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Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC...

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Design and construction of the mechanical structure for thin-gap RPC triplets for the upgrade of the ATLAS muon spectrometer O. Kortner on behalf of the ATLAS Muon Collaboration Max-Planck-Institut f¨ ur Physik, M¨ unchen 12.01.2020 1
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Page 1: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Design and construction of the mechanicalstructure for thin-gap RPC triplets for the upgrade

of the ATLAS muon spectrometer

O. Kortner on behalf of the ATLAS Muon Collaboration

Max-Planck-Institut fur Physik, Munchen

12.01.2020

11

Page 2: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

The ATLAS 1st level muon trigger in LHC run I

The muon spectrometer upgrade is a muon trigger upgrade.

So let me recall the original muon trigger and its weak points!

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Big

wheel

µ

10 1550

5

0

10

y [m]

z [m]

Measure of momentum

µ

Measure of momentum

p

wheel

Small

The level-1 high pT muon trigger is built out of a coincindence of

three RPCs in the barrel or three TGCs in the big end-cap wheel.

Muon momentum estimate from the size of the deviation of hits from

an infinite momentum track from the interaction point.

22

Page 3: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Sources of 1st level muon triggers in LHC run I

Low p muonsT

L1 10 GeV muon trigger

matched to reconstructed muon

Tmatched to p >10 GeV muon

Fakes

BarrelEnd−cap C End−cap A

Tri

gg

er

rate

[a

rbit

ray

un

its

]

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Big

wheel

Fake high−p

muon triggerT

µ

10 1550

5

0

10

y [m]

z [m]

Measure of momentum

µ

p

wheel

Small

Muon trigger rate dominated by fake triggers in the end-caps caused

by charged particle not emerging from the interaction point.

Real muon triggers contaminated with sub-pT-threshold muon due to

the reduced momentum resolution caused by the moderate spatial

resolution of the trigger chambers.

33

Page 4: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Muon spectrometer phase-I upgrade (2019-2021)

small wheel

New

sMDT−RPC

New BIS−78

stations

µ

z [m]2010 1550

5

0

10

y [m]

sTGCs MicroMegas

Part of the end−cap triggernot covered by the

new small wheel

To reject fake muon triggers at trigger level:

New small wheel with high-resolution trigger chambers.

New BIS-78 stations:

New thin-gap RPCs trigger chambers.New BIS sMDT precision chambers to free space for the new RPCs.

44

Page 5: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Muon spectrometer phase-II upgrade (2025-2027)

CERN-LHCC-2017-017; ATLAS-TDR-026

Big

wheel10 1550

5

0

10

y [m]

z [m]p

η=0 η=0.4 η=0.75 η=1.0

NSW

New

sMDT −RPC

stations

η

-1 -0.5 0 0.5 1

L0 e

ffic

iency w

rt o

fflin

e

0

0.2

0.4

0.6

0.8

1

3/4 chambers + BIBO 3/4 chambers 3/3 chambers

ATLAS Simulation

Efficiency drops due to non−instrumented detector regions

Installation of new sMDT-RPC stations in the barrel inner layer

to close the acceptance gaps caused by the non-instrumented regions

due to toroid and rib structures,

to recuperate the reduced muon trigger efficiency cause by the

reduced efficiency of the present RPCs at high rates.

Installation of new front-end electronics

to cope with the new trigger and read-out scheme.

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Page 6: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Challenges for the BI RPC upgrade

Challenging requirement

Very compact mechanical structure needed to fit into the limited

available space.

Very rigid mechanical structure required in order to avoid conflicts

with the sMDT chamber.

Strategy for this presentation: Concentrate on the BIS-78 pilot project in

which all challenges of the BI upgrade are present and are addressed.

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Page 7: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Requirements/boundary conditions for the BI upgrade

Structure of the current ATLAS RPC

Current ATLAS RPC

Double-gap structure.

50 mm thick honeycomb

structure provides mechanical

rigidity.

Height: 92 mm.

New BI RPC

Triple-gap system.

Available space: 60 mm.

Development tasks for the new BI RPCs

Thin RPC singlets which can be assembled without an external

Faraday cage.

Rigid mechanical structure to support the RPC triplet independently

of the accompanying sMDT chamber

Rigid mechanical frame for the RPC singlet which stays within the

tight 60 mm envelope including its deformations under gravity.

77

Page 8: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Structure of an RPC singlet

RPC singlet inclosed in its own Faraday cage consisting of the copper

back plates of the read-out electrodes and an attached lateral copper

foil.

New dielectric, FOREX PVC foam instead of polyester foam in the

old RPCs, was chosen to guarantee minimal thickness variations and

increased rigidity of the read-out panels.

(In the future the FOREX foam will be replaced by 3 mm thick paper honeycomb.)

Dielectric of the read−out panel

FOREX plate

Electrode PCBs

Dielectric of the read−out panel

FOREX plate

Gas gap structure

Electrode PCBs

Cu foilComponent Thickness [mm]

Electrode PCB 0.3

FOREX plate 3.00±0.25

Gas gap 4.2±0.2

PET foil 0.2

Cu foil 0.1

⇒ Thickness of an RPC singlet:

(11.8±0.7) mm

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Page 9: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Measurement of the thickness of prototype RPC singlets

Measurement on a granite table Measurement result

Maximum thickness in the region of the RPC frame (as expected).

Outlier at the location of the gas inlet has been avoided for the series

chambers by a cut-out in the read-out panels.

⇒ Maximum singlet thickness compatible with expectations.

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Page 10: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Mechanical structure for BIS-78 RPC triplets

Rigidity of present RPCs achieved by 5 cm thick honeycomb plates.

⇒ Impossible within 6 cm envelope of BIS-78.

Solution for BIS-78

Clamp with

holes for connectors

to the electronics φ

η

on top and bottom

Stiffening rods2mm prebent Al plates

for compression and force

distribution

Interfaceto rail support

1010

Page 11: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Measurement of the rigidity of the BIS-7 mechanics

Measurement of the height of the bottom of the mechanical structure

under the load of an RPC triplet

0 200 400 600 800 1000y [mm]

4−3.5−

3−2.5−

2−1.5−

1−0.5−

00.5

1

z [m

m]

x=-1000 mmx=-450 mmx=-0 mmx=400 mmx=600 mm

Sag of the stiffening rods <2 mm.

1111

Page 12: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Measurement of the rigidity of the BIS-7 mechanics

Measurement of the height of the bottom of the mechanical structure

under the load of an RPC triplet

2 mm

Maximum sag ∼2 mm.

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Page 13: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

RPC support structure

Rails

RPC support structure

sMDT chamber

BIS−7 RPC triplet

FEA calculation of the deformationof the support structure

RPC support structure to slide and keep the RPC triplet on rails.

Deformation of the support structure under the weight of the BIS-78

RPC of 158 kg: 2.2 mm.

⇒ Acceptable deformation preventing interference with the sMDT

chamber and leaving 60 mm for the RPC frame.

1313

Page 14: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Mechanical structure for BIS RPC triplets

Top RPC singlet

Middle RPC singlet

Bottom RPC singlet

Damp for upper frameLongitudinal stringer for upper frame

Lateral enforcement bar of upper frame

Lateral enforcement bar of bottom frameRPC support on rails

55.4

Max. 60

Prebent Al plates

Prebent Al plates

Bottom frame

3

2

1,8

11,8

11,8

2

35,4

01

40

1

Nominal height: 55.4 mm within 60 mm envelope.

RPC triplet thickness tolerances of 3x0.7 mm = 2.1 mm.

Thickness tolerance of the frame plates of 3x0.3 mm = 0.9 mm.

Total thickness tolerance of 3 mm corresponding to 58.4 mm.

Sag: 1-2 mm (measured), 2.2 mm (FEA simulation).

⇒ Design within the 60 mm envelope at the level of ∼1 mm.

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Page 15: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Validation of the mechanical frame

Crucial for the RPC operation: gap size not decreased due to external

mechanical forces between the spacers.

A decreased gap size would lead to a larger electric field and higher

current at the same operating voltage.

To prove that the gap size is preserved with the present design of the

mechanical frame a voltage-current curve was measured under

different mechanical stresses.

⇒ No effect was observed due to the large rigidity of the frame and the

force distribution by the aluminium plates!

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Page 16: Design and construction of the mechanical structure …...The ATLAS 1st level muon trigger in LHC run I The muon spectrometer upgrade is a muon trigger upgrade. So let me recall the

Summary

The inner layer of the barrel part of the ATLAS muon spectrometer

will be instrumented with a triplet of thin-gap RPCs to recuperate the

efficiency losses of the present RPC system at the HL-LHC.

The presence of these RPCs in the small sectors will also close most

of the acceptance gaps of the barrel muon trigger raising the

acceptance from the current 78% to 95%.

In order to provide the required space for the RPCs in the small

sectors the existing MDT chambers will be replaced by sMDT

chambers.

A mechanical structure for the thin-gap RPC triplets with a height of

less than 60 mm and the required mechanical rigidity was successfully

designed and produced for the upgrade of the ATLAS muon

spectrometer.

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