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Cooling & mechanics

Cooling & mechanics. Georg Viehhauser (recycling material from Steve McMahon). Stability (from LOI back-up draft). Short timescale: No major disturbing events from external causes (magnet ramps, intended or unintended cooling system stops etc.)

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Cooling & mechanics

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  1. Cooling & mechanics Georg Viehhauser (recycling material from Steve McMahon)

  2. Stability (from LOI back-up draft) • Short timescale: • No major disturbing events from external causes (magnet ramps, intended or unintended cooling system stops etc.) • From ATLAS experience: ~24h. Corresponds to the timescale of a track-based alignment cycle. • Typical load variations during this timescale are • External vibration (relevant at time scales of up to 1s), • Power fluctuations of the front-end electronics of about 10%, • Temperature variations at any given position of ±1°C. • In present tracker typically a stability of 1µm was achieved during these periods (in rφ) • For future tracker we require the same performance over this timescale. • Medium timescale: • Timescale over which we currently gather enough data to constrain the weak modes. • During these periods (relatively infrequent) external perturbations can occur, which include • Magnet ramps, • Cooling system cycles, • Power and HV cycles, • Temperature variations at any given position of ±3°C, • Relative humidity variations between 10% and 50% at the operating temperature. • Based on ATLAS experience, this timescale is about one month. • In the present tracker typically a stability of 10µm was achieved during these periods. • For future tracker we require the same performance over this timescale. • Long timescale: • Stability against relaxation caused by creep, possibly accelerated by irradiation. • The timescale is months to years. • Require that the detector positions satisfy the same criteria as in the original placement requirements

  3. What have we achieved (short timescale)? Example: SCT Barrel as measured with FSI LHC fill

  4. What are the load changes (short timescale)? • Changes in front-end electronics power consumption • Rate-dependent • Reduced by L1 levelling • Different run types (calibrations etc.)? • Estimate is that front-end power constant within 10% • That defines an overhead in cooling power • Also need to understand potential temperature changes due to change in return line pressure drop • Example: type I pipe (ID 3.6, 2.2mm) for 5.88g/s: ΔT changes by 13% between x=0.5 and 0.45 at -38°C, so if we assign 9°C equivalent ΔT for all lines from start of evaporator to accumulator and scale naively we get ~1°C variation. This has to be absorbed by the structures. • This is in addition to the local temperature changes because of the changed power load • Are there any other sources of temperature variation in the cooling system (sink temperature,…)?

  5. What have we achieved (medium timescale)? This is driven by ‘seismic events’ • Cooling system stops, magnet quenches, power outages, etc…

  6. Cooling stoppages • An example: Cooling Stoppages in 2011 • A total of 19 stops of the evaporative cooling • 3 scheduled stops Maintenances of the plant by ENCV • 16 un-scheduled stops • 11 due to “external” influences (external to the cooling plant) • 1 fake smoke alarm • 1 Toroid fast dump • 6 power cuts • 2 failures in related systems (ID cable cooling & TRT FE cooling) • 1 fake DSS signal • 5 due to “internal” influences • 3 Minor (failure of TCs x 2 {119,162} + 1x trip of a circuit breaker) • 2 Major (water in filter, massive leak in pressure reducer)

  7. Thermal shocks • Apart from causing deformations, there is evidence which could link them to damage to the systems • Local supports and front-end electronics incl. all connections need to be able to withstand them • Due to proximity of pipes this applies also for all type I connections (incl. PP1) • Design thermal isolation of critical passive components (electrical connectors etc.) from cooling pipes • Prototype • In present system shock at turn-on and stop (lower than operating temperature because small return line pressure drop) • In 2PACL turn-on is more gentle (system loaded with liquid before temperature ramp-down), I suspect turn-off can be controlled similarly, but we need to be prepared to deal with unscheduled cooling stops Pixel module failures Time

  8. Summary • Feedback to local support community • Your structures must be stable at the μm scale for variations of the heat load of 10% and evaporation temperature changes of 1°C • Your structures must be able sustain thermal shocks (all power off, front-end and cooling) and remain stable to 10μm • Feedback to cooling community • Your system needs to keep the evaporation temperature stable on short time scales to 1°C • You should do everything to prevent thermal shocks

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