1

StaFF Progress Report

David Urner

University of Oxford

2

Cast

Dr. David Urner Dr. Paul Cole Dr. Armin Reichold

Stephanie Yang(mechanical engineering)

Tony Handford(workshop)

Roy Wastie(electrical engineering)

3

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.

4

Generic Tools

• Straightness monitor

• Distance meter (build first)

5

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.

6

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.

7

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

8

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

9

The Distance Meter: Michelson mode

• Length motion leads to change in interference pattern– Measure intensity I.

IFixed Laser Frequency

10

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

11

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

12

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

13

3–D mechanical model, detector side removed for clarity

14

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

15

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

16

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

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

18

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

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

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

21

Simulated Interference Patters

22

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

23

A Straightness Monitor Made from Distance Meters

• Information related via central triangle

Floor node

A

B

Ceiling node 1Ceiling node 1

24

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

25

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

26

ATF at KEK

27

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

28

Spider web Design with Opto-Geometrical Simulation: Simulgeo

29

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.

30

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.

31

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.

32

First Concept on how to Align Distance Meters in Network

33

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.

34

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

35

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