Micromegas detectors for the CLAS12 central tracker

Brahim Moreno (for the Saclay group)

CLAS12 central detector meeting : 2 december 2009

Cea Saclay

CERN experiment: resultsi r f u

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Micromegas detectors for the CLAS12 central tracker

CERN experiment: results

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•Introduction

•Experiment at CERN

•Results

•Conclusions and outlook

2

•Micromegas and CLAS12

•What is a spark?

Introduction

4

Micromegas and CLAS12Several points to be adressed before micromegas implementation in CLAS12

Adressed Ongoing Not adressed Value (if applicable)

bMM feasibility cbMM feasibility MM behaviour in

magnetic field

Sparks rate (with/ without magnetic

field)

Spatial resolution (with beam)

Efficiency (with beam)

bMM: bulk micromegascbMM: curved bluk micromegas * bMM and cbMM showed the same behaviour

Experiment at CERN

5

What is a spark? (1)

Drift electrode

Mesh

PCB

600V

400V

Ionizing particle (MIP)

conv

ersi

onam

plif

icat

ion

e-

Signal amplified

Charge collected on the strips

6

What is a spark? (2)

Drift electrode

Mesh

PCB

600V

400V

Ionizing particle (hadron)

conv

ersi

onam

plif

icat

ion

High charge density

Spark = discharge in amplification gap

0V

Discharge blinds MM detector because it sets mesh HV to ground

Recovery time depends on Protection circuit (~1 ms)

Discharge

•Experimental set-up

•Data acquisition

•Running conditions and data

Experiment at CERN

Description

8

Experimental set up (1)Main goal: evaluating sparks rate in presence of or without magnetic field

x

y

z

Pitch: region a → 400μm region b → 1000μm

Distance between strips: 100μm

12345

magnet

B

Goliath

Beam

Scintillator paddles coupled to PMTs

Gaz: 5% Isobutane/Ar

x

yz

Region a

Region b

T4.1;0B

10 cm

9

Experimental set up (2)

MM Type Drift gap Drift material Amplification gap

Mesh material

Orientation

1 Classic 5 mm Aluminized mylar 128 μm Copper X

2 Bulk 5 mm Aluminized mylar 128 μm Stainless steel

Y

3 Bulk 2 mm Aluminized mylar 128 μm Stainless steel

X

4 Bulk 5 mm Stainless steel 128 μm Stainless steel

X

5 Bulk 5 mm Aluminized mylar 128 μm Stainless steel

X

Main detectors characteristics

10

Experimental set up (3)

Magnet

1.77 m

Upper coil

Beam

11

Experimental set up (4)

Beam

Detectors

Electronics

12

Data acquisition (1)Spark monitoring

Amplifier

Mesh

Discriminator

HV filter

Scaler VME

Computer

Data file

MM Detector

•Same principle for all detectors• All detectors monitored simultaneously

Labview based

monitoring

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Data acquisition (2)Spark monitoring: user interface Goes red if one

detector is sparking

Spark list display

Goes red if detector 4 is sparking

Clock: +1 every 5s

Display updated at the clock frequency

Total number of spark VS time

Associated derivative

Total number of

spark

Total number of

coincidences

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Data acquisition (3)Spark monitoring: data format

Text file

Timestamp ClockTotal number of spark: a column for each detector

Total number of coincidences

15

Running conditions and data

Experiment: Oct the 23rd – Nov the 3rd

Beam Characteristics:•Nature: pion or muon•Energy: 150 GeV•Spill duration: 9s•Time between spill: 1mn•Particle/spill: ~106 part/spill

Measurements at: 0, 0.28, 0.56, 0.7, 0.84, 1.12 and 1.4 T

~210 runs

•Spark probability

•Magnetic field effect

Results

Sparks

17

Spark probability (1): as a function of gain

No sizeable different behaviours between classic and bulk micromegas

18

Spark probability (2): transparency effect

Transparency : probability for a primary electron to get through the mesh

Transparency decreases (at fixed mesh HV) as drift HV increases

Lower spark probability

Less electron getting through mesh at 1500V

than at 600V

Increasing drift HV requires to increase the gain in order to compensate the loss

in transparency

HV mesh (V)

Drift HV: 1500V

Drift HV: 600V

Stainless steel drift electrode

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Spark probability (3): magnetic field effect

Classic MM: HV 380/1500

Y Bulk : HV 380/1200

X Bulk : HV 380/1500

No sizeable (transverse) magnetic field effect

High HV drift lowers Lorentz angle

Conclusions and outlook

Conclusions:

-Bulk micromegas behaves the same as classic micromegas

-No strong magnetic field effect observed

Outlook:

-Analysis still ongoing: new results expected

-New experiment next year to perform gaz mixture optimization

-CERN experiment: 150 GeV beam 1.5T magnet

extrapolation to CLAS12 experimental conditions not straightforward (hadron ~1 GeV, 5T)

Back up slides

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Micromegas and CLAS12 (2)Use: alternative/complement to silicon vertex tracker

4 x 2MM

4 x 2SI

2 x 2SI + 3 x 2MM Specs.

pT/pT (%) 2.9 2.1 1.6 5

(mrad) 1.3 15.1 1.4 <10-20

(mrad) 10.9 2.9 2.6 <10

z (μm) 212 1522 267 tbd.

(for @ 0.6 GeV/c , = 90°)

A mixed solution combines advantages of both the silicon (SI) and micromegas (MM) detectors

Curved bulk micromegas

Flat bulk micromegas

Basic principles of a micromegas detector

~100 ~100 mm

thin gapthin gap

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Basic principles of a micromegas detector: bulk-micromegas

Same principle as « classic » micromegas

Difference lies in construction process: mesh embedded on the PCB

Advantages:•Detector built in nearly one process•Geometry (flexible PCB)

Drift electrode

StripsMicromesh

Am

plif

icat

ion

Con

vers

ion

25

Description (2)

Beam

Electronics

Oct the 23rd – Nov the 3rd

Detectors

26

Description (4): measurements

Measurements at: 0, 0.28, 0.56, 0.7, 0.84, 1.12 and 1.5 T

-Mesh high voltage variation with fixed drift HV-Drift HV variation at fixed mesh HV

Hadron beam 150 GeV

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Preliminary results: Gain

Estimated with Fe source

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Preliminary results: sparks rate

Classic MM (5 mm drift gap)bMM (2 mm drift gap, alumized mylar)bMM with Y strips (5 mm drift gap)bMM (5 mm drift gap, inox) bMM (5 mm drift gap)

Tot

al n

umbe

r of

spa

rks

Time (s)

Detector was off

29

Preliminary results: sparks (2)

2 mm drift gap 5 mm drift gap

Y-strips5 mm drift gap5 mm drift gap

X-strips X-strips

X-strips

Spill number

Spill number Spill number

Spill number

Num

ber

of s

park

sN

umbe

r of

spa

rks

Num

ber

of s

park

sN

umbe

r of

spa

rks

Sparks rates stable over time~10-5 sparks/particle

Number of sparks normalized to PMs

coincidences (~106 c/spill)

Hadron beam 150 GeV

HT mesh: 370VHT drift: 600V

Preliminary results: beam profile (1)

Beam profile (classic MM)

Beam profile (bMM 5mm drift gap)

X strips

X strips Y strips

Beam profilesRun with beam spread in Y

Muon beam (~150 GeV)Online

monitoring

X (mm)

X (mm) Y (mm)

Beam profile (bMM 2mm drift gap)

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Preliminary results: beam profile (2)Correlation 1-3 (XX)

X3 (mm)

Correlation 1-2 (XY)X1 (mm)

X1 (mm)

Y2 (mm)

Online monitoring

2D beam profiles

Run with beam spread in Y

Muon beam (~150 GeV)

1 = classic MM (X-strips)2 = bMM (Y-strips)3 = bMM (X-strips)

Preliminary results: tracking

ΔX (strip) = difference between expected and measured hit position

Residual

ΔX (strip)

Before alignment correction

Only the small pitch region (400 μm) is taken into account

σ < pitch/(12)1/2