MONALISAat CLIC

David Urner

Paul Coe

MatthewWarden

Armin Reichold

Monitoring, Alignment & Stabilisation with high Accuracy

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MONALISA

• Is an interferometric metrology system for continuous monitoring of position critical accelerator components

• Consists of a fixed network of evacuated interferometric distance meters

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Concepts

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Compact Straightness Monitor

• 6D position transferred from left to right– breaking of symmetries is important

• Preliminary simulation results of CSM Resolution: – y:10nm – distance meter resolution: 1nm = Resolution in z-direction– Positional change of optics components with respect to each other: 1nm. That’s the challenge!

10cm

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Measurement lines

We measure distances along measurement lines using two techniques:•Absolute distance interferometry <m resolutions•Displacement interferometry nm resolutions

Each line is the same, and is capable of performing both types of measurement.

Absolute distanceDisplacement

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Interferometer operation

Intensity

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Interferometer operation

Phase = 2π (Optical Path Distance) / Wavelength

Φ = 2π D / λ = 2π D (ν / c)

D = (c/ 2π) (ΔΦ/Δnu)

R = (c/ 2π) (Δθ/Δnu)D = R (ΔΦ/Δθ)

ΔD = (c/2π ν) ΔΦ

Fixed Frequency Interferometry

Frequency Scanning Interferometry

frequeny scanning

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Distance meter

• Measurement Frequencies:– FFI: up to 10kHz– FSI: up to 1Hz

• Long term stability determines low frequency behaviour– Minutes possible– Lot of work needed to extend to hours or days.

• Advantage of interferometric measurement system is fairly low cost per line.– Use of telecom frequency allows use of cheap commercial

hardware– Cheap amplification of light– Current estimate: as low as £800 per distance metre

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Current Status

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Fixed Frequency Interferometry

0 200 4000.2

0.4

0.6

0.8

1.0

Ph

oto

dio

de

sig

na

l / a

.u.

time / ms

0 200 400

-4

-2

0

Dis

pla

cem

en

t / m

Time / ms

Measurement over 400mm distance

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Frequency Scanning Interferometry

Measurement over 400mm distance

=750nm=70nm

Add box to reduce air turbulence

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Fixed Frequency Interferometry

• Must reach low level of uncertainty for:– Laser frequency– Refractive index

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Vacuum System

8 way fibre ribbon

Tapered hole

Vacuum vessel wall

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Frequency Stabilisation• Lock laser to spectral feature of rubidium• Use a frequency doubling crystal to reach this

frequency

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Operation at KEK

ATF2 Final focus region

Shintake Monitor

Final Focus Quadrupole

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Summary

• Current status– 5nm FFI resolution (at 400mm distance)– 70nm FSI resolution (at 400mm distance)

• Future– Reduce uncertainties with vacuum and laser

stabilisation for FFI and dual laser scanning for FSI– Test a full system in an accelerator environment at

KEK– Monitor beam-line element at CTF3– Improve resolution to sub-nanometer scale