m icromegas for the atlas muon system upgrade
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M icromegas for the ATLAS Muon System Upgrade . Joerg Wotschack (CERN) MAMMA Collaboration - PowerPoint PPT PresentationTRANSCRIPT
Micromegas for the ATLAS Muon System Upgrade
Joerg Wotschack (CERN)
MAMMA Collaboration
Arizona, Athens (U, NTU, Demokritos), Brandeis, Brookhaven, CERN, Carleton, Istanbul (Bogaziçi, Doğuş), JINR Dubna, LMU Munich, Naples, CEA Saclay, USTC Hefei, South Carolina, St.
Petersburg, Thessaloniki
Joerg Wotschack (CERN) 2
Outline
Introduction Micromegas Making micromegas spark-resistant Two-dimensional readout Development of large-area muon chambers First data from ATLAS Other projects
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 3
The LHC & ATLAS
Hefei, 5 Sept. 2011
ATLAS
CMS
Joerg Wotschack (CERN) 4
The ATLAS detector
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 5
LHC operation & luminosity upgrade LHC is working at √s = 7 TeV and
performs very well Fills routinely L ≥ 2 x 1033 cm-2 s-1
Longest fill lasted 24 hours LHC upgrade schedule:
Physics run until end 2012 Shutdown 2013/14 to prepare for
√s = 14 TeV Physics run 2015–17; hope to reach L =
1 x 1034 cm-2 s-1 Shutdown 2018 to prepare for L = 2–3 x
1034 cm-2 s-1 + experiments upgrade Physics run at L = 2–3 x 1034 cm-2 s-1 Shutdown 2021 or 2022 (?) to prepare
for L = 5 x 1034 cm-2 s-1
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 6
The ATLAS upgrade for 2018ff
The prospect of reaching luminosity larger than 1034 cm-2 s-1 after the 2018 shutdown makes some upgrades of the ATLAS detector mandatory Replacement of pixel vertex detector Replacement of electronics in various sub-
detectors The trigger system Replacement of the first station of the end-cap
muon system: the Small Wheel
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 7
Count rates in ATLAS for L=1034cm-2s-1
Hefei, 5 Sept. 2011
Small WheelRates in Hz/cm2
Rates at inner rim are close to 2 kHz/cm2
Joerg Wotschack (CERN) 8
Why new Small Wheels Small Wheel muon chambers were designed for a
luminosity L = 1 x 1034 cm-2 s-1
The rates measured today are ≈2 x higher than estimated All detectors in the SW are expected to be at their rate limit
Eliminate fake trigger in pT > 20 GeV TriggersAt higher luminosity pT thresholds 20-25 GeV are a MUST Currently over 90% of high pT triggers are fake
Improve pT resolution to sharpen thresholdsNeeds ≤1 mrad pointing resolution
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 9
The problem with the fake tracks
Hefei, 5 Sept. 2011
ProposedTrigger Provide vector A at Small Wheel Powerful constraint for real tracks With a pointing resolution of 1 mrad it will also improve pT resolution Currently 96% of High pT triggers have no track associated with them
Current End-cap Trigger Only a vector BC at the Big Wheels is measured Momentum defined by implicit assumption that track originated at IP Random background tracks can easily fake this
Performance requirements Spatial resolution ≈100 m (Θtrack< 30°) Good double track resolution Efficiency > 98% Trigger capability (time resolution ≈5 ns)
Rate capability ≥ 10 kHz/cm2
Radiation resistance Good ageing properties
Joerg Wotschack (CERN) 10Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 11
2.4 m
The ATLAS Small Wheel upgrade
Hefei, 5 Sept. 2011
CSC chambers
Today:MDT chambers (drift tubes) +TGCs for 2nd coordinate (not visible)
Our proposal Replace the muon chambers
of the Small Wheels with 128 micromegas chambers (0.5–2.5 m2)
These chambers will fulfil both precision measurement and triggering functionality
Each chamber will have eight active layers, arranged in two multilayers a total of about 1200 m2
of detection layers 2M readout channels
Joerg Wotschack (CERN) 12Hefei, 5 Sept. 2011
A tentative Layout of the New Small Wheels and a sketch of an 8-layer chamber built of two multilayers, of four active layers each, separated by an instrumented Al spacer for monitoring the internal chamber deformations
Joerg Wotschack (CERN) 13Hefei, 5 Sept. 2011
A possible segmentation of Large and Small Sectors
Segmentation in radius is indicative
Joerg Wotschack (CERN) 14
The micromegas technology
Hefei, 5 Sept. 2011
-800 V
-550 V
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 metallic mesh
The thin amplification gap (short drift times and fast absorption of the positive ions) makes it particularly suited for high-rate applications
Joerg Wotschack (CERN) 15
The principle of operationof a micromegas chamber
Hefei, 5 Sept. 2011
Conversion & drift space
MeshAmplificationGap 128 µm
(few mm)
Joerg Wotschack (CERN) 16
Pillars ( ≈ 300 µm)
The bulk-micromegas* technique
PCB
Photoresist (64 µm)r/o strips
Mesh
*) I. Giomataris et al., NIM A 560 (2006) 405
The bulk-micromegas technique, developed at CERN, opens the door to industrial fabrication
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 17
Bulk-micromegas structure
Hefei, 5 Sept. 2011
Standard configuration Pillars every 2.5 – 10 mm Pillar diameter ≈300 µm Dead area ≈1% Amplification gap 128 µm Mesh: 325 wires/inch
Pillars (here: distance = 2.5 mm)
The MAMMA R&D project ATLAS MM Upgrade Project: started 2008
Since then, we produced and tested a large number of prototype micromegas chambers By end of 2009 their excellent performance and potential for
large-area muon detectors was demonstrated 2010 was dedicated to make chambers spark resistant 2011 moving to large-area chambers
Growing interest in the community (now ≈20 institutes) Major role in the RD51 Collaboration
Hefei, 5 Sept. 2011 Joerg Wotschack (CERN) 18
Joerg Wotschack (CERN) 19
Performance studies
All initial performance studies were done with ‘standard’ micromegas chambers
We used the ALICE Date system with the ALTRO chip, limited to 64 channels
End 2010 we switched to new readout electronics (APV25, 128 ch/chip) and a new ‘Scalable Readout System’ (SRS) developed in the context of RD51
Hefei, 5 Sept. 2011
2008: Demonstrated performance
Hefei, 5 Sept. 2011 Joerg Wotschack (CERN) 20
Standard micromegas Safe operating point with
excellent efficiency Gas gain: 3–5 x 103
Superb spatial resolution
250 µm strip pitch
σMM = 36 ± 7 µm
Ar:CF4:iC4H10 (88:10:2)
(MM + Si telescope)
X (mm)
y (m
m)
Inefficient areas
Conclusions by end of 2009 Micromegas (standard) work
Clean signals Stable operation for detector gains of 3–5 x 103
Efficiency of 99%, only limited by the dead area from pillars Required spatial resolution can easily be achieved with strip
pitches between 0.5 and 1 mm Timing looks Ok, but performance could not be measured
with our electronics Sparks are a problem
Sparks leads to a partial discharge of the amplification mesh => HV drop & inefficiency during charge-up
But: no damage on chambers, despite many sparks
Hefei, 5 Sept. 2011 Joerg Wotschack (CERN) 21
Joerg Wotschack (CERN) 22
2010: Making MMs spark resistant
Several protection/suppression schemes tested A large variety of resistive coatings of anode Double/triple amplification stages to disperse
charge, as used in GEMs (MM+MM, GEM+MM) Finally settled on a protection layer with
resistive strips Tested the concept successfully in the lab (55Fe
source, Cu X-ray gun, cosmics), H6 pion & muon beam, and with 5.5 MeV neutrons
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 23
The resistive-strip protection concept
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 24
Sparks in resistive chambers Spark signals (currents) for resistive chambers are about a factor 1000 lower than for
standard micromegas (spark pulse in non-resistive MMs: few 100 V) Spark signals fast (<100 ns), recovery time a few µs, slightly shorter for R12 with strips with
higher resistance Frequently multiple sparks
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 25
Several resistive-strip detectors tested Small 10 x 10 cm2 chambers with 250 µm
readout strip pitch Various resistance values
Chamber RGND(MΩ)
Rstrip(MΩ/cm)
NR:Nro
R11 15 2 1:1R12 45 5 1:1R13 20 0.5 1:1R14 100 10 1:1,2,3,4,72R15 250 50 1:1,2,3,4,72R16 55 35 x-y readoutR17 100 45 x-y readoutR18 200 100 x-y readoutR19 50 50 xuv readout
Hefei, 5 Sept. 2011
Gas mixtures Ar:CO2 (85:15 and 93:7)
Gas gains 2–3 x 104
104 for stable operation
R16
Joerg Wotschack (CERN) 26Hefei, 5 Sept. 2011
Detector response
Joerg Wotschack (CERN) 27
Performance in neutron beam
Standard MM could not be operated in neutron beam
HV break-down and currents exceeding several µA already for gains of order 1000–2000
MM with resistive strips operated perfectly well,
No HV drops, small spark currents up to gas gains of 2 x 104
Hefei, 5 Sept. 2011
Standard MM Resistive MM
Joerg Wotschack (CERN) 28
Spark rates in neutron beam (R11)
Typically a few sparks/s for gain 104
About 4 x more sparks with 80:20 than with 93:7 Ar:CO2 mixture
Neutron interaction rate independent of gas
Spark rate/n is a few 10-8 for gain 104
Larger spark rate in 80:20 gas mixture is explained by smaller electron diffusion, i.e. higher charge concentration
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 29
Sparks in 120 GeV pion & muon beams
Pions, no beam, muons Chamber inefficient for O(1s)
when sparks occur
Stable, no HV drops, low currents for resistive MM
Same behaviour up to gas gains of > 104
Hefei, 5 Sept. 2011
Gain ≈ 104Gain ≈ 4000 8000
Joerg Wotschack (CERN) 30
Spatial resolution & efficiency
Hefei, 5 Sept. 2011
More details in talk by M. Villa in RD51 Collaboration meeting (WG2)
Spatial resolution measured with an external Si telescope, shown is convoluted resolutions of Si telescope + extrapol. (≈30 µm) and MM with 250 µm strip pitch
σMM ≈ 30–35 µm
Efficiency measured in H6 pion beam (120 GeV/c); S3 is a non-resistive MM, R12 has resistive-strip protection
R12 (resistive strips)
S3 (non-resistive)
Joerg Wotschack (CERN) 31
Homogeneity and Charge-up
No strong dependence of effective gain on resistance values (within measured range)
Systematical gain drop of 10–15% for resistive & standard chambers; stabilizes after a few minutes
Charge-up of insulator b/w strips ?
Hefei, 5 Sept. 2011
R ≈ 45 MΩ R ≈ 85 MΩ
Joerg Wotschack (CERN) 32
R11 rate studies
Hefei, 5 Sept. 2011
Clean signals up to >1 MHz/cm2,but some loss of gain
Gain ≈ 5000
Joerg Wotschack (CERN) 33
Test beamNov 2010
Hefei, 5 Sept. 2011
Active area10 x 10 cm2
Four chambers with resistive strips aligned along the beam
NEW: Scaleable Readout System (SRS)
APV25 hybrid cards
Joerg Wotschack (CERN) 34Hefei, 5 Sept. 2011
R11
R12
R13
R15
Tim
e bi
ns (2
5 ns
)
Char
ge (2
00 e
- )
Strips (250 µm pitch) Strips (250 µm pitch)
Joerg Wotschack (CERN) 35Hefei, 5 Sept. 2011
R11
R12
R13
R15
Delta ray
Tim
e bi
ns (2
5 ns
)
Char
ge (2
00 e
- )
Joerg Wotschack (CERN) 36
Inclined tracks (40°) – µTPC
Hefei, 5 Sept. 2011
R12
R11
Tim
e bi
ns (2
5 ns
)
Char
ge (2
00 e
- )
Joerg Wotschack (CERN) 37
… and a two-track event
Hefei, 5 Sept. 2011
R11
R12 Tim
e bi
ns (2
5 ns
)
Char
ge (2
00 e
- )
Joerg Wotschack (CERN) 38
Two-dimensional readout
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 39
2D readout (R16 & R19) Readout structure that gives two readout coordinates from the same gas gap;
crossed strips (R16) or xuv with three strip layers (R19) Several chambers successfully tested
Hefei, 5 Sept. 2011
x strips: 250/150 µm r/o and resistive strips
y: 250/80 µm only r/o strips
PCB
Mesh
Resistivity valuesRG ≈ 55 MΩRstrip ≈ 35 MΩ/cm
Resistive strips
x strips
y strips
Joerg Wotschack (CERN) 40
R16 x-y event display (55Fe γ)
Hefei, 5 Sept. 2011
R16 x
R16 y
Char
ge (2
00 e
- )
Tim
e bi
ns (2
5 ns
)
Joerg Wotschack (CERN) 41
R19 with xuv readout strips
x strips parallel to R strips u,v strips ±60 degree
Hefei, 5 Sept. 2011
R strips v stripsu stripsx strips
Mesh
R19 R v u xDepth (µm) 0 -50 -100 -150
Strip width (mm) 0.25 0.1 0.1 0.25
Strip pitch (mm) 0.35 0.9 0.9 0.35
Q collected (rel.) 0.84 0.3 1
Tested two chambers with same readout structure (R19M and R19G) in a pion beam (H6) in July
Clean signals from all three readout coordinates, no cross-talk
Strips of v and x layers well matched, u strips low signal, too narrow
Excellent spatial resolution, even with v and u strips
σ = 94/√2 µm
Joerg Wotschack (CERN) 42
Ageing
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 43
Long-time X-ray exposure A resistive-strip MM has been
exposed at CEA Saclay to 5.28 keV X-rays for ≈12 days
Accumulated charge: 765 mC/4 cm2
No degradation of detector response in irradiated area (nor elsewhere) observed; rather the contrary (to be understood)
Expected accumulated charge at the smallest radius in the ATLAS Small Wheel: 30 mC/cm2 over 5 years at sLHC
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 44
Towards large-area MM chambers
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 45
CSC-size chamber project
The plan Start with a standard (non-resistive), half-size MM (fall 2010) Then a half-size MM chamber with resistive strips (end 2010) Construction of a 4-layer chamber (fall 2011); installation in
ATLAS during X-mas shutdown 2011/12, if possible Full-size layer, when new machines in CERN/TE-MPE
workshop available (spring 2012)
Hefei, 5 Sept. 2011
46
Cover + drift electrode
50 mm
20 mm
10 mm
5 mm
Stiffening panel
530 mm(520 mm active) 5 mm
20 mm20 mm
Connection pad
FE card (2 APV25)
GND
1024 mm
76.3 °
Max width of PCB for production = 645 mm
Width of final PCB = 605 mmGas outlet
Gas inlet
F/E card50 x 120 mm2
Connection padNumber of strips = 2048
Strip pitch = 0.5 mmStrip width = 0.25 mm8 FE cards
Distance b/w screws128 mm
HV mesh + drift (2 x SHV)
Micromegas
Hefei, 5 Sept. 2011Joerg Wotschack (CERN)
Joerg Wotschack (CERN) 47
Mechanics – detector housing
Hefei, 5 Sept. 2011
PCB with micromegas structureTo be inserted here
Foam/FR4 sandwich with aluminium frame
Stiffening panel
Spacer frame, defines drift gap
Cover & drift electrode
Joerg Wotschack (CERN) 48
Assembly of large resistive MM (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
Hefei, 5 Sept. 2011
Dummy PCB
Joerg Wotschack (CERN) 49
Cover and drift electrode
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 50
Drift electrode HV connection
Hefei, 5 Sept. 2011
HV connectionspring
O-ring seal
Al spacer frame
Joerg Wotschack (CERN) 51
Chamber closed Assembly extremely
simple, takes a few minutes
Signals routed out without soldered connectors
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 52
Chamber in H6 test beam (July 2011)
Hefei, 5 Sept. 2011
Large resistive MM
R19 with xuv readout(seen from the back)
Joerg Wotschack (CERN) 53
Experience with large (1.2 x 0.6 m2) MM
A first large MM with resistive strips and 0.5 mm readout strip pitch has been successfully tested this July in the H6 test beam
It has been operating very stably and produced very nice data (analysis just started)
Construction took a few iterations and helped to understand and cure the weak points (see talk by R. de Oliveira)
Will implement what we learned in the next chamber of the same size, hopefully ready for our next test beam run in Oct. 2011
Hefei, 5 Sept. 2011
Event display showing a track traversing the CR2 chamber under 20 degree
Joerg Wotschack (CERN) 54
Micromegas in ATLAS cavern
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 55
MMs in ATLAS cavern Four 10 x 10 cm2 MMs are installed since beginning
of 2011 in the ATLAS cavern on the HO structure behind EOL2A7 …. they work flawlessly
Hefei, 5 Sept. 2011
2 trigger chambers R11, R12
2 chambers are read-out R13, R16(xy-strips) 3 x 3 APV chips (960 ch)
R11 R12R13 R16xy
Trigger (strips)
DCSmmDAQ
Laptopin USA15
≈120 mm
J. Wotschack 56
MM location on HO structure side A
12/08/2011
R11R12
R13 R16xy
Trigger (strips)
DCSmmDAQ
Laptopin USA15
≈120 mm
R16
Joerg Wotschack (CERN) 57Hefei, 5 Sept. 2011
ATLAS cavern
Joerg Wotschack (CERN) 58
Measuring the cavern background
We recorded events taken with a random trigger, with a rate of 156 Hz, during LHC Fill 2000 and 2009, for about 20 hours and 11 hours
Total number of triggers: 11.4 M + 6.2 M For each trigger the detector activity was
measured for 28 time bins of 25 ns, i.e. 700 ns. Events were accepted in a time window from 5 to
25 time bins, i.e. over 500 ns. Total time covered: ≈ 6+3 s, total area: 2 x 81 cm2
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 59
Two types of background events
Photon ? Neutron ? induced nuclear break-up
Total charge: 1700 ADC counts
Total charge: >10000 ADC counts
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 60
R ≈ 2.7±0.2 Hz/cm2 at L=1034 cm-2s-1
Hefei, 5 Sept. 2011
(Measured rate in close-by EOL2A07 MDT ≈ 8 Hz/cm2)
Joerg Wotschack (CERN) 61
Readout electronics & trigger
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 62
Trigger & readout New BNL chip: 64 channels; on-chip zero suppression,
amplitude and peak time finding Trigger out: address of first-in-time channel with signal above
threshold within BX Data out: digital output of charge & time for channels above
threshold + neighbour channels Trigger signals and data driven out through one (same) GBTx
link/layer (one board/layer) Trigger: track-finding algorithm in Content-Addressable Memory
(as FTK) or in FPGA in USA15; latency estimated 25–32 BXs Small data volumes thanks to on-chip zero-suppression and
digitization
Hefei, 5 Sept. 2011
BNL chip specifications (prelim.)64 channels/chip (preamplifier, shaper, peak amplitude detector, ADC) Real time peak amplitude and time detection with on-chip
zero suppression Simultaneous read/write with built-in Derandomizing Buffers Peaking time 20–100 ns; dynamic range: 200 fC Fast trigger signal of all and/or group of channels Rate: 100 kHz SEU tolerant logicA similar BNL chip (with longer integration time and smaller rate
capability) has been tested with MMs and works
Hefei, 5 Sept. 2011 Joerg Wotschack (CERN) 63
Joerg Wotschack (CERN) 64
Trigger/DAQ Block Diagram
Hefei, 5 Sept. 2011
GBTx Gigabit TranceiverChipset being developed at
CERN, will combineData, TTC, DCS on a single fiber
Joerg Wotschack (CERN) 65
Conclusions
Hefei, 5 Sept. 2011
What have we learned so far ? Micromegas fulfil all (of our) requirements
Excellent rate capability, spatial resolution, and efficiency Potential to deliver track vectors in a single plane for track
reconstruction and LV1 trigger We found an efficient spark-protection system that is
easy to implement; sparks are no longer a show-stopper MMs are very robust and (relatively) easy to construct
(once one knows how to do it) Large-area resistive-strip chambers can be built … and work
very well
66Hefei, 5 Sept. 2011 Joerg Wotschack (CERN)
Joerg Wotschack (CERN) 67
What still needs to be done? Optimize the resistance values (not critical) Demonstrate 2D readout for large chambers Demonstrate radiation hardness of all materials & their
ageing properties (partly done) Go to 1 m wide chambers (after the completion of the
upgrade of the CERN PCB workshop) Move to industrial processes for
Resistive strip deposition Mesh placement
… and then we are ready to build MMs for ATLAS
Hefei, 5 Sept. 2011
Joerg Wotschack (CERN) 68
Thank you !for your invitation to speak here
and your attention
Hefei, 5 Sept. 2011