[PPT] - THE EFFECT of COOLING WATER on MAGNET VIBRATIONS R. Amann, W. PowerPoint Presentation

SLIDE 1

NanoBeam2002

26th Advanced ICFA Beam Dynamics Workshop on Nanometer Size Colliding Beams September 2-6, 2002, Lausanne, Switzerland

THE EFFECT of COOLING WATER on MAGNET VIBRATIONS

R. Aßmann, W. Coosemans, S. Redaelli, W. Schnell

CERN CH-1211 Geneva 23 Switzerland

C L I C C L I C

SLIDE 2

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 2

Overview of my talk:

1. Introduction
2. Simple theory of water induced vibrations
3. Experimental set-up
4. Results of the measurements
5. In-situ measurements (vibrations of CTFII quads)
6. Conclusions

Acknowledgments: People of the CLIC Stability Study Group (G. Guigard, N. Leros,

D. Schulte, I. Wilson, F. Zimmermann), A. Seryi, G. Yvon, D. Gros.

SLIDE 3

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 3

1. Introduction

Performance of future Linear Colliders like CLIC will be limited by the vibrations of the focusing quadrupoles

20 nm 0.1 nm 4 Hz

On earth exist places quiet enough for CLIC! But the noise of the accelerator environment disturb this quietness!

0.2 nm 4 nm 2 Final Focus 1.3 nm 14 nm 2600 Linac Vertical Horizontal Number Quad type

CLIC tolerances for uncorrelated motion above 4 Hz

( Work done in the CLIC Stability Group )

Measurements in the LEP tunnel (W. Coosemans et al., 1993)

SLIDE 4

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 4

Why do quadrupoles move?

Natural ground motion
Resonances of the support structures.

Amplification of the ground motion level.

Acoustical noise
Air currents
Mechanical vibrations
COOLING WATER

Cultural noise from equipment in the tunnel (cooling system, vacuum pumps, air conditioning, particle detector,... ). This is what we are going to discuss!

SLIDE 5

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 5

2. Simple theory of water induced vibrations (1)

Theory first proposed by W. Schnell (CLIC Note 468 – Landau-Lifshitz, Vol. VI) Vibrations supposed to by induced by TURBULENCE Reynold’s number:

u: water velocity d: pipe diameter ρ=103 kg m3: water density : viscosity η=0.89 10−3 kg m−1 s−1

Re = udρ η

u d d/2

Turbulence onset: Re ≈ 2000 Eddy-like local motion superimposed to drift u Length of larger coherence domains ~ d/2

fc = u d

Intrinsic frequency associated to turbulence:

Turbulence induced vibrations expected above fc

SLIDE 6

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 6

Simple theory (2) – Energy released in turbulent regime

∆p = ρλ 2 l d u2

In turbulence, pressure drop ~ u2:

Weak dependence on Re (Blasius’ formula)

λ 0.316Re−1/4 = 0.04 ≈

v = mean-square

f local turbulence

velocity

∂V ∂t ∆p = ∂V ∂t ρv2 2

Power pump completely converted in irretrievable kinetic energy: Isotropy ⇒ Local momentum density:

ρvRMS

y

= uρ

λl

3d

3 /

2 2

v vy =

Assumptions: kin energy concentrated in cells of coherence length d/2 All energy released at fc

y

RMS = √ncnq

d 2π mwater MTot

λ

6,

Sum in quadrature of all cells (and magnet coils)

(nc, nq = number of coils/quads)

Small dependence of motion on water flow!

SLIDE 7

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 7

3. Experimental set-up (1) – The CLIC linac quadrupole

142 mm 76 mm Coil Water pipe Yoke

CTFII quadrupole - similar for CLIC
Resistive quadrupoles (copper coil)
Coils with 6 cables
Cooled with water (d = 3 mm)
80mm(long)x76mmx142mm; 6.7 kg
Two quads on one support plate

Geophone for vibration measurements Water feeding pipes Steel plate

SLIDE 8

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 8

L=6m d=13mm L=1m d=8mm Doublet Geophones

Manifold

System for active damping

f ground motion

Experimental set-up (2)

Active system isolates from ground motion, does not

actively damp vibration on table top

Tap water, no pumps
Quadrupole doublet screwed on table top
Floor and table also measured simultaneously
Pipes of different diameter – all relevant for vibration!

Pipe Re d [m] Flow [l/h] fc [Hz] Tap→Manifold 2000 0.013 16.4 10.5 Manif.→Quad 2000 0.008 40.3 27.9 Quadrupole 2000 0.003 15.1 198

d u fc =

SLIDE 9

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 9

4. Results of the Measurements – Turbulence onset

50 100 150 200 10

−12

10

−10

10

−8

10

−6

Frequency [Hz] Power Spectral Density [µm2/Hz] 0 l/h 12.5 l/h 45 l/h

Lines are superimposed

Quadrupole vertical vibration (same feature for horiz) Turbulence is a threshold phenomenon, effects for flow ≥ 15 l/h

Pipe Re Flow[l/h] fc[Hz] Tap Manifold 2000 16.4 10.5

Manif. Quad

2000 40 3 . 27 .9 Quadru pole 2000 15.1 198

This value corresponds to turbulence onset in the pipes feeding the quadrupole and in the quadrupoles themselves

SLIDE 10

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 10

Low frequency content of the vibrations

Pipe Re Flow[l/h] fc[Hz] Tap Manifold 2000 16.4 10.5

Manif. Quad

2000 40 3 . 27 .9 Quadru pole 2000 15.1 198

10 20 30 40 50 60 70 10

−11

10

−10

10

−9

10

−8

10

−7

10

−6

Frequency [Hz] Power Spectral Density [µm2/Hz] 0 l/h 45 l/h 55 l/h

Vertical quadrupole vibrations Overall increase of noise level + new peaks! Main contribution to vibration at low frequency from the FEEDING PIPES. Small quadrupole pipes induce much higher frequency Peaks moving with u?

d u fc =

SLIDE 11

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 11

100 150 200 250 300 10

−13

10

−12

10

−11

10

−10

10

−9

10

−8

Frequency [Hz] Power Spectral Density [µm2/Hz] 0l/h 35l/h 45 l/h 55 l/h 70 l/h

High(er) frequency content of the vibrations

Again: Amplification of existing peaks + new peaks arising Increase of power spectral density of 1000 times! But what about the total motion?

SLIDE 12

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 12

Integrated RMS motion

10 20 30 40 50 60 70 0.5 1 1.5 2 2.5 3 3.5 4 Water flow [l/h] Vertical RMS motion above fmin [nm] fmin = 4 Hz fmin = 10 Hz fmin = 20 Hz fmin = 60 Hz

CLIC tolerances are met!! Quad stabilized at 1.3 nm above 4 Hz
Main contribution induced by vibrations below ~60 Hz (~15Hz peak)
Strong dependence of motion on water flow → careful design!

Vertical RMS motion Nominal of CTFII Effect of water: increase motion above 4 Hz by ~ 3 nm

SLIDE 13

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 13

10 20 30 40 50 60 70 80 90 100 110 10

11

10

10

10

9

10

8

10

7

10

6

Frequency [Hz] Vertical Power Spectral Density [µm2/Hz]

Flow = 25 l/h

April 23rd (night) April 26th (after) April 27th (night) May 3rd (night)

Measure done in the afternoon

Reproducibility of the measurement

Measurements reproducible – similar results over 10 days

SLIDE 14

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 14

Vibration measurement on air pressure stabilization system

10 20 30 40 50 60 70 10 20 30 40 50 60 70 Water flow [l/h] Integrated RMS motion above f0 [nm]

RMS motion above 4 Hz is 3.3 nm for flow = 30 l/h

f0 = 4 Hz f0 = 5 Hz f0 = 6 Hz f0 = 10 Hz 10 20 30 40 50 60 70 10

−10

10

−8

10

−6

10

−4

10

−2

Frequency [Hz] Power Spectral Density [µm2/Hz] 0l/h 40l/h 50 l/h 70 l/h

Peak at ~ 5 Hz

Much larger displacements – system less stiff, larger amplitudes below ~20Hz
RMS motion above 4 Hz at flow = 30 l/h is 3.3 nm
Monotone increase of displacement (at 4 Hz) with flow, driven by ~ 5 Hz peak
Still reduction of vibrations from 20 Hz to 40 Hz for flow above ~ 60 l/h

SLIDE 15

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 15

Recent measurements of stiff stabilization system

20 40 60 80 0.5 1 1.5 2 2.5 3 3.5 Water flow [l/h] Integrated RMS motion above f0 [nm]

f = 4 Hz f = 17 Hz f = 30 Hz f = 60 Hz

100 150 200 250 300 10

−12

10

−11

10

−10

10

−9

10

−8

10

−7

10

−6

Frequency [Hz] Power Spectral Density [µm2/Hz]

0l/h 30l/h 50 l/h 60 l/h 80 l/h

System with four feet (before three) – active feedback not yet optimized
Larger vibration without water (~ 2.5 nm instead of ~ 1 nm)
Smaller contribution from water to overall motion
Relevant contribution from high frequency vibrations (~ 1 nm above 60 Hz)

SLIDE 16

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 16

5. In-situ measurements – Vibration of CTFII quadrupole

50 100 150 200 250 10

−10

10

−8

10

−6

10

−4

10

−2

Frequency [Hz] Power Spectral Density [µm2/Hz] Water OFF Water ON

No big effect from cooling water! Vertical direction Same quadrupole doublets, installed on the main line of the CTFII accelerator No measure of water flow Measurements in noisy conditions (afternoon of a working day)

SLIDE 17

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 17 25 50 75 100 125 150 10

−4

10

−3

10

−2

Frequency [Hz] Integrated RMS motion above f0 [µm]

1 nm 10 nm

Water OFF Water ON

Horizontal

25 50 75 100 125 150 10

−4

10

−3

10

−2

Frequency [Hz] Integrated RMS motion above f0 [µm]

1 nm 10 nm

Water OFF Water ON

Vertical

Effect of water quite small! Background too high to see water effect?
Quadrupole stability: Vert → ~ 15 nm above 4 Hz (CLIC tol = 1.3 nm)

Hor → ~ 26 nm above 4 Hz (CLIC tol = 14 nm)

SLIDE 18

NanoBeam2002, 2-6 September 2002 – Lausanne, Switzerland Stefano Redaelli, Effect of Cooling Water on Magnet Vibrations, page 18

6. Conclusions
Results of water induced vibration of CLIC quadrupoles presented
First measurements encouraging – CLIC linac tolerances are met!

Linac quad stabilized at 1.3 nm above 4 Hz with nominal water flow

Simple theory – good order of magnitude for vibrations frequency,

not good the estimate of vibration amplitudes

Vibration properties of quadrupoles depends on stabilization device
Studies on going to improve theoretical understanding
Importance of the pipes feeding

the magnets

RMS motion above 4 Hz driven