CLIC MDI Working Group Vibration attenuation via passive pre- isolation of the FF quads A. Gaddi, H....
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Transcript of CLIC MDI Working Group Vibration attenuation via passive pre- isolation of the FF quads A. Gaddi, H....
CLIC MDI Working GroupVibration attenuation via passive pre-
isolation of the FF quads
A. Gaddi, H. Gerwig, A. Hervé, N. Siegrist, F. Ramos
Page 2May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Retrospective view.In the first CLIC MDI layout (legacy of ILC MDI), the QD0s were supported by the detector, or by a pillar on the detector moving platform. However it became clear, after the measuring campaign at CMS, that the vibrations generated by the detector itself would make impossible to achieve the stability requirements given for the FF magnets.
Measurements done at CMScourtesy EN-MME
Page 3May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Scope of work.
Try to attenuate, at its source, ground motion vertical excitations, in the range 1 – 20 Hz, to make life easier to the following stabilization systems.
Objective.
Stabilize FF magnets to better than 1 nm (rms) at 4 Hz,using an integrated approach of three systems, each onewith its dynamic range and frequency response:
Passive pre-isolator
Active mechanical stabilization
Beam-based stabilization
Page 4May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Pre-isolator – How does it work?
Low dynamicstiffness mount
natural frequency around 1 Hz
Acts as a low-pass filterfor the ground motion (w)
Large mass
50 to 200 tons
Provides the inertia necessary to withstand the external disturbances (Fa), such as air flow, acoustic pressure, etc.)
+
Page 5May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
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
Page 6May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
RMS vertical displacement reduced by a factor >10 from 4 Hz.
plots by F. Ramos
Page 7May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Where does it fit ?
Ideally located at the end of the machine tunnel,just in front of the detector, on both sides.
drawing by N. Siegrist
Page 8May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
How can it be realized ?
QF1
QD0
MassElasticsupport
Walk-on-
floor
QD0 support tube
conceptual design
Page 9May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Experimental set-up – Why ?
How will it react to different noise sources, else than micro-seism ?
Is the system’s performance amplitude dependent ?
What about energy loss mechanisms (friction...) ?
What performance can we expect ?
We plan to build a prototype to try to answer to these questions.
The idea is promising, but...
Page 10May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Experimental set-up – How ?
The prototype needs to be:
Simple to design/build/assembleEasy to “debug” & tune
Cheap
Proposal:40 ton mass supported by
4 structural beams acting as flexural springs
Displacement @Pre-isolator
Page 11May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Experimental set-up – Expected performance
Performance in ideal conditions (ground motion only).
Transmissibility Displacement P.S.D.
1.55 Hz
@CMS floor
@Pre-isolator
Integrated R.M.S. Displacement
2.2nm @CMS floor
0.15 nm @Pre-isolator
15x
plots by F. Ramos
Page 12May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Future plans.
• A passive low-frequency pre-isolator has been proposed as a support for the FF magnets. It can be integrated at the interface between the machine tunnel and the detector cavern.
• This pre-isolator will constitute the first “layer” of the stabilization chain.
• This concept has already been used in other industrial and research facilities.
• Experimental tests should be performed to understand how the system behaves in “real life” conditions (no simulation can accurately take into account all these effects). A simple and relatively inexpensive experimental set-up has been conceived and proposed.
• Further studies are necessary to integrate the pre-isolator with the civil-engineering and the other MDI systems (pre-alignement, FF magnets, forward detector region, beam-pipe, etc…)
Page 13May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Back-up slides.
Page 14May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Example of pre-isolator application in industry
Vibration isolation system at the Centre for Metrology and Accreditation – Helsinki, Finland
4 independent seismic masses (3x70 ton +
1x140 ton)
0.8 Hz pneumatic vibration isolators
(“air springs”)
Page 15May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Further considerations.
Supporting the FF quads (and in particular QD0) from the tunnel 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.
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.
Page 16May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
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
Measurements have been planned at CMS site, where a 2.25m thick reinforced concret slab, long several tens of meters, and supported by pillars with foundations into the rock, would be the design reference. We aim to understand if a similar design, in the CLIC experiment cavern, would be beneficial for the FF stabilization at low frequency.
Page 17May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Conceptual design: the Quads’ bridge.
The design has evolved from a first sketch, aiming to provide the same foundations for the couple of FFQ, to a more complex design that includes a low-frequency vertical pre-isolator.
Main linac
Pre-alignment & stabilization
FFQ stabilization & alignment
Quads-bridge
Tunnel floor
Page 18May 2010, A. Gaddi, Physics Dept. CERN
Vibration attenuation via passive pre-isolation
Conceptual design: the Quads’ bridge + the pre-isolator.
Main linac
Pre-alignment & stabilization
FFQ stabilization
FFQ pre-isolation& alignment
Quads-bridge
Tunnel floor
The main linac elements are aligned and stabilized on their girders.The FF quads are mounted inside a supporting tube, the stabilization is located inside the support tube.The FF quads pre-alignment is done by positioning the support tube, via the low frequency pre-isolator.The FF bridge has the function of extending the tunnel concrete slab from one side to the other of theexperimental cavern.