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Quality control facilities for large optical reflectors at ENEACasaccia for physics application Stefania Baccaro a,d, Carlo Bosio b,d, Augusto Maccari c, Marco Montecchi a,d a) ENEA FIS-ION, Casaccia, Roma, Italy b) Dipartimento di Fisica Università La Sapienza, Roma, Italy c) ENEA SOLTERM, Casaccia, Roma, Italy d ) INFN – Sezione di Roma1, Roma, Italy Large optical reflectors are used in… • Astronomy: in telescope (imaging) • High Energy Physics: in RICH, to focus Cherenkov radiations on optical sensor (quasi-imaging) • …… • Solar Energy: as sun-power collectors (collecting) … for information completeness • How large? Single panel, up to some meters • Imaging use is much more demanding than collecting one • Composition and shape are designed for the specific application and ..... ... HAVE TO BE TESTED !!! Irradiation plants at ENEA – Casaccia • TAPIRO: fast neutrons • TRIGA: thermal neutrons • CALLIOPE: 1.17 and 1.33 MeV Optical laboratory tender to Calliope: spectrophotometers and spectrometer Light-Yield damped optical top with light sources, lenses, mirrors, detectors, etc.. custom set-up Optical tests at ENEA-Casaccia Reflectance: spectrophotometer – specular and diffused (small flat sample) spectrometer – specular (full scale reflector) Shape performances: 2f optical test pin-hole optical test profilometer focal length and image spot dimension visual inspection of the curvature accurate measurement of the curvature 2f optical test: focal length and image-spot dimension LED ( = 5 mm) image screen 2f in the ideal case, image and source have the same dimension Pin-hole optical test: a visual inspection of the curvature LED surface image pin-hole f1 2f p q where the surface image is dark, the curvature is wrong LHCb RICH mock-up: carbon fiber + honeycomb ~ 600 mm 2f = 1700 20 mm image spot ~ 15 mm LHCb mock-up : polymethylmethacrylate (PMMA) hot bended and honeycomb ~ 400 mm 2f = 2370 20 mm image spot ~ 25 mm LHCb RICH mock-up: PMMA poured liquid on master ~ 350 mm 2f = 2330 20 mm LHCb mock-up: electrodeposited Ni = 200 mm 2f = 315 5 mm Accurate test of the reflector curvature: profilometer In the framework of the Concentrating Solar Power Project, ENEA is providing with an optical profilometer to test large linear parabolic reflectors the measurement is automatic - PC controlled the profilometer can be used also for reflectors differently shaped (e.g. spherical reflector) actually the instrument performs 1D scanning 2D upgrade is imminent ENEA optical profilometer (1D) rotation axis x screen xS (xC,yC) x0 HeNe Nikon D1X, 4.024 x 1.324 px y yS • the surface is scanned by tilting the incident beam () with a high precision rotation stage (20 rad repeatability) • the intersection of the reflected beam with the screen (XS) is deduced by processing the digital image Data processing – 1th method: fit y = f (x,p1,..,pM) x x0 xS simulated xS experimental y yS best fit by minimising xS xS MF p1 ,.., pM Err xS j 1 N sim exp j 2 Data processing - 2nd method: iterative extrapolation (I.E.) A P 2 central point ( = 90°): x B C set dy/dx = 0 by tilting x0 P1 the next point P2 is: along the incident beam, by definition in AB, if 1; P1C, P2C P1P2 univocally determined by assuming: P2 P1 C y P2 y = x2 circular: P1C =CP2 (xc,yc) directly measured P1 x1 xC x2 yS parabolic: xC = (x1+x2)/2 Example: reduced scale linear parabolic reflector (aperture 0.6 m) P4 2 (1 P4 ) 2 f 4f rotational measurement 52 50 XS (cm) best fit parameters: 2 = 1.23 (32/49 data) P4 = 0.32 0.04 = 11.3 0.8 deg f = 185.5 0.5 mm experimental best fit of 32/49 data 48 46 44 42 2 f 2 2 40 38 36 34 32 30 28 26 24 22 high precision 60 70 80 90 (deg) 100 110 120 comparison of the two methods profile slope 1 40 0 30 -1 20 atan(dY/dx) (deg) -2 -3 Y (cm) best fit extrapolation -4 -5 -6 -7 best fit extrapolation -8 10 0 -10 -20 -30 -9 -40 -20 -10 0 10 20 -20 X (cm) -10 0 10 X (cm) I.E. method gives a realistic profile of the reflector I.E. method allows to evaluate the locale deviations from the project specifications of both profile and slope 20 validation of the iterative extrapolation method profile deviation from circle r = 376mm 3.5 3.0 comparator iterative extrapolation 2.5 radial deviations (mm) direct measurement comparator 2.0 1.5 harm 1.0 rotation stage 0.5 0.0 -0.5 reflector -1.0 -20 -10 0 X (cm) 10 20 Conclusions The ENEA-Casaccia facilities allow to measure the most important features of large optical reflectors: specular and hemispherical reflectance focal length surface profile 2D upgrade of the profilometer is imminent