Transcript orsay2006_4_urner

StaFF Progress Report
David Urner
University of Oxford
1
Cast
Dr. David Urner
Stephanie Yang
(mechanical engineering)
Dr. Paul Cole
Tony Handford
(workshop)
Dr. Armin Reichold
Roy Wastie
(electrical engineering)
2
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.
3
Generic Tools
• Straightness monitor
• Distance meter (build first)
4
Distance Meter:
Method of Measurement
Laser
Reference Interferometer
Wavelength: 1550nm
Pump
(optical amplifier)
DAQ
Distance
Meters
Keep costs
down
for distance meters so that overall cost
• Distance
meter
2 modes:
– Michelson
mode:
scale
favourably.
• fast,
• relative distances
• resolution nm
– FSI mode:
• slow
• Absolute distances
• Precision 1mm.
5
The Distance Meter: FSI Mode
I
Laser tune
•
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.
6
Amplitude / Arb units
The Distance Meter: FSI Mode
15
I
10
5
0
0.3
0.4
0.5
Length / m
• 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!
7
FSI: Reference Interferometer
Reference Interferometer
Wavelength: 1550nm
Tuning: 1530-1560
Phase
Laser
DAQ
Distance
Meters
time
• 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.
8
The Distance Meter:
Michelson mode
I
Fixed Laser Frequency
• Length motion leads to change in interference
pattern
– Measure intensity I.
9
The Distance Meter:
Michelson mode
Fixed Laser Frequency
• 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.
10
Pay Attention to Systematic Effects
Laser
Reference Interferometer
Wavelength: 1550nm
Tuning: 1530-1560nm
DAQ
Distance
Meters
• Understanding the behaviour of laser is key!
• FSI mode:
– Can we get better handle on tuning speed?
11
Piezzo Driven Monitor
Laser is tuning continuously
(Derive phases modulo 2p
from intensity data)
PZT
Moving
Mirror
Mirror
Detector
Phase f/radians
4
3
2
1
0
-1
-2
-3
-4
980
Splitter
1000
1020
1040
1060
1080
Phase stepping cycle
Detector
Splitter
Mirror
Single
Point
measurement
Splitter
Mirror
Tuning laser
12
Moving mirror: Measure Intensity pattern
3–D mechanical model, detector side removed for clarity
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Systematic Effects: Laser
Piezzo driven monitor
Laser
Reference Interferometer
Wavelength: 1550nm
Tuning: 1530-1560nm
DAQ
Distance
Meters
• Understanding the behaviour of laser is key!
• FSI mode:
– Can we get better handle on tuning speed?
14
Systematic Effects: Laser
Piezzo driven monitor
Laser
Reference Interferometer
Wavelength: 1550nm
Tuning: 1530-1560nm
Lock to absorption line
DAQ
Distance
Meters
• 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).
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Other Systematic Effects
Piezzo driven monitor
Laser
Reference Interferometer
Wavelength: 1550nm
Tuning: 1530-1560nm
Lock to absorption line
DAQ
Distance
Meters
• 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.
16
First Temperature Measurements
2
Reference channels
10
Ref V / mV
Temperature change / mK
15
Thermometer channels
0
-2
0
10
20
30
40
Time / s
5
0
-5
0
10
20
Time / s
30
40
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• 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
Amplitude / Arb units
Status of Distance Meter
Development
Raw data of 2 channels
recorded simultaniously
15
10
5
0
0.3
0.4
0.5
Length / m18
Fourier spectrum
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
19
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
20
Simulated Interference Patters
21
A Straightness Monitor Made from
Distance Meters
Setup planned at KEK
A
B
• Red lines: Distance meter.
• Multilateration measure 6D coord. of A with respect to B.
22
A Straightness Monitor Made from
Distance Meters
Ceiling node 1
Ceiling node 1
A
B
Floor node
• Information related via central triangle
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A Straightness Monitor Made from
Distance Meters
Ceiling node 1
Ceiling node 1
A
B
Floor node
• 3 nodes on each object, with 3 distance meters to each
triangle node
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A Straightness Monitor Made from
Distance Meters
Ceiling node 1
Ceiling node 1
A
B
Floor node
• 3 nodes on each object, with 3 distance meters to each
triangle node
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ATF at KEK
26
Implement system at ATF/KEK
relating positions of nano-BPM’s
Nano-BPM
Built by
SLAC group
Nano-BPM
Built by
KEK group
• Advantage:
– Nano-BPM have 5-100 nm resolution: cross check of results
– Test of distance meter in accelerator environment
27
Spider web Design with OptoGeometrical Simulation: Simulgeo
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Spider web Design with OptoGeometrical 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 OptoGeometrical Simulation: Simulgeo
• Resolution of distancemeter:
1nm
• Mount precision of
distancemeter: 1nm
• Angle precision of
distancemeter holder: 10 mrad.
SLAC BPM: reference
KEK BPM variable (6D):
Position: x:32 y:19 z:2 nm
Angle: x:0.01 y:0.01 z:0.1 mrad
~1mm 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.
31
First Concept on how to Align
Distance Meters in Network
32
BPM Nodes
• One wide angle retroreflector (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.
33
Force Free Mount
-3N
• 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.
Strain Gauge
2N
1N
0N
-1N
Firm
-2N
connection
Attached to BPM.
-3N
-1mm
1mm
Holds -3mm
retro reflector.
Force exerted on
carbon frame (BPM)
±1mm: < 0.5N/mm
±3mm: < 0.8N/mm
Here attach
vacuum tube for
interferometer
3mm
Force exerted by perpendicular motion
34
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
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