1. Activity of CERN and LNF Groups on Large Area GEM Detectors
11th Pisa Meeting on Advanced Detectors
La Biodola,
Activity of CERN and LNF Groups on Large Area GEM Detectors
Danilo Domenici
INFN - LNF
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2. LNF and CERN in RD51 Collaboration
LNF and CERN groups work together within the RD51 Collaboration: Development of Micro-Pattern Gas Detectors Technologies
WG1/Task1: Technological Aspects and Development of New Detector Structures / Large Area GEM Detectors
Installed and working detectors:
20 31x31cm2 Triple-GEM in COMPASS NIM A490 (2002), 177
cm  Triple-GEM in TOTEM NPPS 172 (2007), 231
24 20x24cm2 Triple-GEM in LHCb NIM A494 (2002), 156
Need for Large-Area GEM
Present size limitation: ~450x450mm2
Width of raw material (457mm roll)
Alignment precision of double-mask procedure
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3. Standard Double-Mask Procedure
Starting raw material: 50μm Kapton foil with 5μm Copper clad
Photoresist coating , Double Mask are laid down and exposed
Double side metal etching
Double side kapton etching. The hole has bi-conical shape
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4. New Single-Mask Procedure
Starting raw material: 50μm Kapton foil with 5μm Copper clad
Photoresist coating, Single Mask are laid down and exposed
Hole is opened with top side metal etching and kapton etching
Bottom side metal etching. Top side metal is preserved with Cathodic Protection technique
Back to kapton etching for 30 s to get cylindrical shaped hole
Eventual quick metal etching to form the rim
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5. Hole Geometry STD GEM NEW GEM 70 50 5um Cu 70 65 5um Cu
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6. Nearly Cylindrical Holes
TOP Kapton
TOP
Sparking voltage 700 V in air
BOT Kapton
BOT
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7. Single-GEM chamber layout
X-Ray Measurements
Single-GEM chamber layout
4 mm Drift Gap
2 mm Induction Gap
Current readout
Single-GEM readout in current mode
2 identical chambers have been tested with X-rays:
1 with single-mask foil
1 with standard foil
Flushed on the same gas line and irradiated with front and side openings of the gun
GAS: Ar/CO2 70/30
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8. Electron Transparency
X-Ray Measurements
Electron Transparency
80% at 0 Field: larger Optical Transparency due to larger diameter
VGEM = 400V
Ed = 1.5kV/cm
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9. X-Ray Measurements Ion Feedback VGEM = 400V Ed = 1.5kV/cm
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10. X-Ray Measurements Charge Sharing
Equal Sharing Field highly dependent on New-GEM orientation
4.6kV/cm
5.7kV/cm
VGEM = 400V
Ed = 1.5kV/cm
5.2kV/cm
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11. X-Ray Measurements Gas Gain G60-70 / Gstd = 0.67 G70-60 / Gstd = 0.80
Additional 10  20 V needed to operate at the same Gain as Standard GEM
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12. Simulation: Drift Lines
95–55
75–55
55–55
55–75
55–95
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13. Simulation: Field Intensity
95–55
75–55
55–55
55–75
55–95
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14. Future Applications CERN TOTEM Upgrade LNF KLOE Upgrade
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15. TOTEM Large Prototype
Idea of upgrade for T1 tracker (now Cathode-strips Wire chamber)
Discs of 2 x 5 chambers, back to back, allow to cover all the surface
Large Triple-GEM prototype (~ 2000 cm2) obtained from two 66x33cm2 foils
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16. Efficiency with X-rays ( 0.5mm collimator)
Splicing GEM
heat
pressure
Foils are spliced over a narrow seam using an adhesive flexible kapton coverlayer (25µm thick)
Efficiency with X-rays ( 0.5mm collimator)
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17. Manufacturing of Prototype
Stretching and framing the spliced single mask gem foils
Making the honeycomb base plane and top cover
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18. Manufacturing of Prototype
Gluing the cathode to the honeycomb frame
Final assembly of all frames
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19. Performance preliminary hole geometry
Energy Resolution with 8.9keV X-rays σE/E = 9.5%
Rate Capability up to 1MHz/mm2
Voltage Sum (V)
Effective Gain
Triple-GEM Gain in Ar/CO2
preliminary hole geometry
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20. Cylindrical Triple GEM
KLOE2 Inner Tracker
3 mm
2 mm
Cathode
GEM 1
GEM 2
GEM 3
Anode
Read-out
Conversion & Drift
Transfer 1
Transfer 2
Induction
Cylindrical Triple GEM
5 independent tracking layers 15 to 25 cm from IP to improve vertex reconstruction
σrφ = 200 µm and σZ = 500 µm spatial resolutions with XV strips-pads readout
700 mm active length
1.5% X0 total radiation length in the active region with Carbon Fiber supports
 300 x 352mm prototype with Std GEM has been assembled and tested
Realized as an innovative Cylindrical-GEM detector
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21. Manufacturing the Prototype
352 mm
960 mm 2 3
Full sensitive and Ultra-light detector 1 4 5
Distribution of epoxy on foil edge
3 spliced foils ~1000mm long
Cylindrical mould in vacuum bag
Cylindrical GEM foil
Cylindrical Cathode with annular fiberglass support flanges
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22. (GEM) =(250µm)2 – (140µm)2  200µm
Performance
Efficiency ε = 99.6%
Performance measured at PS testbeam with GASTONE digital Readout Electronics (INFN-Bari) and external Drift Tubes Tracking System
Spatial Resolution
(GEM) =(250µm)2 – (140µm)2  200µm
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23. Large Planar Prototype
Cathode PCB
70x30 cm2 Triple-GEM planar detector with Single-mask foils for quality and uniformity test
GEM1
GEM2
GEM3
1.5x2.5 cm pad readout PCB
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24. Tooling and Simulations
Meters
With the usual 1 kg/cm, finite element simulation (ANSYS) indicates a maximum gravitational+electrostatic sag of the order of 20 μm
Load Cells
Jaws
A very large tensioning tool has been designed.
The frame gluing will be performed by using the “vacuum bag” technique, tested in the construction of the CGEM
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25. RD51 Testbeam Facility WG7: Common Test Facilities
H4 beam-line at SPS: 150GeV pions
Goliath Magnet: dipole field up to 1.5T in a ~3x3x1m2
Semi-permanent setup for RD51 users
First test June 21st – July 6th
CERN: Large-GEM prototype
LNF: XV readout and BField
Beam direction
RD51 setup
Goliath magnet
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26. Conclusions
A change of the GEM production procedure has been driven by the wide request of Large Detectors by the GEM community
A new Single-Mask and Cathodic Protection etching technique has been tuned, allowing for foils as large as 450x2000mm2
The short size limitation, due to the definite width of the raw-material, can be overcome by splicing more foils together
A Single-Mask 10x10cm2 foil has been tested with X-rays in a Single-GEM detector readout in current mode. Results show slight difference with the standard GEM
LNF and CERN groups are developing Large-GEM detectors for future applications: TOTEM upgrade and KLOE upgrade
Other possible applications are Super-LHC Detector upgrades (LHCb TT and Muon), Screening for homeland security and PET scanners
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27. SPARES

28. An example of active corrosion protection
Cathodic Protection
An example of active corrosion protection
CP is a technique to control the corrosion of a metal surface by making it work as a cathode of an electrochemical cell.
Used to protect ship hulls and oil pipes 0V
+3V
+3V
Resist layer to protect back part from the bath
Bottom electrode at +3V is chemically etched
Bath at +3V
Top electrode at ground is electrically protected
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29. Single-Mask Etching Isotropic metal etching Resist layer
Opening of the hole, but unwanted angles in the copper
Over-etching of the copper
Going back to Polyimide etching for 30 sec
The hole become cylindrical
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30. Helium-Isobuthane
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31. Relative Gain vs GEM Voltage Single-GEM
X-Ray Measurements
Relative Gain vs GEM Voltage Single-GEM
Edrift = 1.5 kV/cm
Eind = 5 kV/cm
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32. Normalized gain vs VGEM
X-Ray Measurements
40V
Normalized gain vs VGEM
Triple-GEM
Data normalized to previous Absolute gain measurements with Ar/CO2 70/30
Fields: Ed=1.5 – Et1=2.5 – Et2=3.0 – Ei=5.0
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33. 2-D Readout Circuits
Both views can be readout from the 2 ends of the circuit: suitable for a cylindric geometry without dead spaces
650 µm pitch V strips
Orthogonal XY
650 µm pitch X strips
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34. Readout studies: 2-D strips
Cluster multiplicity studies on the first two XY chambers
Gast1: induction gap 2 mm
Gast2: induction gap 1 mm
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35. Simulation of effects of a Magnetic Field (B=0.5T) on a Triple-GEM
Readout studies: B-Field
Simulation of effects of a Magnetic Field (B=0.5T) on a Triple-GEM
Ar/CO2=70/30
<α>L ~ 8o 9o
9mm
1.2mm
He/i-C4H10=90/10
<α>L ~ 3o 4o
0.6mm
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