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PERFORMANCES OF THE
MICROMEGAS VERTEX TRACKER AT
THE CLAS12 EXPERIMENT FOR THE 2017-2018 PHYSICS RUN
MPGD CONFERENCE 2019,
LA ROCHELLE, FRANCE
MAXENCE VANDENBROUCKE
ON BEHALF OF THE MVT GROUP AT SACLAY :
D. ATTIE, S. AUNE, J. BALL, Q. BERTRAND, F. BOSSU, G. CHRISTIAEN, M. DEFURNE, J. GIRAUD, R. GRANELLI,, I. MANDJAVIDZE, O. MEUNIER, Y.
MOUDDEN, S. PROCUREUR, M. RIALLOT, J-Y. ROUSSE, F. SABATIE
SUMMARY
The CLAS12 Experiment at Jefferson Lab
The Micromegas Tracker, Forward Detectors, and Cylindrical Detectors
Installation in the CLAS12 spectrometer
First results after data taking2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke 2
* Serving suggestion
THE CLAS12 EXPERIMENT• Upgrade of the CLAS Experiment at Jefferson lab
• Study of the nucleon structure with ~11 GeV electron beam at high luminosity (1035 cm-2s-1)
• Targets : liquid hydrogen (protons), liquid deuterium (neutrons), other nuclei in the future
32019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
Micromegas Vertex Tracker (MVT) :
Improve the track reconstruction in the vicinity of the target
Inserted in the 5T solenoid
Used in combination with the Silicon Vertex Tracker (SVT)
Solenoid + Central Tracker
THE MICROMEGAS VERTEX TRACKER
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
4 m² of Micromegas detectors
DREAM based Front-End Electronics ~ 20k ch.
Remote off-detector frontend electronics connected with 2m micro-coaxial cables
Forward Detectors (Disks)
High particle rate (30MHz)
Resistive strips divided in 2 zones inner/outer
Dimensions: 6x 430 mm diameter disk with a 50 mm diameter hole at the center
Cylindrical Barrel (Curved Tiles)
Low momentum particles => Light Detectors
Limited space of ~10 cm for 6 layers
High magnetic field (5T)
Phase 1 (2016) : 2 Layers (6 Det. of 120°)
Phase 2 (2017) : 6 Layers (18 Det.)
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THE DREAM FRONT-END ELECTRONICS
• Signals are continuously pre-amplified, shaped, sampled at 20-30 MHz and kept in the circular analog memory 512 cells deep
• Covers 16 µs trigger latency
• At each trigger the 4 to 10 corresponding samples are readout and digitized
• Readout does not disturb sampling
• Retained samples are digitally processed
• Pedestal equalization – online
• Common noise subtraction – online
• Zero suppression – online
• Measure charge and time – off-line
• Micro-coax cables – 64 channels – low capacitance 43 pF/m
~1K ch. Detector
16 x 64 ch. Micro-Coax cables (1.5 -2.2m)2 x 512 ch.Front-End Unit2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
CLAS12 MM FORWARD TRACKER• 6 layers of Micromegas with 1D strips alternatively
rotated at 0°, 60°, 120°
• 86 mm to 380 mm diameter active area
• Bulk MM + Resistive Layer
• Same detector design for the 6 detectors :
• Dimensions: 430 mm diameter disk with a 50 mm diameter hole at the center; 5mm drift gap
• 100 µm PCB glued on ROHACELL
• 525 µm pitch, with 120 µm between two strips, 1024 strips
• 2 independent resistive strips zones (inner/outer)
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Black : no ladders
Charging up effect studies with X-Rays
Resistive Strips w/o interconnections (ladders)
FORWARD DETECTORS IN COSMIC TEST BENCH
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FORWARD DETECTOR COSMIC RAYS TEST• 6 Detectors fully operational with no current on the resistive layer after
many cleaning procedures
• 6 Detectors have been delivered to J-Lab in Sept. 2016
• Radiation length of 0.70% X/X0 => To be be lowered for the next run
• Close to full efficiency (98%) in the active area
• Resolution better than 200 µm (limited by tracking of the test-bench)
• Time Resolution better than 20 ns (same)
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Efficiency map
Cut for eff. calc
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
CLA
S12
BA
RR
EL D
ETEC
TOR
S
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CLAS12 BARREL DETECTORS PRODUCTION
• Total of 6 layers segmented in phi (3 x 120° sectors) = 18 detectors total
• 6 Different detector’s radii
• 2 different types (C and Z types)
• Material (PCB/Bulk + Drift) from the CERN Workshop
• Assembly to cylindrical shape at Saclay
• Test and Characterization at Saclay before shipping to J-Lab
• 8-9 days to assemble one detector + 1 week of test
“C” Barrel“Z” Barrel
Layer Production ch. Radius Length Width
CR4-C 3 + 1spare 896 146mm 712mm 302mm
CR4-Z 3 + 1spare 640 161mm 712mm 333mm
CR5-Z 3 + 1spare 640 176mm 712mm 364mm
CR5-C 3 + 1spare 1024 191mm 712mm 396mm
CR6-Z 3 + 1spare 768 206mm 712mm 427mm
CR6-C 3 + 1spare 1152 221mm 712mm 459mm
CR6-C new 3 spare 1152 221mm 712mm 459mm
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COMPACT DESIGN
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INTEGRATION OF ONE 120° SECTOR
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OPERATION IN CLAS12 AND THE 5T MAGNETIC FIELD
• Small volume for instrumentation (6x15mm)
• Remote off-detector frontend electronics using 2.2m long coaxial cable + DREAM FEE
• No fan for cooling
• EM Shielding challenging
• Lorentz Angle
• Slow gas to reduce drift velocity
• Small drift gap
• High electric field
• 6kV/cm for C
• 5kV/cm for Z
• Degradation of spatial resolution
• Effect depends on the charge
of the particle
• Modify transverse diffusion
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Detector Radius (mm)
CR6C 222.53
CR6Z 207.54
CR5C 192.65
CR5Z 177.57
CR4Z 162.56
CR4C 147.57
825V on 3mm 3825V on 3mm Effect on Ion Backflow
=> Clas-note 2007-004: Simulations of Micromegas detectors for the CLAS12 experiment (S. Procureur)
[V/mm]driftE0 100 200 300 400 500 600 700 800 900
Lo
ren
tz a
ng
le [
de
g]
0
10
20
30
40
50
60
70
80
90Hall B data, B=1.4T
Hall B data, B=2.8T
Hall B data, B=4.2T
Magboltz, B=1.4T
Magboltz, B=2.8T
Magboltz, B=4.2T
Lorentz Angle Vs HV
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
BARREL DETECTORS: PERFORMANCE WITH COSMIC RAYS
14LAYER 6 LAYER 5 LAYER 4
• 6 Layers of cylindrical detectors divided in 120° sectors = 18 Micromegas tiles
• Bulk + Resistive Micromegas
• Less than 0.5% of a radiation length per layer
• Cylindricity measured to be precise up to ~2mm in radius
• Resolution better than 200µm per layer with cosmic rays
• Time resolution of ~25ns with cosmic rays
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
FIRST INTEGRATION AT J-LAB
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In 2016 Successful integration at JLAB of ~1/2 of the layers together with the Silicon tracker and joint test with cosmic rays
Residuals of MM : ~ 400 µm for Z det.~ 5 mm for “C” det.
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MVT ARRIVES AT CLAS12 IN FALL 2017
ENVIROMENTAL CHALLENGE
• Unexpected high background increased the silicon vertex tracker leakage current and force to increase cooling in the central tracker
• First cooling brought humidity issues fixed by nitrogen flushing
• A few detectors had to be replaced
• Micromegas tiles have been operated below freezing with no further issues
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Temperature recorded on the detectors for 2018-2019
Sensors on BMT
Humidity on barrel detectors
DETECTOR CURRENT
• Detector current vs beam luminosity
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Up to 2µA per Micromegas at nominal beam intensity
DETECTOR OCCUPANCY WITH BEAM
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a)
c) d)
Hit occupancies for C-tiles at 2.2 GeV (left) and 10.6 (right). The elastic recoil protons are responsible for the large excess of events at 2.2 GeV, between strip number 400 and 500. The cross sections is too small at 10.6 GeV to see the protons.
Occupancies of FMT (left) and BMT (right) as a function of the beam current. Half of the FMT disks has a lower occupancy since only their inner region is active.
Forward Barrel
CENTRAL TRACKER– 1 TRACK EVENT
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Silicon
MM
TOF
Neutron Det.
April 2019 - 10.2 GeV electron on LH2 target
CENTRAL TRACKER– 2 TRACKS EVENT
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April 2019 - 10.2 GeV electron on LH2 target
CENTRAL TRACKER– 3 TRACKS EVENT
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April 2019 - 10.2 GeV electron on LH2 target
EFFICIENCY AND HV PLATEAU SCAN
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• Tracking algorithms are not final yet=> Very Preliminary Results
• 90%-100% efficiency reached in physics data taking conditions
• Working point for the mesh HV at ~500V in Ar:Iso 90:10
STATUS
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• The CLAS12 experiment MM Vertex Tracker has been assembled and delivered to Jefferson Lab is on its way after 10 years since the first proposal
• Resistive Micromegas have been build and characterized
• 18 + 6 (spares) cylindrical MM for the CLAS12 barrel detectors
• 6 disks for the Forward Micromegas Tracker
• The Micromegas detectors have been taking data since fall 2017
• At nominal luminosity, detectors operate with a 2µA current on the mesh
• Unstable environmental conditions (temperature and discontinuous gas flow) damaged a few detectors that had to be placed
• Since December, we have stable condition and no detector issue
• Now CLAS12 is off for the HPS experiment (Heavy Photon Search)
• Fall 2019 : LD2 data taking
• Winter 2019-2020 : replacement of the central tracker by a radial TPC using the same mechanics and DREAM electronics (BONUS)
• 2021 : Central tracker is put back and data taking with nuclear target (carbon, …)
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
OUTLOOK
www.cea.frwww.cea.fr
THE MVT GROUP AT SACLAY:
D. ATTIE, S. AUNE, J. BALL, Q. BERTRAND, F. BOSSU, G. CHRISTIAEN, M. DEFURNE, J. GIRAUD, R. GRANELLI,, I.
MANDJAVIDZE, O. MEUNIER, Y. MOUDDEN, S. PROCUREUR, M. RIALLOT, J-Y. ROUSSE, F. SABATIE
Contact : maxence.vandenbroucke@cea.fr
REQUIREMENTS
• Compact tracker => Cylindrical detectors
• High magnetic field => High lorentz Angle => small gap, slow gas, high drift field, high gain,
deported electronics
• Low Energy proton/electron => Low X0
• High rate in the forward region => Low spark rate, fast gas
High gain, low spark => Resistive MM
Cylindrical Det. => Bulk
Low X0 => Light material, glued
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CYLINDRICAL MICROMEGAS
Electric leak testSegmentation and preparation Gluing of the side carbon ribs on circular shape
Gluing of additional ribs Setting drift plane Gluing of the drift plane2019 MPGD Conference - CEA Saclay - Maxence
Vandenbroucke
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• 3D probing machine measuring points :
• 270 points on top (drift side)
• 120 points under (readout side)
• Cosmic rays data for cross-check
List of measured points
X Y Z
PT-Arceau1_1 -3.588 231.995 -0.005
PT-Arceau1_2 28.993 231.995 33.071
PT-Arceau1_3 64.992 231.994 57.126
…
CLAS12 BARREL : GEOMETRY
Mechanical precision up to ~2mm in radius
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Crosscheck using cosmic rays data reconstruction
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PRE-PRODUCTION FORWARD DISK FOR CLAS12: ISSUE WITH RESISTIVE LADDERS
• 2 pre-production (2015) detector tested, One was not ok :
• High current due to a contact in the active area (can’t burn it with sparks)
• Current flows from the contact to ground (black dots)
• Large impacted zone due to ladders
• Drift electrode glued (intervention impossible)
• Carbon frame for gas distribution
Before the current appeared With current
40mm
0.5mm
Resistive StripsS. ProcureurS. Procureur
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Efficiency maps
Current without ladders
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
PRE-SERIE BARREL DETECTORS TEST
Zoom on a part of the CLAS12 Barrel with thermal cam, with HV on and current of about 300 mA
Solutions :
No resistive interconnection (ladders)
Aluminum frame at the gas inlet
More ground connections
“C” Barrel detectors had no problem !
Fixing is possible by filing the area with a drop of polymer
Efficiency Map
without current with currentposition of the noisy strip
position of resistive contacts
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S. Procureur S. Procureur
Fixing Procedure : A lot of HV Test -> Soft Cleaning (aspiration, antistatic roller)
imaging the problem -> HV + current (10-500µA) and IR imaging Cleaning -> water cleaning (karcher) -> drying (air+oven)
-> Sodium Chlorate 60ºC -> TrashOr if possible -> passivation with a drop of glue
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
NEW CONNECTION SCHEME,NEW PROBLEMS
SILVER PASTE ISSUE
• The CR4Z layer has been the first produced using this method
• => All 4 of them died after ~2 weeks of tests
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=> Thermal imaging shows that high current appeared on the silver paste connection between the resistive layer and the PCB
TIME RESOLUTION
• Time Resolution with resistive detectors is ~25ns instead of ~15ns (depending on the conditions)
• Time resolution not critical for the CLAS12 barrel
• Inhomogeneities over the detector surface observed
Time Vs Det. X 2D Time distribution
Solutions : Electronic parameters optimization (~3ns) - done 1D (2D?) corrections (~5ns) but difficult with cosmic rays
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THE ASACUSA MICROMEGAS TRACKER
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
[V]MESH
HV
410 420 430 440 450
Effic
iency
0.75
0.8
0.85
0.9
0.95
1
AMT Detector
RminC
RmaxC
RminZ
RmaxZ
2
Front-end crate
Cold head
Readout
connectors
Cold head
L = 61.5 cm
Micromegas
Anti Helmhotlz
coils
FIG. 2. Technical drawing of the AMT detector installedaround the cent ral CUSP trap. The detector in the drawing
is surrounded by the magnet ic coils, which are drawn witht ransparent rendering. The two cold heads, used for the cryo-
genic t rap system, on the two sides of the t rap are also visible.
and at 7 cm with several thermal isolat ion layers in be-tween. A B = 0-4 T magnet ic field with double-cusp con-figurat ion is provided by ant i-Helmholtz coils, as shownin Figure 3 together with the posit ion of the AMT detec-tor. The bore radius of the shield of the magnet is at 10cm.
-400 -300 -200 -100 0 100 200 300 400
-3
-2
-1
0
1
2
3
4
Bz
[T]
Z [mm]
FIG. 3. Schemat ic view of the nominal cusp magnet ic field
configurat ion on axis (R= 0 mm) and at the Micromegas de-tector layers (R= 78.5 mm, R= 88.5 mm).
The main design parameter of the detector was to re-solve ant iproton-nucleon annihilat ion vertex posit ion insuch an environment with a resolut ion of σver t ex ' 1 cm,in order to be able to dist inguish between annihilat ion
events occurring near the cent re of the trap and on thet rap elect rodes at 4 cm radius. The major limitat ionin the possible resolut ion is the mult iple Coulomb scat -tering inside the various t rap materials. In order to es-t imate the resolut ion the elect rodes, vacuum chambers,thermal isolat ion materials and the lever arms of eachlayers were taken into account . The overall gaussian un-certainty of a single t rack point ing at a cent ral vertexis est imated to be σCoul .
hi t ' 2 mm for a charged pionwith p = 600 MeV/ c momentum, and σCoul .
hi t ' 4.5 mmfor the same part icle with p = 300 MeV/ c momentum.From GEANT4 Monte Carlo simulat ion [8] of ant ipro-ton annihilat ion events, combined with t rack and vertexreconst ruct ion, we obtain an overall vertex resolut ion ofσver t ex ' 7 mm, which value is within the target resolu-t ion.
I I I . T H E A SA CU SA M I CROM EG A S T R A CK ER
A . M icr om egas det ect or
The AMT is a t racker detector with two half-cylinderlayers of Micromegas and with one full cylinder layer ofplast ic scint illator bars (providing t rigger signal) sand-wiched in between, all curved to fit into the cylindricalst ructure of the ASACUSA double-cusp trap. The over-all length of the detector is 61.5 cm with an act ive areaof ⇠ 40 cm. The inner and outer Micromegas layershave radius of 78.5 mm and 88.5 mm, respect ively. TheMicromegas detector operat ion principle is illust rated inFig 4. Elect rons are released, as a result of a passageof a charged part icle through a few mm wide drift re-gion, and they drift to a thin amplificat ion region sepa-rated by a transparent mesh elect rode. The high elect ricfield in the amplificat ion gap provides elect ron mult ipli-cat ion. The amplified signal is collected by micro st ripswhich are sampled by custom built front -end electron-ics. In case of the presence of external magnet ic field thedrift ing elect rons are under the influence of an addit ional~F = q(~v⇥ ~B ) Lorentz force.
The st ructure of the detector, from bot tom to top, ismade of a 250 µm FR4 printed-circuit board base, with5 µm thick gold-coated copper anode strips on top of thePCB. The amplificat ion gap of 128 µm is followed vert i-cally by a 25 µm thick stainless steel woven micro-mesh(wire of 18 µm and opening of 45 µm), supported by anarray of pillars. The pillars have diameter of 300 µm andpitch of 2 mm, and addit ionally smaller diameter pillarswereadded with diameter of 150 µm, between each largerpillar, in order to support the curvature of the micro-mesh. The fract ion of the surface area covered by thepillars relat ive to the total act ive area is ' 2 %. Abovethe micro-mesh a drift gap follows with a thickness of 3mm. The structure is closed with a 250 µm kapton driftcathode with 5 µm of copper on both sides, to provideexternal shielding. The st rip layout of the Micromegasis illust rated in Figure 5. In the case of AMT one layer
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Characterization at Saclay :
Rmin C [strip]0 50 100 150 200 250 300 350 400 450 500
Rm
ax
C [
str
ip]
0
50
100
150
200
250
300
350
400
450
500
Rmin C [strip]0 50 100 150 200 250 300 350 400 450 500
Rm
ax
C [
str
ip]
0
50
100
150
200
250
300
350
400
450
500
2 x 6 Months of smooth data taking !
Effect of the magnetic field (80º Lorentz angle at low drift field)
B Field ONB Field OFF
S. ProcureurS. Procureur
AMT – MICROTPC ALGORITHM
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
Resolution Vs Track Angle
Antiproton distribution(calibration data)
Filtered distribution
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Fitted signal in the drift space
The MicroTPC algorithm uses the time information on multi-strip clusters to extrapolate the track angle :
MicroTPC algo on anti-p data :
Track angle from a single layer barrel
tim
e
space
µTPCCut
CORRELATION BETWEEN SVT AND MVT
| PAGE 35
DAQ including both SVT and MVT data is working
Mapping and Geometry understoodTrack reconstruction with cosmic rays is working
Correlation bet. SVT tracks and BMT in Micromegas coordinates
Residuals* : ~ 400 µm for Z det.~ 5 mm for “C” det.
* MC simulations show that 400µm residuals correspond to a 350µm resolution
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
2D EFFICIENCY MAPS
| PAGE 36
2019 MPGD Conference - CEA Saclay - Maxence Vandenbroucke
sector1detectorBLayer2
layer1
sector2detectorA
sector3detectorC
Detectors’ efficiency with cosmic rays tracks from the SVT
No major defect in BMT detectors
SVT “ghost” due to shallow tracks in the SVT not reconstructed properly at that point
Eff. Vs HV (gain)
DREAM FRONT-END ELECTRONICS
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