Design and Construction

1

• Design and Construction
• of the
• ATLAS Barrel TRT
• 
  Chiho Wang
• Duke University

2
Design Parameters
Barrel TRT

• Straw based tracking chamber with TR capability
  for electron identification.
• Straws run in parallel to beam line.
• Active gas is Xe/CO2/O2 (70/27/3) operated at
  2x104 gas gain
• Counting rate 6-18 MHz at LHC design luminosity
  1034 cm-2s-1

3

• Design is modular for
• reduced risk
• distributed production to multiple sites

• Basic Design of the Module
• Straws are embedded in Radiators and supported
  by Dividers and Endplates which are connected
  across the module by a carbon-fiber shell

Module Length 1.5 m
Sense Wire Length 2 x 0.75 m
Straw Diameter 4 mm
Wire Diameter 30 um
Distance between straws 6.8 mm
High Voltage Grouping 8 straws
4

• Entire barrel is divided into 3 rings of 32
  modules.
• Straws are distributed for a Continuous tracking
  geometry
• 52,544 straws,
• 105,088 readout channels
• Average Number of straws crossed by a track 36,
  out of 73 layers
• Average number of TR-hits for 20GeV Pt electron
  7

Type 1 Type 2 Type 3
Number of Modules 32 32 32
Straws per Module 329 520 793
Straw Layer Number 19 24 30
Inner Radius (mm) 560 697 864
Outer Radius (mm) 697 864 1070
5
Splitting the Wires
Regular Wires Single Joint
Wire Support
Wire Joint
Wire Support
Wire Support
80cm
Inner Wires Double Joint
Wire Joint
Wire Joint

• Sense wires are split in half to reduce counting
  rate.
• This is not enough for the 11 inner most layers
  of wires!
• 40cm from the center of these wires are deadened
  by using 2 wire joints.
• All straws are the same, but there are 2
  different kinds of wires Single joint
  Double Joint

6
Module End Plate Region
7
Components

• Every component has its own QC process to go
  through when received from manufacturer, or when
  its prepared (pre-assembled) for installation

8
Straws

• Straw is made by spirally winding and fusing 2
  bands of aluminized kapton.
• The aluminized surface is protected by
  carbon-polyimide coating.
• Outside surface of straw is laminated with 4
  bundles of carbon-fiber filament to improve
  electrical/thermal conductivity and mechanical
  strength.
• Straw material has been tested in for radiation
  hardness in nuclear reactor up to
• g 800kGy (100 LHC years)
• Fast n 4x1014 cm-2 (20 LHC years)
• Slow n 1.7x1015 cm-2 (30 LHC years)
• Anode ageing was tested to withstand
• 18 C/cm (20 LHC year)

Enforcement carbon-fiber bundle
9
Wire Wire Joint

• Wire
• 30 0.3 mm gold plated tungsten wire
• Wire joint
• Glass capillary tube
• Length 6mm
• OD 250 um
• ID 125 um
• Melted at center to isolate 2 wire segments
• Insert wire segments.
• Sliding torches fuse glass to wire segments
• Stronger than wire itself

Wire/Glass fusion
Center-melt
Glass Holder
Torch
10
Radiator

• Stacks of polypropylene fiber sheets
• Fiber is 15 mm diameter
• Packed to 66 mg/cm3 density
• Somewhat oriented and orthogonal to incident
  particle

Optimal TR threshold
Foil
Fiber
200um
11
Divider Radiator patterns
Divider Ear Fixation hole to assembly
frame. Trimmed off later

• Kapton-foam sandwich
• Align straws along module every 25 cm

12
Carbon-Fiber Shell
Cooling Tubes

• Structural support for module.
• Heat exchanger for module cooling

Kapton lamination
Holes for Divider ears
13
High Voltage Plate

• Made of 3 parts
• Precision machined FR4 tray
• Kapton circuit in the back
• Thin HV circuit pattern in the front
• Bring HV to straws
• Position straws in the module
• Mount module to support structure
• Individual traces tested to 3kV

14
Tension Plate

• Double sided PC board
• Holds wire tension
• Connect wires to electronics
• House gas fittings for gas system

Gas fitting
15
Small Parts
Mid-Wire Support
Twister

• Centers wire at middle of the straw

End Plug

• Center wires at the end of the straw
• Electrically connect inside and outside of a
  straw through conductive glue

Taper Pin
Eyelet

• Wire fixation on tension plate

Capacitor Barrel

• Isolate capacitor from gas volume so that it can
  be replaced
• Partially transfer wire tension from Tension
  plate to HV plate

16
Construction of Barrel Modules

• Starts with checking alignment elements
• Shell, HV plates, Dividers are pre-assembled in
  the calibrated assembly frame on optical table.
• 9 fiducial straws inserted, and their
  straightness along the module measured with laser
  alignment system.

17
Laser alignment data
18
Insert Radiator Divider into shell attach HV
plate
Assembly Frame
Radiator
Alignment Rods
Guiding Platform
Divider Fixation Pins
3kV tested between HV plate Shell
19
Insert Straws

• Use straw insertion bullet
• Guide straws through holes in HV plate, radiator
  divider
• Protect straw re-enforcement carbon fiber strips
  from de-lamination
• To avoid deforming radiator
• Spiral insertion sequence, from center outward
• Alternate insertion direction every straw
• After insertion
• Test Individual straw group to 2.5kV

Short straw buffer
Mylar Sleeve
Delrin Head
20
Conductive Glue

• Use endplug to glue straws from inside to outside
  and to HV plate
• Measure straw resistance after gluing each side
• HV test each straw group to 2.5kV before and
  after gluing each side

Glue dispenser
Rotor
End Plug
A ring of Conductive glue
End plug holder
After gluing one side
After gluing both sides
21
Seal between High Voltage Plate and Straws
3 plastic syringe tip
Glue Divider

• Seal around straw end-plug and HV plate surface
  with AY103

• Pot back side of HV plate 2.4 mm thick with
  Stycast 1266.

22
End of Mechanical Assembly
Leak test system

• Clean up
• Check cooling tube holes with gauge rod
  (rim/clean as needed).
• Clean capacitor socket for blockage
• Clean excessive glue on HV plate walls
• Clean gas fitting seats on HV plate
• Check
• HV test (last at 2.5kV)
• 2.5kV through each individual straw group
• Module leak test
• lt 1 mBar / Bar / min

Gas seal plate fitting for leak test
HV Tester
HV Relay box
23
Assemble/Attach Tension Plate

• Tension plate assembly
• Thousands of components assembled each plate
  thousands of possible leak
• Eyelets, Sockets, Capacitor barrels, Gas
  fittings.
• Seal inner surface with a layer of glue (AY103)
  for gas tightness
• After tension plate attached, check HV paths
  continuity between Kapton traces and Capacitor
  pins.

HV trace
Capacitor barrel pin
24
Stringing Sense Wire
Ultrasound bath

• Prepare sense wire
• Pre-set sense wire length for wire joint
  positioning in the straw.
• Stringing process
• Blow a lead wire through straw.
• Tie lead wire with sense wire (a knot)
• Pull sense wire into straw through an ultra-sound
  cleaner
• Apply weight and pin wire on eyelet

Wire Joint Stop
Crimp on wire length setting anchor
Wire Spool
65 gm
Preset length
60 gm
Air
Air
Motorized Lead Wire Spool
Weight applying pulley
Lead Wire
25
Tension Measurement HV Test

• While stringing
• Measure wire tension.
• Re-string if out of range (55gm-85gm) .
• After stringing
• HV test 1700V each wire
• Re-string if failed or
• drawing gt 10 mA
• Rework until all wires pass HV tension
  requirements.

Ultrasound bath
Speaker
DAQ Electronics
Wire natural resonant frequency scan
26
Mobile16-Channel Tension Tester

• After re-work
• Measure wire tensions on both sides.
• Re-work if low tension (lt50gm )
• Re-work if front back gt 5gm
• (wire joint hits mid-wire support)

Front side
Back side
27
Finishing Up Module
Conductive gluing ground wire to shell
Seal taper pin/eyelet
Seal tension plate edge to HV plate
Ground Wire
Seal Shell holes with Kapton disks
Solder Ground wire To tension plate ground
28
Module Passport Verification

• On X-ray Scanner
• Signal test to ensure every channel functional,
  or documented if otherwise.
• Gain map 25 positions each wire segment. Gain
  variation lt 5 or documented
• HV soaking during signal test gain mapping (2-3
  days) identifies/remove unstable wires record
  current draw
• Re-work wires if removed wires gt 1.

• Measure ionization volume leak rate
• Measure purging volume leak rate
• Measure wire tensions.
• Check Dimension Envelope
• Test module mounting

29
X-ray system for signal test gain mapping
W target X-ray
Slit Cu foil filter
Fe55
DAQ
Rotation Mounting Ring
Slides
30
Signal Test Example
Wire shorted across wire-joint
A normal channel but picking up noise from the
shorted wire
31
Gain Mapping Examples

• DG/G gt 8 wires require action

Front
Back
Front
Back
No Action
Low gain point Dirty wire
High gain point between dividers Bent straw
Remove wire
Front
Back
Front
Back
Replace wire
High gain point at wire end Wire hung at end
plug twister
Replace wire
High gain point at wire end Wire hung at mid
twister
32
Summary

• QC procedures are in every step of production
  procedures.
• A QC passport is generated before a module
  leaves production site.
• Module production is near its completion. 10
  modules have been completed and shipped to CERN
  in the past month or so.
• In early 2004, modules will begin to assemble
  into barrel support structure.