Micro Channel Cooling at the GTK

1. Micro Channel Cooling at the GTK Georg Nüssle & Alex Kluge

2. NA62 Gigatracker demands The NA62 experiment proposes to study a very rare Kaon decay at the CERN SPS. In order to track the high intensity Kaon beam before its decay a set of three high precision silicon pixel detector planes has been proposed (GigaTracKer - GTK). In the current layout three hybrid silicon pixel detector layers will be operated in a high fluence environment and provide precise tracking and timing information. The GTK modules will operate in vacuum and under high radiation, which will damage the sensor. So it has to be replaceable with a reasonable effort on a yearly base. This requires an efficient cooling system, which however must be very low mass in order to avoid degradation in the performance and efficiency of the detector. The highest allowable operation temperature for the readout chip has been set to 5°C. A lower operation temperature is desirable. The use of microchannel cooling directly on the chip or on the cooling/support plate seems very promising.

3. NA62 Gigatracker demands Cooling/Support plate Readout Chip Sensor The GTK module will consist of: • one silicon pixel sensor (60x200 mm) • bump bonded to 2 x 5 readout chips (12.5 x 20 mm), heat dissipation ca. 3.2 W per chip • a carbon cooling/support plate with high heat conduction • support and alignement structure outside of the beam area schematic sketch of the GTK module

4. Micro-Evaporators: Basic Geometry and Flow Stabilization EPFL Lausanne, Prof. Thome

5. LTCM/IBM Micro-Evaporator Test Section in Silicon Si microchannel evaporator: • Channel widths: 200, 100, and 50 microns • Manifolds: 1 inlet/1 outlet or 1 inlet/2 outlets • Slits at inlet create orifices that prevent flow instabilities and generates bubbles to avoid temperature overshoot • Can be bonded to top of microprocessor • Cobra Heater on backside of silicon chip: • Simulates heat dissipated by a microprocessor • Better measurement accuracy • Lower thermal resistance to evaporation surface • 5 RTD sensors along channel length, span across 1/3rd of width (red arrow) Channel Orientation on backside of chip EPFL Lausanne, Prof. Thome > 200 W/cm2

6. GTK-CoolingwithMicrochannels • Microchannels in Si supportplate: • Channel cross section: 50 x 50 microns • Manifolds: inlet and outlet outside the sensor area • In sensor area channels are covered by a thin foil • Thermal contact to readout chips via thermal grease or ‘liquidmetal’ (liquifiesunderelectricity) schematic sketch of the GTK module

7. A 3D computer chip with integrated cooling system is expected to: • Overcome the limits of air cooling • Compress ~1012 nanometer sized functional units (1 Tera) into one cubic centimeter • Yield 10 to 100 fold higher connectivity • Cut energy consumption and CO2 emissions drastically • A new $4million consortium project lead by Prof. Thome

8. Work ongoing at EPFL in two institutes • LTCM, Heat and Mass Transfer Laboratory • Microsystems laboratory • CERN DT

9. Advantages Micro channelcooling • Uniform temperaturedistribution in thesensorarea • Less thermal stress • Technology knownat EPFL, Transfer toourapplicationhastobedone • Support by CERN PH-DT todevelopthistechnology

10. Radiation lengthforsensor The total material budget (material in the beam) allowed fot the GTK module is 0.5% X0(radiation length). In the current proposed layout the material inside the beam area will consist of the ones listed in the table with values for the radiation length and hence their thickness.

11. Cooling proposals and simulations until now PCB convective cooling in a vessel: VESSEL WALL GTK module will be encapsulated in a vessel and will be cooled via a gas flow of cold nitrogen. The vessel will have Kapton windows for the beam to pass through. VESSEL FRAME • good cooling • gas leakage into beam vacuum? • high flow rate > vibrations? COOLING PLATE HEAT FLUX ELECTRICAL CONNECTIONS DETECTOR

12. Cooling proposals and simulations until now conductive cooling via a carbon plate: GTK module will be cooled via a carbon plate with high heat conduction. On the carbon plate the heat will be extracted outside of the beam area by a pipe with liquid or two-phase cooling. • non-uniform temperature distribution • thermal stress in the module? • known technology in vacuum MAX THERMAL CONDUCTIVITY