1. A two-stage system for the future cooling system

2. 2 What do we want to achieve? (in addition to achieving T evap and P) Re-use the existing transfer pipework. → warm transfer pipes (need heaters, maybe HEXs?). Minimize complexity of cooling system close to detector → robustness Potentially faulty (complex) objects should be accessible. Minimize possibility of single point failures: look for simplicity and compartmentalization. Minimize on-detector material –Minimize x in → minimize mass flow → minimize ID, –Minimize pressure → minimize wall thickness. Minimize space needed by cooling system components and services inside ID.

3. 3 A two stage system Primary (plant) stage: –conventional (oily?) Compressor-condensor-throttle-evaporator system. –Technology (coolant) is flexible. –This has warm transfer pipes (if CO 2 with high feed pressure ~100 bar a ). –Evaporates at ~ -40°C. –Return lines have electrical heaters (accessible) to keep return fluid warm. Secondary (detector) stage: –Condensor-pump-evaporator –This would have cold, low-pressure lines. –Condenses at ~ -40°C, evaporates at ~-35°C. –While in principle you don’t need a throttle (capillary), it will probably be required for control of the circuit. –To minimize mass flow (pipe diameter) the coolant in this stage should be CO 2. Pressure in the detector stage loops would be <20bar a if connected to a buffer system, which takes pressure when system is going warm (e.g. after fault in plant stage). However, this prohibits warm testing.

4. 4 Detector stage Plant stage (need not be CO 2 )

5. 5 ID Locations HEX is located at PP2 –Ex-TRT space available (+more? Other φ?), –Needs to be thermally neutral. Plant stage –uses existing transfer network underneath inner muon system. –Throttling, back pressure regulation and heater close to HEX → accessible and “moderate” radiation. Detector stage –uses new, insulated pipes from PP2 along calorimeter endplate to ID. –Pump close to PP2 → accessible and “moderate” radiation, but in magnetic field –No heaters or further HEXs needed. –If we need throttle, it should also be located close to HEX for access, if the control allows. Calorimeter Inner muon Middle muon Access Conceptual, not to scale

6. 6 Control Plant stage: –Temperature control: control p back through regulators or other means. –Flow: controlled flow system, technology to be decided, but components are accessibly and radiation “moderate”. Detector stage: –Temperature control: through temperature of HEX. –Flow: Either variable pump speed or head. Excess mass flow –not necessarily a problem, liquid coolant simply returns to HEX, return lines are insulated, –But: would change impedance and hydrostatic head of the loop → mass flow control has to cope with this (while keeping temperature stable). → Probably need throttle (capillary), which could be variable. –Need to study this, I’m a little concerned about this, as the detector loop will reference off the plant loop.

7. 7 Plant loop technology Could use any coolant: FC: –Could use existing plant (scaled in size), –Surface condenser would still be useful, –Present return pipe pressure drop still an issue (we even need to get slightly colder), but we would get rid of smallest diameter pipe sections (incl. internal HEX etc.). CO 2 : –Can use oily compressors, –Could obtain commercial units, –Could use several units of a few 10kW in separate loops, only come together thermally in HEX → redundancy and robustness. Other commercial cooling systems? (radiation less of a problem, never sees the ID). Baltic 460LT, -35°C, 60kW http://www.greenandcoolco2.com/en/index.html

8. 8 Advantages Separation of different sections (plant and detector stage, and different segments) –allows for separate optimization, –limits impact of faults, –Detector stage can be low-pressure (<20bar a, needs connection to vent system), –Plant stage could be oily. Complicated components are accessible. No heaters, HEXs, possibly no capillary in ID, just a pipe, probably manifolds (and a few fittings). Full latent heat is exploited in detector stage. A decision for a CO 2 detector stage would allow detector designs to make progress, while there is still time to optimize the plant stage of the future cooling system.

9. 9 Challenges Space –Need to verify that space for HEX, and plant (throttle, heater) and detector (pumps) components available. –Insulation of detector stage pipework. Pumps –Have to work in magnetic environment Hydraulic or pneumatic drive (could use existing TRT Cu pipes for drive) –The pump head probably does not have to be very high (depends on control requirements), but the pump has to have reasonable leak rate at ~20bar a. –Need to be designed to avoid cavitation Might need to be cold. –Would be nice to have many smaller pumps for different detector stage loops. Detector loops could (should) be completely separate → robustness. Something like a battery of peristaltic pumps?.... Control of detector loop (needs to cope with detector load variations). Detector loop coolant sees more radiation per unit mass. –Might need easy replacement system.