Mechanical design

1
Mechanical design

• Geoff Barber,
• Pete Cooke,
• Peter Hobson
• Joe Walding
• presented by KL

2
Developments during Tracker workshop

• Contents-
• New Station Layout
• Light Guide Map
• Station Connectors
• Patch Panel Connectors
• Progress at Liverpool
• Assembly Area
• Fabrication Plan
• Measurement of mechanical properties of fibre
• Quality assurance procedures first thoughts

3
New Station Layout

• The new station layout has a total of 30
  connectors, 10 per view. Each connector has 22
  holes instead of the previous 18 but all of these
  are not used in every connector (this is shown in
  the light guide map).

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Light Guide Map
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Station Connectors

• This is the new Station connector. The
  re-design will allow for easier assembly of the
  detector. We still need to carry out light
  transmission tests on this connector but cannot
  see any reason why it should perform less
  efficiently than the previous square connectors

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Patch Panel Connectors
This is the 128 way patch panel connector. It is
designed to maintain a vacuum in the bore of the
cryostat The 128 channels make it a match for
the VLPC cassette. All the routing of the fibres
takes place inside the chamber.
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Patch Panel
This is the the patch panel model. It is not the
definitive model as detailed drawings will be
required to mate it to the magnet. This model
gives space for 26 connectors, as only 25 are
needed the 26th opening can be used for field
monitoring services.
8
Progress at Liverpool
This sequence shows the station mould being
produced in the Liverpool workshop
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Assembly Area
The area is now empty and will be painted next
week. It will then be made light tight and
kitted out for the assembly of the stations.
This will give us a spacious (relative) area for
the production line.
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Fabrication Plan

• This is an outline of the tasks required to
  assemble the stations. It needs to be expanded
  and QA systems put in place. When all is agreed
  an assembly document can be compiled.
• Receive the planes from Fermilab
• Inspect the planes to ensure that they have not
  been damaged in transit
• The fibres are then grouped into sevens and
  rubber sleeves fitted
• The plane is then fitted onto the vacuum chuck
  and aligned
• The vacuum chuck is transferred onto the assembly
  jig
• The first plane is glued onto the station and
  allowed to cure
• The second plane is then aligned on the vacuum
  chuck
• The vacuum chuck is transferred onto the assembly
  jig
• The second plane is glued onto the station and
  allowed to cure
• The third plane is then aligned on the vacuum
  chuck
• The vacuum chuck is transferred onto the assembly
  jig
• The third plane is glued onto the station and
  allowed to cure

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Fabrication Plan pt2

• The station will now need the connectors fitted
• The centre fibre (this should be marked) is
  fitted in the correct position
• The fibre bunches are then fitted sequentially
  into the connectors
• When a complete plane is threaded the fibres
  are tidied up
• This plane is then potted using vacuum to pull
  epoxy through the holes
• This procedure is repeated for the other 2 planes
• When the epoxy has cured the station is taken to
  be diamond polished
• It should now be possible to conduct a series of
  tests to ascertain its final quality
• This is not exhaustive and will be added to
  during the coming weeks

12
Fibre shrinkage and the force it exerts on the
carbon fibre rings.

• Shrinkage due to water diffusion out of the
  fibres
• Orientation of the fibres allows the
  approximation that the force is uniformly
  distributed about the rings
• Results are for normal optical fibres,
  scintillating fibres will be tested in due course
  (fibre diameter 220 ?m)
• The optical fibre is used to get a feel for the
  magnitude of the force and the time constant of
  the contraction

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Experimental method

• Two stages to the experiment
• Young's Modulus of the fibre is found
• A fibre in an evacuated chamber and a control
  fibre are run simultaneously and the relative
  shrinkage is observed
• Applying Hookes Law a force on the ring can be
  calculated

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Set-up

• Two 1.5 metre steel tubes containing the fibres
• A Vernier Telescope is used to read the position
  of the fibres
• The left tube is the control whilst the right one
  is evacuated using a standard vacuum pump to a
  pressure of 5x10-2 mbar (5 Pa)
• The two Perspex viewing cylinders
• The clamps hold the fibres under tension
• NOTE The scintillating fibre will be run under
  light that is non-damaging to the fibre

15
Results

• Youngs modulus found to be 2.2x10100.2x1010Nm-2
• The contraction for the fibre with 2.38g
  suspended from it was 15030µm
• This gives a force/fibre of 0.080.02N

• Note The results are NOT for the scintillating
  fibres but as their only difference is a small
  level of a fluorescent dopant it is expected that
  they will behave in much the same way

• Fig. 1 Shear Stress vs. Shear Strain, the
  gradient of which corresponds to Youngs Modulus

• Fig. 2 The contraction of the fibre against time
  (hours), the dotted lines refer to the value of
  the contraction and its upper and lower bounds

• Each frame supports 4473 fibres therefore the
  total force exerted will be 36090N

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Conclusions

• This result has with it a large error but it
  gives a sense of the force involved one whose
  magnitude is such that it cant be ignored
• To get around this the fibres could be stored in
  evacuated crates prior to assembly. As the time
  constant for contraction is of the order of days
  exposure to air for small periods of time should
  not have any adverse affects but a dry
  environment would be ideal for fibre handling
• This treatment of the fibres would also get over
  the problem of fibre slippage whilst the glue is
  drying

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QA for fibres Brunel University

• Method to assist with fibre identification before
  putting into bunches of 7
• Assist with QA of fibres once in connectors
  (breaks, relative light yield)
• Provide precision optical assembly and 400 mm
  precision stage and associated control system for
  QA laboratory.

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Scanning Light source

• Excite the 3HF fluorescence with light around 390
  nm.
• Use low average power to preserve fibre secondary
  fluorescence.
• Excite group of 7 fibres in two planes then step
  to next 7 etc.
• Still at the concept stage, but simulations
  underway, and tests on fibre planned for soon
  after end of August.

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ZEMAX-EE simulations
Virtual source
True 3D simulation (non-sequential). Includes ray
splitting, polarisation, scatter and absorption
effects. Horizontal lines through fibres on this
view are detector planes to measure the energy
passing through the mid-planes of the
fibres. Cuboid volume represents the inter-plane
glue.
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ZEMAX-EE simulations
Power crossing the midline of the upper 4 fibres.
Energy in gap doesnt excite these fibres (but
does excite the bottom row) A lot of optimising
to do to get the best discrimination for the
lower row and to understand what sort of
illumination would be best (e.g. narrower but
more collimated etc.)
Fibre
Gap
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ZEMAX-EE simulations
Power crossing the midline of the upper 4 fibres,
with much more collimated illumination. Basic
simulation principle developed and it doesnt
seem to be a priori impossible.
Upper 4
Light inside fibre
Lower 3