1. Charged Particle Tracking for CLAS12
Physics a tracking requirements a detector specifications Detector Design Barrel Vertex Tracker (BVT) Forward Vertex Tracker (FVT) Drift Chambers (DC) Optimizing the Design BVT (mixed Si/MM?) FVT (stereo angle?)
Basic overview
Design options
Simulation results
Technology reviews
Maximizing efficiency and resolution at high rates
Key decision points
December 2, 2009
CLAS12 Detector Review

2. Tracking: physics a design spec’s
Experiment Characteristics
electron beam
small cross-sections (exclusive reactions, Q2-dep.)
measure hadronic state
establish exclusivity (missing mass)
other cuts: co-planarity, etc.
forward-going particles
small laboratory angles
broad coverage in center-of-mass
December 2, 2009
CLAS12 Detector Review

3. Physics goals a general design spec’s
Specifications:
measure flux-factor accurately
q ~ 1 mrad
dp/p < 1%
select an exclusive reaction; e.g. only one missing pion
dp < .05 GeV/c
dq p < .02 GeV/c
sinq df p < .02 GeV/c
small
cross-sections
L = 1035/cm2/s
high efficiency
good acceptance
Df ~ 50% at 5o
December 2, 2009
CLAS12 Detector Review

4. Tracking Specifications Summary
Fwd. Tracker
Central Tracker
Angular coverage
5o – 40o
(50% f-coverage at 5o)
35o – 125o
(> 90% f-coverage)
Momentum resolution
dp/p < 1%
dp/p < 5%
q Resolution
1 mrad
5 – 10 mrad
f Resolution
1 mrad/sinq
5 mrad/sinq
Luminosity
1035 cm-2 s-1
December 2, 2009
CLAS12 Detector Review

5. CLAS12 tracking: ca. 2008 torus solenoid Si tracker DC’s reg. 1 reg. 2
May 8, 2008
CLAS12 Detector Review

6. Silicon trackers and drift chambers
Central tracker:
single-sided Si strips
150 mm pitch
barrel: 4 x 2, graded 3o stereo
fwd: 3 x 2, +/- 12o stereo
DC’s: same concept
as present chambers
6 sectors, 3 regions
2 super-layers/region
+/- 6o stereo
regions at ~ 2, 3, 4 m.
112 wires/layer (24192)
250 mm resolution
May 8, 2008
CLAS12 Detector Review

7. BST & FVT Assembly Silicon vertex tracker reviewed on April 2:
design meets physics requirements
design is technically feasible
recommend we do the following:
develop alignment specifications
develop an operational plan
develop a grounding scheme
no further discussion of Si tracker in this review; unless requested
May 8, 2008
CLAS12 Detector Review

8. Central vertex tracking
Central or “barrel” vertex detector (BVT)
mixed: inner - Silicon, outer – Micromegas
Silicon:
better position resolution
but, more multiple scattering
and, very small stereo angle
all-Si design good for dp/p, df; bad for dq, dz
December 2, 2009
CLAS12 Detector Review

9. Résultats pT/pT  SI(+MM)   MM 3 dispositifs ont été étudiés:
- 4x2 SI ( = 1.5°, et  = 43 m)
4x2 MM ( = 0 et 90°)
2x2 SI+ 3x2 MM
pT/pT  SI(+MM)
  MM

10. Résultats - 2
  SI(+MM)
z  MM

11. Silicon + Micromegas ? simulations show mixed solution best, but
can Micromegas work with a cylindrical geometry?
can Micromegas work in a high, transverse B-field ?
Review the technology
December 2, 2009
CLAS12 Detector Review

12. Review of Micromegas Tracking Detectors for CLAS12 – May 7, 2009
Reviewers: Madhu Dixit, Mac Mestayer
Presentations covered the following topics:
detector overview: layers, strip pitch, segmentation for central & forward regions
fabrication overview: principles and prototype testing of “bulk” technology
detector simulation: GARFIELD results on drift, diffusion, gain
tracking simulation: particle backgrounds, tracking efficiency and resolution
acceptance and quality assurance: methods to validate component performance
prototype testing: measurements of position resolution, Lorentz angle, gain times transmission and tracking efficiency for minimum-ionizing tracks; including tests of curved detectors and tests in magnetic fields
electronics: overview of requirements for charge and time measurements; options for an integrated system: amplification/discrimination/digitization/ readout.
Impressive new pioneering work on curved Micromegas technology and operation in transverse magnetic fields

13. Resolution of the charges:
The simulated performance for resolution, solid angle coverage and efficiency meet or exceed CLAS12 requirements.
The design is based upon existing technology, simulated at both the signal and track-finding level with key parameters verified by prototype tests. The simulations are consistent with the test results.
The conceptual plans for detector integration (including safety systems) are consistent with the overall CLAS12 detector layout.
The schedule and allocated manpower seem reasonable.
The group is competent; recognized world leaders in this technology.
We are confident that the group can successfully design and build the proposed tracking detectors for CLAS12.

14. Optimizing the BST design
what’s best mixture of Si. vs. MM? 2 X 3 ?
integrated vs. independent mech. structure
best combination E field/ drift gap?
stereo angle:
smaller than 90 deg.?
fewer ‘ghost’ hits, worse resolution
need flex-cable readout for “y” strips
mesh segmentation
December 2, 2009
CLAS12 Detector Review

15. Why do we need a forward vertex detector?
might find ‘stub’ tracks pointing to coils
might help with track-finding
vastly improves vertex information
improves other track parameters
better knowledge of Int(B X dl)
December 2, 2009
CLAS12 Detector Review

16. How will the FVT be used? stand-alone tracker (no)
‘seed’ for forward track (?)
vernier for dc-only track (yes)
need good background rejection
Requirements
Efficiency
prob. of >1 hit in ‘matching circle’ < 20%
Resolution
~100 micron spatial resolution
December 2, 2009
CLAS12 Detector Review

17. Present forward tracker (DC, FST)
6 independent sectors
3 chambers (‘regions’) per sector
2 six-layer superlayers (+/- 6 °)
plane tilted by 25° wrt the beam axis
acceptance: 5°40° DC
Strip layout:
3x2 layers
trapezoidal tiles
12° stereo angle
acceptance: 5°35°
FST
Simulation & Reconstruction 10/30/ S.Procureur

18. Torus magnetic field ∫B∙dl ~ 3 T-m highest field for forward tracks
B (tesla)
Scattering angle (degrees)
December 2, 2009
CLAS12 Detector Review

19. Match DC track to FST hit
98% of DC tracks
extrapolate within
+/- 1 cm.
So, how many background hits in the ‘circle of confusion’?
December 2, 2009
CLAS12 Detector Review

20. Resolutions with DC+FST
(electrons at  = 15°, now from GEMC!):
20 times better
5 times better
FST greatly improves the vertex resolution, ,  and p
Simulation & Reconstruction 10/30/ S.Procureur

21. DC+FST – resolution with protons
(protons at  = 15°):
3-4 times better
8-10 times better
Much better vertex resolution with FST (and  resolution at high p)

22. Change FST to Micromegas?
Difficulties with FST
massive cooling structure in live area
no cooling in live area for Micromegas
dead area around each trapezoidal sensor
very small dead areas for Micromegas
hard to deal with high rate at small radius
Difficulties with Micromegas
parallel E and B-fields
very little charge spreading
charged track hits look like x-ray hits
December 2, 2009
CLAS12 Detector Review

23. Optimize FST parameters?
optimum stereo angle? - more choice
large angle gives better theta resolution
but, also gives more fake strip matches
mixed strip and pixel segmentation
want fewer strip crossings at small radius
ghost hits will appear at larger radius
can we cover the full azimuth?
what is the mesh segmentation? radial?
December 2, 2009
CLAS12 Detector Review

24. Key Decision Points BST how many layers of Si? …MM?
2 – 3? 3 – 3?
unified or independent structure ?
internal accuracy vs. ease of installation/repair
layout details: stereo angle, mesh segmentation
study two-layer ‘punch-through’ background
sensor design: drift gap, field strength
reduce sparking rate
December 2, 2009
CLAS12 Detector Review

25. Key Decision Points FST Super-layer structure okay?
3 units, each u – v
Background is very radially-dependent
want radial segmentation?
if so, how do we get signals out?
What is the optimum stereo angle?
balance dq vs. ghost hits
Can we cover the full azimuth?
December 2, 2009
CLAS12 Detector Review

26. CLAS12 Tracking: Summary
Si + MM provides excellent resolution in central region: better than Si or MM alone
FVT: better vertex than DC12 alone
Si disk design works well, but
MM design offers more readout flexibility
finer segmentation in ‘hot’ region
full azimuthal coverage
Micromegas has a major role in CLAS12
December 2, 2009
CLAS12 Detector Review

27. Backup slides on DC12
December 2, 2009
CLAS12 Detector Review

28. Physics goal Physics spec. Design feature
measure cross-section accurately
q ~ 1 mrad
dp/p < 1%
planar chambers
identical cells (easy to calibrate)
250 mm accuracy/layer
select an exclusive reaction; e.g. only one missing pion
dp < .05 GeV/c
dq p < .02 GeV/c
sinq df p < .02 GeV/c
~linear drift velocity
+/- 6o stereo angle
small
cross-sections
L = 1035/cm2/s
high efficiency
small cells
six 6-layer superlayers
30 mm wires
good acceptance
Df ~ 50% of 2p at 5o
pre-bowed frames
low wire tensions
self-supporting design
December 2, 2009
CLAS12 Detector Review

29. Superlayer Wire Layout Staggered “Brick-Wall” Hexagonal
field
sense .
colored circles represent
drift distances
6 sense layers, 2 guard layers, 14 field layers: 1 superlayer
December 2, 2009
CLAS12 Detector Review

30. Rationale for Design Decisions
6x6 layers
robust track-finding
+/- 6o stereo
better f resolution than CLAS
planar; self-supporting
identical cells, easy to calibrate, survey, repair
112 wires/layer
enough for 1035 operation
30 mm sense wire
92/08 Ar:CO2
faster, linear distance-vs-time, strong, more reliable stringing
low wire tension
thinner endplates
on-chamber amplifiers
good signal/noise
re-use HV, LV, ADB, TDC
lots of spares; cost savings; better segmentation
Backup slide is recent design decisions.
December 2, 2009
CLAS12 Detector Review

31. Drift Velocity Calculation use 30 mm wire! 20 mm wire 2325 V
88:12 AR:CO2
30 mm wire
2475 V
92:08 AR:CO2
same gain
58% faster
- and more linear !
GARFIELD calculations; backup is table of surface fields, gains for different configurations
use 30 mm wire!
December 2, 2009
CLAS12 Detector Review

32. Endplates: many precise holes
Number of Holes
4925 feedthrough holes
12 survey
3 datum & alignment
28 bolt & attachment
1.7 m
December 2, 2009
CLAS12 Detector Review

33. Endplate Details 0.200 mm true position a “50 mm”
Backup is mechanical specifications document, including mechanical error budget
December 2, 2009
CLAS12 Detector Review

34. Endplates fit into Frames
Receive endplates
- inspect
- measure hole positions
- clean
Receive frames
- inspect and clean
pre-bow endplate and frames
bolt and glue into frames
Back-up slide showing pre-bowing
December 2, 2009
CLAS12 Detector Review

35. Chamber Ready to String
Box Assembled
-endplates attached
-attachment brackets affixed
Next ---
- mount on stringing fixture
- insert feedthroughs
- install survey points
- string wires
- attach circuit boards
- QA/QC
December 2, 2009
CLAS12 Detector Review

36. CLAS12 Stringing Fixture
Backup is recent photo
December 2, 2009
CLAS12 Detector Review

37. Parts: wire a circuit board
signal routing:
wires a pre-amp
conductive rubber
circuit board
crimp pin
feedthrough
endplate
circuit board
Backup is drawing of feedthrough designs
wire
December 2, 2009
CLAS12 Detector Review

38. Stringing wires between “slanted” endplates
“gravity” stringing
wires: 9 cm m long
wires strung individually
wires attached by crimping
wires positioned by “trumpet”
endplates
Backup is photo of stringing
December 2, 2009
CLAS12 Detector Review

39. Steps in Stringing
December 2, 2009
CLAS12 Detector Review

40. Installing Pre-tensioning Wires
- before we start stringing
- use springs on guard wires
- gradual release of tension
December 2, 2009
CLAS12 Detector Review

41. Stringing the Chamber
December 2, 2009
CLAS12 Detector Review

42. Installing Pre-amplifier Boards
On-board pre-amplifier boards and high-voltage distribution boards are installed after wires are strung.
December 2, 2009
CLAS12 Detector Review

43. Electronics: Chamber a TDC
75 ft. cable
Post-amp
x 10 - x 30
30 mV disc.
drift chamber
Pre-amp
2 mV/mA
1 mA
2 - 3 electrons
re-use post-amps, TDC’s
backup is schematic of CP01
new circuit boards
based on old SIP’s
TDC’s
Lecroy 1877
December 2, 2009
CLAS12 Detector Review

44. Model of Torus and Chambers
very useful:
installation
cabling
access
December 2, 2009
CLAS12 Detector Review

45. Tight-packing of Cables, Connectors
CAD layouts
verified on a model:
tight spacing dictated by requirement of
50% f-coverage at 5o
multi-layer
composite
endplate !!
December 2, 2009
CLAS12 Detector Review

46. Installation and mounting scheme
Linkage system allows quick and accurate installation
Positioning accuracy
reproducible to 25 mm
December 2, 2009
CLAS12 Detector Review

47. Schedule: Stringing the Chambers
~2 yrs./ 6 chambers
~1/2 time for stringing
backup is top-down and bottoms-up estimate of time per wire
December 2, 2009
CLAS12 Detector Review

48. Safety and Quality Assurance
Issue
Mitigation
heavy equipment
engineering review; procedures; training; clasweb.jlab.org/wiki/index.php/Safety
cleanliness
Class-10,000 clean-room, cleaning procedures, protective clothing
high-voltage power
current-limited to 40 mA
low-voltage power
voltage limited to 7.5 V
use of magnets, motors
follow EH&S manual on elec. safety
electrical connections
continuity and isolation checks
wire placement accuracy
parts inspections, surveys; tight controls on wire tension and end-plate deflection
wire breakage
“stress-tests”, temp., g-force limits
pre-installation operability
full commissioning plans (on wiki)
installation accuracy
micro-switches, post-installation surveys
December 2, 2009
CLAS12 Detector Review

49. Project Overview & Responsibilities
Oversight: Jefferson Lab
Prototyping
full-sized Reg. 1 prototype: Jlab, ODU
beam tests: Jlab, ISU
Design
Region 1 & 2: JLab
Region 3: Idaho State
Build, String & Commission
Reg. 1 - Idaho State
Reg. 2 - ODU
Reg. 3 - JLab
December 2, 2009
CLAS12 Detector Review

50. CLAS Drift Chambers : History
Operating successfully for ~10 years ….
A photo of the first
“Reg. 3” chamber
moving into Hall B
December 2, 2009
CLAS12 Detector Review

51. Problems in the CLAS Drift Chambers
We’ve had a couple of problems:
~60 severe* / year
16 broken wires
adb per yr.
better now?
~ 10 lv per yr.
worse now?
* severe problems/ breakthroughs in elog
December 2, 2009
CLAS12 Detector Review

52. CLAS Drift Chambers : History
…. with good resolution
mid-cell resolution is mm
cell average: 310, 315, 380 mm; for R1, R2, R3
…. at the same voltage, with same efficiency
a Ar/CO2 shows no conventional aging
NIM A449 (2000) 81
December 2, 2009
CLAS12 Detector Review

53. Conclusions Large project: 18 chambers, 90K total wires
Reliable design:
will achieve resolution and efficiency goals
Low risk cost and schedule:
based on detailed knowledge from CLAS
High probability of success:
experienced people
December 2, 2009
CLAS12 Detector Review