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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 3 / 20
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 4 / 20
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?
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 5 / 20
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 6 / 20
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 7 / 20
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)
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 8 / 20
Pion Testbeam Setup at H6
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)
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 9 / 20
Pion Testbeam Setup at H6
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)
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 9 / 20
Pion Testbeam Setup at H6
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 10 / 20
Pion Testbeam Setup at H6
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 10 / 20
Pion Testbeam Setup at H6
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 11 / 20
Pion Testbeam Setup at H6
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 11 / 20
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 12 / 20
Performance of 50 × 48 cm2 Micromegas
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 13 / 20
Performance of 50 × 48 cm2 Micromegas
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
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 in floating strip Micromegas, 160 GeV pions
mµ1±= 53σΔx
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 14 / 20
Performance of 50 × 48 cm2 Micromegas
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
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
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 in floating strip Micromegas, 160 GeV pions
mµ1±= 53σΔx
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 14 / 20
Performance of 50 × 48 cm2 Micromegas
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 15 / 20
Performance of 50 × 48 cm2 Micromegas
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)
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 16 / 20
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 17 / 20
Floating Strip Principle
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 18 / 20
Floating Strip Principle
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
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 19 / 20
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!
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 20 / 20
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!
Jona Bortfeldt (LMU Munchen) Floating Strip Micromegas 23/04/2013 20 / 20
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