micromegas detectors for the clas12 central tracker
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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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1
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
13
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
14
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
19
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
22
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
24
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
27
Preliminary results: Gain
Estimated with Fe source
28
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)
31
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
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