1. Micromegas for the ATLAS Muon System Upgrade
Jörg Wotschack (CERN)
MAMMA Collaboration
Arizona, Athens (U, NTU, Demokritos), Brandeis, Brookhaven, CERN, Carleton, Istanbul (Bogaziçi, Doğuş), JINR Dubna, LN Frascati, MEPHI Moscow, LMU Munich, Naples, CEA Saclay, USTC Hefei, Roma 1 and 3, South Carolina, Thessaloniki, … (growing community)
Work performed in close collaboration with CERN/TE-MPE PCB workshop (Rui de Oliveira)
Lots of synergy from the RD51 Collaboration

2. ATLAS Small Wheel upgrade
Today:
MDT chambers (drift tubes) +
TGCs for 2nd coordinate (not visible)
2.4 m
Equip the Small Wheels*) with 128 micromegas chambers (0.5–2.5 m2)
Combine precision and 2nd coord. measurement as well as trigger functionality in a single device
Each chamber comprises eight active layers, arranged in two multilayers
a total of about 1200 m2 of detection layers
2M readout channels
CSC chambers
*) combined systems of MMs and TGCs
LAPP, Annecy, 26 April 2012
Joerg Wotschack (CERN)

3. Rates: measurement vs simulation
Measured and expected count rates and in the Small Wheel detectors Data correspond to L = 0.9 x 1033 cm-2s-1 at √s = 7 TeV
Ratio between MDT data and FLUGG*) simulation (CSC region not shown)
Rate in Hz/cm2 as a function of radius in the large sectors
*) FLUGG simulation gives rates about factor 1.5 – 2 higher than old simulation
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

4. At least two reasons for new Small Wheels
Small Wheel muon chambers were designed for a luminosity of L = 1 x 1034 cm-2 s-1
The rates measured today are 2–3 x higher than estimated
All detectors in the SW will be at their rate limit at L ≥ 5 x 1034 cm-2 s-1
Eliminate fakes in high-pT (> 20 GeV) triggers
Currently over 95 % of forward high pT triggers are fake (removed at LV2)
Use tracks in SW as LV1 confirmation Requires pointing precision of 1 mrad
Today
2018
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

5. Small Wheel performance requirements
Rate capability 15 kHz/cm2 (L ≈ 5 x 1034 cm-2s-1)
Efficiency > 98%
Spatial resolution ≤100 m (Θtrack< 30°)
Good double track resolution
Trigger capability (BCID, time resolution ≤ 5–10 ns)
Radiation resistance
Good ageing properties
All requirements can be met with micromegas
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

6. The micromegas technology
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

7. Micromegas operating principle
Micromegas (I. Giomataris et al., NIM A 376 (1996) 29) are parallel-plate chambers where the amplification takes place in a thin gap, separated from the conversion region by a fine and semi-transparent metallic mesh
The thin amplification gap (short drift times and fast absorption of the positive ions) makes it particularly suited for high-rate applications
The price to pay is time resolution, e.g., compared to RPCs
-800 V
-550 V
Conversion & drift space
Mesh
Amplification
Gap 128 µm
(few mm)
The principle of operation
of a micromegas chamber
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

8. Micromegas µTPC principle
Access to 3rd coordinate
Wide conversion and drift region (typically a few mm) with moderate electric field of 100–1000 V/cm
Narrow (100 µm) amplification gap with high electrical field (40–50 kV/cm)
With drift velocities of 5 cm/µs (or 20 ns/mm) electrons for Ar:CO2 (93:7) need 100 ns for a 5 mm gap
By measuring the arrival time of the signals a MM functions like a TPC
=> Track vectors for inclined tracks
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

9. The bulk-micromegas* technique
The bulk-micromegas technique, developed at CERN, opens the door to industrial fabrication
Pillars ( ≈ 300 µm)
Mesh
Photoresist (64 µm)
r/o strips
PCB
*) I. Giomataris et al., NIM A 560 (2006) 405
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

10. Bulk-micromegas structure
Pillars (here: distance = 2.5 mm)
Standard configuration
Pillars every 2.5 – 10 mm
Pillar diameter ≈300 µm
Dead area ≈1–2%
Amplification gap 128 µm
Mesh: 350 wires/inch
Wire diameter 20 µm
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

11. Sparks made inoffensive by the resistive-strip protection concept
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

12. Joerg Wotschack (CERN)
Spatial resolution & efficiency for R12 (250 µm strips) Analysis of data taken in July 2010
Inefficiency compatible with area of mesh support pillars (d=2.5 mm)
Resistive strip chambers are fully efficient (≈98%)over a wide range of gains
Spatial resolution with 250 µm strip: ≈30 µm with Ar:CO2 (93:7), even better with 85:15
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

13. Micromegas in ATLAS cavern
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

14. 2011: four resistive MMs installed behind EO station
Stand-alone readout
Worked through the full year flawlessly
Nice, clean tracks and background measurement
R11
R12
R13x
R16xy
Trigger (strips)
DCS
mmDAQ
Laptop
in USA15
≈120 mm
R16
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

15. Joerg Wotschack (CERN)
2012
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

16. Joerg Wotschack (CERN)
Small Wheel: four small (10 x 10 cm2) MMs
Installed four MMs on CSCs on Small Wheel (Side A, Sector 9) in early 2012
Readout (standalone) of chambers after this Tech. Stop
Readout integration into ATLAS DAQ being prepared (M. Byszewski et al.)
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

17. Joerg Wotschack (CERN)
MBT0: Double gap chamber with x and u (v) readout
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

18. Joerg Wotschack (CERN)
MBT0: Double gap chamber with x and u (v) readout
MBT0 chamber switched on last week
Only HV/current monitoring so far (readout as of this week-end)
Current follows very nicely the luminosity (max: 5 x 1033 cm-2s-1)
Rate ≈100 kHz/cm2 (extrapolated from current measurement)
Frascati, 7 Dec 2011
Joerg Wotschack (CERN)

19. Time line of Small Wheel project
2012: Large-area prototypes
1 x 1 m2 prototype (July)
1 x 2 m2 prototypes (end of year)
2013: Technology transfer to industry
Optimization of production steps in industry
Development of QA procedures
Module 0 (1 x 2.4 m2; 2 x 4 planes)
2014: Setup of production & test facilities
2015/16: Production of about 1200 MMs
Testing, assembly, commissioning (128 chambers)
2017: Installation on NSW structure
2018: Installation in ATLAS
LAPP, Annecy, 26 April 2012
Joerg Wotschack (CERN)

20. Minimum-bias trigger (MBT)
Disk of ≈2 m diameter on face of end-cap calorimeter, 60 mm thick
Two disks (side A and C)
Particle rates: ≤ 1 MHz/cm2
3–4 planes of MMs/disk
8 or 12 sectors
Segmentation to be defined
Max. dim. ≤ 0.6 x 0.8 m2
Total of 100 detectors to be made
Time scale
Design & production: 2013
Installation: early 2014
Project under discussion in ATLAS
Replacement of MBT scintillator disks by micromegas detectors
LAPP, Annecy, 26 April 2012
Joerg Wotschack (CERN)

21. Who is involved (CERN personnel)
PH-ADE-MU
Staff: J. Wotschack
Fellow: Marcin Byszewski (DAQ, mon. & offline reconstruction) – until 31 July, if no extension (very critical)
Techn. Student: Maria Hoffmann (as of 1 August 2012)
PJAS: George Glonti (until July 2012); Givi Sekhniaidze (as of June 2012)
(Also: MBT project: David Berge, Ch. Rembser, A. Salzburger, M. Schott)
PCB workshop (TE-MPE-EM)
Rui de Oliveira
Olivier Pizzorusso, Antonio Texeira
PH-DT-EM2 (support with mechanics, design and construction)
Hans Danielsson et al. (small fraction of his time)
also
Leszek Ropelewski et al. (PH-DT-TP) for Lab space and support
Hand Muller et al. (PH-AID-DT) for SRS readout support
LAPP, Annecy, 26 April 2012
Joerg Wotschack (CERN)