1. WBS:1.4.2.2.1: Tracking for CLAS12
Agenda, Aug 31 meeting:
forward DC prototyping
rate effects in central detector and forward SVT
SVT technology and development
Meetings every two weeks - Wednesday - 10 pm
Progress in all 3 areas; at this meeting I’ll concentrate on:
The physics at 12 GeV is typified by higher momentum tracks and the reactions of interest have smaller cross-sections, so the main requirements for the tracking system is good momentum resolution, e.g. 1% at 5 GeV/c is good for our missing-mass resolution, and also the ability to operate at a higher luminsosity fo 10^35. The detector solution is a Silicon vertex tracker and the forward drift chambers. We have highlighted this sub-system because it is vital to the physics program and is relatively expensive to build.

2. Forward Drift Chambers
Measure charged tracks (5o – 40o)
Forward drift chambers
Design: same concept
as present chambers:
NIM A449(2000)81
6 sectors, 3 regions
2 super-layers/region
6 layers/super-layer
112 wires/layer (24000)
on-board pre-amps
Here again is a picture of the CLAS12 detector with the fwd. dc’s highlighted. They are designed using the same concepts as the present chambers which have been operating successfully since the winter of 97/98 and are described in a NIM article. In each sector of CLAS12 we plan to have three chambers (we call them “regions”); each region has two superlayers of six-layers each; each layer has 112 sense wires for a total of about instrumented sense wires. Pre-amps are mounted on the chamber on specially-built printed circuit boards (PCB).
CLAS12

3. Forward Tracker
hexagonal cells
6-layer superlayers

4. Forward Drift Chamber: new features
Better momentum and angle resolution
more constant velocity, good mechanical tolerance
Higher rate capability
smaller cell solid angle, shorter time window
closer wire spacing (~ 70%)
thicker wire (20 mm a30 mm)
faster gas (88:12 Ar:C02 a92:08 Ar:CO2)
Need prototypes !
goals
features
To reiterate: to get good resolution we need an approx. constant drift velocity (easier to calibrate) and good mechanical tolerance on the chambers themselves and to operate at high luminosity we need many, small drift cells. These new features, smaller cells, thicker wire, faster gas, need prototyping.

5. Forward Tracker: R&D and Design
New features that require prototypes
smaller cells, thicker wire, less CO2
higher voltages, denser-spacing on pcb’s
multi-cell prototype: study hv plateau, signal cross-talk, noise levels, movement of wires
Features that require most design work
Chamber “boxes” - esp. attachments, relative alignments, ease of installation and surveying
On-chamber custom circuit boards
Our most important prototype is the multi-cell prototype. It will specifically look for possible negative consequences of going to smaller cells with thicker wire and using a faster gas: e.g. the possibility that the chamber could be “noisy”, that the wires might move from higher electrostatic forces, and that the higher voltages might cause excessive current draw on pcb’s. To emphasize: our design is a SMALL extrapolation from our current design, but we reduce the technical risk to insignificant levels by prototyping. On the issue of design work, we need to design in from the start the alignment and installation procedures. Although technologically straignt-forward, our on-chamber circuit boards are a custom design and will take a fair amount of design labor.

6. Forward DC Prototype facsimile of Region 1 area (highest wire density)
subtend both superlayers (36 wires wide X 12 high)
12 X 12 wires actually strung
144 sense wires, ~350 field wires
~ 500 wires, 1000 feed-throughs
eight perimenter posts -> realistic endplate ‘sag’
1.5 m X 0.35 m endplates
four circuit boards
two ‘HVTB’, two ‘STB’

7. Forward DC Protoype: parts
endplates: two (1.5 X 0.35 m.), 500 holes
eight post assemblies
gas bag: foils and sealing assemblies
four circuit boards: 15 X 15 cm each, 72 thru-holes
STB: 72 SIP’s each (144 total), 6 regulators, layers?
HVTB:
1000 feed-through assemblies: plastic, trumpet, crimp pin
250 m. Gold-plated Tungsten wire
750 m. Gold-plated Aluminum wire

8. Forward DC Protoype: procurement costs
Item
Description
Estimate
Scaled
Cost
endplates
500 holes
1.5 X 0.35 m.
15 k$
CLAS:
50$/total wire
a 17 K$
X 3 (small order)
a 50 k$
wires, pins, feedthroughs
250 m. - tungsten
750 m. - aluminum
1000 feedthroughs
20 k$
posts, gas bag attachments, other parts
10 k$
circuit boards
2 STB’s
2 HVTB’s
2 k$ X 5 (small order)
a 10 k$
Total
60 k$

9. Forward DC Protoype: procurement costs
Item
Description
Labor needs
endplates
500 holes
1.5 X 0.35 m.
specifications, vendor selection, quality control
wires, pins, feedthroughs
250 m. - tungsten
750 m. - aluminum
1000 feedthroughs
specifications, vendor selection,
quality control
posts, gas bag attachments, other parts
design, procurement, construction
circuit boards
2 STB’s
2 HVTB’s
design, specifications, vendor selection, quality control
Total
~ ½ FTE mech., ~1/2 FTE elec.