1. NA62-GTK special meeting on cooling options
Microchannel Cooling
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 – Université Catholique de 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)
Self-adapting to changing conditions
Conventional single phase cooling plant
M&O by proximity team (EN/CV for the plant and PH/DT for the assembly replacement)

3. Main conditions to be met by a candidate cooling system as defined by NA62 GTK
1 Cooling System Requirements
3 Integration Aspects
Absorption of nominal dissipated power ~100%
Preliminary integration design
Stabilization of detector temperature ~5 C
Assembly operation sequence
Surface temperature uniformity ±3 C
Test Plan
Material budget 0.15% Xo
4 Cooling System Details
2 Operation Aspects
Conceptual Design
Meeting stable temperature
Cost Estimate
Reaction time to power failure
Safety and reliability issues
Reaction time for hydraulic failure
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: Overall design and production (Petagna)
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 / Battistin)
Safety, reliability, failure prevention (Nuessle)
Summary (Petagna)

5. Microfabrication
Microfabrication technologies are derived from the microelectronics industry. They comprise a wide variety of techniques used for manufacturing micro-devices. In the last decades, they have been widely used to manufacture micro-electro-mechanical systems (MEMS) and microfluidic devices.
These devices are typically made out of silicon wafers but other types of substrates are commonly used such as plastics and glasses.
Common steps in microfabrication comprise photolithography, thin films deposition and structuration, etching, thinning by grinding and chemical mechanical polishing (CMP), bonding, and dicing.
Microfabricated cooling plates are presently under investigation in our team for the upgrade programmes of the ALICE ITS and the LHCb VELO

6. Final cross section of the cooling plate
Channels =200 x 70 mm
Wall thickness = 200 mm
Cover thickness = 30 mm
mm Silicon = % X0
(above and below channels)
mm Silicon = % X0
(between channels)
70 mm C6F14 = % X0
30 mm epoxy = % X0
Acceptance
10 mm Pyrex = % X0
(removed in final production)
Total material budget in the acceptance area = X0%
(min 0.011% - Max 0.015%)

7. Final top shape of the cooling plate
Optimized geometry for minimal pressure drop with double inlet / outlet
Operational pressure at nominal flow rate ~ 7 bars
(see presentation of E. Da Riva)

8. Estimated cost of the final cooling plate
Silicon Fusion Bonded cooling plates (All silicon devices with no Pyrex).
About 1.5 kCHF / cooling plate for 20 plates with such offers…

9. Cross section of the vehicle for thermo-hydraulic tests
Channels =100 x 100 mm
Wall thickness = 100 mm
10 x Silicon thickness between channels and heat load with respect to the final device: all thermal test results are conservatives. Test device with “thinned area” hydraulically tested
525 µm
Pyrex
60 µm
380 µm
Same structural critical point than the final device: 100 mm thick silicon cover over a 1.6 mm wide channel: operated without damage at 12 bars and tested to withstand > 18 bars

10. Operational pressure at nominal flow rate > 12 bars
Top shape of the test vehicle in use
Simplified geometry for ease of production and test with single inlet / outlet
Operational pressure at nominal flow rate > 12 bars

11. Thermal performance Power absorption Temperature stability
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 80% the nominal flow rate. A simple extrapolation allows for an exact forecast of the performance under nominal conditions

12. 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 prototypes based on the new optimized design are presently under production.

13. 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. The most critical issue, the gluing of the sensor assembly to the cooling plate, is being now directly tested in realistic conditions.

14. Cooling plant Local infrastructure Cooling plant specification
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. The system is designed with full redundancy in order to minimize its downtime. EN/CV will be available to follow the production of the final cooling station as well as it maintenance and operation.

15. Safety, Reliability, Failure prevention
The concept is robust against system failures with extremely limited control needs.
The microfabrication procedure is now consistently producing highly reliable devices.
A sound assembly concept is being developed to maximize the yield during integration.
Preliminary studies performed by RP rule out any concern about fluid activation.
Local vacuum monitoring interlocked to shut-off vacuum valves will be introduced for each GTK station for a timely action in case of highly unlikely accidental leaks.
Safety, Reliability and Failure prevention issues
The proposed cooling is highly reliable in operation and only requires extremely limited “slow controls”. No problem is expected by RP due to the irradiation levels. All details of the assembly procedures are being worked out and tested on realistic mock-ups in order to maximize the yield during the final module integration.

16. 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, etc)
A CFD optimization study led to the definition of new geometry (“design 2”) 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 2”) have been implemented in a full CATIA model of the GTK module and a full electro-mechanical integration study has been launched. Tests on ad-hoc produced mock-ups ongoing.
The specifications for the cooling station have been defined and a preliminary design study has been performed by EN/CV-DC

17. SUMMARY: 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
All inclusive average material budget in the sensitive area: X/X0 =0.13%
(min 0.11%, Max 0.15%)
(Might finally go down to 0.11%)

18. SUMMARY: GLOBAL COST AND AVAILABLE TEAM
Finalization of a few “design 2” prototypes
Completion of the integration studies
Construction of assembly/integration jigs
Small items and contingency
… …….20 kCHF
Outsourced production of 30 “design 2” cold plates
…….…….50 kCHF
Cooling plant
(Design, production and commissioning: M&O
Included in the M&O agreement with EN/CV)
……………………………………………………………………180 kCHF
TOTAL
……………………..……………………………………………………250 kCHF
PH/DT team (including technicians) available for module production and assembly / integration
EN/CV team available for cooling plant design production and commissioning
Availability to launch the activity: as from NA62 decision

19. OPTION: R&D ON “FRAME CONFIGURATION”
R/O chips
Acceptance
No CTE b/t Si chips and Si frame
Adhesive thermal interface
Silicon
(ALICE’s test cooling plates)
A detailed study about the “frame” configuration (similar to the one ongoing for ALICE ITS) can be launched as from January. However this would require additional resources:
30 kCHF for cold plate prototyping / testing and to adapt the module integration procedure
Ideally, procurement of a few “flip-chip” silicon thermal mock-ups (CSEM investigating this)
CFD support from EN/CV team to be discussed