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  ![](media/image1.wmf){width="0.9326388888888889in"   Pixel Detector                           
  height="0.975in"}                                    Mechanics Conceptual                     
                                                       Design Review                            

  ATLAS Project Document No:                           Institute Document No.  Created :        Page: **1
                                                                               **24/06/2001**   of** **2**

  ATL-IP-ES-0018                                                               Modified :       Rev. No .:
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Table of Contents

1 Introduction [4](#introduction)

2 Dimensions and Envelopes [4](#dimensions-and-envelopes)

2.1 Disk Support Rings [6](#disk-support-rings)

2.2 Layer 1 and Layer 2 Barrel Shells
[6](#layer-1-and-layer-2-barrel-shells)

2.3 B-layer Support Shell. [6](#b-layer-support-shell.)

2.4 Mounts To SCT [6](#mounts-to-sct)

2.5 Services [7](#services)

2.6 Services Support Panels [7](#services-support-panels)

2.7 Pixel Support Tube [7](#pixel-support-tube)

3 Final Assembly [7](#final-assembly)

4 Survey Requirements [7](#survey-requirements)

5 Load Conditions, Stability and Analysis
[8](#load-conditions-stability-and-analysis)

6 Other Requirements [9](#other-requirements)

7 Materials [9](#materials)

8 Qualification Tests [10](#qualification-tests)

8.1 Material Coupon Testing [10](#material-coupon-testing)

8.2 As-built Dimensions [10](#as-built-dimensions)

8.3 Load Tests [10](#load-tests)

8.4 Assembly Test [10](#assembly-test)

9 Quality Assurance [10](#quality-assurance)

# Introduction

![](media/image2.jpeg){width="4.7340277777777775in"
height="2.670138888888889in"}The global support frame consists of a
flat-panel space frame in three sections - a barrel section and two,
identical disk sections as shown in Figure 1. These sections are joined
to make the complete frame.

Figure 1. ATLAS Pixel global support frame, which consists of three
sections - barrel and two disk sections. The barrel and two disk
sections are shown joined on the left. One of the support cones for the
barrel shells is shown in the right model.

Included in the barrel section are two End Cone supports for the barrel
shells as also shown in Figure 1.

A complete prototype disk section of the global support frame has been
fabricated and tested. A prototype of an End Cone is under fabrication
and test.

The three sections of the support frame and the two End Cones will be
fabricated by a vendor under contract to LBNL.

# Dimensions and Envelopes

The current baseline dimensions of the global support frame are shown in
Figure 2. Detailed envelopes will be addressed later in the creation of
fabrication drawings for the global support sections. The current
envelopes for the radial dimensions of the global support exceed the
nominal by 0.5 mm both on the inner and outer surfaces. The envelope for
the total length is also 0.5mm(each side) greater than the nominal
dimension

![](media/image4.wmf)

Figure 2. Current baseline dimensions of the barrel and disk sections of
the global support frame.

The current baseline dimensions of the End Cones are shown in Figure 3
and Figure 4.

![](media/image5.png){width="4.125in" height="2.65625in"}

Figure 3. Current baseline dimensions of the End Cone, side A.

![](media/image6.png){width="4.125in" height="2.65625in"}

Figure 4: Current dimensions of the End Cone, Side C.

# Interfaces

The principal interfaces to the global support frame are (1) the disk
support rings; (2) the Layer 1 and Layer 2 barrel, stave support shells;
(3) the B-layer support shell; (4) the mounting structure to attach the
global support frame to the SCT barrel structure; (5) services(cables
and pipes) from the modules mounted on the barrel staves and disk
sectors; (6) services support panels that hold services within the pixel
support tube; and (7) to the pixel support tube(PST).

## Disk Support Rings

Interfaces to the disk support rings are covered in the Technical
Specification for the Disk Support Rings.[^1]

## Layer 1 and Layer 2 Barrel Shells

Interfaces to these shells are covered in the Technical Specification
for the Layer 1 and Layer 2 Barrel Shells.[^2]

## B-layer Support Shell.

\*\*Eric can you provide something eg. a figure for this and some short
text. If we don\'t know just say not defined at this time.\*\*\*

Figure 5. B-layer shell interface region.

## Mounts To SCT

The global support frame is attached to the SCT barrel structure at four
locations. The mounting conditions are shown in Figure 6(\*\*\*Eric
please provide\*\*\*).

Figure 6. Support conditions for the global support frame attached to
the SCT barrel structure.

A preliminary definition of the dimensional interfaces to the SCT
structure are shown in Figure 7(\*\*\*Eric please provide figure and
short text if needed\*\*\*).

Figure 7. Dimensional interfaces of the global support frame to the SCT
barrel structure.

## Services

Barrel electrical services and coolant piping run from the ends of the
bi-stave assemblies across the support cone, through a gap between the
barrel and disk sections of the frame, and then along the outside of the
disk sections of the frame. Disk electrical services run along the
inside of the disk sections of the frame. Strain relief fixtures will be
attached to the endcones and to the disk sections using a regular array
of PEEK inserts for support of the fixtures. The location of these
inserts is fixed for the End Cone(see Figure 3 and Figure 4) but remains
to be determined for the disk frame sections.

## Services Support Panels

Services support panels hold cables and pipes inside the PST and slide
with the global support frame inside the PST during installation or
removal. There is a mechanical connection between each end of the global
support frame and the service panels so that they may slide together
inside the PST. The design of this interface does not yet exist. The
fabrication of these interfaces pieces is the responsibility of LBNL,
not the vendor manufacturing the global support frame.

## Pixel Support Tube

The global support frame slides on four riders attached at the ends of
the frame on the detector V- and flat-rails inside the PST. The design
of this interface does not yet exist. The fabrication of these riders is
the responsibility of LBNL, not the vendor manufacturing the global
support frame.

# Final Assembly

The End Cones and barrel shells are mounted in to the barrel section of
the support frame. No design exists yet for the tooling and procedures
needed for this assembly step. The disks are mounted into the disk
section and the disk sections are joined to the barrel section as
illustrated in Figure 8).

![](media/image7.wmf)

Figure 8. Illustration of the method for joining the barrel and disk
sections of the support frame.

An initial conceptual design for the procedures necessary to mount the
disks and to join the disk and barrel sections has been done and is
illustrated at <http://www-atlas.lbl.gov/~goozen/assdetset.html>.
Attachment of tooling for barrel and disk assembly, and for joining the
barrel and disk sections, will be made to the corner blocks in the frame
sections shown in Figure 8Figure 8.

# Survey Requirements

The locations of the pixel modules must be referenced to the mounting
structure connecting the global support frame to the SCT barrel
structure. This is to be done in multiple steps

-   Modules referenced to the local supports(staves and disk sectors)

-   Local supports referenced to the intermediate supports(barrel shells
    and disk rings)

-   Intermediate supports referenced to the global support frame - to
    survey references mounted in or attached to the corner blocks in
    each section

-   Support frame referenced to SCT mounts after final assembly of the
    barrel and disk sections.

The procedures, survey markers and tools for accomplishing the surveys
referenced to the support frame have not yet been developed.

# Load Conditions, Stability and Analysis

The conceptual analysis of the Global Support frame has been completed.
The objective of the analysis was to confirm that reducing the frame
dimensions from the original baseline did not invalidate the extensive
analysis and prototype testing conducted previously. This task was
accomplished.

Stability requirements are estimated assuming a maximum of 20%
degradation in the (rms) φ, R or Z measurements. The \"stability
budget\" is arbitrarily apportioned among the local supports(staves or
sectors), intermediate supports(shells or rings) and the support frame.
Tolerances are assumed to be √12 x the rms value. In the barrel region,
the apportionment is 8:1:1 for stave, shell and frame, respectively. In
the disk region, it is 1:2:4 for sector, ring and frame, respectively.
The tolerance(rms) values are given in Table 1.

The recent analysis[^3] of the Global Supports conceptual design
specifically addressed gravitational loading, dynamic stiffness, and
torsional stiffness. Gravitational sag is of concern in the context of
maintaining detector alignment. Dynamic stiffness on the other hand
quantifies the susceptibility of the detector to unforseen vibration.
Torsional stiffness is assessed to ascertain what level of disturbance
is required to twist the detector assembly. The final Global Support
configuration incorporated end plate stiffening panels to provide radial
stiffness in the plane of Pixel to SCT support. The total mass of the
structure and non-structure mass derived from the FE model was 28.89kg,
with the two end plate stiffeners being 0.25kg.

+----------------------+-----------------------+-----------------------+
| Stability Item       | Tolerance(rms) in     | Analysis              |
|                      | microns               |                       |
+----------------------+-----------------------+-----------------------+
| Radial and lateral   | Disk: 200(58)         | Gravitational         |
| motion -"R"          |                       | sag-11.5μm; response  |
|                      | Barrel: 5(1.5)        | to random vibration   |
|                      |                       | in R \<\<1μm (lateral |
|                      |                       | motion suppressed by  |
|                      |                       | frame end plate)      |
+----------------------+-----------------------+-----------------------+
| Tangential           | Disk: 24(7)           | ϕ-position set by     |
| motion-"ϕ"           |                       | planarity and         |
|                      | Barrel: 1.8(0.5)      | rigidity of the frame |
|                      |                       | 4-point support;      |
|                      |                       | detector twist with   |
|                      |                       | 1-support point       |
|                      |                       | removed is 53.5μm     |
+----------------------+-----------------------+-----------------------+
| Axial motion-"Z"     | Disk: 425(122)        | Thermal length change |
|                      |                       | \~1.4μm/°C            |
|                      | Barrel: 14(4)         |                       |
+----------------------+-----------------------+-----------------------+

Table 1. Stability tolerance(rms) values for barrel and disk regions and
estimates of frame motions.

Internally, relative positional change between the pixel disks and the
barrel detector elements is controlled by using materials with very low
coefficients of thermal expansion (CTE), in most cases approaching zero
CTE. Temperature control of the evaporative coolant system, ensures
virtually no change in length or radial position between the pixel
sections, the disk array and staves. Initially, the detector will
potentially expand in length 56μm when cooling from room temperature to
-15°C, thereafter the sensitivity in Z to a change temperature is less
than 1.4μm/°C. Consequently, from outer disk array to outer disk array
for a 5°C change (cyclical in time, short term periodicity) the detector
stability is within 7μm, well within the stability limit of 425μm for Z.
Radial positional changes due to the same effect is much less. Time
varying, spatial temperature changes that cause bending of the frame
have not been address. This effect is anticipated to be within the
required limits because the global CTE effect is small. This effect will
be evaluated once the Pixel Detector system is completely defined.

The detector vibration stability without reinforcing end plates is
marginal. If exposed to a harmonic input of 0.01G's the detector motion
would be less than 10μm laterally, and 2.82μm *rms* if subjected to a
random vibration. The response may grow to an unacceptable amount if the
fundamental mode dropped to roughly 30Hz. The non-structural mass from
services, strain relief, etc., is expected to increase above the current
assumed values, during the preliminary design phase. An increase in
non-structural mass impacts frame dynamic stiffness, lowering the frame
fundamental mode. To offset this prospect, end reinforcment plates were
added to raise the fundamental mode to 89Hz, above potential vibration
sources. These plates, at this stage of our design formulation, ensure
vibration will not be a stability issue, unless non-structural mass
grows out of expected proportions. Of equal importance, these plates
simplify the design of the connection between the Global Support frame
and the Pixel Detector Support tube.

# Other Requirements

The sections of the global support frame will be coated with
Parylene(0.008-0.012 mm thick) after fabrication to contain conducting
carbon dust or fragments.

# Materials 

The materials of construction to be used in constructing the Global
Support frame and sub-components will use commercially available
composite materials. The outer frame, end cones, and end plate
reinforcement panels use a sandwich construction. All sandwich facings
will use very high modulus pitch based graphite fibers for maximum
stiffness. Prototype frame tests were conducted with a quasi-isotropic
panel composed of XN80 (Nippon) fibers and EX1515 cyanate ester resin
from Bryte Technology. (It appears that Nippon is replacing the XN fiber
series with their new fiber series, designated YSH). Recent prototpyes
have been constructed with the YSH 50, a replacement for XN50 and M55J.
Results of the prototype tests were satisfactory and met our
expectations. Table 2 lists the materials chosen for the Global Support
frame.

Table 2. Global Support Frame Materials

  ------------------------------ ----------------------------------------
  Global Support Frame Item      Material

  Outer Frame                    

  Sandwich Facings               YSH90 unitape with RS3 or EX1515 cyanate
                                 ester resin, quasi-isotropic laminate

  Honeycomb Core                 XN50 woven cloth/cyanate ester resin, by
                                 YLA Cellular, 6.35mm cell, density
                                 48kg/m^3^

  Vertex Corner Mounts (frame    YSH50 woven cloth and RS3 cyanate ester
  section connections)           resin laminate

  Corner Tubes                   YSH90 unitape and RS3 cyanate ester
                                 resin

  Corner Splice                  YSH90 unitape and RS3 cyanate ester
                                 resin

  Vertex Joint Inserts           Aluminum

  End Cones                      

  Sandwich Facings               YSH90 or P30cyanate ester
                                 quasi-isotropic laminate

  Honeycomb Core                 XN50/cyanate ester resin, by YLA
                                 Cellular, 6.35mm cell, 48kg/m^3^

  Inner and Outer Mounting Tabs  YSH50/RS3 cyanate ester

  End Plates                     Same materials as end cone

                                 
  ------------------------------ ----------------------------------------

# Qualification Tests

Qualifications tests are to be performed by the fabrication vendor on
materials to be used in the ring construction and on each ring after
fabrication. LBNL will also perform qualification tests.

## Material Coupon Testing

Tensile test coupons will be cut from a sample of the laminates (0.43mm
thick) prepared for the sandwich facings. Tensile tests, for tensile
modulus and strength, will be performed to ASTM D3039. No specialized
tests are planned for solid laminate material (4mm thick) used in the
support tabs and mounting connections.

## As-built Dimensions

The fabrication vendor will measure the as-built dimensions of the
subcomponents(flat panels, etc) before assembly of the individual frame
sections. The as-built dimensions will also be measured by the vendor
and cross checked by LBNL.

## Load Tests

A static load will be performed on each completed outer frame section.
The test will be a simple cantilever test, to 1.5 times the required
load transfer between frame sections. The test will verify the
structural integrity of the composite construction.

A separate static load test of the complete outer Global Support frame
will be performed. Non-structural mass equivalent to 1.5 times design
load will be added to the frame, at the appropriate Z locations. The
static load test will verify the structural design and validate the
fabrication quality.

## Assembly Test

A trial assembly of the endcones to the barrel section and of the disk
sections to the barrel section(with endcone) will be done by the
fabrication vendor and by LBNL. It is planned to have a trial assembly
of the intermediate supports into the support frame as well.

# Quality Assurance

The fabrication vendor will provide a quality control plan to LBNL as
part of the fabrication contract.

###  {#section .unnumbered}

####  {#section-1 .unnumbered}

[^1]: ATL-IP-ES-0025, \"Technical Specification for Pixel Detector Disk
    Support Rings\". June 2001.

[^2]: ATL-IP-CS-0007, \"Specification for Barrel Layer 1 and 2 Support
    Structures\", November 2000.

[^3]: W. O. Miller, Structural Analysis of ATLAS Pixel Detector Global
    Support Frame-432mm Envelope, HTN-106210-0002, HYTEC, Inc., dated
    May 18, 2001