JINR: V. Batusov, J. Budagov, M. Lyablin, G. Shirkov CERN: J-Ch. Gayde, B. Di Girolamo, H. Mainaud

Durand, D.Mergelkuhl, M. Nessi, G. Stern

Presented by M. Lyablin

Precision laser metrology for the modern Accelerators

2

Precision Laser Fiducial line in air Introduction The next generation of linear colliders is very

demanding concerning the alignment tolerances of their components. For the CLIC project, the reference axis of the components will have to be pre-aligned within 10 µm at 1 sigma with respect to a straight line in a sliding window of 200 m

A new proposal is using a laser beam over 150 m as a straight alignment reference.

The method is based on the laser beam space stabilization effect when a beam propagates in atmospheric air inside a pipe with standing acoustic wave.

Observation of the effect of the stabilization of the laser ray space location inside the tube with the standing acoustic waves

Demonstration to the CERN delegation (R.Cashmore at all) of the laser ray stabilization effect inside the tube. This photo was made during the period of high precision laser controlled assembly in Dubna of the MODULES of ATLAS TAIL Hadron Calorimeter.

Our experimental R&D’s have shown that independent of direct sun rays and of an air heat fluxes we found as a very significance by an order of magnitude- decrease of the laser beam space noise oscillation.

We found that the laser beam space uncertainty is strongly decreased upon ray exit of a tube with the STANDING ACOUSTIC WAVES in an atmospheric air inside.

The left Figure is the σT uncertainty for the “case with the tube“.The right Figure is the R= σA/ σT ratio with σA for “no tube ” case.The factor R≈120x gain is an impressive result we observed for 70 m tube.

0 10 20 30 40 50 60 70 800,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

т(m)

L(m)0 10 20 30 40 50 60 70 800

20

40

60

80

100

120

140

160

180

R=В/

Т

L(m)

σT(μ) R=σA(μ)/ σT(μ)

We propose to use as an EXTENDED COORDINATE AXIS the low σT laser beam obtained on the base of above described new

effect.

5

Laser Fiducial line: operation and design

QPre

Ae

Ab

Am

δ

Laser spot

Laser

ColimatorQPrm

The Laser Fiducial Line (LFL) measuring system uses a laser beam as the reference of alignment, with its beginning and end points Ab and Ae

determined in the global reference frame of the tunnel.

6

Final QPR

Two-axis linear positioner

Concrete basis

SupportLaser beam

Ae

2-axis positioners are neededfor precise alignment center of the quadrant photodetectorwith the laser beam axis

Optical fiber

Laser beam

CollimatorConcrete basis

SupportLaser

Angular positioner

The fiber-optic input of the laser radiation into the LFL

Beginning and end points of the Laser Fiducial Line

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Intermediate points of measurements

Plane-parallel plate(PP)

Measuring station with measurd point-O

Measured point-O

Two-axis linear positioners

Space stabilized laser beam

(fiducial line)

Measuring QPR

Not destroying control system position measured point O

8

Thermal stability of the laser ray positionTube

Laser beam

Transparent glass

The short term laser ray stabilization scheme

We use effect of laser beam stabilization when it propagates inside an atmospheric air filled pipe with standing acoustic waves

Thermostabilizedair flux

Laser beam

Outer tube with a heat insulation coating

System of short-term stabilization

Long term stability system

Two tubes set was used. Between tubes the termostabilised air flux is propagating

With allowed few microns for the laser ray displacement from primary direction the long-term temperature stabilization is to be in the level of 0.5 0C

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Optimal collimation laser beamZmax

D0

The telescopic collimator

Zmax

√2 D0=Dmax

The profile of collimated laser beam

√2 D0

The laser beam profile with optimal collimation

0 1 2 3 4 5 6 7 8 9 100

50

100

150

200

The laser beam optimal propagation length in function of Laser single-mode beam diameter

Leng

ht (m

)

Diameter laser beam (mm)

laser

=0.4

laser=0.63

Laser beam diameter(mm)

Lk(m)

0 5 10 15 20 25 30 35 40 45 500

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

laser

=0.4

laser=0.63

Lk (m)

Diameter laser beam (mm)

The laser beam optimal propagation length in function of Laser single-mode beam diameter

The collimation length Lk of single mode laser beam in function of beam starting diameter: (A) for D by 10mm ;(B) for D by 50 mm

(A) (B)

The measurement stations– global coordinate system

BALaser beam

Y

Z

X

Laser

The quadrant photoreceiver QPr1

with adapterA2

The Total Station target with adapter A1

DC

В2В1

Т2D – linear positioner

Т1 Т2

O

X’Z’

Y’

For the 50m laser line an Total Station measurements the difference was nearly 100μm for 16 meters length

 Including of the Laser Fiducial Line to the global coordinate system; the LFL precision control by Total Station in an open air media

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Main principle : use reflected laser beam from horizontal surface liquid

θ

ψ

LaserQPR

Original direction of the reflected beam

BaseCuvette with a liquid The surface of the liquidin case of horizontal basis The surface of the liquid

with tilt base

Directionof the reflected beamafter tilt of base

The principle of construction of the registration device to measure the seismic slope of the Earth’s surface.

Angular seismic stabilization by the precision INCLINOMETER

The experimental set-up

L

QPr

C

О1

О2

Sensor S

О

SMCF

50 cm

50 cm

•L-laser•QPr-quadrant photodiode•O,O1,O2- bases•SM-semitransparent mirror •C-calibration screw•CF- collimator with changeable focus

frequency internal of 10-4Hz÷1HzThe achieved inclinometer angular precision is 5 10-9 rad

The inclinometer tests

7,7 7,8 7,9 8,0 8,1 8,2 8,38,0

8,5

9,0

9,5

10,0

10,5Beginning of earthquake7h 50min (Geneva time):26 February 2011

B

Earthquake In Sibiria 26 February 2011; 6h 17min (World time)

A

(r

ad)

Geneva time(h)

•The Earth quake in Siberia on February 26, 2011•Average amplitude of quake in Siberia was 6.5 units•The distance to Geneva- L=6160km•Calculated time of Earth quake begin Tcalc=6h 21 min in Siberia (world time)

practically coincides with the published Tpub=6h 17 min •Amplitude of angular oscillations was 2 10-6 rad

The angular component of the Earth quake

0 1 2 32,4

2,6

2,8

3,0

3,2

3,4

3,6

3,8

4,0

4,2

4,4 Measurement 28 Febr. 2012 3h 17min AM

Dev(rad

)

Time (min)

Earth surface single oscillation

•The observation of an earth surface “single inclination” effect•Amplitude was a few μrad

Earth angular surface oscillations of an industrial noise origin

11 12 131

2

3

4

5

6

7

DC

BA

Dinner time

De

v(r

ad

)

Time (h)

Industrial origin noise: -high activity of auto– traffic,-works in the neighboring (with our set-up) Lab room,-people movement close to detecting set-up etc.

σ values : -in work period(CD) 0.3 μrad-In dinner time(AB) 0.04 μrad

0 1 2 311,4

11,5

11,6

11,7

11,8

11,9

12,0

12,1

12,2

12,3

12,4

12,5

0.3 radDe

v (

rad

)

Time (min)

The measured inclination of the concrete floor

Concrete floor inclination dueto man presence in 3 meters distance from the experimental set-upAmplitude was 0.3μrad

The day measurement angular movement of the concrete floor

The microseismic peak observation by ground angular motion

0 10 20 30 40 50 60 70 80 90 100 110 1200,04

0,06

0,08

0,10

0,12

0,14

0,16

De

v(

rad

)

Time(sek)

The seismogram of an earth surface angular oscillation at the “microseismic peak” frequency

0,01 0,1 10,00

0,01

0,02

0,03

0,04

0,05

fd

BA

Am

plitu

de

(r

ad

)

Frequency (Hz)

Fourier analyses of oscillation at the “microseismic peak

Amplitude of Earth surface oscillation at the “microseismic peak” frequency was 0.03μrad with frequency fd=0.13Hz.Inclinometer sensitivity estimate gives ≈5·10-9 rad.

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The long experimental setups space location stability and an earth surface angular oscillations

θmpθmp

Linear accelerator-colliderExperimental Hall

The Earth surface fixed time picture:

surface deformation induced by the standing waves originated by the interference of “microseicmic peak”

Line of horizon

The accelerator-collider positioning on the earth surface deformed by the microseismic peak wave

Different accelerator parts are inclined relative to the ”basic” horizontal

line and consequently particle beams going through the focusing elements

leave them with some angular spread θmp relative to the nominal. As a result it leads to random motion of position of focuses

accelerators

If we can stabilize the angular movements of the accelerator

with an accuracy of 10-9rad we will be able to stabilize position of its focuses to within 50 nm

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Conclusion As a summary, different technical issues of a 150 m and accuracy 10μm LFL in atmospheric air were discussed, showing that the combination of: Single mode laser associated with a fiber beam coupler for the light emitting point An optimal laser ray focusing collimation An intermediate sensor having no impact on the straightness of the beam The calibration of each sensor The suppression of air media refraction index and long term variation of temperature The isolation of the laser source from angular seismic industrial noisecan lead to an alignment system providing the location of points within 10µm.Such an alignment system opens new perspectives to reach a new precision level of alignment for projects like CLIC, ILC.

 

An original method for precision measurements when alignment of beam pipe ends on a reference axis has been proposed and tested. The test measurements have been performed using jointly the LRL in a 2D local coordinate system and a Total Station survey instrument in a global 3D coordinate system. The fiducial marks at the pipe ends have been measured with both instrumentations. A transformation to a common coordinate system has been applied to allow the comparison of the results.The results of the measurements coincide to an accuracy of approximately ±100 µm in the directions perpendicular to a common reference line close to the laser beam and for a pipe placed at the middle of a 50m line.

ConclusionThe ground motion was studied by the detection of an earth

surface angular oscillation. Instrumentally method is based on the conceptually new design laser inclinometer using the reflecting surface liquid, as a space stable (horizontal) reference level. The achieved inclinometer measurement precision was experimentally proved to be ≈5·10-9 rad.

The achieved laser inclinometer sensitivity was proved by observation (in Geneva) of:

Ground 2µrad oscillation caused by the Siberian earth quake (6160 km);

Single 1÷2 µrad oscillation of origin to be studied;Industrial origin noise of about 3 10-7 rad amplitude;Microseismic peak for the first time recognized as a ground

≈3 10-8rad angular oscillation at 0.13Hz frequency.The last observed effect if properly “compensated” by

adequate instrumental method could give significant colliders luminosity increase by reduction of beams intersection area to about 50nm level (an estimate) due to some suppression of the lateral focus effect.

The instrument of this sort may happen to be useful for modern high precision research equipment stabilization, for example, of large telescope to reach an extreme resolution.