1. Z. Szillasi On behalf of GEM Alignment group November 15, 2017

2. The general concept of GEM alignment
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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3. Must be aligned to precision ~ spatial resolution
Phase II Muon Detector
Must be aligned to precision ~ spatial resolution
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4. Alignment elements on the chamber - recap
Survey target holder (S) R φ S Z
R-measurement
Also sensors between the chambers and the base-plate are considered (z-measurement)
φ-measurement
The total number of align. elements per chamber and their locations are still under discussion
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5. Study with simplified model
Survey targets
Distance sensors
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.
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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6. Calibration of the readout boards - 1
Readout board of the long chamber (strips on the back side)
R-sensors
Phi-sensors
Sensors on the readout board of the long chamber

7. Fiber Bragg Grating (FBG) Concept
TEMPERATURE CHANGE
Thermal expansion for
Termo-optic effect for
STRESS
Where:
neff is the effective refractive index of the fiber,
Λ is the grating pitch and
λB is the reflected Bragg wavelength.
Elasto-optic effect for
Direct Strain for
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8. Fiber Bragg Grating (FBG) Concept
STRAIN AND TEMPERATURE Sensitivity : FBG Spectral Response (Temperature) T
FBG SPECTRAL RESPONSE:
Temperature Shift
Temperature Sensitivity ≈10pm/°K
@ λB=1550nm
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9. Fiber Bragg Grating (FBG) Concept
STRAIN AND TEMPERATURE Sensitivity:
FBG Spectral Response (Axial Strain) ε
FBG SPECTRAL RESPONSE:
Axial Strain Shift
Strain
Sensitivity ≈1pm/με
@ λB=1550nm
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10. Temperature (T) sensor
The sensor
Two FBGs in a sensor:
Strain (S) sensor
Temperature (T) sensor
Glued under tension
Glued under tension
Optical fiber
Glued with no tension

11. Sensor on the readout board
17mm x 50mm cutout requested on the GEB for long chambers
The sensor holder (bracket) glued on the readout board
The sensor fixed to the bracket after the GEB installation
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12. Mechanical design
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13. LINEAR MOTOR DRIVES & RAILS
CAMERA
LINEAR MAGNETIC ENCODER
GEM-PLATE
INTERCHANGEABLE BASE-PLATE
LINEAR GUIDE
OPTICAL TABLE
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14. POSITIONONG BRACKET
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16. Positioning Bracket
Reference point
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17. Reference point of Sensor
Reference Edge
Bracket
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18. 3 4 2 1 Measuring and technological order
Determination of the inner reference points from the outers with coordinate measuring system. (Calibration of the base plate)
Optometric check of the base plate with the designed measuring and bonding system.
Fixation of sensor brackets onto the base plate
GEM plate bonding to brackets
Determination of the position of strips from the outer references with optometric method.
Calculation of the positions of strips from the bracket’s references 3 4 2 1
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19. Scanning table in the lab
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20. Displacement Sensor dY dX Force(N) Fiber sensor Fixed side 9/12/2018
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21. Displacement Sensors
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22. Displacement sensor
Force
Spring
Sensor Head
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23. Displacement Sensor
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24. Displacement Sensor
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25. Displacement Sensor
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26. Slice test chamber
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27. Sensor – finite element analysis
5mm here
20 micrometer here
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28. Slice test chamber with Alignment sensors
Alignment sensor body without spring (for reference measurement)
ST2
ST1
Alignment sensor bracket for R sensor
Alignment sensor body with spring
ST3
ST4
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29. Slice test chamber in CMS
Chamber name where the alignment sensor is installed:
SCL-01 super chamber
Barcode on patch panel: GE1/1-SCL-001 /
Name on chimney: GEII-VII-L-CERN 0002 (Top chamber)
This chamber is installed on position YE-1 GE1/1/28
Continuous data taking and monitoring of the peaks during sensor installation on chamber and also before and after the installation of the chamber in P5.
As soon as the final optical cable installed the chamber connected to the FOS readout optical system. Since then it is included in the FOS DCS system.
Each peak on this spectrum represents either a strain (distance) sensor or a temperature compensator sensor
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30. sensors are not calibrated!
Sensor behaviors during the first magnet ramp up sensor response vs. magnetic field
sensors are not calibrated!
ST3S and ST4S are the strain sensor part and they equipped with spring
and the temperature change is compensated
ST3S sensor show correlation with magnetic field while ST4S not very much
ST3S and ST4S show correlation something witch is induced by a temperature change (see next slides)
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31. sensors are not calibrated!
Sensor behaviors during the first magnet ramp up sensor response vs. magnetic field
sensors are not calibrated!
ST3S and ST4S are the strain sensor part and they equipped with spring
and the temperature change is compensated
Magnified view, clear correlation of ST3S with magnetic field
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32. sensors are not calibrated!
Sensor behaviors during the first magnet ramp up sensor response vs. LV VFAT status
sensors are not calibrated!
ST3S and ST4S are the strain sensor part and they equipped with spring
and the temperature change is compensated
LV VFAT ON
~0.1nm
Magnetic field is stable in this period
LV VFAT OFF
ST3S and ST4S sensors show correlation with the LV switch on of the chamber  heat dilatational movement between chambers
This is Δλ = ~0.1nm 
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33. ST3S sensor delta 0T vs 3.8T (LV ON) comparison
sensors are not calibrated!
ST3S and ST4S are the strain sensor part and they equipped with spring
and the temperature change is compensated
~0.1nm
ST3S sensor response to magnetic field:
Δλ = ~0.1nm 
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34. Observed movements of the chambers
ST3
ST4 X
magnetic field response
heat dilatation of the chambers
Chambers fixed with screw in outer R
Chambers fixation is a pin in a rail in inner R
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