Mechanics, Status, and Plans for VXD Module Development

1. Mechanics: Status and Plans (Layer 1) Bill Cooper (Fermilab) VXD

2. Considerations and Status • Overall layout • Developed last spring • Existence proof for a reasonable track-trigger geometry • Provides guidance on module dimensions, module mechanical infrastructure, arrangement of stacks, cooling, and rod lengths • Module mechanical design • We are waiting for guidance from prototype submissions and input on interposer design parameters. • Module and rod assembly • Aimed at allowing parallel fabrication at multiple locations. • Allows decoupling of R&D on single-stacks, double-stacks, services, rods, and rod support. • Support disks for rod arrays • Concept specific, so R&D on this has been deferred. • Cooling • Evaporative CO2 cooling is assumed. • Analysis and prototyping • Given CMS and Fermilab approval, we can start on finite element analysis and prototyping in a few weeks. • Guidance we received and have followed • Concentrate R&D on aspects which relate to a local track-trigger, that is, on sensor modules and services. • Defer R&D on overall geometry and support, which tend to assume a particular scheme for implementing a track-trigger. • Defer R&D on cooling systems, which will be developed by others. Track-trigger Meeting – 15 September 2009

3. Overall Layout • The overall R-Z layout from last January is shown below. • Maximum rod length is about 2.77 m for sensors of cut length 98 mm. • The suggestion has been to limit rod prototypes to about 1 m. • I would prefer not to leave prototyping of full-length rods too late • Measurements of prototypes would confirm that deflections related to ply angles of the carbon fiber laminate agree with predictions and ply angles are appropriate for the finite element thermal analyses. R-Z view Track-trigger Meeting – 15 September 2009

4. R -  Layout • Existence proof for one concept of a track-trigger • All five layers of the left side are shown below. • Central radii of silicon range from 278 to 1126 mm for the left side. • Radii for the right side are 6 to 9 mm smaller. • The number of  locations is an even multiple of 8 for each layer (both sides identical). Track-trigger Meeting – 15 September 2009

5. Z = 0 Overlap • One possibility for overlaps in layers 1, 2, and 5 is shown. • In this case, carbon fiber support structures of rods of the two sides are aligned transversely and notched back to allow overlap of sensors and interposers. • Longitudinal clearance ~ 2 mm. • Transverse clearance ~ 3 mm, but the clearance needed will be determined by rod deflections as they are installed and rod installation tooling. Track-trigger Meeting – 15 September 2009

6. Finite Element Analysis (FEA) • Requisites • Effective thermal conductivities and dimensions of interposer materials • Power dissipation and locations at which power is dissipated • Working assumptions of rod dimensions • Locations and dimensions of material layers which thermally insulate • Selection of carbon fiber pre-preg for support structures and determination of the laminate thickness and fiber direction within each laminate layer • Given that information and the assumption that the temperature of a cooling tube surface is uniform, FEA should be straight-forward. • Heat flux from the surrounding air would be ignored during the first pass and early iterations. • At least one FEA expert at Fermilab could begin work roughly a week after the effort is approved by CMS and Fermilab. • Cooling tube sizing • The surface area of a cooling tube determines its effectiveness as a heat sink, thereby indirectly constraining the minimum tube size. • The heat flux, wall thickness, and coolant properties determine the validity of the assumption of a uniform wall temperature. • Coolant flow rate, heat input over the cooling tube length, and allowed coolant pressure drop impose additional constraints on the cooling tube size. • We should anticipate that the FEA will be iterative in order to take into account improved knowledge of heat sources, material thicknesses, laminate ply directions, cooling system requirements, and rod geometry. • Perhaps 0.5 FTE x 6 weeks for the first pass, 0.5 FTE x 4 weeks for subsequent iterations, depending on the extent of changes Track-trigger Meeting – 15 September 2009

7. Proposed Plan for Thermal FEA • Proposed initial assumptions: • Assumptions are based upon dimensions developed in spring 2009. • A continuous interposer (no openings to reduce mass) with silicon thermal-mechanical properties • Openings can be added to the FEA when their locations and shapes are known. • Thermal FEA may set limits on the numbers and sizes of openings, and features needed to augment heat conduction with openings. • Interposer dimensions = 93.25 mm x 96.5 mm x 1 mm • Sensor dimensions = 98 mm x 98 mm x 0.3 mm • Uniform power dissipation of 4.5x10-4 W/mm2 over the full extent of each sensor • Details of power sources and their locations can be added when they are known. • Rod box structure outer transverse dimensions of approximately 41.5 mm wide x 40.4 mm tall • K13C2U carbon fiber pre-preg for support structures • Ply directions as suggested last spring: quasi-isotropic in modules, favoring the longitudinal direction in rods • Stainless steel cooling tubes with OD = 2 mm, ID = 1.3 mm • Carbon fiber laminate sheathes to position and hold cooling tubes • Locations and dimensions of material layers which thermally insulate need to be known early. Track-trigger Meeting – 15 September 2009

8. A Reminder of the Rod Mechanical Fabrication Sequence • Each piece needs to be prototyped and tested. • The assembly needs to be prototyped and tested at each stage. Track-trigger Meeting – 15 September 2009

9. Prototyping • Goals • Structures which allow: • Realistic geometries to be developed for interposers, modules, and rods • Measurements of heat flow, shielding and grounding, rod precision, and rod stiffness • Requisites for rod and module prototyping • Selection of carbon fiber • Mandrels • Engineering and drafting support • Technicians and an autoclave or equivalent to fabricate CF parts • Tooling, technicians, and access to a CMM for assembly and testing • Cooling tube sizing • Carbon fiber • We have enough K13C2U fiber for a few module prototypes, but will need to purchase fiber for larger structures. • K13C2U fiber cost has varied with time. • Typically $1500 per pound with a minimum, cost-effective order of about 15 pounds • Past deliveries have taken 4 to 6 weeks, but delivery times as long as 12 to 16 weeks cannot be excluded. • Mandrels • We have often used aluminum for first pass mandrels and then switched to carbon steel for later prototyping and production. • Mandrel and tooling design and fabrication efforts could be shared with universities that have engineering resources and good access to machine shops. Track-trigger Meeting – 15 September 2009

10. A Few Prototyping Details • Mechanical support structures have been intentionally kept simple. • It may be possible to fabricate initial prototype modules with minimal fixturing. • Basic requirements: • Module surfaces should be flat and parallel. • Material thicknesses should be adequately controlled. • Voids in adhesive layers should be minimized. • Transverse alignment should be well-controlled. • Flat sheets of carbon fiber laminate should be straight-forward. • Depending on the required features, at least two methods are available to make module pieces from sheets: • Shearing • Cutting on a CNC machine such as one of the Thermwoods in Lab 8 • Interconnections and cables may complicate fabrication. • Long term, automation should be considered and module fixturing consistent with the required precision and through-put should be developed. • Tooling for rod components • We have typically utilized internal mandrels for shapes of comparable transverse dimensions. • That should be fine for early prototypes. • However, external mandrels should produce smoother and flatter surfaces on which modules would be mounted. • Developing external mandrels and procedures for carbon fiber laminates will take R&D. • We will need to understand mandrel stiffness and support. • We will need to understand cable and access openings and how to cut openings in the rod “boxes”. Track-trigger Meeting – 15 September 2009

11. A Few Prototyping Details • The equivalent of an autoclave can be fabricated from tubing or pipe plus end-closure heads. • Heat tape with a controller can provide an adequate temperature versus time profile. • Through-put from a given mandrel set is limited by the temperature cycle of the laminate cure, which takes up to five hours. • Production fabrication would benefit if it were distributed over multiple locations. • Prototyping provides an opportunity to develop expertise at multiple locations. • We have not discussed it, but I suggest that the University of Rochester, other interested institutions, and Fermilab work together to develop mandrels, autoclave equivalents, and other fabrication and assembly tooling. • Until the transition to experiment-specific designs, we may want to defer work on support disks and their prototyping. • Temperature distribution studies would be aided by an evaporative, CO2 cooling system. • Development of a closed-loop system at Fermilab had been planned, but has been delayed. • We may need to use an open-loop system for testing of prototypes, though a closed-loop system should provide better temperature stability. Track-trigger Meeting – 15 September 2009

12. In Summary • We are prepared to assist with interposer and module mechanics. • We would begin finite element analyses and prototyping as soon as the effort is approved. • Distributing the effort among CMS institutions would allow expertise to be developed in specific fabrication techniques and help ensure that good facilities will be available for production. Track-trigger Meeting – 15 September 2009