1. CLIC MDI Working Group QD0 external reference structure A. Gaddi, H. Gerwig, H. Hervé, N. Siegrist, F. Ramos

2. Page 2 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Preliminary considerations. Supporting QD0s sets some parameters that seem to be difficult to be met with a conventional design of the tunnel-experiment cavern interface, specially for what concerns the civil engineering. Alignment is critical, in particular between the two tunnel sides. It would be better if the two sides were moving coherently, I will present here a possibility to do so. What counts to maximize machine luminosity is the relative alignment of the two QD0s, rather than their absolute position. We shall profit of the relatively short distance between QD0s, to try to mechanically link them through a rigid structure that bridges the gap between the two tunnel ends. This would also increase the coherence of low frequency seismic waves across the UX cavern. Such a structure opens new possibilities for integrating a pre-isolation system that would reduce the vertical component of seismic noise at QD0 by a large factor and in addition will simplify the pre-alignment.

3. Page 3 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Coherence of seismic vibration important for QD0 relative displacement. Relative (nm) 3m4m5m7m509m10mAbs (nm) ATF212.3 (/10)15.6 (/8.2)24.6 (/5.2)34.7 (/3.7)42.0 (/3.1)37.0 (/3.5)128.4 LHC1.0 (/12.5)1.3 (/9.6)1.8 (/6.9)2.6 (/4.8)2.8 (/4.5)3.1 (/4.0)12.5 LAPP0.4 (/7.5)=========0.7 (/4.3)1.0 (/3.0) 0.9 (/3.3)3 Integrated RMS (nm) of relative and absolute motion above 1Hz with a rigid fixation. B.Bolzon, march 2009

4. Page 4 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure UX Cavern Tunnels protruding make cavern excavation difficult. No effective mechanical link between the two tunnels. N. Siegrist

5. Page 5 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Actual design of detector forward region, with QD0 support tube, beam-pipe, calorimeters and machine ancillaries. from H. Gerwig, N. Siegrist

6. Page 6 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure In the present integration scheme, QD0s are supported at tunnel ends. QD0 supported at each tunnel end

7. Page 7 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Two QD0, supported (ideally) in the same tunnel or via a traversing tube to improve coherence. Massive & noisy detector between the two QD0: no effective link beteween QD0s.

8. Page 8 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Proposed solution: a rigid « space frame » bridge, connecting again the two QD0.

9. Page 9 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Same idea, but different approach…eventually made of reinforced concrete. (Measure of seismic waves coherence through USC55/UXC55 pillar wall has been suggested).

10. Page 10 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure …or even a complete rigid ring around the two QD0s.

11. Page 11 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Tubular space frame 1x1x1 m (first natural frequency above 50 Hz).

12. Page 12 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Evolution towards an integrated isolation system. Low-frequency, 1 d.o.f. Pre-Isolator system Active stabilizationPre-Isolator cinematics: The QD0 tube moves only vertically, the springs and dumpers located above the mid-plane provide for the seismic isolation (see next slide). Low frequency means low forces to apply for pre-alignement: F=m  2 Low forces  Low injected noise!

13. Page 13 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Preliminary fem analysis give encouraging results. model from F. Ramos, PH-CMX

14. Page 14 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Vibrational mode at 40 Hz. simulation done by F. Ramos

15. Page 15 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Transfer function of an ideal (*) pre-Isolator with first frequency at 1Hz (*) massless spring k=118 kN/m, QD0 + support tube total mass 3 tons. Tunable frequencies plots by F. Ramos

16. Page 16 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure

17. Page 17 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure RMS vertical displacement reduced by a factor >10 from 3 Hz.

18. Page 18 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure VIRGO (a joint INFN-CNRS experiment on gravitational waves) has an horizontal pre-isolator working at 30 mHz and reaching an effective attenuation of 50 dB at 1Hz. An example of low-frequency pre-isolation system.

19. Page 19 November 2009, A. Gaddi, Physics Dept. CERN QD0 external reference structure Future plans. Clearly validation by futher computations and measurements will be needed to justify such a structure, but if it appear useful it must be considered from the beginning. In particular, more engineering work is needed. Open points for the coming weeks: 1.Coordinate with the civil engineering study group. 2.Coordinate with the stabilization group. 3.Make a first design of the pre-isolator (spring + damper + actuators). 4.Evaluate the costs vs benefits of the proposed scheme.