Chamber Design Performance Validation

1. Chamber Design Performance Validation Marcus Hohlmann (FIT) GE2/1 Engineering Design Review May 22, 2019

2. Performance Requirements Check t (incl. SF 3) (incl (hole diam. var.) from Muon Upgrade TDR, p.209

3. GE1/1 Gap Sizes Drawing on GE1/1 Experience 3 mm • The gain elements of GE2/1 and GE1/1 are identical: Triple-GEM detector with 3/1/2/1 mm gaps in Ar/CO2 70:30 • Basic GE2/1 performance can be expected to be the same as basic GE1/1 performance 1 mm 2 mm 1 mm

4. GE2/1 Improvements over GE1/1 • In TDR: • Center pillars that connect drift and readout PCB to reduce bulging of gas volume and to improve gain uniformity • Since TDR: • HV segmentation on both sides of GEM foils to reduce energy of discharges propagated to readout strips (GE1/1 has only segmentation on top side) • Halvingof readout strip lengths to reduce the interstrip capacitance and consequently the noise (otherwise strips in lowest eta partition get too long)

5. Efficiency GE1/1 data => GE2/1 noise level should benear 1.2 fC to achieve this efficiency GE1/1 TDR meets requirement of ≥ 97%

6. Spatial Resolution • For binary readout, resolution can be estimated as: σ = pitch / √12 = 920 μrad / √12 = 266 μrad • Meets the requirement of σ < 500 μrad. • The pitch of 920 μrad reflects the doubling of the strip width relative to the TDR value due to the halving of the strip length. • This change has been codified as official change control GE2/1-001A. • Note: Due to the ganging of two azimuthally adjacent strips for trigger purposes in the original TDR design, the doubling of the strip width does not impact the trigger.

7. Time Resolution GE1/1 data GE1/1-II prototype 10cm × 10cm prototype Muon Upgrade TDR meets requirement of 8-10 ns

8. Quality Control – Gas Tightness GE2/1 data As established for GE1/1 production (module type)

9. Quality Control – Gain Curves GE2/1 data (hole geometry not to spec.; see Inseok’s talk)

10. QC – Gain Uniformity across Modules GE2/1 data (hole geometry not to spec.; see Inseok’s talk)

11. Gain Equalization across Modules GE1/1 data • HV trimming results in a narrow distribution of gains across modules with only 5% variation (gain 10,012 with rms = 498) • Meets the requirement of < 50% variation (next slide)

12. Impact of Gain Variations • On the efficiency plateau, a gain variation of up to ± 50% (blue lines) can be tolerated without adversely impacting the efficiency or the time resolution 3/1/2/1 3/1/2/1

13. Gain Equalization across Modules • GE1/1 modules are paired in superchambers and each pair is supplied with same HV • Two modules with similar gain performance are selected for each superchamber • Gain in different module pairs, i.e. superchambers, can be equalized by trimming applied HV appropriately • Remaining gain variation across modules is about 5% (blue curve in plot on p.11) => Similarly, four GE2/1 modules will be paired in a chamber and connected to an HV supply; expect to equalize gain across modules at a similar level.

14. QC – Gain Uniformity within Modules GE1/1 data slice

15. QC – Gain Uniformity within Modules GE2/1 data (= # slices) GE2/1-I-M1-CERN-0001 meets requirement of < 15 %

16. QC – Gain Uniformity within Modules GE2/1 data meets requirement of < 15 %

17. QC – Gain Uniformity within Modules GE2/1 data Best case: M6 Worst case: M3

18. Intrinsic Chamber Noise GE2/1 data As established for GE1/1 production Variation mainly due to varying positioning of GEM stack relative to inner frames

19. Interstrip Capacitance – Special ROB Readout Board with 12 sectors - each with a different readout strip or trace design; fits a GE1/1 detector (addresses risk 4.9 in risk register) ROB facing a solid Cu plate across a 1mm gap to simulate presence of GEM3

20. Measured Interstrip Capacitance Halving strip length and doubling strip width reduces interstrip capacitance by 20-30% (new baseline; also used in M1-8 prototype modules)

21. InterstripCapacitances within a Sector Longer strips & traces Shorter strips & traces

22. Noise Performance with VFAT3 GE2/1 data • Six VFATS reading out one eta partition • Noise measurement derived from VFAT3 response (width of S-curves) • Note: With a noise level of 0.8-1.2 fC, a 97% efficiency is unchanged on plateau (see p. 5)

23. Strip Charge for MIPs Measured at Test Beam GE1/1 data Landau distribution Most probable value (MPV)

24. Strip Charge MPV for MIPs vs. Noise Charge GE1/1 data [fC] Operating range Measured M1, M2 VFAT3 noise level

25. Impact of Wider Strips on pTResolution Ratio in track pT resolution for 768 strips per eta sector (original TDR design) over 384 strips per eta sector (new baseline) From simulation Expected as GEM hits have little impact on offline muon reconstruction

26. Longevity – Aging Performance GE1/1 data (GIF++) GE1/1 with Korean foils GE1/1 with CERN foils after correction after correction NO aging observed up to = Safety factor 73 for GE2/1 at HL-LHC NO aging observed up to = Safety factor 27 for GE2/1 at HL-LHC

27. Longevity – Discharges GE1/1 data • Observed long-term behavior: • First opportunity to observe real-life discharges with the entire system (detector+HV+electronics+BKG particles) • Observation of gradual channel loss in the electronics caused by a specific type of discharges that propagate to the RO board • Triggered a new R&D campaign to understand the discharge propagation process and determine mitigation techniques as part of our risk management strategy • Slice Test Experience • Installation of 5 super-chambers in the negative end-cap • Continuous operation within the CMS framework • First experience with detectors & services installation, DCS, DSS, DAQ, DQM and analysis

28. Longevity - Discharge Status • Conducted an extensive R&D program to address observed discharge issue • Problem is now resolved by severely reducing discharge propagation probability and strip damage probability • Expected number of damaged GE2/1 readout channels over 10 years at HL-LHC is now < 1%

29. Longevity – Discharge Loss Estimate • Very conservative upper limit on damaged channels per GE2/1 chamber at the HL-LHC over 10 years: discharge density × Ppropagation× Pdamage × Achamber < (0.4-11.7)/cm2 × 0.01 × 0.03 × 14,500 cm2 < 1.8 – 51 lost channels per chamber (< 1%) Muon Upgrade TDR

30. Longevity – Discharge Propagation Mechanism 10 MΩ : 6.4 nF (1 discharge) Propagated Primary Typical EM interferences caused by propagating discharges in GEM detectors Typical development of avalanche into a streamer A. Utrobičić et al. (University of Zagreb), MPGD Stability Workshop June 2018 SEM picture of a GEM hole (bottom) after one discharge with an energy of 2.0 mJ • Step 2: • Creation of a hot spot on the copper near the hole rim >2500 °C • Step 3: • Thermionic emission of electrons in the gas, enhanced by local electric field (Schottky effect) • Step 4: • Development of the precursor current into a streamer causing a second discharge • Step 1: • Primary discharged caused by the increase of the space charge density in the avalanche primary

31. Discharge Propagation Dependence GE1/1 data • No dependence on the GEM foil capacitance  no influence of the primary discharge energy • Clear increase of the propagation probability with the induction capacitance  i.e. sufficient amount of energy on the foil to feed the precursor current and trigger discharge propagation • The discharge propagation is more likely to happen in large foils due to the size of charge and energy directly stored in the foil

32. Longevity – Discharge Mitigation Channel loss rate = BKG rate * discharge prob. * propagation prob. * damage prob. Damage Probability Propagation Probability Discharge Probability • Understood the process of propagation in large detectors •  Mainly driven by the large capacitance of the foils • Found 3 ways to mitigate discharge propagation: • Reduce foil capacitance by segmenting bottom of foil • Increase filter resistance • Use drain resistors • Understood the process of damage in large detectors •  Mainly due to propagation re-ignitions • Found 2 ways to mitigate VFAT damage: • Improve electronics input protection • Increase the de-coupling with the filter capacitance Intrinsic to all gaseous technologies Low probability with triple-GEM (~10-9-10-10)

33. Propagation Probability after Mitigation Implementation of double-segmented foils GE1/1 data CMS nominal GE1/1 field Zero observed propagated discharges at 4 kV/cm => limit of < 1.1% discharge prob. (@95%CL)

34. Damage Probability after Mitigation GE1/1 data Protection Elements tested for effectiveness: HV 10 kΩ 100 kΩ HV Filter Baseline configuration during Slice Test: 95-100% damage probability 10 MΩ 10 MΩ 10 MΩ 10 MΩ 10 MΩ HV Filter <100 cm2 HV 10 kΩ 100 kΩ GEM Top GEM Bottom on all 7 electrodes 200 kΩ Rprot = 470 Ω VFAT3 hybrid Optimum configurations: <3% damage probability Hardware Configuration [a.u]

35. Rate Capability with Prot. Resistor GE2/1 data

36. Summary – Long Version

37. Summary – Short version from Muon Upgrade TDR, p.209

38. Backup

39. Backup – Discharges Do Not Impact Gain • Measuring the probability of discharges: • Tests in laboratory (alpha particles) with both small and large detectors • Tests in neutron facilities with CMS-like particle background • Test results: • Determined lower and upper limits for discharge probability • Estimate total No. of discharges per cm2 in the hottest region • No temporary or permanent degradation of the detector performance could be measured after alpha irradiation, nor in neutron environment After ~ 500 discharges • Additional Studies: • In-depth analysis with single-hole GEMs proved the robustness of the technology against discharges, even in extreme conditions • Large accumulation of data during the R&D phase with no indications of performance loss degradation nor visible damages I. Yoon, LHC KCMS Workshop, 09/01/2019

40. Backup – Single-Hole Discharge Robustness • Specific study on single GEM hole systems: • Special GEM foil design with single hole to control the conditions of discharges and isolate the elements that play a role • Test results: • Measurements reveal high resistance to discharges, even at high energy (>103) • Slight increase of the hole diameter after 10-20 discharges • No effect on detector gain since sharing of amplification over several layers and several holes