1. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC ATLAS Meeting ATLAS Meeting August 12, 2008 University of Santa Cruz Cooling System Work Marco Oriunno, SLAC

2. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Carbon Dioxide is under consideration to replace fluorocarbon as a refrigerant fluid for the upgrade of the ATLAS inner detector (Pixel/Strips) Direct advantages inside the tracker volume compared to the present fluorocarbon based system: Lower temperatures easily achievable O(-50 o C) -> high protection against the risk of thermal runway Higher refrigeration capability -> smaller pipes (integration/material budget) Reduced mass flow per refrigerated power -> pressure drops & pipe size Compact cooling system plant Distinctive features: High standstill pressure (10÷60 bars) Natural gas, not flammable, dielectric and not toxic Negligible Global Warming Potential and Ozone Depletion Impact Fluorocarbons will be soon banned, the refrigeration industry has started the CO2 Rush as the next refrigeration standard. Considerations I

3. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Although the CO2 advantages are acknowledged, there is not yet any official endorsement of CO2 cooling system for ATLAS Several groups are already working on cooling calculations, but only few experimental installations are available only in Europe: NIKHEF, Liverpool both with basic blown systems CMS also has expressed interest in carbon dioxide cooling for the Tracker upgrade: CERN plans to organize few one-day technical forums starting next October. On the path of growing the ATLAS upgrade effort at SLAC, the involvement of SLAC in the CO2 cooling project has a two-fold advantage : it is a complement to the US ATLAS activities and encourages the growth of user presence on the site. To develop the possibility of a SLAC involvement took an explorative trip on week June 23-27 : One day meeting at NIKHEF to discuss ( with Nigel and Georg) the ATLAS cooling needs, technical visit of the CO2 Blown system. Meeting with the CMS engineers involved in the CO2 upgrade to establishing communication, plan to exchange information to solve common problems Technical Visit at CERN of the CO2 plant of LHCb VELO detector, running stable at -30 o C Independent private discussions with the ATLAS colleagues based at CERN (Neal, Vic, Andrea, Christophe) on the features of the present cooling system and various integration aspects Attempt to take the most updated and unbiased picture of the ATLAS cooling upgrade project Considerations II

4. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC STEP 1, Development of a blown CO2 plant with small refrigeration capacity, Unavoidable move to coalesce people and resources around the project Characterization of the boiling parameters and the heat transfer Pipes characterization under high pressure: materials, sizes Thermal test of small detector prototypes from other US ATLAS group STEP 2, development of a real vapor-compression plant with larger refrigeration capacity, few kW : a non trivial extrapolation of the previous exercise. Test of full scale stave/disk prototypes Characterization of components : capillaries, heat exchangers, evaporators Parallel activity, Participation to the definition of specs for the upgraded cooling plant: Thermal issues detector related : mat. budget, heat transfer, pressure drops Plant design: choice of compressors, heaters, heat exchangers, piping, integration. SLAC PLAN

5. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC SLAC PLAN, details (*) (*) To be consolidated after real knowledge of the %effort of people involved. I counted myself at 100% which is not the case at the present Today 08.12 Start experimental Data Procurement Launch $ $ $

6. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC

7. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Step 1, The Blown System The maximum refrigeration power is limited and defined by a reasonable time to swap the CO2 cylinder: for 10 watts are needed 0.085 g/s, i.e. 80 hours continuously Start with a dummy heater on a ¼” pipe to commission the system at few mg/s Boiling heat transfer studies : Several mathematical models available for different boiling regimes Very scarce data in the open literature Effect of evaporator shape and surface material finishing Pressure drop studies with different evaporator shapes and sizes Thermal test of stave module detector prototypes: thermal resistance fluid-sensor

8. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Step 2, A medium size vapor-compression cycle As soon as large size stave prototypes become available in the US ATLAS community, the blown CO2 plant must be upgraded to a medium size vapor-compression plant of ~10kW The design will require some time because of the several details to be proper addresses The safety and installation issues will require also more attention and time The financial investment will be more important Such architecture may well be adopted for the ATLASup ID, therefore it is worth to start to look at general technical solutions which can be scaled up or down for both systems.

9. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC We have started think about the global architecture of the final cooling system Many options and variants are possible using CO2 : 1.Adopt the same design as for the fluorocarbon, but at least try to improve the known weak points 2.Adopt a modified vapor-compression cycle (trans critical cycle) 3.Adopt a completely different solution, similar to the LHCb VELO, with an Accumulator Pressure Loop Performances and costs for all the options should be fairly compared before to make the final choice but it could be a long process. We need soon a document with the minimal functional requirements of the cooling system upgrade : heat loads, temperature range, radiation environment, tracker opening scenario, B-layer insertion, beam pipe bake out, thermal barriers and controls. Such document should be brief and leave out the technical solutions as much as possible. ATLAS ID cooling plant, first thoughts

10. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC At the present we consider the option 1, the less steep to climb because : 1.It is a well proven scheme in refrigeration industry for large installation 2.There are not practical limitations to the refrigeration power ( worth to recall that ATLAS ID-up is close to 0.25 MW) 3.Allow naturally the reliable location of the plant in a radiation protected environment 4.Minimize the integration space through warm transfer line 5.Long time experience and trained people in the ATLAS community 6.The factorial risk increase innovating on fluid and cooling plant architecture at the same time, i.e. know how, people and costs. Since we believe that a vapor-compression remains after all a good solution for the ATLAS ID upgrade, exploring the conceptual design for such a system, not only will provide some preliminary answers but also the guidelines for the Step 2, a medium size vapor-compression cycle. ATLAS ID cooling plant, first thoughts

11. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC ItemPower (kW) Pixel10 Barrel Strips70 Disks50 Heat losses20 TOTAL150 Total with safety factor 250 CO2 plant with unchanged C3F8 architecture CO2 plant with upgraded architecture Heaters and Heat Exchangers outside tracker volume Heat loads expected

12. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Global architecture

13. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Estimated Performances Distinctive features: Low mass flow Low volumetric flow None or light sub-cooling but in the experimental cavern Heater and/or heat exchanger outside the cold volume Significant increase of the condensers capacity Higher gas rejection temperature at the compressors

14. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Parameters of adiabatic capillary flow: Inlet pressure of sub cooled liquid … pin = 58 bar Inlet temperature of sub cooled liquid … Tin = 18°C Capillary tube inner diameter … ID = 0.60 mm and 0.80 mm Relative inner wall roughness: ε ID = 0.003 ID=0.6 mm ID=0.8 mm Capillaries Capillaries are fully passive devices and therefore are the most reliable devices to drop pressure inside an inaccessible and harsh environment. Length very dependent on several parameters like inlet conditions and mass flow Preliminary simulations done by Vic Vacek, CTU Prague (private communication) confirm that the final capillary length for CO2 is not so different form C3F8 ~2-3 meters V.Vacek

15. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC The high standstill pressure of the CO2 (~60 bar) is generally raising questions and concerns about the size and the reliability of pipes and connectors One should note that high pressure piping with ~ 150 bars and beyond, are routinely handled in large chemical process plants with a satisfying level of reliability and safety Of course this should not relax the effort of to design the pipe work in very detail, especially of the part inside the cold volume, which will not be anymore accessible after the sealing and the irradiation Pressurized piping must be compliant with the code ASME B31.3 where the material grades, the minimum wall thickness and the allowable stresses are given as function of pipe diameter and the design gage pressure. For straight pipe under internal pressure the minimum wall thickness is given by: Where d is the inner diameter, P the design pressure, S the allowable stress, Y, E and W are coefficients depending on the quality of the material. The following figures show the size of the pipes for the two cases of high pressure (60 bar) and low pressure (10 bar) : High Pressure and piping Copper Steel Al Copper Steel Al

16. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC We can adopt for CO2 the same distribution used for the C3F8. The Inner detector is subdivide in four quadrant fed independently by a  30/34 mm liquid line and a  72/76 mm vapor line. Distribution racks fan in to ~ 50 liquid lines  4/6 mm and fan out  18/20 mm vapor lines. The racks contain also the pressure and the back pressure regulators valve which set, independently for each channel, the mass flow and the evaporation temperature Pressure drops calculations pressure drops

17. Santa Cruz, August 12 th 2008 UPGRADE M.Oriunno, SLAC Conclusions Plan to develop at SLAC an US ATLAS CO2 cooling facility Blown CO2 system in construction -> expected to run end of September Larger plant in design phase, main components have been sized Preliminary calculations shows that for the final ATALSup ID, adopting CO2 in a vapor-compression cycle similar to the present plant running with C3F8, is feasible and offers many advantages due to the better physical properties of CO2. It provide also enough margin to eliminate the weak points shown so far by the present C3F8 system It fit well in super high irradiated environment like SLHC It minimize the unavoidable take of risk stemming from the adoption of too many technological unknowns.