David Urner, Oxford University, RHUL – June 2005

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StaFF Stabilization of Final Focus

Motion Stabilization with Nano-Meter Precision

David UrnerPaul Coe

Armin ReicholdOxford University

David Urner, Oxford University, RHUL – June 2005

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Task• Development of active feedback systems for

e.g. final focus quadrupoles or beam position monitors in the energy chicane. – Develop laser-interferometric methods

to monitor relative position of 2 objects • at nanometer scale • at separations of order 10m.• Timescales of 100-0.01 Hz

– Develop and implement algorithms for active stabilization.

KEK: Integrated spectrum of vertical motion

David Urner, Oxford University, RHUL – June 2005

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Measurement of Relative Motion

• Typical situation:

– Need straightness monitor to measure relative motion.

(Leave for development later).

– Need distance meter to project out. (Develop first).

Quadrupole Quadrupole~10m

Reference Structure Reference

Structure

Vertical & angular position measurement of ref. structure

Straightness monitor to measure relative vertical movement between ref. structures

David Urner, Oxford University, RHUL – June 2005

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A Straightness Monitor Made from Distance Meters

• Measure relative vertical motion of object A versus object B. (in fact measure 6D coordinates)

A

B

David Urner, Oxford University, RHUL – June 2005

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A Straightness Monitor Made from Distance Meters

• Red lines: Michelson interferometer displacement meter nm resolution.• Multilateration requires absolute distance meter with m resolution: FSI.• Both systems with same setup!

A

B

David Urner, Oxford University, RHUL – June 2005

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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

David Urner, Oxford University, RHUL – June 2005

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A Straightness Monitor Made from Distance Meters

• 3 nodes on each object, with 3 distance meters to each triangle node• Network has to be placed in vacuum tubes to achieve nm resolutions.

Floor node

A

B

Ceiling node 1Ceiling node 1

David Urner, Oxford University, RHUL – June 2005

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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

David Urner, Oxford University, RHUL – June 2005

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Relevance of StaFF Experiment for Nano-BPM Studies

• Unfold nano-BPM resolution and broadening caused by mechanical relative motion between the two BPM setups.

• Each setup uses 3 BPM’s also establishing beam angles. Two sets can in principle measure relative displacements– Each beam bunch differs in position and angle → over-

constrained system needed.

• 2-platform stability important for energy chicane– BPMs measure beam position, StaFF measures relative position

motion.

David Urner, Oxford University, RHUL – June 2005

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Spider web Design with Opto-Geometrical Simulation: Simulgeo

David Urner, Oxford University, RHUL – June 2005

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Spider web Design with Opto-Geometrical Simulation: Simulgeo

David Urner, Oxford University, RHUL – June 2005

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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).– Variible 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.

David Urner, Oxford University, RHUL – June 2005

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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.

David Urner, Oxford University, RHUL – June 2005

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Progress Since last Meeting

• Chose grid setup based on simulation results.

• Presented proposal for experiment at KEK.

• Started to setup first prototype of displacement meter.

• Started to design vacuum system.

David Urner, Oxford University, RHUL – June 2005

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Some things we learned from the Simulgeo simulation

• Distance meter holder:

SLAC BPM: referenceKEK BPM variable (6D):

Position: x:32 y:19 z:2 nmAngle: x:0.01 y:0.01 z:0.1 rad

Distance meter holder

Focusingoptics

Focusingoptics

Fiber inputs/outputs

1 cm

Virtual spot

- Virtual spot of 100 m: Angle precision of

distancemeter holder: 10 rad.

- Angle precision needed: 0.1 rad!!!

David Urner, Oxford University, RHUL – June 2005

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Distance Meter

• Michelson at least 4 measurements to determine length of fringe spacing.– Imbalance of arm length

requires very 10-10 stability in frequency

• FSI: scan over large frequency range, count number of fringes and infer absolute distance.

• Collimating lens produces plane waves.

• Virtual spot can be achieved by dual lens system and cylindrical waves.

David Urner, Oxford University, RHUL – June 2005

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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.• All triangle nodes

– Angular stability of node needed to about 10 rad.

David Urner, Oxford University, RHUL – June 2005

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BPM Nodes

• One wide angle retro- reflector (cateye) for each node– Removes angular stability

problem for retro-reflector 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.

David Urner, Oxford University, RHUL – June 2005

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Steps needed to build an optical anchor • R&D at Oxford:

– Michelson Interferometer prototype in Lab.– FSI with same setup.– Build frequency stabilized laser. – Test zero force mounting mechanics prototype. – Design vacuum system.– Build triangle and BPM nodes ready for KEK.– Write algorithm and software for active stabilization.– Closing of feedback loop.

• R&D at KEK:– Run single arm prototype in accelerator environment.– Measure angular deflection of I beam.– Mount floor and BPM nodes.– Survey mounted nodes.

– Mount vacuum tubes.– Install interferometer.– Setup and first test of system.

Nov 05Nov 05Jun 06Aug 05Sep 05Dec 05Aug 06Dec 06

Jan 06

Apr 06

David Urner, Oxford University, RHUL – June 2005

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Stabilization

• Actively stabilize setup using input from interferometers: – Both Nano-BPM setups are mounted on actuators.– Use movers on SLAC setup for coarse angle adjustment.– Use piezo movers on KEK setup for small adjustments.

• We measure the relative motion of the two reference frames of the SLAC and KEK BPM’s– Closed loop feedback system relates the KEK reference bar to

the KEK nano-BPM’s.– Independent information from relative motion measurement

relating SLAC carbon fibre frame to the SLAC nano-BPM’s.– Overall feedback loop has to integrate 3 measurements!

• 100-0.01Hz (or preferably even slower) is unusual frequency range for feedback system and might require some fundamental study.

David Urner, Oxford University, RHUL – June 2005

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An Interesting Stabilization Task

• Integrate information from StaFF and KEK stabilization feedback loop.

• Anticipate interesting effects if two feedback systems are combined• BPM groups would like us to extend stabilization range into the hour

range.• We need help!

– Simulation of double feedback system.– Development of algorithms, which are able to cancel slow drifts.

KEK SLAC

Closed loop feedback for each BPM Take into account

relative motion Between BPM and tube

David Urner, Oxford University, RHUL – June 2005

22

An Interesting Stabilization Task

• Integrate information from StaFF and KEK stabilization feedback loop.

• Anticipate interesting effects if two feedback systems are combined• BPM groups would like us to extend stabilization range into the hour

range.• We need help!

– Simulation of double feedback system– Development of algorithms, which are able to cancel slow drifts

KEK SLAC

Closed loop feedback for each BPM Take into account

relative motion Between BPM and tube

David Urner, Oxford University, RHUL – June 2005

23

An Interesting Stabilization Task

• Integrate information from StaFF and KEK stabilization feedback loop.

• Anticipate interesting effects if two feedback systems are combined• BPM groups would like us to extend stabilization range into the hour

range.• We need help!

– Simulation of double feedback system.– Development of algorithms, which are able to cancel slow drifts.

KEK SLAC

Closed loop feedback for each BPM Take into account

relative motion Between BPM and tube