1. 1 VI Single-wall Beam Pipe Option: status and plans M.Olcese TMB June 6th 2002

2. TMB: CERN June 2002 M.Olcese2 Double Vs. Single Wall Design  Same heater  Same outer envelope  Same reflective layer (moved outside)

3. TMB: CERN June 2002 M.Olcese3 Implications  beam pipe design is simpler and less expensive  less material: total % of radiation length of the single wall beam pipe 0.49 vs. 0.56 of current baseline  We can get rid of the vacuum pumping line (beneficial impact on services and on the design of ID end plate)  beam pipe strength still adequate (see calculations presented at the bp review)  moderate impact on current beam pipe design: we basically remove the outer wall and the inner wall and flange design remains unchanged  The aluminized kapton encapsulation might be useful to effectively close the pixel Faraday cage  increased axial displacements of the non fixed wire supports and gas seal bellows to be accounted for

4. TMB: CERN June 2002 M.Olcese4 Proposed thermal insulation  Nano-porous Silica Aerogel in flexible quartz fiber carrier Very low thermal conductivity: 10-12 mW/mK Very low density: 0.09-0.12 g/cm3 Radiation length: 250 cm (worst density) Resistant up to 600 °C Contains: mostly inert materials Si oxides, quartz fibers, not sensitive to irradiation Can be tailored to specific requirements: carbon opacified, doped with hydrophobic agents

5. TMB: CERN June 2002 M.Olcese5 Thermal Analysis: the approach  A full simulation of the heat transfer from the heater through the insulation and the nitrogen gap to the B- layer has been done  All the three heat transfer mechanisms (conduction, convection and radiation) through the gap have been considered  Effect of a beam pipe offset up to a max of 5 mm has been analyzed  Effect of non uniform convective heat transfer has been estimated  Assumed boundary conditions: Beam pipe bake out temperature = heater temperature = 250 °C Temperature of the B-layer surface = 0 °C (max operating temperature of B-layer modules)

6. TMB: CERN June 2002 M.Olcese6 Average Thermal Analysis: the Results  The temperature of the beam pipe surface facing the B-layer is not an issue: what matters is the heat flux, which is determining the B-layer thermal conditions  total heat flux to the B-layer is about the 6% of the nominal capacity of the B-layer cooling system, so it should be handled with no problem Total out coming heat flux (W/m) Temperature on the outer surface of the beam pipe insulation (°C) conductionconvectionradiationtotal No radiation 56600116 100 Max radiation 342885 147 61

7. TMB: CERN June 2002 M.Olcese7 Local effects and beam pipe offset  Conduction and radiation are uniform in , while the convective heat flux varies significantly with  his is due to the non  symmetric flow pattern in the gap  I have found an article on an experimental study in equivalent conditions (in terms of characteristic dimensionless Ra number). The proposed correlations lead in our case to a max local heat flux 2.6 times higher than the average (on the top).  Other experimental studies show that the influence of the beam pipe offset up to 5 mm produce a change of both the average and local heat flux of less than 10% The worst case heat flux, which the top B-layer stave will have to dissipate during the bake out is 10 W (9% of nominal cooling capacity) conclusion

8. TMB: CERN June 2002 M.Olcese8 Thermal Conditions of the B-layer Modules  The major difference between normal operation and bake out is that in normal operation the heat is produced in the electronics while during the bake out is coming through the flex  FE-chips and sensor are very well thermally coupled (same temperature) FE chips sensor Flex hybrid direction of heat flux and temperature gradient during the bakeout Beam pipe Carbon-carbon tile Cooling channel

9. TMB: CERN June 2002 M.Olcese9 Thermal Conditions of the B-layer Modules, Cont.  There is a stack of thermal impedances from the module surface and the cooling tube  In normal operation the sensor temperature is maintained below 0 °C with coolant temperature of about –20 °C  during the bake out the temperature gradient between the sensor and the coolant will be far below (factor of 6), i.e. about 3 °C  The temperature on the flex hybrid (the hottest module part) would be about 4 °C above the sensor temperature  The temperature distribution in the b- layer modules will be almost uniform during the bake out: it will be sufficient to keep the coolant T at about –7 °C to have the whole module below 0 °C ° -7 ° C ° -4 ° C ° 0 ° C 0.7 W/module

10. TMB: CERN June 2002 M.Olcese10 Qualification test plan  Qualify the Aerogel insulation to our specific application. Two parameters to be investigated: Radiation hardness in terms of mechanical properties Radiation hardness in terms of thermal properties  Make a full test of the thermal conditions in the gap B-layer/beam pipe on a mockup as close as possible to the proposed solution to validate the thermal analysis

11. TMB: CERN June 2002 M.Olcese11 Thermal tests on insulation: the setup Samples to be tested with black Al layer to create a uniform surface Heated Al Plate thermocamera non irradiated sampleIrradiated sample Thick insulating screen

12. TMB: CERN June 2002 M.Olcese12 Thermal tests on insulation: the results  No visible mechanical degradation after irradiation  Surface temperature difference of about 6 °C (4% of the total  T across), small and might be due to non uniformities material rather than to the irradiation  No surface temperature change after squeezing the samples with 2 N/cm2 Aerogel sample with polyester fiber carrier and thickness of 2 mmAerogel sample with polyester fiber carrier and thickness of 2 mm Sample irradiated up to 60 MradSample irradiated up to 60 Mrad We observed DT across the insulation = 170 °C  The material is mechanically radiation hard (although we tested the polyester carrier type, more sensitive than quartz)  The thermal conductivity might be not affected at all or only marginally by the irradiation and by a possible accidental pressure on the insulation we conclude

13. TMB: CERN June 2002 M.Olcese13 Thermal tests on real scale mockup  Same beam pipe geometry  Proposed insulation with aluminized kapton encapsulation  Dummy B-layer cold structure Tube cooled and maintained at a T = 0 °C Insulating plug Beam pipe with heater and insulation  During the bake out we want to measure: the total heat flux going through the gap to the B-layer The temperature distribution on the outer surface of the insulation (this can then be correlated to the local heal flux) 1000 mm

14. TMB: CERN June 2002 M.Olcese14 Next steps  validate the calculations on a real scale prototype (end of June beginning of July)  check the radiation hardness of silica aerogel with quartz fiber carrier and at higher doses: end of June, but need to check where and what source  Verify feasibility of kapton encapsulation (ongoing discussion with the beam pipe group: seems not to a a problem)  Study design changes to be incorporated in the current baseline: redesign the support collars, assess the design impact on the wire supports