High-Rate Capable Micromegas Detectors for ... - LMU Munich€¦ · true, simulation •...
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High-Rate Capable Micromegas Detectorsfor Ion Transmission Radiography Applications
Jona Bortfeldt et al.
LS SchaileLudwig-Maximilians-Universitat Munchen
Symposium: Advanced Semiconductor Detectors for Medical ApplicationsFebruary 13th 2015
Introduction
Katia Parodi: Motivation and Requirements
Ion Transmission Radiography
• ions with known initial energy, higher than intherapy
• residual energy measurement→ energy loss→ contrast
range telescopehead tumor
ions
430MeV/u
Present Setup at HIT
• mean particle position from steering magnets (carbon beam ∼3.4 mm FWHM)
• integrate over several 102 to 104 particles
Future
• single particle tracks from Micromegas• spatial resolution ∼0.1 mm• MHz/cm2 particle rate (multi-hit separation, signal duration)• low material budget
• single particle range/energy from suitable telescope• scintillator based• maximum rate O(MHz)
→ improve spatial resolution, decrease dose
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 2
Introduction
Katia Parodi: Motivation and Requirements
Ion Transmission Radiography
• ions with known initial energy, higher than intherapy
• residual energy measurement→ energy loss→ contrast
range telescopehead tumor
ions
tracking Micromegas
Present Setup at HIT
• mean particle position from steering magnets (carbon beam ∼3.4 mm FWHM)
• integrate over several 102 to 104 particles
Future
• single particle tracks from Micromegas• spatial resolution ∼0.1 mm• MHz/cm2 particle rate (multi-hit separation, signal duration)• low material budget
• single particle range/energy from suitable telescope• scintillator based• maximum rate O(MHz)
→ improve spatial resolution, decrease dose
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 2
Introduction
The Micromegas Detector
cathode
mesh
copperanode strips
pillars 128μm
Ar:CO2
6mm0.5kV/cm0.047mm/ns
39kV/cm
250μm
charged particle
ioni
zatio
n
• gas amplification 103 to 104
• charge signal on stripssingle strip readout→ spatial resolution O(50µm)→ timing O(ns)
• thin amplification gap & finesegmentation→ fast drain of positive ions→ high-rate capable
• COMPASS: precision tracker, highflux
• CAST: photon detector, good energyresolution, low background
• T2K: TPC readout, large area
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 3
Floating Strip Micromegas Principles
Floating Strip Micromegas
-500V
-800Vcathode
mesh
copperanode strips
pillars 128μm
6mmAr:CO2
250μm 150μm
0.5kV/cm
39kV/cm
time [ms]-10 0 10 20 30 40 50 60 70 80 90
volta
ge [V
]
300
350
400
450
500
550
600
standard Micromegas
challenge: discharges
• charge density ≥ 2× 106 e/0.01 mm2
(Raether limit)
• conductive channel→ potentials equalize
• non-destructive,but dead time→ efficiency drop
idea: minimize the affected region
• “floating” copper strips:• strip can “float” in a discharge• individually connected to HV via 22MΩ• capacitively coupled to readout electronics
via pF HV capacitor• only two or three strips need to be
recharged
→ optimization in dedicated measurements& detailed simulation
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 4
Floating Strip Micromegas Principles
Floating Strip Micromegas
+500V
-300Vcathode
mesh
copperanode strips
pillars 128μm
6mmAr:CO2
250μm 150μm
0.5kV/cm
39kV/cm
large R
small C
time [ms]-10 0 10 20 30 40 50 60 70 80 90
volta
ge [V
]
300
350
400
450
500
550
600
standard Micromegas
floating strip MM
challenge: discharges
• charge density ≥ 2× 106 e/0.01 mm2
(Raether limit)
• conductive channel→ potentials equalize
• non-destructive,but dead time→ efficiency drop
idea: minimize the affected region
• “floating” copper strips:• strip can “float” in a discharge• individually connected to HV via 22MΩ• capacitively coupled to readout electronics
via pF HV capacitor• only two or three strips need to be
recharged
→ optimization in dedicated measurements& detailed simulation
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 4
Floating Strip Micromegas Principles
Discharge Study with Floating Strip Micromegas
22M
22M
22M
22M
1k
+HV
10nF
anode strips
mesh
15pF22MΩ
cathode
• alpha source→ induces discharges
• voltage drop on one to threestrips→ recharge current
• global high voltage drop→ affects all strips
• voltage signal on sevenneighboring strips→ discharge topology
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 5
Floating Strip Micromegas Principles
Optimization of the Floating Strip Principle
• standard Micromegas (approximate): 100 kΩ300 V drop, dead time ∼80 ms
• intermediate: 1 MΩ20 V drop, dead time ∼10 ms
• floating strip: 22 MΩ0.5 V drop → negligible
ground
signal
mesh +594V
SMD resistorcopper strips
cathode -300V
SMD capacitor 15pF
signal
measured average voltage pulse
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 6
Floating Strip Micromegas Principles
Detailed Investigation of the Global Voltage Drop
maximum voltage drop [V]0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
disc
harg
es /
1mV
0
20
40
60
80
100
120
140
160
180
200
220
• measure voltage drop of common HVpotential
• discrete structure→ probably corresponds to discharge ofone, two or three strips
• how can we show this?→ investigate discharge topology→ develop simulation→ compare predicted with measuredvoltage drop
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 7
Floating Strip Micromegas Principles
Discharge Topology - Expected Amplitude Correlation
amplitude strip 3
am
plit
ud
e s
trip
2
only 2
only 3
4...
...1
1 2 3 4
expected correlation
• measure voltage signal on neighboringstrips
• two reasons for signals on strips:• discharge onto strip• capacitive coupling from neighboring
strips
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 8
Floating Strip Micromegas Principles
Discharge Topology - One Strip
voltage channel 3 [V]0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
volta
gech
anne
l2[V
]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
2
4
6
8
10
12
2L34L
34L
2L3
3L45L3L4
45L
1L23L
23L
1L2
0L12L12L
0L1
• discharges on separate stripsdistinguishable
• substructure quantitativelydescribed by simulation
amplitude strip 3
am
plit
ud
e s
trip
2
only 2
only 3
4...
...1
1 2 3 4
expected correlation
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 9
Floating Strip Micromegas Principles
LTSpice Detector Simulation
mesh strip
mesh strip
mesh stripCcable
Casas
Casas
CmsCcoupl
Rhv
HV
Cslsl
Cslsl
Cslg
Rvd1
Rvd2
Chvgdetector HV
Chvcoupl 1MΩ
Ustrip
Uhv
• consider the involved capacitances e.g. between neighboring strips, couplingcapacitors, cable capacitance ...
• simulate discharges (blue switch)
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 10
Floating Strip Micromegas Principles
Optimum Configuration: Global Voltage Drop
maximum voltage drop [V]0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
disc
harg
es /
1mV
0
20
40
60
80
100
120
140
160
180
200
220
measurementsimulation: one strip
simulation: two strips
simulation: three strips • good agreement between simulation andmeasurement
• only two free parameters• response time of HV supply: 500 ms• voltage difference between strips at which
leakage stops: 220 V
• peaks correspond indeed to discharge ofone, two or three strip
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 11
Floating Strip Micromegas Principles
floating strip principle works
• discharges: negligible effect on common high-voltage
• discharges are localized
measurements
• ion tracking at highest rates at HIT – Micromegas tests
• gas studies and µTPC reconstruction at Tandem/Garching
• first test of a 2d ion radiography system at Tandem/Garching
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 12
Measurement: Highest-Rate Ion Tracking
Ion Tracking with Thin Micromegas at Highest Rates @ HIT
APV25frontend
APV25frontend
scintillators + photomultipliers
particlebeam
APV25frontend
APV25frontend
scatteredparticles
Micromegas 0,one-dimensionalreadout
Micromegas 1,one-dimensionalreadout
Micromegas 2,two-dimensionalreadout
y
z
beams
• 12C @ 88 MeV/u to 430 MeV/u2MHz to 80MHz
• p @ 48 MeV to 221 MeV80MHz to 2GHz
• thanks to S. Brons and the HITaccelerator team for the support
floating strip Micromegas
• 6.4×6.4 cm2 doublet
• low material budget(FR4 + Cu ≤ 200 µm)
• Ar:CO2 93:7 gas mixture
additional detectors
• 9×9 cm2 monitoring Micromegas withx-y-readout
• trigger on secondary charged particles
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 13
Measurement: Highest-Rate Ion Tracking
Pulse Height for 88 MeV/u 12C
pulse height vs Eamp
[kV/cm]ampE25 26 27 28 29 30 31
puls
e he
ight
[adc
cha
nnel
s]
300
400
500600700
1000
2000
3000
4000
micom 0
micom 1
• exponential rise as expected(Townsend theory)
• gas gain can be selected overwide range as needed
• 30 kV/cm = 450 V
cathode
anode
Edrift
Eamp
mesh
pulse height vs Edrift
[kV/cm]driftE0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
puls
e he
ight
[adc
cha
nnel
s]
0
200
400
600
800
1000
1200
1400
1600
1800
2000micom 0
micom 1
Edrift < 0.15 kV/cm:
• low charge separation
• low drift velocity
large Edrift > 0.5 kV/cm:
• low electron mesh transparency
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 14
Measurement: Highest-Rate Ion Tracking
Efficiency for 88 MeV/u 12C
efficiency vs Eamp
[kV/cm]ampE25 26 27 28 29 30 31
effic
ienc
y
0.84
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
micom0
micom1
efficiency vs Edrift
[kV/cm]ampE0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
effic
ienc
y
0.84
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
micom0
micom1
optimum value:> 99% in micom0> 94% in micom 1 due to production fault
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 15
Measurement: Highest-Rate Ion Tracking
Beam Characterization
signal timing 12C, 5× 106 Hz
signal timing [25ns]0 2 4 6 8 10 12 14 16 18
sign
als
/ ns
0
100
200
300
400
500
600
bunch spacing
beam energy [MeV/u]0 50 100 150 200 250 300 350 400 450
bunc
h sp
acin
g [n
s]
100
120
140
160
180
200
220
240
260
280
300
micom 0
micom 1
expected
• good multihit resolution
• bunch spacing measureable
• bunch filling measureable
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 16
Measurement: Highest-Rate Ion Tracking
Signals at Lowest and Highest Rate
12C, E = 430 MeV/u, 5 MHz
strip20 40 60 80 100 120
time [25ns]0246810121416
0
200
400
600
800
1000
1200
1400
1600
puls
e he
ight
[arb
. uni
ts]
3 particles clearly distinguishable→ single particle tracking possible
p, E = 221 MeV, 2 GHz
strips20 40 60 80 100 120
time [25ns]0246810121416
-500
0
500
1000
1500
puls
e he
ight
[arb
. uni
ts]
integration over ∼ 800 coincident particles→ envelope of beam profile
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 17
Measurement: Highest-Rate Ion Tracking
Pulse Height & Spatial Resolution vs Rate for 88 MeV/u 12C
mean particle rate [Hz]0 10 20 30 40 50 60 70 80
610×
puls
e he
ight
[adc
cha
nnel
s]
500
1000
1500
2000
2500
1000
2000
3000
4000
5000
micom0micom1micom2
C beam12
• up to 80 MHz single particle tracks visiblebut not all of them separable
• only 20% pulse height reduction @80 MHz
mean particle rate [Hz]0 10 20 30 40 50 60 70 80
610×
m]
µsp
atia
l res
olut
ion
[
0
20
40
60
80
100
120
140
160
180
• highest rates: slight distortion of hitposition by hits on adjacent strips
• limited by multiple scattering
• sufficient for medical application
→ tracking of carbon ions at highest rates possible
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 18
Measurement: Highest-Rate Ion Tracking
Detection Efficiency and Up-Time
p, 221 MeV
mean particle rate [Hz]0 500 1000 1500 2000
610×
effic
ienc
y
0.7
0.75
0.8
0.85
0.9
0.95
1
proton beammicom0micom1micom2
single particle detection efficiency
detector up-time
→ no efficiency & up-time reduction in floating strip Micromegas
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 19
Measurement: Highest-Rate Ion Tracking
Rate Capability & Multi-hit Resolution
reconstructed hits per multi-event
mean particle rate [Hz]0 10 20 30 40 50 60 70 80
610×
num
ber
of h
its in
det
ecto
r
1
2
3
456
10
20
30
40
reconstr., measurementreconstr., simulationtrue, simulation
• reconstruction of all particlesup to 10 MHz = 7 MHz/cm2
track finding algorithm
[rad]αtrack inclination -0.15 -0.1 -0.05 0 0.05 0.1 0.15
trac
k di
stan
ce r
[mm
]10
20
30
40
50
60
0
20
40
60
80
100
120
140
160
180
• Hough transform: d = x · cos(α) + z · sin(α)point in position space ⇔ line in Hough spaceline in position space ⇔ point in Hough space
• up to seven coincident tracks reconstructable
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 20
Mesurement: Gas Studies, µTPC and Range Telescope
23 MeV Proton Tracking at the Tandem/Garching
vacuum-flange
Kapton window
protonbeam
2 Micromegas doublets
z
x
multi-anode-
PM
Scintillator Range Telescope
absorber
goal
• further improve Micromegas high-rate capability↔ decrease signal duration→ fast Ne:CF4 gas mixtures
• investigate single plane track inclination reconstruction
• commission range telescope
• test custom amplifier electronics
floating strip Micromegas
• two 6.4×6.4 cm2 doublets,128 strips
• low material budget(FR4 + Cu ≤ 200 µm)
• APV25 based readout
range telescope
• 13 layers 1 mm scintillator
• two wavelength-shiftingfibers per layer
• read out with 64 pixelmulti-anode photomultiplier
• discrete voltage &spectroscopy amplifiers
• VME based QDC & TDCreadout system
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 21
Mesurement: Gas Studies, µTPC and Range Telescope
Pulse Height and Efficiency for Ne:CF4 80:20
pulse height vs Edrift
[kV/cm]dE0 0.2 0.4 0.6 0.8 1 1.2 1.4
puls
e he
ight
[adc
cha
nnel
s]
0
1000
2000
3000
4000
5000
6000
• high gas gain
• low diffusion→ moderate decrease withincreasing drift field
cathode
anode
Edrift
Eamp
mesh
efficiency vs Edrift
[kV/cm]driftE0 0.2 0.4 0.6 0.8 1 1.2 1.4
effic
ienc
y
0.96
0.965
0.97
0.975
0.98
0.985
0.99
0.995
1
• above 96% for all drift fields
→ excellent performance with new mixture
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 22
Mesurement: Gas Studies, µTPC and Range Telescope
Track Inclination Reconstruction in a Single Detector Plane
cathode
mesh
8mmϑ zcluster= t vdrift
xcluster
linear fit to data points
strip83 84 85 86 87 88 89 90
time
[25n
s]-1
0
1
2
3
4
5
6
rise time fit
time [25ns]0 2 4 6 8 10 12 14 16 18
char
ge[a
dcch
anne
ls]
0
100
200
300
400
500
600
700
800
50%
90%
10%
t0 tF
pF
simulated signals
time [s]0 0.2 0.4 0.6 0.8 1
-610×
char
ge [a
rb. u
nits
]
0
0.05
0.1
0.15
0.2strip 5strip 6strip 7strip 8strip 9strip 10strip 11
method:
• arrival time ↔ drift distance
• measure arrival time of chargecluster on strip→ signal timing t0
• linear fit to time-strip data points→ track inclination→ alternative hit position→ drift velocity
systematics:
• capacitive coupling of signals ontoneighboring strips
• simulation with parameter-freeLTSpice detector model
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 23
Mesurement: Gas Studies, µTPC and Range Telescope
Track Inclination Measurement in a Single Detector Plane with Ar:CO2 93:7
]°reconstructed track inclination [15 20 25 30 35 40 45 50
entr
ies
0
50
100
150
200
250
300
°10°20°30°40
measurement
]°track inclination [
]°re
cons
truc
ted
angl
e [
20
25
30
35
40datasimulation
]°track inclination [0 5 10 15 20 25 30 35 40 45
]°an
gula
r re
solu
tion
[-10
-505
101520 measurement
• track inclination reconstruction possible for angles 20 ≤ ϑ ≤ 40
with angular resolution(
+6−4
)• systematic effect understood → calibration possible
• combined position reco possible (µTPC + centroid)
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 24
Mesurement: Gas Studies, µTPC and Range Telescope
Track Inclination Measurement with the New Gas Ne:CF4
80:20 75:25
• track inclination reconstruction possible with fast Ne:CF4 gas mixture
• angular resolution(
+5−4
)for Edrift < 0.6 kV/cm
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 25
Mesurement: Gas Studies, µTPC and Range Telescope
Improvement of High-Rate Capability with Ne:CF4
measured electron drift velocity
• signal duration =electron drift time + ion drift time
• electron drift time: 150 ns → 60 ns
• ion drift time: 260 ns → 85 ns
→ factor 3 improvement
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 26
Mesurement: Gas Studies, µTPC and Range Telescope
Range Telescope Commissioning – Pulse Height Behavior
proton traverses layer→ constant energy loss
pulse height fiber 0 [arb. units]0 100 200 300 400 500 600
puls
e he
ight
fibe
r 1
[arb
. uni
ts]
0
100
200
300
400
500
600
700
800
0
5
10
15
20
25
30
proton stops in layer→ variable energy loss
pulse height fiber 0 [arb. units]0 100 200 300 400 500 600
puls
e he
ight
fibe
r 1
[arb
. uni
ts]
0
100
200
300
400
500
600
700
800
0
2
4
6
8
10
12
14
16
18
only 0.1% of the photons detectable→ ∼ 30± 10 photons→ ∆EFWHM/E ∼ 1
mean pulse height vs depth
• pulse height increases less thanexpected
• probably considerable quenching
→ difficult to use pulse height information→ rather use hit/miss info
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 27
Mesurement: Gas Studies, µTPC and Range Telescope
Range Telescope Commissioning – One-Dimensional Position Resolution
vacuum-flange
Kapton window
protonbeam
Micromegas doublet
z
x
multi-anode-
PM
Scintillator Range Telescope
absorber
• Tandem beam not mono-energetic→ use additional collimators behindbending dipole
• mean range homogeneous over detector
• absorber edge visibletrack resolution ∼ 0.8 mm due tomultiple scattering
mean range vs position
hit position x [mm]18 20 22 24 26 28 30 32 34
mea
n pa
rtic
le r
ange
[mm
]
-1
0
1
2
3
no absorber1mm absorberdifference
ana_rt_tanaug14_0284_scaledph_perp_layphrange_rvsx_evsx_rangetelRangePos0rt0_ProjY0_has_supimp
Entries 6020Mean 48.05RMS 5.647Integral 280.7
hit position x [mm]0 10 20 30 40 50 60
mea
n pa
rtic
le r
ange
[mm
]
0
0.5
1
1.5
2
2.5
3
3.5
ana_rt_tanaug14_0284_scaledph_perp_layphrange_rvsx_evsx_rangetelRangePos0rt0_ProjY0_has_supimp
Entries 6020Mean 48.05RMS 5.647Integral 280.7
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 28
Mesurement: Gas Studies, µTPC and Range Telescope
First Two-Dimensional Ion Radiography
MM doublets
phantombeam
RT
0
1
2
3
4
5
6
0
1
2
3
4
5
6
position y [mm]25 30 35 40 45 50 55 60
posi
tion
x [m
m]
25
30
35
40
45
50
55
60
0
1
2
3
4
5
6
• PLA step phantom visible
• ball point pen visible
• spatial resolution limited by multiple scattering
• resolution improvable by additional MM layers
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 29
Mesurement: Gas Studies, µTPC and Range Telescope
First Two-Dimensional Ion Radiography
MM doublets
phantombeam
RT
0
1
2
3
4
5
6
0
1
2
3
4
5
6
position y [mm]16 18 20 22 24 26 28 30 32 34
posi
tion
x [m
m]
25
30
35
40
45
50
55
0
1
2
3
4
5
6
• PLA step phantom visible
• ball point pen visible
• spatial resolution limited by multiple scattering
• resolution improvable by additional MM layers
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 29
Summary
Summary
• floating strip Micromegas were optimized and work• discharges:
• behavior and topology understood• negligible influence on efficiency
• carbon ion and proton tracking at highest rates at HIT• separation of all particles at rates ≤10 MHz• spatial resolution better 180 µm at all rates ≤80 MHz• stable operation up to highest rates of 2 GHz
• 23 MeV proton tracking at Tandem/Garching• successful: fast Ne:CF4 gas mixture→ decrease signal duration by factor 3
• single plane track inclination reconstruction possible
• Micromegas + scintillator range telescope in 23 MeV proton beams• single particle range determination using hit/miss information• first 2d ion radiography successful• spatial resolution limited by multiple scattering
floating strip Micromegas:discharge tolerant, high-rate capable tracking detectors with good spatial resolution→ suitable for medical applications
Thank you!
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 30
Summary
Summary
• floating strip Micromegas were optimized and work• discharges:
• behavior and topology understood• negligible influence on efficiency
• carbon ion and proton tracking at highest rates at HIT• separation of all particles at rates ≤10 MHz• spatial resolution better 180 µm at all rates ≤80 MHz• stable operation up to highest rates of 2 GHz
• 23 MeV proton tracking at Tandem/Garching• successful: fast Ne:CF4 gas mixture→ decrease signal duration by factor 3
• single plane track inclination reconstruction possible
• Micromegas + scintillator range telescope in 23 MeV proton beams• single particle range determination using hit/miss information• first 2d ion radiography successful• spatial resolution limited by multiple scattering
floating strip Micromegas:discharge tolerant, high-rate capable tracking detectors with good spatial resolution→ suitable for medical applications
Thank you!
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 30
backup
backup – Discrete & Integrated Floating Strip Micromegas
discrete
ground
signal
mesh +500V
SMD resistor 22MΩ
copper strips
cathode -300V
6mm
128µm
SMD capacitor 15pF
• exchangable Rs and Cs→ optimization possible
• more complicated assembly→ soldering ×2 for each strip
• space requirements due to HV sustainingcomponents→ strip pitch limited to 0.5 mm
integrated
copper strips
mesh+HV
resistor 10MΩcopper strips
cathode -HV
signal
128μm
6mm
• anode strips: connected to HV viaprintable paste resistors
• readout strips: second layer of copperstripscapacitive coupling through the board,intrinsically HV sustaining
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 31
backup
backup – Track Inclination Reconstruction Systematics: LTSpice-Simulation
mesh strip
mesh strip
mesh strip
Casas
Casas
CmsCcoupl
Rhv
HV
Cslsl
Cslsl
Cslg
Chvgdetector HV
Chvcoupl 1MΩ
Ccr Ccc
signal
time
current
cathode
mesh
6 7 8 9 10 115
• use LTSpice to simulate 16 neighboring strips, readout via charge-sens.-preamps
• consider mesh-anode strip, anode strip-ground,anode strip-anode strip, coupling, stripline-striplineand stripline-ground capacitance, no free parameter
• inject time dependent current on anode strips →study signals on all other strips
time [s]0 0.2 0.4 0.6 0.8 1
-610×
char
ge [a
rb. u
nits
]
0
0.05
0.1
0.15
0.2strip 5strip 6strip 7strip 8strip 9strip 10strip 11
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 32
backup
backup – Hough Transform Based Track Building
x
z
x1
z1
point in position space (zi,xi) line in Hough space a = zib + xi
a
b
point in Hough space (bj,aj)line in position space x = -bjz + aj
x2
x3
x4
z2 z3
a1
b1
track with slope -b1 & intersect a1
• for improved stability: use Hesse normal form as transform function
• up to seven valid tracks reconstructed per event
Jona Bortfeldt (LMU Munchen) High-Rate Capable Micromegas for Ion Radiography 13/02/15 33