ATLAS Micromegas Project
--- an update --Jörg Wotschack (CERN)
MAMMA Collaboration
Arizona, Athens (U, NTU, Demokritos), Brandeis, Brookhaven, CERN,
Carleton, Istanbul (Bogaziçi, Doğuş), JINR Dubna, MEPHI Moscow, LMU
Munich, Naples, CEA Saclay, USTC Hefei, South Carolina, Thessaloniki
Activities since Kobe
New chambers:
Construction efforts concentrate now on simplification and cost
reduction issues
 R21 following inverted HV scheme of R20 (R strips on +HV potential,
mesh at ground potential); x-y readout strips, new structure
 MBT0: two-gap chamber to be installed in ATLAS in front of the
electromagnetic calorimeter this winter shutdown
 CR4: 1.2 x 0.5 m2 resistive-strip chamber, with mesh at Ground and R
strip on +HV potential
Test beam activities:
 H6 (October 12–22)
 Neutron beam at Garching (Munich)
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
2
R20 (inverted HV schema)
 Resistive strip chamber
with inverted HV
scheme
 Single coordinate (x)
with 250 µm strip pitch
 Fairly high resistivity
values
 RGND ≈ 200 MΩ
 Rstrip ≈ 150 MΩ/cm
Drift electrode (-HV)
R20
Resistive Strips (+HV)
Mesh
PCB
Insulator
Copper readout strip
Inverting the HV connection scheme with the mesh on ground potential and
the resistive strips on +HV leads to a considerable simplification of the
manufacturing process
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
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Performance of R20 (+HV on strips)
R20 (mesh at GND) -- Gain vs R-strip HV Ar:CO2 (93:7)
55Fe
100000
γ (5.9 keV)
Ar:CO2 93:7
Gain
G≈5000
G≈10000
10000
R20 meas. 1
R20 meas. 2
R14
1000
450
470
490
510
530
550
570
590
HVstrips (V)
R20 -- Charge-up (HVStrips = 530 V, rate = 1 kHz)
535.00
600
530.00
520.00
Cu Xray peak
5.9 keV peak
500
Signal drop: 5 % (compared
to 10–15% for R11, R12,…)
525.00
R20 -- rate dependence, G ≈ 10000, Ar:CO2 93:7
515.00
510.00
505.00
500.00
400
8 keV Cu X-rays
300
Signal drop
compatible with HV
drop over resistive
strips (0.5–1 GΩ)
200
100
495.00
0
490.00
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0.01
Time (s)
RD51 mini week, 22 Nov 2011
0.1
1
10
100
Rate (kHz/mm2)
Joerg Wotschack (CERN)
4
R21 (x-y readout coordinates)
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Readout strips on two sides
of thin PCB (0.8–1 mm)
carrying the MM structure
No through holes;
connectors on both sides of
the PCB
Avoids multi-layer PCBs
Simplification of production
and cost reduction
Strips




x pitch = 0.5 mm (0.1 mm)
Y: pitch = 1 mm (0.9 mm)
PCB = 1 mm
Resistivity values too high


RGND ≈ 250 MΩ
Rstrip ≈ 150 MΩ/cm
RD51 mini week, 22 Nov 2011
Charge sharing not (yet) well matched
 Q(x):Q(y) ≈ 5:1
Joerg Wotschack (CERN)
5
R21 gain measurement
R21 gain
Gain
100000
Ar:CO2 (93:7)
Chamber extremely
quiet
10000
Gains above 105 for x
strips
1000
Charge sharing not
(yet) well matched
 Q(x):Q(y) ≈ 5:1
X - gain
Y - gain
100
480
500
520
540
560
580
600
HV (resis ve strips) [V]
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
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Other recent chambers: MBT0
150 mm
 Small chamber to be installed in
ATLAS in front of the electromagnetic
calorimeter, at the outer rim of the
MBTS
Expected particle rates: 1 MHz/cm2
 Double gap chamber with x and u (v)
readout strips
 190 x strips: 0.5 mm pitch
 66 u(v) strips: 1.5 mm pitch


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
Readout planes face-to-face
Common drift electrode
Inverted HV scheme
Thickness 16 mm
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
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Recent test beam activities
 13-22 Oct.: H6 test beam at
CERN (120 GeV pions)
 Five chambers tested: R18,
R19, R20, R21, MBT0, CR2
(large MM)
 Rate and resolution studies
 3-9 Nov.: 2.4 MeV neutron
beam at Garching/Munich
(up to 1.5 x 106 n/cm2/s)
 Three chambers exposed:
R20, R21, MBT0
 All chambers worked nicely
 Took successfully data with
cosmics and random
triggers to study the
interaction probability of
neutrons and photons
RD51 mini week, 22 Nov 2011
Test setup in neutron beam at Garching (Nov 2011)
Joerg Wotschack (CERN)
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Charge (arb. Units)
The charge in strips 110
– 170 exceeding the
dynamic range of the
APV25; the ADC is in
overflow
Time (25 ns bins)
Neutron interaction ?
Strip number (0.25 mm pitch)
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
Strip number (0.25 mm pitch)
9
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
Time (25 ns bins)
Time (25 ns bins)
Time (25 ns bins)
Time (25 ns bins)
Charge (arb. Units)
Charge (arb. Units)
Charge (arb. Units)
Chambers are not well
aligned.
Strip pitch in MBT0 and
R21 is 0.5 mm, R21 has
0.25 mm pitch.
R20 and R21 are back-toback, i.e. strip no. 360 in
R20 and strip no. 1 in R21
are at the position in x.
Charge (arb. Units)
Cosmic track during
neutron beam (100 nA)
Strip number (0.25/0.5 mm pitch)
10
The large-area MM chambers
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
11
Assembly of 1st large resistive MM in March 2011
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Dummy PCB


RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
Size: 1.2 x 0.6 m2
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
12
Chamber in H6 test beam (July 2011)
Large resistive MM
R19 with xuv readout
(seen from the back)
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
13
Experience with large (1.2 x 0.6 m2) MM


The large MM with resistive strips and
0.5 mm pitch has been successfully tested in
July and November in the H6 beam
Stable operation and clean data
Strip # (pitch 0.5 mm)
Charge (arb. units)
Hit map showing the beam profile (top)
and charge spectrum (bottom)
RD51 mini week, 22 Nov 2011
Event display showing a track traversing
the CR2 chamber under 20 degree
Joerg Wotschack (CERN)
14
The 2nd large resistive chamber
 Chamber was completed
end of last week
 Waiting to be assembled
 Electrical tests are OK
 Chamber employs the
new HV scheme with the
mesh on ground potential
and the resistive strips on
+HV
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
15
Next steps
 Qualify the 2nd large chamber with cosmics and possibly in a
neutron beam (spring 2012 at Demokritos/Athens)
 Installation of MBT0 chamber in ATLAS during Xmas shutdown
 Construction of four 1.2 x 0.5 m2 large chambers, assembled
into a multilayer, to be installed during the Xmas shutdown in
Sector 9, side A on the large CSC on the Small Wheel
 Each plane will have x and u strips with pitches 0.5 and 1.5 mm
 Design is completed; construction is expected to be finished by end of
2011
 Work on integration of data readout into ATLAS DAQ started
 Go to 1 m wide chambers (after the completion of the upgrade
of the CERN PCB workshop, early 2012 ?)
RD51 mini week, 22 Nov 2011
Joerg Wotschack (CERN)
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