Slide 1

Cascina, June 19th, 20071 Brewster window noise ? Raffaele Flaminio EGO and CNRS/LAPP Summary - Original observations - Brewster window replacement - New problems - Solutions - Conclusions? Slide 2 Cascina, June 19th, 20072 Scattered light noise Environmental noise acting on in air components + Scattered light from in air components = ------------------------------------------------------------- Phase noise in the interferometer (with the typical environmental-like noise structures) Laser Brewsters End benches Detection bench Injection bench Slide 3 Cascina, June 19th, 20073 Brewster windows Brewster windows separating different vacuum regions Laser Brewsters End benches Detection bench Injection bench Slide 4 Cascina, June 19th, 20074 DETECTION BENCH DETECTION BREWSTER 160 110 DN250CF Slide 5 Cascina, June 19th, 20075 IB PR Al BAFFLEGLASS BAFFLE INJECTION BREWSTER Slide 6 Cascina, June 19th, 20076 Acoustic noise entering from the Brewster (Radio Brewster) - Several test and studies made by Irene Fiori - Predictions strange; expected ITF noise larger than measured ITF noise (and coherence with Brewster seismometer pretty bad) - Explication: maybe seismometer not measuring the good surface Original observations Brewster replaced with a larger one - From 16 cm diameter to 19.6 cm diameter Slide 7 Cascina, June 19th, 20077 Slide 8 8 Slide 9 9 With new Brewster ITF noise worst than before New Observations (I) Slide 10 Cascina, June 19th, 200710 With new Brewster ITF noise worst than before Foreword (II) Slide 11 Cascina, June 19th, 200711 Coherence with Brewster seismometer better than before New observations (II) Slide 12 Cascina, June 19th, 200712 With new larger Brewster new light visible on the detection bench - Light visible at ~10 cm from the axis of the main beam - This light is missing the first detection lens (L1, diameter 12 cm) - This light is diffused on a couple of supports on the detection bench New observations (III) B1s B1 B1p B5 L3 /2 OMC M1 M5 L7 Slide 13 Cascina, June 19th, 200713 Julien Marque (2004) Old prediction: spurious beams Bd1 Bi2Bi1 Bd2 Slide 14 Cascina, June 19th, 200714 Julien Marque (2004) Old prediction: spurious beams Bd1 Bd2 Slide 15 Cascina, June 19th, 200715 Julien Marque (2004) Old prediction: spurious beams Bd3 Bd4 Bi1 Slide 16 Cascina, June 19th, 200716 Julien Marque (2004) Old prediction: spurious beams Bd3 and 4 Slide 17 Cascina, June 19th, 200717 Julien Marque (2004) Old prediction: spurious beams Bd5 Bd6 and 7 Bd8 Bi2 Slide 18 Cascina, June 19th, 200718 Julien Marque (2004) Old prediction: spurious beams Bd5 Bd7 and 8 Bd6 Slide 19 Cascina, June 19th, 200719 With the old brewster One of the predicted spurious beams Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam Slide 20 Cascina, June 19th, 200720 With the new brewster One of the predicted spurious beams Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam Slide 21 Cascina, June 19th, 200721 With the new brewster Considering beam diameter defined as 2 w 0 One of the predicted spurious beams Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam Slide 22 Cascina, June 19th, 200722 A possible scenario: - Brewster noise due to spurious beams - Scattering from the Brewster link lateral wall into the B1 beam Another discussed scenario: - More spurious beams reaching the detection bench - Then scattered into B1 - Difficulty: bench is suspended in vacuum, no direct coupling with environmental noise Another possible scenario: - More spurious beams reaching the detection bench - Then scattered on the tower wall or on the Brewster - Then scattered back into B1 Discussion Slide 23 Cascina, June 19th, 200723 Additional diaphragm before the Brewster A possible mitigation Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam Slide 24 Cascina, June 19th, 200724 Additional diaphragm before the Brewster Other predicted beams - more uncertain - less powerful A possible mitigation Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) One spurious beam Slide 25 Cascina, June 19th, 200725 Additional diaphragm before the Brewster Considering full BS aperture A possible mitigation Diaphragms Brewster B1 B5 Brewster link axis Distance from BS (m) Distance from west axis (cm) Slide 26 Cascina, June 19th, 200726 Scattering of spurious light from the ITF ? Yes, but . no difference in the ITF noise Slide 27 Cascina, June 19th, 200727 Noise injections (May 2 nd ) Slide 28 Cascina, June 19th, 200728 Injection with shaker: comparison with old Brewster Noise injections (May 2 nd ) Slide 29 Cascina, June 19th, 200729 Injection with loudspeaker: comparison with old Brewster Noise injections (May 2 nd ) Slide 30 Cascina, June 19th, 200730 Damping the Brewster Slide 31 Cascina, June 19th, 200731 ITF noise: damped Brewster Slide 32 Cascina, June 19th, 200732 ITF noise:damped Brewster Slide 33 Cascina, June 19th, 200733 Noise projection I. Fiori and G. Vajente Slide 34 Cascina, June 19th, 200734 Discussion ITF noise larger because of new Brewster Brewster link vibrating more than before? No. Sensitivity to Brewster vibrations larger than before? Yes Why? What is the mechanisms ? BEAM SPLITTER DETECTION 1) Scattering of spurious light coming from the ITF 2) Scattering of spurious light generated in the Brewster 3) Scattering of spurious light coming from the detection Slide 35 Cascina, June 19th, 200735 Scattering of spurious light generated in the Brewster Possible but new Brewster is expected to be better - larger Brewster window - larger exit windows - Brewster window with larger roughness? No (source: L. Pinard) - Brewster window with larger residual reflection? with 600-700 mW incident ~ 270 mW reflected 200 mW on P pol and 70 mW on S-pol (source: P. La Penna) - Brewster link vibrating more? No. - Something in the Brewster vibrating more? Candidate: aluminum baffle Slide 36 Cascina, June 19th, 200736 Scattering of spurious light coming from the detection BEAM SPLITTER DETECTION 3) Scattering of spurious light coming from the detection Decision to better protect the Brewster from light coming from the detection side Slide 37 Cascina, June 19th, 200737 Conclusion Slide 38 Cascina, June 19th, 200738 Conclusion Slide 39 Cascina, June 19th, 200739 Injection with shaker: comparison with old Brewster Noise injections (May 9 th ) Slide 40 Cascina, June 19th, 200740 Injection with loudspeaker: comparison with old Brewster Noise injections (May 9 th ) Slide 41 Cascina, June 19th, 200741 Identification of 122 Hz with one of the Brewster link supporting legs Change of Brewster link damping configuration Change of SR pump with a smaller one More investigations (I) Slide 42 Cascina, June 19th, 200742 Clear excitation of 136 Hz and 241 Hz tapping on DT east flange Damping on DT east tube Large effect on ITF sensitivity when tapping on DT west flange Damping on DT west tube No effect on sensitivity More investigations (II) Slide 43 Cascina, June 19th, 200743 Observation of diffused light coming from detection output window Cleaning of window No effect on sensitivity More investigations (III) Slide 44 Cascina, June 19th, 200744 Tapping tests on injection Brewster, injection tower, injection table - Small effects on ITF sensitivity - No excitation of ITF noise structures/resonances - Much less sensitive than detection tower and Brewster Tapping tests on injection Brewster, injection tower, injection table - Very small effects on ITF sensitivity - No excitation of ITF noise structures/resonances Tapping test attempted on NI - failed due to unlock Need to study sensitivity to all towers vibration - need to learn how to excite towers without unlock - place seismometers in more useful positions (now measuring vertical seismic noise near tower base) More investigations (IV) Slide 45 Cascina, June 19th, 200745 Result Slide 46 Cascina, June 19th, 200746 Conclusion - The new Brewster was limiting the sensitivity - The sensitivity is back to what it was on April the 6 th (before the Brewster was changed) - Sensitivity to environmental noise still there - No big improvement with new Brewster (why?) - Tapping test and injections continue to tell that the detection tower and the Brewster are the most sensitive parts of the ITF (but several tests still to be done) - How to make the difference between the tower and the Brewster? Slide 47 Cascina, June 19th, 200747 Result Slide 48 Cascina, June 19th, 200748 Mystery noise Slide 49 Cascina, June 19th, 200749 Mystery noise Slide 50 Cascina, June 19th, 200750 Mystery noise Slide 51 Cascina, June 19th, 200751 Mystery noise