Pixel Support Tube Requirements and Interfaces - PowerPoint PPT Presentation

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Pixel Support Tube Requirements and Interfaces

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Pixel system and beam pipe integrated together on surface ... beam pipe bake-out in situ with B-layer in place. access to any part of pixel detector requires ... – PowerPoint PPT presentation

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Title: Pixel Support Tube Requirements and Interfaces


1
Pixel Support TubeRequirements and Interfaces
  • M.Olcese
  • PST CDR CERN Oct. 17th 2001

2
Assumptions
  • Pixel system and beam pipe integrated together on
    surface and installed as a package.
  • Prerequisites
  • beam pipe bake-out in situ with B-layer in place
  • access to any part of pixel detector requires
    removal of the whole pixel detector, to bring
    it to the surface this requires
  • an ID installation/removal shutdown
  • breaking of the vacuum

3
Outline and Definitions
  • PST is a cylinder about 7 long, 480 mm OD,
    coaxial to the beam pipe, going all the way
    through the ID volume and closed on the beam pipe
    at the two ends with two end plugs
  • PST main functions are
  • allowing an independent installation and removal
    of pixel detector with all the rest of ID in
    place
  • supporting the Pixel detector, the services along
    the beam pipe and the beam pipe itself
  • keeping the pixel volume thermally and
    electrically independent from the rest of ATLAS
  • all the pixel services have to pass through the
    two end plugs

4
PST Requirements major categories
  • mechanical
  • environmental
  • electrical
  • service penetration
  • installation of pixel package

5
PST mechanical requirements
  • geometry and envelopes
  • support conditions
  • alignment
  • assembly
  • stability
  • operating loads

6
Envelopes
  • Radial envelopes PST-SCT defined and agreed
  • Z-envelope in the end region still undefined
    this is driven by pixel service connections, PST
    end support, polymoderator geometry.
  • envelopes account for shape errors, deflection
    under load in the case of forward PST, the
    envelope has to account for gravity sag with no
    support at the ends and with the pixel system in
    place (VI section of beam pipe included)
  • envelopes do not account for relative motions of
    different blocks and adjustments

7
Interface to SCT barrel
  • Recent decision to have an independent thermal
    barrier for the barrel SCT
  • this implies
  • more schedule flexibility
  • no temporary thermal barrier for x-ray testing of
    SCT barrel
  • possible adjustment of PST in pit without opening
    the SCT thermal barrier
  • PST structurally independent from SCT thermal
    barrier
  • concept and geometry of the 4 PST support
    penetration through the SCT thermal barrier have
    been defined and agreed

8
Support conditions internal
9
Support conditions external
10
Beam pipe supports
  • There are four internal supports 1 external
  • all the 4 internal supports are remotely (outside
    the end plug) adjustable in X,Y
  • the adjustment range is /- 9 mm (nominal
    clearance B-Layer/beam pipe)
  • however this will be mechanically limited to /-
    5 mm for the two internal supports by means of
    hard stops on the B-layer structure. This will
    avoid in any condition the risk of collision with
    the B-layer modules

11
Alignment
  • The PST central section has to be as much as
    possible coaxial to the theoretical beam axis
    (TBA) this allows for the max adjustment
    flexibility of the beam pipe wrt pixel B-layer
  • emergency X,Y adjustments of /-3 mm of the PST
    after ID is in place will be allowed within the
    PST barrel envelope.
  • They are going to be used only in case of
    macroscopic (surveyable) misalignment. However
    this might not be enough to accommodate all
    foreseeable errors.
  • The /-3 mm X,Y adjustments are not included in
    the forward PST envelope and they have to be
    accounted in the 9 mm gap

12
Assembly
  • PST is split in three parts (one barrel and two
    forward) for assembly reasons
  • assembly sequence
  • A. the barrel PST is installed on surface inside
    the barrel SCT on nominal centre
  • B. if necessary,after the barrel ID is in place
    the barrel PST is adjusted to theoretical beam
    axis
  • C. the two forward sections of PST are connected
    and PST is adjusted wrt the ID rails on cryostat
    wall if necessary
  • D. the forward SCT and TRT are slid in, the PST
    end supports are installed and connected to the
    PST

13
Stability
  • PST is an intermediate support structure in
    between SCT and Pixel detector.
  • The support points of Pixel detector - PST are
    located very close to the PST-SCT supports
  • natural stability requirement for the PST is
  • to provide a link between SCT-PST-Pixel support
    points as stiff as possible with a stability of
    the same order as the one of Pixel detector. Max
    gravity sag Pixel wrt SCT fixed points should be
    about 20 mm, this is equivalent to a first mode
    at 80 Hz
  • to minimize the perturbation of the pixel and SCT
    stability due to operating loads
  • thermal deformations,
  • change of relative positions
  • vibration of forward tube and services
  • the injection of such loads is function of the
    stiffness of the PST, of the support conditions
    at the end of PST and of the beam pipe support
    conditions

14
Operating loads
  • As function of the support conditions of PST and
    beam pipe, 4 design load cases are identified

() Note that these are based on assumptions from
current models
15
PST environmental requirements
  • Pixel volume has to be maintained
  • cold (modules at 0 C)
  • dry (to avoid condensation)
  • dry and clean conditions are achieved by means of
    a continuous N2 flow (about 0.5 m3/h) entering at
    one side and going out from the opposite side
  • cold conditions are maintained by the internal
    cooling system however the gas temperature is not
    controlled. The design range of the gas
    temperature is -10/10 C
  • PST has to be designed as a thermal and gas
    sealed enclosure which will separate the internal
    pixel volume from the rest of ATLAS. The max
    leak rate budget is determined by the nitrogen
    flow and a nominal overpressure which has to be
    maintained in the pixel volume of 5 mbar
  • the whole PST external surface has to be actively
    heated (Tgt 15 C) to prevent condensation some
    areas during operation others during access

16
PST active heating scenarios
17
PST electrical requirements
  • Pixel detector need to be shielded as efficiently
    as possible from the external sources of
    electromagnetic noise
  • a Faraday cage has to be built around the
    detector
  • the most natural solution is to have an built-in
    Faraday cage on the PST
  • this will be implemented with a continuous thin
    Al layer. Special care will has to be paid in the
    connection areas to achieve a good electrical
    continuity of the shielding
  • electrical requirements indicate a suitable
    thickness range 50-100 mm
  • it is not clear yet whether the Faraday cage has
    to be extended along the beam pipe outer surface
    inside the pixel volume

18
PST service penetration
  • This is a very congested area with many
    constraints
  • all the services need to be broken here
  • beam pipe has to be floating wrt the end plugs
    and free to be adjusted to /- 9 mm (but
    practically limited to /-5 mm, see previous
    comment)
  • tube feed throughs will have to be axially
    floating to minimize the axial loads on Pixel
    detector due to temperature change.
  • External environment is in principle cavern air
    (dew point about 10C), actions will have to be
    implemented to avoid condensation on cold tubes
    and surfaces

19
Pixel package installation requirements
  • The Pixel package is lowered into the pit inside
    an Integration Testing Tool (ITT)
  • the ITT has to be aligned to the PST for the
    insertion same tool used for other ID parts?

ITT
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