1 StaFF Progress Report David Urner University of Oxford.
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Transcript of 1 StaFF Progress Report David Urner University of Oxford.
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1
StaFF Progress Report
David Urner
University of Oxford
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2
Cast
Dr. David Urner Dr. Paul Cole Dr. Armin Reichold
Stephanie Yang(mechanical engineering)
Tony Handford(workshop)
Roy Wastie(electrical engineering)
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Measuring Motion
• At the ILC beam delivery system many magnets have to be stable with respect to each other to achieve high luminosities. – Final focus doublet– Critical magnets in BDS– Position monitoring of BPM’s in energy chicane.
• Often no direct line of sight:– Correlate position information of magnet to stable
platform (e.g. anchored in ground) interferometrically.– Can be coupled with very large accelerometer
performing better at small frequencies.– Correlate the stable platforms interferometrically.
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4
Generic Tools
• Straightness monitor
• Distance meter (build first)
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Distance Meter: Method of Measurement
• Distance meter 2 modes:– Michelson mode:
• fast, • relative distances • resolution nm
– FSI mode:• slow• Absolute distances • Precision 1m.
DistanceMeters
Laser Reference Interferometer
Wavelength: 1550nm DAQ
Pump(optical amplifier)
• Keep costs down for distance meters so that overall cost scale favourably.
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Laser tune
I
The Distance Meter: FSI Mode
• Blue (long) arm reflected at Retro-reflector returning light at same angle– Slightly defocus lens → returning light is spread to ~1mm circle at launch plane.
• Red (short arm) reflected at far end of lens– Both arms cross same amount of material (1. order) – Close end of lens has to be anti-reflection coated.– Chose lens: short arm is reflected into small region.
• Red (short arm) and blue (long arm) interfere.• FSI: Needs only one return line.• Tune laser from 1530-1560 nm.
– #wavelength-#wavelength changes – For constant tuning speed: constant FSI frequency.
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The Distance Meter: FSI Mode
• Measure fringe frequency using fast Fourier transformation.– #fringes * frequency → total phase advance.– Known effective length of reference → effective length of
distance meter.– Fourier spectrum measures all frequencies → all interferences at
all distances!
I
0.3 0.4 0.5
0
5
10
15
Am
plitu
de /
Arb
uni
ts
Length / m
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Laser Reference Interferometer
DistanceMeters
Wavelength: 1550nmTuning: 1530-1560
DAQ
FSI: Reference Interferometer
• Laser: Constant tuning speed?– Unfortunately no.
• Reference interferometer developed for LiCAS.• Use Reference interferometer to unfold phase advance. • Then correct phase information from all distance meters.
time
Phas
e
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The Distance Meter: Michelson mode
• Length motion leads to change in interference pattern– Measure intensity I.
IFixed Laser Frequency
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The Distance Meter: Michelson mode
• Length motion leads to change in interference pattern– Measure intensity I.
• Add more lines– Each line will have another path length difference.– 4 lines enough to calculate exact motion.
Fixed Laser Frequency
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Pay Attention to Systematic Effects
• Understanding the behaviour of laser is key!
• FSI mode: – Can we get better handle on tuning speed?
Reference Interferometer
DistanceMeters
Wavelength: 1550nmTuning: 1530-1560nm
DAQ
Laser
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Piezzo Driven Monitor
Detector
Detector
PZT
MovingMirror
Mirror
Mirror
Mirror
Splitter
Splitter
Splitter
Tuning laser
SinglePointmeasurement
980 1000 1020 1040 1060 1080
-4
-3
-2
-1
0
1
2
3
4
Phase stepping cycle
Laser is tuning continuously
Pha
se
/rad
ian
s
(Derive phases modulo 2from intensity data)
Moving mirror: Measure Intensity pattern
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3–D mechanical model, detector side removed for clarity
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Systematic Effects: Laser
• Understanding the behaviour of laser is key!
• FSI mode: – Can we get better handle on tuning speed?
Reference Interferometer
DistanceMeters
Wavelength: 1550nmTuning: 1530-1560nm
DAQ
Laser
Piezzo driven monitor
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Systematic Effects: Laser
• Understanding the behaviour of laser is key!• Michelson mode:
– Stable frequency needed (unbalanced arm length) at level ~30kHz!
• Lock Laser to absorption line (very hard at 1550nm).• Equip reference with Michelson Mode readout. → Change of
reference interferometer information measures frequency change (assuming length is stable).
Reference Interferometer
DistanceMeters
Wavelength: 1550nmTuning: 1530-1560nm
DAQ
Laser
Piezzo driven monitor
Lock to absorption line
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Other Systematic Effects
• FSI mode: – Length change of distance meter during tuning (1nm → ~40nm error).
• Scan rapidly → Piezzo driven monitor will not work!• Use Michelson information of distance meter to track length change.• Use both methods.
• Vacuum enclosure of distance meters needed.• Temperature effects.
Reference Interferometer
DistanceMeters
Wavelength: 1550nmTuning: 1530-1560nm
DAQ
Laser
Piezzo driven monitor
Lock to absorption line
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170 10 20 30 40
-5
0
5
10
15
0 10 20 30 40-2
0
2
Te
mp
era
ture
ch
an
ge
/ m
K
Time / s
Re
f V
/ m
V
Time / s
Reference channels Thermometer channels
First Temperature Measurements
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Status of Distance Meter Development
• Double peak found in two different prototypes.
• Ruled out possibility of analysis artefact.
• No obvious reflective surfaces
• Software in place now to analyse data within minutes after data taking should enable us to trace the problem
0.3 0.4 0.5
0
5
10
15
Am
plitu
de /
Arb
uni
ts
Length / m
Raw data of 2 channels recorded simultaniously
Fourier spectrum
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Distance meter simulation
• Simulation done with Zemax
• Use non-sequential mode– Take into account
polarisation → correct interference pattern
– Allows stray light analysis
• Allow analysis of chromatic aberrations
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Distance meter simulation
• Simulation done with Zemax
• Use non-sequential mode– Take into account
polarisation → correct interference pattern
– Allows stray light analysis
• Allow analysis of chromatic aberrations
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Simulated Interference Patters
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A Straightness Monitor Made from Distance Meters
Setup planned at KEK
• Red lines: Distance meter. • Multilateration measure 6D coord. of A with respect to B.
A
B
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A Straightness Monitor Made from Distance Meters
• Information related via central triangle
Floor node
A
B
Ceiling node 1Ceiling node 1
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A Straightness Monitor Made from Distance Meters
• 3 nodes on each object, with 3 distance meters to each triangle node
Floor node
A
B
Ceiling node 1Ceiling node 1
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A Straightness Monitor Made from Distance Meters
• 3 nodes on each object, with 3 distance meters to each triangle node
Floor node
A
B
Ceiling node 1Ceiling node 1
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ATF at KEK
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Implement system at ATF/KEK relating positions of nano-BPM’s
• Advantage: – Nano-BPM have 5-100 nm resolution: cross check of results– Test of distance meter in accelerator environment
Nano-BPM Built by SLAC group Nano-BPM
Built byKEK group
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Spider web Design with Opto-Geometrical Simulation: Simulgeo
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Spider web Design with Opto-Geometrical Simulation: Simulgeo
• Allows objects to be placed (6D) in hierarchal structure– Reference placements.– Fixed placements (with error).– Variable placements (the
objects to measure).
• Objects can be points, mirrors, distance meters…– Distance meter assume
measurement between points with error.
• Big matrix inversion takes into account all errors and constrains 6D position of all points.
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Spider web Design with Opto-Geometrical Simulation: Simulgeo
• Resolution of distancemeter: 1nm
• Mount precision of distancemeter: 1nm
• Angle precision of distancemeter holder: 10 rad.
SLAC BPM: referenceKEK BPM variable (6D):
Position: x:32 y:19 z:2 nmAngle: x:0.01 y:0.01 z:0.1 rad
~1m absolute distance resolution needed to determine constants required to solve geometry.
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Triangle Nodes
• Distance meter heads located in triangle nodes.
• Floor node– Overall resolution improves if
firmly anchored.– Dome anchored separately
from interferometers.
• Ceiling nodes: position stability unimportant.
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First Concept on how to Align Distance Meters in Network
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BPM Nodes
• One wide angle retro- reflector (cateye) for each node
• Challenges: – Relative position between
retro-reflector needs to be known to 1nm
• Requires measurement between 3 nodes on each nano-BPM.(blue lines).
– Attachment of vacuum lines to BPM’s
• Requires zero-force design.
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Force Free Mount
Here attach vacuum tube for interferometerAttached to BPM.
Holds retro reflector.
Firmconnection
Strain Gauge• Needs bellow to allow motion of BPM– Vacuum causes a force
order of 100N!
• Develop small force vacuum mount using double bellow system.
• Allows small motion (~1 mm) of BPM-system
• Test stand to measure remaining (perpendicular) force on BPM frame. -1mm-3mm 1mm 3mm
1N
2N
-1N
0N
-2N
-3N
-3N
Force exerted on carbon frame (BPM)±1mm: < 0.5N/mm±3mm: < 0.8N/mm
Force exerted by perpendicular motion
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Concluding Remarks
• Developing– Software to understand distance meter.– Hardware to characterize laser.– Temperature sensing system.
• First optical simulation in place.• Force Free mount system seems to work.• Starting work on Mount/Alignment system for
distance meter setup at KEK• Still much to do
– but things start to fall into place