FF magnets pre-isolator & experimental set-up proposal2nd WG5 Meeting

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

April 20, 2010

Objective

Stabilize FF magnets to:

0.1 nm RMS @ 4 Hz

Using an integrated approach:

- passive pre-isolator- active mechanical stabilization

- beam-based stabilization

1

Pre-isolator – How does it work?

Low dynamic stiffness mounts

(nat. frequency around 1 Hz)

Acts as a low-pass filter for the ground motion

Large mass

(50 to 200 ton)

Provides the inertia necessary to withstand the external disturbances (air flow, acoustic pressure, etc.)

+

2

How can it be accomplished?

Drawings by N. Siegrist*Conceptual design 3

How can it be accomplished?

QF1

QD0

MassMount

Walk-on-floor

QD0 support

tube

*Conceptual design 4

“State of the art” exampleVibration 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”)

*Infos provided by 5

“State of the art” exampleProvided measurement data

Transmissibility

10x

Vertical displacements

1 Hz

@Ground

@Mass

Note: Ground motion noise level below CMS measurements (A. Kuzmin – EDMS 1027459)

*Infos provided by 6

Experimental set-up – Why?

How will it react to different noise sources?

We need tounequivocally demonstrate that the concept can work

Is the system’s performance amplitude dependant?

What about energy loss mechanisms (friction...)?What performance can we expect?

And air blows?

There are lot of unanswered questions.

The previous example is promising, but...

7

Experimental set-up – How?It needs to be:

Simple to design/build/assembleEasy to “debug” & tune

Cheap

Proposal:

40 ton masssupported by

4 structural beams8

Experimental set-up – How?

Drawings by N. Siegrist 9

Experimental set-up – Design

Design criterias:High deformations (i.e. low bending stiffness)

Acceptable stressesShape optimization

Average stress: <280 MPaDeformation: 187 mm

10

Experimental set-up – PerformancePerformance in ideal conditions (ground motion only)

Transmissibility Displacement P.S.D.

1.55 Hz@CMS

@Pre-isolator

Integrated R.M.S. Displacement

2.2nm @CMS

0.15 nm @Pre-isolator

15xGround Motion

Displacement @Pre-isolator

11

Experimental set-up – Measurements

At least 3 seismometers/geophonesSynchronous measurements

Help needed for the measurements

Reference 1 Reference 2

Measure

~10 m

A set-up like the one below is foreseen

12

Summary• A passive low-frequency pre-isolator has been proposed as a support for the FF magnets;

• This pre-isolator will constitute the first “layer” of the stabilization chain;

• This concept has already been used in other 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.

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