1. CLAS12 Tracking Design (ca. 2005) a basic design parameters
Central tracker:
single-sided Si strips
150 mm pitch
barrel: 4 x 2, +/- 2o stereo
fwd: 3 x 2, +/- 12o stereo
SVT
DC’s: same concept
as present chambers
hexagonal cells
6 sectors, 3 regions
2 super-layers/region
+/- 6o stereo
regions at ~ 2, 3, 4 m.
112 wires/layer (24192)
250 mm resolution
reg. 1
reg. 2
reg. 3
March 23, 2009
Hall B meeting

2. 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, 112 wires/lyr.
six 6-layer superlayers
30 mm wires
good acceptance
Df ~ 50% of 2p at 5o
pre-bowed frames
low wire tensions
self-supporting design
March 23, 2009
Hall B meeting

3. Forward Tracker: Expected Resolution
dp/p, dq,
df, dx
- plotted versus p
- at 35o 1%
0.5 mrad
These results were calculated with MOMRES; in good agreement with sim/rec results from GEANT3/RECSIS12 and GEANT4/trak. Backup slide shows what happens with/wo a vtx. tracker and at 350 micron accuracy.
0.5 mrad
100 microns
March 23, 2009
Hall B meeting

4. 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
March 23, 2009
Hall B meeting

5. 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.
March 23, 2009
Hall B meeting

6. 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!
March 23, 2009
Hall B meeting

7. Endplates: many precise holes
Number of Holes
4925 feedthrough holes
12 survey
3 datum & alignment
28 bolt & attachment
0.200 mm
true position
a “50 mm”
1.7 m
March 23, 2009
Hall B meeting

8. 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
March 23, 2009
Hall B meeting

9. CLAS12 Stringing Fixture
Backup is recent photo
March 23, 2009
Hall B meeting

10. 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
March 23, 2009
Hall B meeting

11. Steps in Stringing
March 23, 2009
Hall B meeting

12. Installing Pre-tensioning Wires
- before we start stringing
- use springs on guard wires
- gradual release of tension
March 23, 2009
Hall B meeting

13. Stringing the Chamber
March 23, 2009
Hall B meeting

14. Installing Pre-amplifier Boards
On-board pre-amplifier boards and high-voltage distribution boards are installed after wires are strung.
March 23, 2009
Hall B meeting

15. 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
March 23, 2009
Hall B meeting

16. Model of Torus and Chambers
very useful:
installation
cabling
access
March 23, 2009
Hall B meeting

17. 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 !!
March 23, 2009
Hall B meeting

18. Installation and mounting scheme
Linkage system allows quick and accurate installation
Positioning accuracy
reproducible to 25 mm
March 23, 2009
Hall B meeting

19. 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
March 23, 2009
Hall B meeting

20. Total cost: 4.6 M$ March 23, 2009 Hall B meeting Forward Tracker
Outside Costs
Labor (man-weeks)
Total (k$)
Techs.
Engrs.
Designers
Scientists
Pd. Univ.
Total Labor
Sub-tasks MT ET ME EE MD ED VU S
U. Cont.
U. Staff
man-wks k$
Design chamber 21 10 36 1
110
135
Buy endplates, frames
368 11 4 7 3 6 28 59
114
482
Buy wires, pins, feedthroughs
655 13 16 52 90
745
Buy cleanroom supplies 80 5 9 20 91
171
Box assembly 19 8 32 82
151
Design stringing fixture 2 26 44
Build clean room, stringer
141 17 53 86
226
String, instrument chamber
1550
102 60
150
328
560
2,110
Design stb/hvtb 15 45
Lay out, buy stb/hvtb
321 40
116
437
Total
$3,115
202 35 25 65 85 66
146
264
924
$1,522
$4,637
PED 30 12
216
$314
CONSTRUCTION
172 24 34
263
708
$1,208
$4,323
PED: labor
Const: procurements
$1,565
Const: expenses
$1,550
Const: labor
PED: total
Const: Total
CLAS12 Total
March 23, 2009
Hall B meeting

21. Lots of work !
March 23, 2009
Hall B meeting

22. Lot to buy !
March 23, 2009
Hall B meeting

23. Plans for next year: Buy reg. 2 endplates, frames Build reg. 2 boxes
hire lead dc technician in July
work in Jlab’s, ODU’s cleanrooms
Buy wire, feedthroughs, misc.
Build strong-backs, installation fixtures
String first Reg. 2 chamber
hire first stringing crew in fall
March 23, 2009
Hall B meeting