M icromegas for the ATLAS Muon System Upgrade

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


The LHC & ATLAS

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ATLAS

CMS


The ATLAS detector

Hefei, 5 Sept. 2011


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


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


Count rates in ATLAS for L=1034cm-2s-1

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Small WheelRates in Hz/cm2

Rates at inner rim are close to 2 kHz/cm2


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

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The problem with the fake tracks

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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


2.4 m

The ATLAS Small Wheel upgrade

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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


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


A possible segmentation of Large and Small Sectors

Segmentation in radius is indicative


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


The principle of operationof a micromegas chamber

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Conversion & drift space

MeshAmplificationGap 128 µm

(few mm)


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

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Bulk-micromegas structure

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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


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


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



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

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The resistive-strip protection concept

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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


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


Detector response


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


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


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

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Gain ≈ 104Gain ≈ 4000 8000


Spatial resolution & efficiency

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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)


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 ?

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R ≈ 45 MΩ R ≈ 85 MΩ


R11 rate studies

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Clean signals up to >1 MHz/cm2,but some loss of gain

Gain ≈ 5000


Test beamNov 2010

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Active area10 x 10 cm2

Four chambers with resistive strips aligned along the beam

NEW: Scaleable Readout System (SRS)

APV25 hybrid cards


R11

R12

R13

R15

Tim

e bi

ns (2

5 ns

)

Char

ge (2

00 e

- )

Strips (250 µm pitch) Strips (250 µm pitch)


R11

R12

R13

R15

Delta ray

Tim

e bi

ns (2

5 ns

)

Char

ge (2

00 e

- )


Inclined tracks (40°) – µTPC

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R12

R11

Tim

e bi

ns (2

5 ns

)

Char

ge (2

00 e

- )


… and a two-track event

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R11

R12 Tim

e bi

ns (2

5 ns

)

Char

ge (2

00 e

- )


Two-dimensional readout

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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

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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


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

)


R19 with xuv readout strips

x strips parallel to R strips u,v strips ±60 degree

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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


Ageing

Hefei, 5 Sept. 2011


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

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Towards large-area MM chambers

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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)


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


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

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Dummy PCB


Cover and drift electrode

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Drift electrode HV connection

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HV connectionspring

O-ring seal

Al spacer frame


Chamber closed Assembly extremely

simple, takes a few minutes

Signals routed out without soldered connectors

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Chamber in H6 test beam (July 2011)

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Large resistive MM

R19 with xuv readout(seen from the back)


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


Micromegas in ATLAS cavern

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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

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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


ATLAS cavern


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


Two types of background events

Photon ? Neutron ? induced nuclear break-up

Total charge: 1700 ADC counts

Total charge: >10000 ADC counts

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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)


Readout electronics & trigger

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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



Trigger/DAQ Block Diagram

Hefei, 5 Sept. 2011

GBTx Gigabit TranceiverChipset being developed at

CERN, will combineData, TTC, DCS on a single fiber


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)


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


Thank you !for your invitation to speak here

and your attention

Hefei, 5 Sept. 2011

Documents

M icromegas for the ATLAS Muon System Upgrade