1. The principle of operation of a micromegas chamber
The MAMMA project Large-area micromegas muon chambers for the ATLAS upgrade
Arizona, Athens (U, NTU, Demokritos), Brookhaven, CERN, JINR Dubna, Harvard, USTC Hefei, Istanbul (Bogaziçi, Doğuş), LMU Munich, Naples, South Carolina, CEA Saclay, Shandong, Stony Brook, St. Petersburg, Thessaloniki, U Washington
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The principle of operation of a micromegas chamber
Amplification
Gap 128 µm
Conversion & drift space
(few mm)
To cope with the luminosity upgrade of the Large Hadron Collider at CERN (sLHC) ATLAS prepares for an upgrade of the muon system in, at least, the highest rapidity region.
The MAMMA R&D activity focuses on the development of large-area muon detectors based on the bulk-micromegas technology as candidates for such an upgrade.
The detectors will combine trigger and precision tracking in a single device. Their low costs, compared to other detector technologies, and their potential for industrial production make the bulk-micromegas excellent candidates for mass-construction of large muon chambers.
Excellent performance
Time bins (25 ns)
Charge (200 e-)
Strips (250 µm pitch)
R14
R13
R12
R11
Standard Ar:CO2 gas mixtures (93:7, 85:15)
Safe operating point with excellent efficiency for gas gains
3–5 x 103 (standard MMs)
1 x 104 (resistive MMs)
Superb spatial resolution
Rate capability > 106 Hz/cm2
500 µm
strip pitch
σMM = 36 ± 7 µm
R ≈ 45 MΩ
R ≈ 85 MΩ
Convoluted resolution
MM + external tracker
Standard MM
Straight Track through four chambers, in R14 the resistive layer is not segmented into strips
5.9 keV
55Fe γ’s
cosmics
R12
Ar:CO2 85:15
Gain ≈ 8000
x (mm)
y (mm)
Inefficient area (pillars) ≈1%
R11
R12
Charge (200 e-)
Time bins (25 ns)
Cosmics spectrum
MMs with resistive strips
Inclined track (40°) through R11 and R12, illustrating the µTPC capability of MMs
A novel scheme to make micromegas spark insensitive: resistive strips
So far, six small prototype chambers (10 x 10 cm2 active area) with 250 µm r/o strip pitch
Variety of resistance values
Typical spark signals in a MM with resistive strips (terminated with 50 Ω)
Spark signal is reduced by a factor of 1000 compared to a standard MM
2D readout
x strips: 250/150 µm
r/o and resistive strips
y: 250/80 µm
only r/o strips
R16
Readout strips (0.25 mm)
Charge (200 e– )
Time (25 ns )
Readout strips (0.25 mm)
Charge (200 e– )
Time (25 ns )
PCB
Mesh
Resistive strips
x strips
y strips
x strips
y strips
R12 chamber with 2D readout
5.9 keV 55Fe photon conversion signals as measured by the x and y strips in the R16 chamber
Towards large-area detectors: the 1m2 chamber
2048 circular strips
Strip pitch: 0.5 mm
8 connectors with 256 contacts each
Mesh: 400 lines/inch
5 mm high frame defines drift space
O-ring for gas seal
Closed by a 10 mm foam sandwich panel serving at the same time as drift electrode
This work is carried out in close collaboration with CERN/TE-MPE (R. de Oliveira) and in the context of the RD51 Collaboration