The stabilisation of the final focus (StaFF) system

Sun 12th March 2006 MDI – LCWS06 at I I Sc Bangalore

David Urner, Paul Coe, Armin Reichold

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Linear Collider : $ into Luminosity

• LC physics output ~ Collision precision

• Collisions rely on bunches :– Bunch “quality” approaching collision– Transverse positions approaching collision

• and magnet stability :– stability of final focci producing the collision

where StaFF comes in

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Aims of StaFF

• To monitor relative stability of vital components down to the nm scale

• To use interferometers in a grid around the vital components

• To use established interferometry techniques with novel design interferometers

• To measure positions at least at 100 Hz

Detector

Quadrupole

Quadrupole10 m

Detector

Detector

Detector

ProjectOut

ReferenceObjects

Direct line of sight

Machine – Detector Interface

No Direct line of sight

ReferenceObjects

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Other uses e.g. Beam - delivery

~1 km

Same system can be deployed forbeam – delivery magnets, BPMs etc

energychicane

Example nano-BPMs at KEK / ATFConvenient Ceiling

Floor

Convenient ceiling object

Beamlineaxis Optical Grid

(Vacuum lines)

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

A

BNANO BPMsAt A & B

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Example nano-BPMs at KEK / ATF

Triangle across girderdown to Floor node

Floor node

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

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 rel. unimportant.

• All triangle nodes– Angular stability of node

needed to about 10 rad.FLOOR NODE

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

• Allows objects to be placed (6D) in hierarchal structure– Reference positions.– Fixed positions (with error).– Variable placements (the

objects to be measured).

• Objects can be points, mirrors, distance meters…– e.g. Distance meter assumes

measurement between points with error.

• Matrix inversion accounts for errors and attempts to constrain 6D position of all points.

ATF at KEK

Written by Laurent Brunel : for CMS alignment c.1999

Spider web Design with Opto-Geometrical Simulation: Simulgeo

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

• Resolution of distancemeter: 1nm• Mounting precision of

distancemeter: 1nm• Angular precision of

distancemeter holder: 10 rad.

SLAC BPM: referenceKEK BPM variable (6D):

Position/nm x 32 y 19 z 2 Angle/rad x 0.01 y 0.01 z 0.1

~1m absolute distance resolution needed to determine constants required to solve geometry.

Spider web Design with Opto-Geometrical Simulation: Simulgeo

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

• Timescale: 0.01-100 Hz– Laser interferometers ideal.

• Typical motion amplitudes:– On the order of a micron

KEK ground motion

1m

1 Hz

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Interferometer Studies

• A number of designs are being studied

• Currently setting up lab space in Oxford

• Plan to test interferometers at ATF

• Final interferometers MUST be in vacuuo• Combine fixed and swept wavelengths• Nanometre resolution is routine in interferometry –

The devil is in the details

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Initial interferometer tests

0.25

300 - 6000

S hort arm

Long arm

F ibreM T connec to r

R etrore flectorAnti-reflection coated Lens

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Ideally this would produce...

0 2 4

1

2

3In

tens

ity /

a.u.

Laser Frequency change / GHz

when the signals from neighbouring fibres are read out

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

3 channels recorded in same scan

0 10 20 30 40 50

-0.5

0.0

0.5

-0.4

-0.2

0.0

0.2

0.4

-2

0

2

Change in Laser frequency / GHz

Inte

nsi

ty /

a.u

. In

ten

sity

/ a.

u.

Inte

nsi

ty /

a.u

.

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

These signals can be analysed...

• Or by fitting to a sinusoid

Length

• Either by calculating a

periodogram using FFT

0.3 0.4 0.5

0

5

10

15

Am

plitu

de /

Arb

uni

ts

Length / m

N.B. These are only generic examples!!They do not correspond to signals shown earlier – but similar

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Work in progress...Setting up a new test area (lab corner) - Highly sensitive thermometer system - New optical table

Testing a zero-force bellows for vacuum connections

Designing, constructing and testing new interferometer designs

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

StaFF summary

• Proposed experiment conducted within framework of StaFF (Stabilization of Final Focus for ILC).

• Funded by EuroTEV.

• Development of active feedback systems to monitor and stabilise, for example, final focus quadrupoles or beam position monitors in the energy chicane.

– Develop laser interferometric methods to monitor relative position of two

objects at nanometer scale when ~10m apart.

– Develop and implement algorithms for active stabilization.

• StaFF at KEK: Stabilize Nano-BPM systems relative to each other.

P Coe et al LCWS06 I I Sc. BangaloreThe StaFF project

Thank you for listening