development of micromegas detectors with novel floating ......novel floating strip anode jona...

Development of Micromegas Detectors withNovel Floating Strip Anode

Jona BortfeldtO. Biebel, R. Hertenberger, P. Losel, S. Moll, A. Zibell

LS SchaileLudwig-Maximilians-Universitat Munich, Germany

RD51 mini weekApril 23rd 2013

Introduction

Motivation

large area Micromegas based muon detectorO(m2

) high spatial resolution ↔ small strip pitch

robust and very little aging ↔ avoid non-metalmaterials inside active volume as much as possible

high efficiency ↔ discharges should have negligibleinfluence on performance

possible application: spatially resolving X-raydetector

build detectors in Munich

→ novel concept: Floating Strip Micromegas

Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 2 / 20

Introduction

Outline

1 IntroductionStandard, resistive & floating strip Micromegas50× 48 cm2 Floating Strip Micromegas

2 Pion Testbeam Setup at H6Testbeam SetupReadout Electronics

3 Performance of 50× 48 cm2 Micromegas

4 Floating Strip Principle6.4× 6.4 cm2 Floating Strip MicromegasLTSpice SimulationVoltage Drop Measurement with 6.4× 6.4 cm2 Micromegas

5 Summary


Introduction

Up to now: Standard Micromegas

-500V

-1000Vcathode

mesh

anode strips

position / timing timing

pillars 128μm

6mmAr:CO2

250μm 150μm

0.8kV/cm

39kV/cm

ionization in 6 mm drift gap,0.5 kV/cm

gas amplification in 128 µmamplification gap, 39 kV/cm,gas gain 103 to 104

signal detection on strips(150 µm width and 250 µm pitch)→ spatial resolution (35µm)/timing (ns)

gas: Ar:CO2 93:7 @ NTP

PRO

well tested

relatively easy to produce

metal strips → no agingexpected, no charge up

CONdischarges:

induced by strongly ionizingparticles (> 107 e in avalanche)

complete discharge of mesh→ large voltage drop on wholedetector

large detector capacitance (nF)→ long recharge time

→ considerable deadtime andefficiency drop


Introduction

Solution 1: Resistive Strip Micromegas

signalcopper strips

mesh +HV

resistive strips ~MΩ/cm

cathode

~20MΩ

-HV

resistive strips: carbon loadedepoxy, R∼MΩ/cm

capacitively coupled copperreadout strips, same pitch andwidth

discharges: only local charge up,very fast suppression

PRO

well tested

very efficient dischargesuppression even in high-rate γ-& neutron-background(Φn ∼ 107 Hz/cm2)

CON

more complicated production

might be more prone to ageing(although we don’t observe thatyet)

spatial gas gain variation

temporal gas gain variation→ influence on spatial resolution?


Introduction

Solution 2: Floating Strip Micromegas

mesh

resistor ~10MΩcopper strips

cathode -HV

+HV

C ~ 10 - 60pF

“floating” copper strips:

individually connected to HV via10MΩ

capacitively coupled to readoutelectronics via pF HV capacitor

discharges: only two or threestrips charge up

proposed by: A. Bay, I. Giomataris etal., Nucl.Instrum.Meth. A488:162-174,2002

PRO

relatively easy to produce

no rate dependant charge up

metal strips → less agingexpected

discharges: small capacitanceCFS ∼ Cstd × 0.01 (τ = RC)

discharges: only one or two stripsaffected, 1/#strips efficiencydecrease

→ low deadtime and efficiency drop

CON

discharge suppression not aseffective as in resistive stripMicromegas

2-dim. readout questionable


Introduction

50× 48 cm2 Floating Strip Micromegas

copper strips

mesh+HV

resistor 10MΩcopper strips

cathode -HV

signal

128μm

6mm

bulk Micromegas with 128 µmamplification gap and 6 mm driftregion

50× 48 cm2 active area, 1920copper strips, 150 µm width,250 µm pitch

integrated floating strip solution:∼50 pF coupling capacitance &10 MΩ recharge resistor

gas: Ar:CO2 93:7 @ 1013mbar


Pion Testbeam Setup at H6

50× 48 cm2 Micromegas in 120 GeV Pion Beam @ H6 SPS

0 1020

51525

35

45

50

30m

m

42.5mm

21

5m

m

21

5m

m

30m

m

30m

m

42

.5m

m

42.5mm

21

5m

m

40mm

25mm

21

5m

m

21

5m

m

2700mm

6 reference Micromegas, x-readout 10 x 9 cm2 , Gassiplex

2 reference Micromegas, x-y-readout 9 x 9 cm2, APV

3 trigger scintillators, y-readout

floating strip Micromegas, x-readout, 50 x 48 cm2, APV

z

xy

steel support frame angle: [-45°,45°] height and y-position adjustable

precision detector support

3 trigger scintillators, y-readout

precision detector support

track reference track reference

floating strip Micromegasx-y- and angular scansScalable Readout System

tracking system:

six non resistiveMicromegasactive area 10× 9 cm2,360 stripsGassiplex readout (VME)

two resistive Micromegasactive area 9× 9 cm2, 2dreadout anode, 2× 358stripsScalable Readout System

2× 3 trigger scintillatorsTDC readout (VME)



Gassiplex Readout Electronics

analog input

Gassiplex ADCmultiplexing amplifier

FPGA

FIFOs

digital output

frontend boards:

4× 16 channels, chargesensitive Gassiplex chips

A/D conversion→ 1 ADC value per channeland trigger = pulse height

digital baseline suppression

backend: RIO2: VME embedded PowerPC

readout control data transfer

two 16 channel VME TDCs: get scintillator hits & trigger number (→ later)

DAQ computer:

ssh interface to RIO2

data storage

slow control (HV, flux, pressure)



Scalable Readout System

16 APV25 frontend boards: 128 channels, charge sensitive,

pipelined APV chip 3 to 21 charge values with 25 ns

spacing per channel and trigger 8 master: direct communication

with digitizer 8 slave: communication via

master

40 MHz digitizer: paralleldigitization of 8 master/slave pairs

Frontend Converter Card:sequence control, Gigabit Ethernetlink to DAQ computer



Synchronization of Data Streams

trigger

Gassiplex SRS

123

456789..

12

34

5

6..

internal readout specific trigger counter, unequal, no alignment possible

12345678910..

true trigger number

challenge: how to align two datastreams?

triggered by same scintillatortrigger

both systems (especially SRS) misstriggers

solution: add the true trigger numberto each data stream

triggerbox = 12 bit scaler, countstriggers, output: trigger number as12 bit NIM signal

Gassiplex system: VME based, useadditional 16 channel TDC torecord trigger number

SRS: attenuate NIM signals, recordwith an APV frontend board

→ offline synchronization possible



Synchronization of Data Streams

triggerbox

gate generator

trigger

Gassiplex veto

TDC 12 bit

SRSattenuation

board → APV12 bit

123

456789..

12

34

5

6..

internal readout specific trigger counter, unequal, no alignment possible

12345678910..

true trigger number

123

5678910..

12

45

8

10..

external trigger number, added to both data streams, always equal

challenge: how to align two datastreams?

triggered by same scintillatortrigger

both systems (especially SRS) misstriggers

solution: add the true trigger numberto each data stream

triggerbox = 12 bit scaler, countstriggers, output: trigger number as12 bit NIM signal

Gassiplex system: VME based, useadditional 16 channel TDC torecord trigger number

SRS: attenuate NIM signals, recordwith an APV frontend board

→ offline synchronization possible


Performance of 50 × 48 cm2 Micromegas

Pulse Height & Efficiency Optimization

[kV/cm]driftE0 0.2 0.4 0.6 0.8 1 1.2

effi

cien

cy

0.5

0.6

0.7

0.8

0.9

1

= 37.5kV/cm, FS Micomamp

@ Edrift

Efficiency vs E

efficiency vs. Edrift

optimum value: 97%,limited by mesh supportingpillars

cathode

anode

Edrift

Eamp

mesh

[kV/cm]ampE34.5 35 35.5 36 36.5 37 37.5 38 38.5 39

char

ge [a

dc c

hann

els]

300

400

500

600

700

800

900

1000

= 0.5 kV/cmdrift at Eamp

most probable pulse height vs. E

pulse height vs. Eamp

exponential rise asexpected

gas gain can beselected over widerange as needed

[kV/cm]driftE0 0.2 0.4 0.6 0.8 1 1.2

char

ge [a

dc c

hann

els]

200

250

300

350

400

450

500

= 36.7 kV/cmamp at Edrift

most probable pulse height vs E

pulse height vs. Edrift

small Edrift:

low charge seperation

attachement

large Edrift:

low electron meshtransparency



Homogenity

[kV/cm]driftE0 0.2 0.4 0.6 0.8 1

char

ge [a

dc c

hann

els]

0

100

200

300

400

500

600

700

for different beam positionsdrift

pulse height vs. E

a)b)c)d)

a) b) c)

d)

measure signal response at four differentdetector positionscompare pulse height vs. Edrift

at Eamp = 36.7 kV/cm

difference of max(charge(Edrift)) betweendatasets→ variation of gas gain

shift of datasets→ variation of drift gap

no shift visiblecharge variation ∼ 15%→ gas amplification and ionizationhomogeneous for large area detector



Spatial Resolution

σtrack

σSR σ

SR,i

track reference

Δx

x

z

floating strip Micromegas

the dots refer to a single event, error bars are given by spatial and track resolution respectively

∆x = xtrack − xmeas

doing this for many tracks→ distribution

σSR =√σ∆x

2 − σtrack2

Entries 6254

/ ndf2χ 157.1 / 184

mainheight 2.4±105.8

mainmax 0.001064±0.001785

mainsigma 0.00111±0.05318

tailheight 0.887±7.259

tailmax 0.00909±-0.03056

tailsigma 0.0147±0.2052

residual [mm]-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

mµ#

track

s/4

0

20

40

60

80

100

120

Entries 6254

/ ndf2χ 157.1 / 184


mainmax 0.001064±0.001785

mainsigma 0.00111±0.05318


tailmax 0.00909±-0.03056

tailsigma 0.0147±0.2052

residual in floating strip Micromegas, 160 GeV pions

mµ1±= 53σΔx



Spatial Resolution

[kV/cm]driftE0 0.2 0.4 0.6 0.8 1 1.2

m]

µsp

atia

l res

olut

ion

[

40

45

50

55

60

65

=36.7kV/cm, floating strip Micromegasamp

spatial resolution, E

mµ 48≈ SR, optimumσ

work in progress

∆x = xtrack − xmeas

doing this for many tracks→ distribution

σSR =√σ∆x

2 − σtrack2

Entries 6254

/ ndf2χ 157.1 / 184


mainmax 0.001064±0.001785

mainsigma 0.00111±0.05318


tailmax 0.00909±-0.03056

tailsigma 0.0147±0.2052

residual [mm]-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

mµ#

track

s/4

0

20

40

60

80

100

120

Entries 6254

/ ndf2χ 157.1 / 184


mainmax 0.001064±0.001785

mainsigma 0.00111±0.05318


tailmax 0.00909±-0.03056

tailsigma 0.0147±0.2052

residual in floating strip Micromegas, 160 GeV pions

mµ1±= 53σΔx



TPC-like Track Reconstruction for Inclined Tracks

strip720 722 724 726 728 730 732 734 736 738

sign

al ti

me

[tim

e bi

ns]

0

1

2

3

4

5

6

7

8

°TPC-like track fit, floating strip Micromegas, 30

tbin t∆

strip∆

t + b⋅strip(t) = a

tbin t∆

strip∆a =

drift v⋅ 25ns ⋅ tbin t∆

0.25mm⋅ strip ∆ = z∆

x∆a' =

= tan(a')ϑ ⇒

cathode

mesh

anode

with APV electronics:measurement of clusterarrival time

maximum drift time in6 mm drift region ∼ 180 ns

→ arrival time t ∝ z-position

→ track inclinationϑ = tan(∆x/∆z): single planeangular resolution possible



TPC-like Tracks: Reconstructed Angles

Entries 11562

Integral 9933

reconstructed track inclination [degrees]-50 -40 -30 -20 -10 0

°#

trac

ks /

0.2

0

50

100

150

200

250 Entries 11562

Integral 9933

incidence° - 40°reconstructed track inclination for 10

°10°20°30°40

small inclination ∼ 10:

asymmetric distribution with highertails towards larger angles due toδ-electrons

reconstructed angles slightly too large

medium inclination:

narrower, more symmetric distributionwith tails, resolution σϑ ∼ 5

larger inclination ∼ 40:

asymmetric distribution with highertails towards smaller angles due toδ-electrons

reconstructed angles slightly too small

→ single plane angular resolutionpossible with resolution O (5)


Floating Strip Principle

6.4× 6.4 cm2 Floating Strip Micromegas

aluminum base plate

mesh

anode strips

cathode: 10μm aluminized Kapton

1.5mm FR4 lid

aluminum gas & mesh frame

solder resist support structure

aluminum frame

gas inlet non-bulk Micromegas with

150 µm amplification gapand 6 mm drift region

6.4× 6.4 cm2 active area,128 copper strips, 300 µmwidth, 500 µm pitch

discrete floating stripsolution: 15 pF couplingcapacitors & 10 MΩrecharge resistor,exchangeable

mesh glued to gas frame,exchangable

drift cathode: 10 µmaluminized Kapton → useα-source to triggerdischarges



LTSpice Simulation

mesh

Rstrip

= 100kΩ -

22MΩ

cathode -HV

+HV

C = 15pF

R = 1kΩ - 10MΩ

simulate discharges from mesh ontoone strip

vary Rstrip

adapt recharge R such thatIrecharge ≤ 60 µA

global voltage drop affects wholedetector

standard Micromegas:complete discharge of meshpossible

Floating Strip Micromegas:massive reduction of voltagedrop and recharge time



Voltage Drop Measurement in 6.4× 6.4 cm2 Micromegas

mixed nuclide α-source: induce discharges in detector @ ∼1 Hz

measure global voltage drop with high-ohmic voltage divider

100 kΩ strip resistor: standard MM-like

1 MΩ strip resistor: ∼25 V drop

22 MΩ strip resistor: ∼0.5 V drop → negligible

time [ms]0 20 40 60 80

voltage

[V]

300

350

400

450

500

550

600

Measured Mean Voltage Drop after Discharge, Standard MM

Rstrip = 100kΩ

time [ms]-2 0 2 4 6 8 10 12 14 16 18

volt

age

[V]

575

580

585

590

595

Ω = 1MstripR

Ω = 22MstripR

Measured Mean Voltage Drop after Discharge


Summary

Summary commissioned 50× 48 cm2 Micromegas with novel “floating strip” anode

constructed, built and commisioned 6.4× 6.4 floating strip Micromegaswith exchangable capacitors and resistors

pion test beam @ CERN: synchronization of Gassiplex system (track telescope) with Scalable Readout

System (floating strip Micromegas) possible and robust pulse height homogeneous within 15% efficiency 97% spatial resolution better 50 µm - work in progress

TPC-like track reconstruction → single plane angular resolution O (5) -work in progress

LTSpice simulation of discharges in floating strip Micromegas in qualitativeagreement with measurements

optimum: global voltage drop < 0.5 V

→ floating strip Micromegas is working!

Thank you!


development of micromegas detectors with novel floating ......novel floating strip anode jona...

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