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

CLIC MDI Working GroupQD0 external reference structure

A. Gaddi, H. Gerwig, H. Hervé, N. Siegrist, F. Ramos

Page 2November 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 structurethat 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.



Coherence of seismic vibration important for QD0 relative displacement.

Relative (nm)

3m 4m 5m 7m50 9m 10m Abs (nm)

ATF2 12.3 (/10) 15.6 (/8.2) 24.6 (/5.2) 34.7 (/3.7) 42.0 (/3.1) 37.0 (/3.5) 128.4

LHC 1.0 (/12.5) 1.3 (/9.6) 1.8 (/6.9) 2.6 (/4.8) 2.8 (/4.5) 3.1 (/4.0) 12.5

LAPP 0.4 (/7.5) ========= 0.7 (/4.3) 1.0 (/3.0) 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



UX CavernTunnels protruding make cavern excavation difficult.No effective mechanical link between the two tunnels.

N. Siegrist



Actual design of detector forward region, with QD0 support tube, beam-pipe, calorimeters and machine ancillaries.

from H. Gerwig, N. Siegrist



In the present integration scheme, QD0s are supported at tunnel ends.

QD0 supported at each tunnel end



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.



Proposed solution: a rigid « space frame » bridge, connecting again the two QD0.



Same idea, but different approach…eventually made of reinforced concrete. (Measure of seismic waves coherence through USC55/UXC55 pillar wall has been suggested).



…or even a complete rigid ring around the two QD0s.



Tubular space frame 1x1x1 m (first natural frequency above 50 Hz).



Evolution towards an integrated isolation system.

Low-frequency, 1 d.o.f.Pre-Isolator system

Active stabilization

€

f =1

2π

k

m

Pre-Isolator cinematics:The QD0 tube moves only vertically, the springs and dumpers locatedabove the mid-plane provide for theseismic isolation (see next slide).

Low frequency means low forcesto apply for pre-alignement:

F=m2

Low forces Low injected noise!



Preliminary fem analysis give encouraging results.

model from F. Ramos, PH-CMX



Vibrational mode at 40 Hz. simulation done by F. Ramos



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





RMS vertical displacement reduced by a factor >10 from 3 Hz.



VIRGO (a joint INFN-CNRS experiment on gravitationalwaves) has an horizontal pre-isolator working at 30 mHzand reaching an effective attenuation of 50 dB at 1Hz.

An example of low-frequency pre-isolation system.



Future plans.

Clearly validation by futher computations and measurements will be needed to justifysuch 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.

Documents

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