Main Injector at Fermilab
Silicon Vertex Tracker
Integrated system of barrels and disks
~ 800k total channels
Silicon Tracker Layout
1/7 of the detector
(large-z disks not shown)
387k ch in 4-layer double
sided Si barrel (stereo)
405k ch in interspersed
disks (double sided stereo)
and large-z disks
Silicon Tracking System
50 cm
1/2 of detector
1.1
1.7
Silicon Tracker
7 barrels
12 Disks “F”
3
8 Disks“H”
Central Fiber Tracker Layout
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8 nested cylinders
– radius = 20 51 cm
Each layer
– 1 axial doublet
– 1 stereo (u or v)
xu - xv - xu - xv - ….
Constant angle =3o
Layers
– 1,2 - 1.8 m long
– 2,8 - 2.6 m long
Total channel count 
Clear fiber brings signal to
VLPCs - 7 - 11m
Why a Fiber Tracker?
A SciFi Tracker provides the following features:
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Fast response
Good granularity
Track triggering at Level 1
High efficiency
Accurate rposition measurement
Compact design
Seamless coverage
A Little History
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Snowmass 1984 - Binnie, Kirkby, Ruchti propose inner tracker for
SSC based on 25 mm scintillating glass fibers. II + CCD readout
CERN, 1988-1990 - Wood (and the rest of UA2) run with SFD,
60,000 1mm plastic fibers with II + CCD readout
FNAL, 1988 - Reucroft and Ruchti co-chair workshop on SciFi
detector development for the SSC
CERN, 1989 - ?? - Taylor (and the rest of L3) run with PSF detector to
calibrate the TEC. 3,600 plastic fibers coupled to MCP phototubes
Snowmass 1990 - A scintillating fiber outer tracker is proposed for the
DØ upgrade at the Tevatron
Notre Dame 1993 - Tests of Kuraray fiber doped with PTP+3HF and
read out by a VLPC demonstrate sufficient light yield for fiber tracking
FNAL, 1994-1995 - A 3,000 channel cosmic ray test of scintillating
fibers read out by VLPCs measures high light yield, good position
resolution and long-term stability of the VLPC system
A Little History
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Snowmass 1984 - Binnie, Kirkby, Ruchti propose inner tracker for
SSC based on 25 mm scintillating glass fibers. II + CCD readout
CERN, 1988-1990 - UA2 runs with SFD. 60,000 1mm plastic fibers
with II + CCD readout
CERN, 1989 - L3 runs with PSF detector to calibrate the TEC. 3,600
plastic fibers coupled to MCP phototubes
Snowmass 1990 - A scintillating fiber outer tracker is proposed for the
DØ upgrade at the Tevatron
Notre Dame 1993 - Tests of Kuraray fiber doped with PTP+3HF and
read out by a VLPC demonstrate sufficient light yield for fiber tracking
FNAL, 1994-1995 - A 3,000 channel cosmic ray test of scintillating
fibers read out by VLPCs measures high light yield, good position
resolution and long-term stability of the VLPC system
Single Element of Scintillating Fiber Tracker
Scintillating Fiber
Optical Connector
Mirror
Waveguide Fiber
Electrical Signal Out
Photodetector Cassette
Cryostat
Key Features of the CFT
 Scintillation
dyes - 1% PTP + 1500 PPM of 3HF
 Fiber construction - 830 mm PS core, multiclad
 Photodetectors - Visible Light Photon Counter
 Fiber ribbon manufacture - grooved jig plate
 Fiber ribbon placement - located with CMM
 Fiber-to-fiber connectors - curved, grooved,
diamond finished
 Support cylinders - double-walled carbon fiber
Visible Light Photon Counters
 Key
features of the VLPC
– Solid state detectors of photons, manufactured at Boeing
(originated at Rockwell International)
– Operate at the temperature of a few degrees Kelvin
– Capable of detecting single photons
– High quantum efficiency for photon detection ~80%
– High gain ~40 000 electrons per converted photon
– Low gain dispersion
– Can operate in a high background radiation environment
– Used for CFT, CPS and FPS
VLPC Operation
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Based on the phenomenon of Impurity Band
Conduction, occurring when a semiconductor is
heavily doped with shallow donors or acceptors
– Electrical transport occurs by charges hopping from
impurity site to impurity site
 In
the VLPC for DØ silicon heavily doped with
arsenic atoms
– Impurity band 0.05 eV below the conduction band
– Normal 1.12 eV valence band used to absorb photons
– The 0.05 eV gap used to create an electron-D+
avalanche multiplication
» Small gap means low field needed
VLPC Operation
Intrinsic
Region
Gain
Region
Drift
Region
Spacer and
Substrate
Cross Section
•e •h
•-
•+
Photon
Electric Field
Distribution
E field
D+ flow
Undoped Silicon
Doped Silicon Layer
VLPC Development History
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1987 published paper on SSPM Solid State PhotoMultipliers
– sensitive into infra-red region
1989 HISTE Proposal Submitted
High-Resolution Scintillating Fiber Tracker
Experiment
– Main goal: to suppress sensitivity in infrared region
1991-1992 HISTE I, HISTE II, HISTE III
1993 HISTE IV
– Visible QE ~60%, Cosmic Ray Test at Fermilab
1994 HISTE V High QE High Gain
HISTE VI large scale production based on HISTE V
HISTE-VI VLPC chip
A
C
A
B
B
A = VLPC die
B = Aluminum Nitride substrate
C = Solder preform
1
mm pixels
 2x4 array (HISTE-VI)
VLPC Cassette and Readout
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1024 VLPC pixels in one cassette
Electronic readout:
– custom SVXII chips
SVX Readout (ADC Counts) of Cassette A (T=8.2K, V=7V)
600
500
3’
400
300
200
100
0
40
60
80 100 120 140 160 180 200
VLPC Production at Boeing
 13
300 needed
including 10%
spares
 17 845 tested
 15 529 accepted
– Yield: 87%
VLPC Performance Summary
Fiber Placement
Inherent fiber doublet resolution is on the order of
100 microns
 want to know fiber locations to < 50 microns
However, for the Level 1 trigger must place
fibers with a skew < 40 microns end-to-end
 implications for ribbon fabrication, ribbon
mounting and cylinder construction
CFT Track Trigger
Trigger response for Z ee with 4 min.bias
(1) Fiber light signals  electronic signals
(2) Feed all axial fibers into logic gates/cells in
Programmable Logical Devices
(3) Fiber hit pattern recognition to look for tracks
consistent with momentum PT > 1.5 GeV/c
(4) Send out the track information to outside L1 CFT
Fiber Ribbon Fabrication
Doublet ribbons of
2  128 fibers
 Flexible grooved
Delrin plate locates
fibers
 Aluminum curved
back plate sets the
radius
 Same mold used for
ribbon mounting
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Thin Flexible
Jig Plate
Curved Back
Plate
Fiber Ribbon Fabrication
Doublet ribbons of
2  128 fibers
 Flexible grooved
Delrin plate locates
fibers
 Aluminum curved
back plate sets the
radius
 Same mold used for
ribbon mounting
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Fiber Ribbon Quality Control
Ribbon Quality Control
Ribbon Production
Weekly Ribbon Production
( 85% Overall Pass-Rate )
18
16
14
12
10
8
6
4
2
0
20-May
9-Jun
29-Jun
19-Jul
8-Aug
28-Aug
17-Sep
The problem with Torlon
 During
assembly of cylinder 3, interference
between ribbon connectors observed
 Torlon connectors had grown!
– Humidity effect
– Studies inconclusive, so …
 Torlon
has now been rejected
– Barrels 7,8 will use aluminum connectors
– Other barrels, either Al or Techtron
CFT Support Cylinders
 Fabricated
“in house” at
Fermilab
 Double wall design carbon fiber walls with
Rohacell core
 Built up on precision
steel mandrels
CFT Support Cylinders
CFT Support Cylinders
Status - Ribbon Mounting
 Ribbon
Mounting
machine/tooling
complete
 Test Ribbons have been
mounted
– Look good
– Still need alignment
correction (CMM) at 150
mm level - spec 25 mm
CFT Ribbon Mounting
CFT Ribbon Mounting
CFT Ribbon Mounting
Ribbon Mounting
Cylinder 3B completed - 30 ribbons total
36 m rms
Fiber Mapping and Routing
Long clear waveguide bundles map 256 fibers
from SciFi ribbon to 2  128 connectors at
VLPC end
 Bundles vary from 7-12 meters
 Must be light-tight, flexible, narrow, flame
retardant and “custom-shaped” at curved end
 Mapping of axial fibers critical to trigger
 Out
of 300 bundles, nearly 100 are unique
Waveguide Fiber Routing
CFT Calibration
Uses flat optical panel + LED to illuminate fibers
from above. One panel for each of 300 ribbons.
LED
Flat
Panel
Flat Optical Calibration Panels
300 panels total in system
 Panels are inexpensive, uniform, made to order
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Panel Uniformity
Calibration Mounting Scheme
SciFi Ribbons
LEDs
 Each
ribbon lit by up to 3 panels
– Redundancy
– Large dynamic range
 Each
LED output is variable
 Panels at both ends detector
Flat Panels
Status and Summary
 DØ
upgrade progressing - ready for physics
in early 2001
 Central Fiber Tracker in production
–
–
–
–
fabrication complete in April 2000
cabling completed in summer 2000
Silicon tracker inserted in fall 2000
commission with cosmic rays from summer 2000
until start of Run II
CFT Status - Waveguides
– Fiber sorted
» Best (attn.L from
Kuraray) - longest runs
[8-11.5m]
– Connectorization
» At ND + Fermilab +IU
– QC with x-ray source at
Lab3
 Expect
to complete
production in August
CFT Status - Tracker Mechanical
All axial layers, r and r (incl. correct.)
Mean
RMS
Constant
Mean
Sigma
3500
3000
2500
2000
0.3375E-05
0.1455E-02
2284.
0.2749E-04
0.1323E-02
1500
1000
500
0
-0.01 -0.008 -0.006 -0.004 -0.002
(r)measured
Complete
4000
3500
3000
2500
2000
1500
1000
500
0
-0.02
0
0.002 0.004 0.006 0.008 0.01
inch 
- (r)
predicted
Mean
RMS
Constant
Mean
Sigma
-0.015
-0.01
-0.005
0
0.005
(r) measured - (r) 0
0.01
-0.6468E-03
0.2633E-02
2903.
-0.6892E-03
0.2527E-02
0.015
0.02
inch 
Global precision 33 mm (Measured vs Desired)
Fiber Ribbon Quality Control
Ribbon Quality Control
CFT Moved to DAB
CFT Status - Waveguides
– Fiber sorted
» Best (attn.L from
Kuraray) - longest runs
[8-11.5m]
– Connectorization
» At ND + Fermilab +IU
– QC with x-ray source at
Lab3
 Expect
to complete
production in August
Fiber Tracker Layout
Axial doublet layers
on each of 8 cylinders
 Alternate u or v stereo
layers on successive
cylinders
 ~ 78k total channels
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