PMG Meeting February 2000 A Split Central Silicon Tracker W. E. Cooper on Behalf of the D0 Silicon Group 3 February 2000

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PMG MeetingFebruary 2000

A Split Central Silicon Tracker

W. E. Cooperon Behalf of the D0 Silicon Group

3 February 2000

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Motivation

The baseline D0 silicon tracker uses a 66” long carbon-fiber / epoxy cylinder to support and align the barrel and F-disk modules.

Each end calorimeter can normally be opened 39” from its closed position.

That limited motion prohibits installation and removal of a 66” support cylinder in the collision hall and requires installation of the central silicon from the south in the assembly hall.

To eliminate those restrictions, we have begun investigating the possibility of splitting the central silicon into two halves about z = 0.

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Potential Benefits

The ability to install or remove silicon with the detector in the collision hall

The ability to install and begin testing one half of the silicon while the second half is being completed

Better internal alignment of silicon within one cylinder half

Added flexibility during upgrade installation

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Tracker Region

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Central Silicon Installation in the Baseline Design

ECS is off the platform; ECN is open 39”

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Proposal under Investigation

Split the support cylinder into two pieces, each ~33” long

We believe that the present support cylinder can be completed and then divided into two halves.

Support each piece at its outer end from CFT barrel 1 as before

A ring is used to connect the end of the support cylinder to the end ring of CFT barrel 1.

Support each piece at its inner end, near z=0, from the inner surface of CFT barrel 1

Carbon-fiber reinforcement would be added to the inner surface of CFT barrel 1 to control out-of-round distortions.

Beam-like transverse deflections should be acceptable (<1 mil).

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Installation Space

Both EC’s are shown withdrawn 39”. The beryllium beam pipe has been moved

39” to the left of its normal position Sections of beam pipe outside the EC’s

have been removed to allow the pipes through the EC’s to be withdrawn 39”.

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Installation Space

One possible cable arrangement during installation

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Positioning and Alignment

Near z=0, radial support from CFT barrel 1 is proposed at ±45o from 6 o’clock. A limiting or spring loaded radial support may be provided at 12 o’clock.

The half-length support cylinders will be installed and positioned within CFT barrel 1 at Lab 3.

Reference spheres on each half-length cylinder will be measured.

The z=0 measurements will require care. Either the Hamar laser alignment system or the Lab 3 LK could be used.

Absolute precision is expected to be ±20 m near z=0.

Precision from one half to the other is expected to be ±10 m near z=0.

The support cylinders will be moved to SiDet for silicon installation.

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Support at z=0

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Issues

This would be a major undertaking. We will need to be sure that it works and that backup plans are in place should there be complications.

Alignment at z=0 is critical and would need to be done well.

Handling Each silicon half, including support

structures, cooling manifolds, and the portion of cables in that region weighs about 20 LB.

The cables extending from the support cylinder along the CC face weigh another 30 LB per silicon half.

Proper support and means of guiding the cables will be needed.

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Issues

Beam pipe Temporary fixturing will be needed to

position the beam pipe while allowing it to be moved longitudinally.

Protection will be needed to ensure that the beam pipe will not contact silicon.

Cooling Presently, two lines supply coolant

from one tracker end and two lines return coolant from the other. Coolant manifolds run the full length of the silicon tracker.

We will need two supply and two return lines at each end. Separate manifolds will be needed for each tracker half.

Engineering Additional engineering effort will be

needed.

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Acknowledgements

Many of the ideas proposed for positioning and alignment came from Hans Jöstlein.

Many considerations in the design came from discussions among members of the D0 silicon group and the D0 upgrade.

Documents

PMG Meeting February 2000 A Split Central Silicon Tracker W. E. Cooper on Behalf of the D0 Silicon Group 3 February 2000