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Armin Reichold. David Urner. Paul Coe. Matthew Warden. MONALISA at CLIC. Mon itoring , Ali gnment & S tabilisation with high A ccuracy. MONALISA. Is an interferometric metrology system for continuous monitoring of position critical accelerator components - PowerPoint PPT Presentation
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MONALISAat CLIC
David Urner
Paul Coe
MatthewWarden
Armin Reichold
Monitoring, Alignment & Stabilisation with high Accuracy
18. 3. 08 D. Urner 2
MONALISA
• Is an interferometric metrology system for continuous monitoring of position critical accelerator components
• Consists of a fixed network of evacuated interferometric distance meters
18. 3. 08 D. Urner 3
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