, doi:10.18429/JACoW-MEDSI2016-FRAA03
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