Microchannel Cooling

1. MicrochannelCooling D. Bouit, J. Daguin, A. Jilg, L. Kottelat, A. Mapelli, J. Noel, P. Petagna, G. Romagnoli– CERN PH-DT K. Howell – Georges Mason University / CERN PH-UFT G. Nuessle – UniversitéCatholiquede Louvain / CERN PH-UFT A. Pezous- CSEM P. Renaud – EPFL-LMIS4 E. Da Riva, V. Singh Rao, P. Valente– CERN EN-CV October, 28th 2011, CERN NA62-GTK special meeting on cooling options

2. Basic concept: couple to the heat production region a thin silicon layer structured with m-channels, where coolant is circulated • ADVANTAGES: • Low material budget • High thermal stability • High thermal uniformity • High efficiency (low fluid-sensor DT) • Easily adaptable to changing conditions • Conventional single phase cooling plant

3. Main conditions to be met by a candidate cooling system as defined by NA62 GTK 1 Cooling System Requirements Absorption of nominal dissipated power ~100% Stabilization of detector temperature ~5 C Surface temperature uniformity ±3 C Material budget 0.15% Xo 2 Operation Aspects Meeting stable temperature Reaction time to power failure Reaction time for hydraulic failure 3 Integration Aspects Preliminary integration design Assembly operation sequence Test Plan 4 Cooling System Details Conceptual Design Cost Estimate Radiation Effects Infrastructure Requirements In the following presentations we will cover this list of conditions and prove that m-channel cooling is indeed a solid and satisfactory option for application to the NA62 GTK

4. Sequence of talks: • Microfabrication: design and production (Mapelli) • Experimental analysis of the thermal performance (Howell / Nuessle) • Optimization of the geometrical configuration (Da Riva / Singh Rao) • Electro-mechanical integration (Jilg / Romagnoli) • Cooling plant (Valente) • Radiation effects (Nuessle)

5. Microfabrication • Micro techniques involved • Design • Process flow • Final geometry • Potential commercial partners • Cost estimate

6. Thermal performance Sample cooling plates following a first proposed design have been produced in-house (EPFL CMI) and tested for thermal performance. The production process is fully under control and the produced plates prove to be reliable. An extensive testing activity has been performed in realistic conditions: • Power absorption • Temperature stability • Temperature uniformity • Reaction to failures Initially designed under the assumption of a uniform power distribution over the surface of the sensor assembly, the cooling plates have been successfully tested again more realistic conditions of uneven power distribution between the digital and the analog part of the chip. Due to inherent limitations of the cooling station available for the tests, the thermal performances have been analysed up to ~ ½ the nominal flow rate and ~ ½ the nominal power distribution. A simple extrapolation allows for an exact forecast of the performance under nominal conditions

7. Geometrical optimization The tests performed on sample cooling plates produced with the “design 0” geometry showed their fully satisfactory behaviour with respect to the specifications on the thermal performance. However, there is space for further optimization towards material budget reduction and reliability enhancement (structural safety factor). This has been accomplished through a detailed CFD analysis. • Manifold geometry optimization (pressure drop and flow uniformity) • Channel cross section optimization (pressure drop and material budget) The CFD optimization performed brings to an optimized geometry with double inlet / double outlet and minimized channel depth (i.e. enhanced performance, larger structural safety margin and reduced material budget). Cooling plates based on the new optimized design are presently under production.

8. Electro-mechanical integration The geometry produced by the CFD optimization has been integrated with the detailed understanding of the production cycle and led to a final cooling plate configuration. This configuration has been implemented in a full 3D CATIA model of the GTK module and a complete study of the electro-mechanical integration of the module has started. • Concept of integrated module • Precision / repeatability issues during production • Study of the jigs required for the production • Preparation to the prototyping phase The integration concept moves from the experience of the Totem Roman Pots, and LHC detector with several similarities to the GTK. The integration process proposed appears feasible and solid. A first prototyping phase has now been launched.

9. Cooling plant The proposed microchannel cooling is based on a conventional single phase refrigeration plant. With a sound production, integration and operation process available, it is possible to correctly define the specifications for the cooling plant and therefore launch its definition. • Local infrastructure • Cooling plant specification • Cooling plant draft P&I • Cost estimates The proposed cooling plant falls into the category of standard design and production already managed by CERN EN/CV-DC. All components and solutions are standardized on the basis of the LHC experimental cooling plants. EN/CV will be available to follow the production of the final cooling station as well as it maintenance and operation.

10. Radiation effects The monophase cooling fluid circulating in the cooling plate will be placed directly in the primary beam, downstream of the target. Although the selected fluid (C6F14=FC72), largely adopted in LHC experiments, has been certified to be stable under irradiation, some questioning about the possible level of activation and the related impact on access and maintenance operation has been raised. A preliminary study has been performed by RP. • Preliminary activation study of FC72 Although the study is still in a preliminary phase, as not all the detailed information required for a more accurate analysis is available yet, all indications point towards vey low activation levels, negligible for all scenarios of access and maintenance.

11. CONCLUSIONS • A fully reliable production technique for Si m-channel structured cooling plates suited for application in the NA62 GTK has been individuated • A first design proposed for integration in the module (“design 0”) has been thoroughly tested for thermal performance in realistic conditions and proved to be fully compliant with respect to the specification proposed (temperature stability and uniformity, reaction to failures) • A CFD optimization study led to the definition of new geometry (“design 1”) enhancing the thermo-hydraulic performance, reducing the material budget and increasing the structural safety margin. Cooling plates based on the new design are presently in production. • The optimized geometry (“design 1”) have been implemented in a full CATIA model of the GTK module and a full electro-mechanical integration study has been launched. • The specifications for the cooling station have been defined and a preliminary design study has been performed by EN/CV-DC

12. THE PROPOSED COOLING PLATE Flat coupling (direct adhesive gluing) to the sensor assembly Dual inlet/outlet and manifolds (additional thickness) outside the sensitive area PEEK connectors Minimized material (double sided local thinning) on the sensitive area 130 mm Average material budget in the sensitive area: X/X0 =0.11% (min 0.1%, Max 0,14%)