DESY, Sep. 27, 2005 Warsaw University LiCAS Linear Collider Alignment & Survey A. Reichold, JAI @...

A. Reichold, JAI @ Oxford for the LiCAS collaboration

1DESY, Sep. 27, 2005

WarsawUniversity

LiCAS

Linear Collider Alignment & Survey

Survey and Alignment of the ILC

Alignment Errors

DESY, Sep. 27, 2005


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Overview The ILC survey and alignment process RTRS measurement principle for the reference survey Simulations of the survey process

Reference survey SIMULGEO models for short distance (<100m) Random walk models for long distance

Stake Out and alignment Interface to Placet

Systematic errors in the reference survey Error Reduction

How accurate can position alignment really be Cryo-module improvements

fiducialisation build tolerances

Survey and Alignment of non-Linac components Sources, DR, turnaround, BC, BDS, IP, spectrometer, polarimeter,

dumps

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The ILC survey and alignment process

(in the tunnel)

1. Reference survey (the hard part):stat<200m/600m

rapidly establish co-ordinates of regular array of reference markers along entire tunnel wall

rapid = much faster then drift of tunnel rapid = as fast as possible since time = money hard = keep accuracy over large distance new instrument = RTRS (Rapid Tunnel Reference Surveyor) instrument developed by LiCAS group

2. Stake out: <50m any point

Relate external accelerator component’s markers to reference markers measurement distance = across the tunnel diameter manually operated classical instruments could work but should be

incorporated into RTRS if possible (speed, automation)3. Alignment: <100m any

point adjust position of accelerator element to get closer to nominal no automated process for cryo-modules exist yet manual action with a large wrench needed so far least accurate of steps so far

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4. Fiducialisation (under development):≥300m Relate external markers to relevant active centre line of accelerator

element If necessary define an average active centre line if many elements

determine the centre line as done in cryo-module Center line may dynamically change during cool down and

transport. This is the biggest contribution to the fiducialisation error.5. Build tolerances:

Internal to an accelerator element there could be static variation of several active elements around the centre line (scatter

of cavities in cryo-module) adjusted to =100m dynamic changes of elements with load, current, trim, external

temperature, etc. =???m

Externally there could be variations in target marker position when placing the markers repeatedly

into their nests (dirt, dust, wear) ≤1m marker centring errors (markers are usually sphere mounted to allow for

large acceptance angles by repointing. If target not correctly centred in sphere you get an error) 0.5m

The ILC survey and alignment process

(outside the tunnel)

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Notes about the process Notation:

offset = one instance of statistical quantity called error error = sigma of the offset distribution

Some offsets correlate within groups of accelerator elements all elements in a cryo-module share the same offset due to stake out

and alignment 100% correlation External build tolerances also apply identically to all elements in a

module but they are usually negligible The fraction of the fiducialisation error due to cool-down distortions is

not the same for all elements but is systematically distributed to the elements some correlation function dependent on module mechanics

Offsets from reference survey are strongly correlated over very long distances. I.e. better then 200 m over 600m (see simulaions)

All other offset sources are uncorrelated over distances > 1 cryo-module length

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collider component

RTRS concept

Tunnel Wall

Reconstructed tunnel shapes(relative co-ordinates)

wall markers internal FSI external FSISM beam

LiCAS technologyfor automated stake-out process

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LiCAS Measurement Principle

External FSI System measures

Wall marker location

Internal FSI System z. &

x,y & ,between

cars

Straightness Monitor x,y & ,between

cars

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Build opto-geometric model of all measurements in a 6-car train and all reference wall markers using SIMULGEO

Add up to 20 trains in advancing locations into the model model consists of 20 trains measuring 26 wall markers. total of O(10.000) elements and measurements with individual

errors in the model Most wall markers get measured 6 times in overlapping

measurements this is how trains correlate with each other Perform error propagation:

from: position errors of elements in the cars and measurement errors

to : errors of wall markers, i.e. invert error matrix of rank N2 = 10.0002

Limit of this procedure is memory of computer 20 trains need close to 1 GByte and 34h on 2GHz CPU

Reference Survey Simulations(short distance < 100m)

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Simulgeo Model of RTRSonly first and last car of

6-car train shown

retroreflector

Laser beam parallelto Gravity @ car 1

2nd CCD faking clinometer

1st CCD faking clinometer

Laser beam parallelto Gravity @ car 6

internal FSI lines

wall marker

straightnessmonitor laserbeamintermediate

cars not shown

LSM-CCDs for incoming beam

LSM-CCDs for return beam

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Reference Survey Simulations(long distance >100m)

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Stake out and Alignment Simulations

Both processes so far only add a Gaussian random offset to the reference survey

Width of these Gaussians is so far based on separate instrument errors and error propagation by surveyors. Assumptions: horiz=0.3mgon, vert=0.3mgon,

dist=0.1mm, DL between reference markers = 5m, Note: 1gon = 2p/100, 1mgon = 63rad

In future we will fully simulate an integrated stake out with SIMULGEO and determine the errors to see if we can decrease them.

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Interface to Placet(licas_sim)

Fortran program tested on Linux licas_sim produces the offsets of components given

their z positions All internal tuning parameters (measurement

resolutions) are in a control card file and can be modified by users

Input: two flat text files (one for each arm of the machine) with one z position per line, representing the nominal z of the component to be aligned.

Output: each line of input replaced with: z-original, x-offset, y-offset, z-offset

All units are meters

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Systematic errors in reference survey

We have no measure of them yet Hard to measure because LiCAS “would” be the highest

accuracy instrument Mainly to be determined via consistency checks during

LiCAS test runs at DESY next year Potential sources of systematics exists in:

miscalibration of components (predominant source) scale-mismatch between sub-systems drift errors on precision components systematic atmospheric effects

Most of them would be addressed by calibration procedures

Which systematic errors would be dangerous for LET?

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Error Reduction Position Alignment:

Today’s movers for cryo-modules manual coarse movers (lots of force needed) few cm range hardened steel feet on hardened steel plate

If the estimated 100 m accuracy prove to be insufficient and money is available one can:

Mount modules using bearings motorise adjusters achieve O(10 microns)

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Error Reduction Cryo-module fiducialisation

300 microns is limit with current module design better is possible but at great cost part of 300 microns is currently uncertainty

rather then error. I.e. expected scatter of beam line positions in a large number of modules. if you measure each one of them internally (wire system) you can get better

transport and handling is a large unknown factor

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Error Reduction

Cryo-Module build tolerances scatter of cavities in a string = 100 m <

fiducialisation error no need to improve offset of quads from beam line = 100 m This is currently not the leading error

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Survey and Alignment of non-Linac components

We know neither specs nor methods yet We are working on a document to

collect these Would be very useful to prioritise the

list by knowing which part is most sensitive

Input from WG1 of highest importance

DESY, Sep. 27, 2005 Warsaw University LiCAS Linear Collider Alignment & Survey A. Reichold, JAI @...

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