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GE alignment- status, proposal

N. Béni, Z.Szillási (ATOMKI, Debrecen, HU)

G. Bencze, G. Endrőczi (Wigner RCP, Budapest, HU)

30.06.2014. GMM meeting

The general concept

The aim of the GE-alignment: to locate the strips of the read-out boards in the CMS coordinate system and monitor their movements.

The general alignment concept:

• The strips are sealed during the production and not observable.Therefore the strip positions have to be transferred to the observable (outer) part of the chambers during the construction

• The chamber bodies have to be equipped with the necessary elements for position monitoring.

• The alignment readout+control should provide the operation of the system.

• The opto-geometrical data analysis provides the position data.• Track-analysis can improve the final accuracy.

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Chamber position monitoring

Three levels:

1) Survey-measurement

2) Hardware alignment system

3) Integration into the existing HWALI

4) Track-based alignment

Survey:

Survey-targets mounted on the outer edges of the chambers (see later) are measured by photogrammetry after the installation (red points: short chambers; blue points: long chambers).

This gives a ~1 mm precision information on the relative positions of the chambers (super-chambers) wrt each other and the surrounding CMS-elements.

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Chamber position monitoring

Hardware alignment system:Based on capacitive distance-sensors determines the positions and monitors the movements of the chambers in the GE-disk* coordinate system during the running period with the accuracy of the HW alignment system. The data is validated by the survey measurement.This rigid body could then be linked to the ME1/1 (Link Ali)

* GE-disk: the full GE-detector composed of 72 chambers (one GE-disk/CMS-side)

Track-based alignment:The location of the „GE-disk” in CMS coordinate system is provided by the track-based alignment . Also, the track-based alignment is able to locate the chambers with higher accuracy. The results are validated by the HW-measurement.

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Strip-position transfer to outer side

The idea is to use the via holes (sealed by capton) provided the precision of their position is good enough (in the middle of the strips with 20-30 micrometer(?) accuracy) .

The advantage of this method: no special fiducials are needed for the alignment in the readout plate design.

If the hole-precision is not enough then the red-out plane has to be mesured (scanned) also inside before the chamber assembly.

This step, on the other hand, could also be used as a quality check of the plates (strips) in case of need.

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Study analysis for finding the vias

Image scan of the via holes at

inner R

Image scan of the via holes at

outer R

A preliminary study has been made to check the feasibility and evaluate the difficulty of the accurate location of the holes from a scanned image.

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Study analysis for finding the vias

Image taken by camera

8-bit grayscale transformation +thresholding + region finding

Selection of regions with good sphericity

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Study analysis for finding the vias

In this case the systematics is affected by the threshold value:

• At threshold ~ 130 strips and holes start to mix, • but at around thr ~100 variation of centroid is ~0.2 px 2

micron (via distance assumed 1mm)• at low threshold only the holes are seen • therefore analysis starts with a low threshold to get points in

hole then at high threshold precise hole position can be determined

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Capacitive sensor

The capacitive sensors are widely used in the industry for distance measurement, vibration analysis, etc.

There are many types on the market but can also be home-made.

They are ideal for the GE-conditions: few mm distance, small available space, micrometer accuracy.. The elecronics can be located far away (at 10-15m distance). The sensor is connected via thin (<Ø1mm) coax cable.

The Wigner Institute already used home-made capacitive sensors in the past for aeroplane-diagnostics. These sensors can easily be adapted to GE-needs.

Target (grounded)

Transducer

Capacitive sensors are planned to be used as active distance measuring elements.

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Capacitive sensor @ Wigner

Thesetup

The sensor

(The nose is not needed for us)

The foil is representing the chamber frame

~5mm gap

„Quick demonstration” setup at Wigner (5 March 2014):

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Alignment elements on the chamber

Also sensors between the chambers and the base-plate are considered (z-measurement)

φ-measurement

R-measurement

The total number of align. elements per chamber and their locations are still under discussion

R

φ

SS

ZSurvey target holder (S)

The elements are glued on the chamber.Details (when, on which part) still to be determined.

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Survey target holder

The idea is to use holders similar in construction to those used for the barrel muon:

The present size is ~50x50x13 mm3 (without the base) but can be minimized, optimized. (A different type of target is planned be used for GE.)

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Phi measurement

Cover

Fra

me

(tar

get)

Transducer under the cover

Typical transducer size for this application:

10x10x50 mm3

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Radial (R) measurement

TargetTransducer

All the transducers are on the long chambers.

The phi-tranducers can be used also here.

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Z-measurement

The idea is to measure (monitor) the distance between the chambers and the back-plane of the HCAL (to which

the chambers are attached).

For that more information is needed on the flatness of this element and its possible deformation.

The transducer size applied here can be round, max. Ø15mm.

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Calibration

Determination of the positions of all the alignment-related elements in the chamber coordinate system.by survey and proximity-measurements performed on the calibration bench

Two steps are considered:

Step 1 – Scan the assembled chamber (determination of the via holes and part of the alignment elements)

Step 2 – Measure the rest of the elements (e.g. frames used as target for the cpcitive sensors) by Coordinate Measuring Machine (CMM).

Calibration:

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Scanning table

„Fantasy” picture

The device can be home-made or purchased on the market

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Calibration step 2 – CMM** CMM: Coordinate Measuring Mchine

(Illustration, taken from the net)

A machine similar to thisto locate the frame surfaces in the chamber or super-chamber coordinate system:

CMM to be purchased or found/loaned at CERN or outside

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Opto-geometrical model

COCOA*: CMSSW software package that can be used to simulate the expected accuracy of the measurement of the position monitoring.

For that the opto-geometric model of the system has to be defined: positions of the alignment-related elements, the calibrated data and their errors, the measuring elements (sensors) and the accuracy of the sensor-measurements.

The same model can be used later to analyse the real data by simply introducing the results of the sensor measurements.

* CMS Object-oriented Code for Optical Alignment

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Study with simplified model

A s the first step a simplified arrangement (see on the picture) has been studied to gin experience with such a system. The „chambers” contain survey targets and a pair of distance sensors on both edges.

The model seems to work and converge to correct results. The next step is to describe the real system and substitute the survey measurement by the R and Z measurements.

Survey targets

Distance sensors

The opto-geometrical modelling will give the final answer to the question of the achievable alignment precision and helps to optimize the configurtion of the alignment elements on the chambers (super-chambers).

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Phase II Muon Detector

Must be aligned to precision ~ spatial resolution

G. Gomez

30.06.2014

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Link Alignment System

• LD wrt AR (wrt TK)• MAB wrt LD• ME1/2 wrt LD• ME1/1 wrt LD (less precise)• ME1/2 wrt MAB • Endcap deformation• ~1/6 of endcap monitored• Barrel wrt TK ~1mm• Fast check of relative movements

G. Gomez

30.06.2014

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Endcap Deformation

• Disk movement along z • Disk deformation• Tracks marginally sensitive• Physics marginally sensitive• Link only YE1• Need endcap SLMs for others

G. Gomez

30.06.2014

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Weak Mode Constrains• Tracks vs Barrel HW provides important x-check• Suggestion for HW: aim for accuracy rather than precision

twist angle “twist” examplefrom Run 1 experience

G. Gomez

30.06.2014

Summary

Concept: •Survey (partial, during installation)•Hardware alignment based on capacitive sensors (full measurement)•Link to the existing Alignment systems (Link-MAB-Barrel)•Track-based alignment: connection of the GE-disks to CMS, higher accuracy

Calibration: •Connection of the strips to outer side of the chambers•Location of the alignment elements wrt the strips: scanning, CMM

Open questions: •Flatness of the base-plate of the nose•Accuracy of the via holes on the read-out plate

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