1. Dept. of Physics and Space Sciences, Florida Institute of Technology
Quality Control of the Large-area GEM detectors at Production Sites for the CMS Muon Endcap Upgrade
Mehdi Rahmani
Dept. of Physics and Space Sciences, Florida Institute of Technology
(On Behalf of FIT Site) 1 1

2. Outline Introduction Detector Construction & Quality Control (QC)
What is a GEM Detector?
Why GEM Detectors for CMS?
Detector Construction & Quality Control (QC)
Construction of GE1/1 Prototypes for Large-Area GEM Detector
Layout - Cleanroom
QC2: GEM Foil Testing
QC3: Gas Leak Test
QC4: High Voltage Test
QC5: Gain Measurements
Gain Calibration
Response Uniformity
Status of Production Sites
Summary & Conclusion 2

3. Introduction What is a GEM detector? -
GEM foil is a Kapton foil coated with copper on both sides that has an array of microscopic holes (typically 140µm pitch).
These foils are inserted between a drift and a charge collection electrode.
By application of the right potentials on the foils, a high electric field will be developed in the GEM holes.
Electrons released in the upper region drift towards the holes and acquire sufficient energy in the holes to cause ionizing collisions with the gas molecules filling the structure creating an avalanche of electron-ion pairs. - + V 3

4. Introduction Why GEM Detectors for CMS?
During the phase II upgrade of the CMS detector at CERN for the High-Luminosity LHC, CMS group will install large-area GEM detectors in the forward muon region
This installation will help to restore redundancy for tracking and triggering in muon system.
GEM detector can operate in a high-rate environment, provides precise tracking, which improves muon momentum resolution.
The combination of GEM+CSC )Cathode Strip Chambers( can provide an accurate measurement of the muon bending angle unaffected by multiple scattering, which can be used in the L1 muon trigger to reduce the soft muon rate.
A QC procedure has to be developed to ensure a successful production run meter long GEM detectors will be produced. They are scheduled to be installed in the CMS endcap in 2019. 4

5. Slice Test Slice test: Install 50°coverage
on one endcap of CMS built 10 detectors for installation.
The detectors are installed at 3 o'clock and 6 o'clock positions. 5

6. Construction a. Mounting inner frames b. Assembling three GEM foils
c. GEM stack on the drift
d. Stretching foils with tension
e. Stretched foils in frames
f. Mounting readout board 6

7. Example Assembly & QC Site Layout (FIT)
Because of the small holes (70 μm hole diameter) in the GEM foils, we can’t expose them to unfiltered air because otherwise dust might get into the holes and cause electrical shorts in the foil.
For example, at Florida Tech we have a class 1000 clean room.
CO2 7

8. QC Step 2 : GEM Foil acceptance
Long test
Monitoring the leakage current and any possible sparks:
HV  (600V(.
Period 30 minutes - 1hour
The foils  Plexiglass box filled with pure nitrogen.
The GEM foils are accepted if the mean current is below 5 n amps.
__________________________________
Fast test
Applying voltage to the GEM foils and measuring the leakage current between top and bottom electrodes.
The GEM foil is accepted if its impedance is above 10 GΩ, with relative humidity lower than 40% and the number of spark per minutes is lower than 2/3 during the last three minutes.
QC2_Long_FIT_Foil2_V
Data Taken By Student 8

9. QC Step 3: Gas Leak Test 1. Calibration of leak-check system FIT_QC3_V
After pressurizing the chamber to 25mbar,
the pressure drop should not exceed 1 mbar per hour.
FIT_QC3_V
Data Taken By Student
2. Leak measurement of detector
GE1/1 Quality Control : instructions
Michele Bianco, Brian Dorney, Jeremie A. Merlin
CERN On behalf of the CMS GEM Collaboration September 28, 2016 9 9

10. QC Step 4: High Voltage Test
Detector under CO2
High voltage can not ionize the CO2 so we
expect to see no signals. If we any signals
we consider them as spurious signal.
The QC4 test aims to determine the
V vs. I curve and rate of a GE1/1 detector and identify possible malfunctions, defects in the HV circuit, and spurious signals.
Data Taken By Student
GE1/1 Quality Control : instructions
Michele Bianco, Brian Dorney, Jeremie A. Merlin
CERN On behalf of the CMS GEM Collaboration September 28, 2016 10

11. QC Step 5a: Effective Gain
In order to confirm the high-rate
capability of the GE1/1, we
measure the gain vs. incident
rate using X-ray source.
The gas gain is measured via the
anode current produced in the
chamber during this irradiation
QC5_FIT_V
Data Taken By Student 11

12. QC Step 5b: Gain Uniformity
The camber response analysis routine produces an x-y color map of pulse height information.
The response uniformity is performed at a gas gain of ≈ 600 using Ar/CO2 (70:30) in all sites.
Given the large area of the CMS GEM chambers, the uniformity of the detector response across the surface should be assured. A basic quantity to verify that is the gain of the detector.
Mass produced chambers are accepted if their response if within 15% of the average and efficiency is more than 97%. 12

13. Status of The Production/QC Sites
All Sites must take an old generation GE1/1 chamber through all QC steps and produce all deliverables compatible with CERN instructions.
Stage 1 - QC3 to QC5 effective gain - Deliverables reviewed by collaboration
Stage 2 - QC2 (fast) to QC5 effective gain + QC5 gain uniformity - deliverables reviewed by collaboration + clean room status review - visit checkout on site - Shipment of GE1/1 kit
Stage 3 - Repeat QC2 to QC5, including assembly - Deliverables reviewed by collaboration - Final validation by collaboration 13

14. Summary and Conclusion
In order to cope with the harsh environment expected at the high- luminosity LHC, the CMS forward muon system requires an upgrade.
Following an extensive R&D program, CMS has identified triple-foil gas electron multiplier (GEM) detectors as a solution.
These detector will be constructed at CERN and at five external sites.
A stringent quality control procedure has been developed to ensure a successful production run. A total of meter long GEM detectors will be produced. They are scheduled to be installed in the CMS endcap in 2019.
At Florida Tech we implemented all the Quality Control systems and successfully took a GE1/1-V GEM prototype through all QC steps.
As a conclusion, all the sites are on the schedule for 2019 installation. 14