PMT Array Cooling

1. PMT Array Cooling Tim

2. Overview • Cooling System Parameters • Estimate Power Loads • Active components • Extraneous heat sources • Develop methodology for exploring cooling system parameter space • Flow rate • Pressure drop • Pipe bores • Control and Monitoring • Strategies • Implementation PMT Array Cooling

3. Cooling System Parameters • Working document - “Specifications for the Cooling System for the NA62 CEDAR KaonTagger” • Considers 2 sides as being separate sub-systems • Chiller/Heater • Interconnect pipe-work • Internal pipe-work, etc.. • System specification driven from a desired inlet-to-outlet bulk temperature rise PMT Array Cooling

4. Considerations • Desired temperature rise and total power defines the mass-flow; • 1g/s cools 4.2W for 1C • Mass flow, density and tube bore defines volume flow and velocity. • Velocity defines Reynolds Number. • Reynolds Number defines pressure dropand HTC • HTC defines tube wall temperature PMT Array Cooling

5. Power Estimate • FE • 32 PMTs per array • 4 arrays per cooling circuit connected in series • 0.5W per PMT • 16W per PMT array, 64W for four arrays on one side • Environment • Box dimensions 1.2(h) x 0.6(w) x 0.3(d). • Area of 5 sides = 2.16sq.m • Box insulation k=0.05 W.m-1.K-1 • Wall thickness 50mm • Assume external wall is at 40C and internal wall is at 20C • Power = 0.05 x 2.16 x 20 / 0.05 = 47W • Total Power • 64 (FE) + 47(env) = 107W PMT Array Cooling

6. Pipe-work Geometry • External Interconnect • Flow and return lines 7m long with a bore of 12mm • Internal • Heat exchanger: heated length 0.5m per array • Interconnect: 4m in total • Bore: 4, 6, 8mm PMT Array Cooling

7. System Properties • Volume Flow • Inversely proportional to desired temperature rise • Independent of tube bore • Flow = 1.54/T lpm PMT Array Cooling

8. System Properties • Pressure Drop • Depends on fluid velocity (strong dependence on tube bore) PMT Array Cooling

9. Draft Chiller Requirements • Tabulate Flow and pressure for different bores of the internal pipe work and desired temperature rise • Chiller Specifications (preliminary web-trawl) PMT Array Cooling

10. Chiller Parameters • Cooling Specification • Cooling Power (W) • Flow Rate (lpm) • Maximum Pressure (bar) • Control • Set-point stability • Heater Power (W) • PID / remote control • Control Temperature (internal / external) • Alarm signal (low flow, low level, ….) PMT Array Cooling

11. Monitoring • DCS Monitoring • ELMB (ATLAS) – quote from ELMB128 User Guide • “It should be usable in USA15 outside of the calorimeter in the area of the MDTs and further out. This implies tolerance (with safety factors) to radiation up to about 5 Gy and 3·1010 neutrons/cm2 for a period of 10 years and to a magnetic field up to 1.5 T.” • Automated reading, archival & presentation in central DCS • Inputs • 128 floating input (2 wire) channels • Can be configured for DCV, Ohms… • Can be used in pairs for 4-wire RTD (PT100) • DSS • Detector Safety System • High level alarms relating to safety ONLY • Independent of DCS PMT Array Cooling

12. Control • Issues • Maintain the PMT arrays at a given temperature • Control the heat transfer between the box and the CEDAR • Options • Control the PMT array temperatures such that the global temperature of the box is close to the CEDAR. Provide sufficient thermal insulation to minimise coupling between box and CEDAR. • Monitor the CEDAR temperature and control the temperature of the PMT arrays such that the temperature difference between the box and the CEDAR is minimised. • Control the PMT array temperatures such that the global temperature of the box is just below the CEDAR. Provide an ACTIVE thermal enclosure between the box and the CEDAR and control the temperature on the CEDAR side to minimise heat flow. • Need more engineering input to define interfaces between CEDAR and box PMT Array Cooling

13. Thermal Interfaces • For Option 1 and Option 3 - need to consider Thermal Interfaces • Option 1: Passive thermal interfaces between PMT array box and CEDAR • Control of thermal exchange between box and CEDAR would have to be through adjusting the set-point on the chiller PID • Option 3: ACTIVE Thermal Interfaces between PMT array box and CEDAR • Control of thermal exchange between box and CEDAR would be through regulation of the power to the heaters o the active thermal enclosure. PMT Array Cooling

14. Thermal Interfaces • Heat Paths • Box/beam pipe/CEDAR • Box/Support Tube/CEDAR (is steel the right material?) • NB • Option 3 heat generated on CEDAR side of thermal enclosures will need to be absorbed by the cooling system PMT Array Cooling

15. Option 1 PMT Array Cooling

16. Option 2 PMT Array Cooling

17. Option 3 PMT Array Cooling

18. Comments • Option 1: • Likely to need greatest number of interventions to adjust chiller PID controller • Needs chiller with in-built heater • Needs high precision chiller set-point & stability • Option 2: • Highest cooling power requirement • Need to develop fault tolerant PLC /heater sub-system • Option 3: • Chiller may not need in-built heater • May allow low precision chiller set-point & stability • Complete segmentation of control sub-systems • Needs detailed engineering analysis / design & manufacture of active thermal enclosure PMT Array Cooling