Overview of VELO system Current design of cooling system requirements, environment

1. Cooling system of the LHCbVErtex LOcator • Overview of VELO system • Current design of cooling system • requirements, environment • principle of mixed-phase CO2 cooling system • layout • Discussion

2. towards spectrometer Z 80 [cm] r 0 f -20 0 8 45 mm LHCb Si Vertex Locator Modules etc. r|f f|r r|f • 300 mm thick Si single-side n-on-n • Design work ongoing for front-end chip • (DMILL and subm technologies) • total of 220 k channels, analogue, S/N=15 • one module: r and f measuring planes • with stereo angle • small overlap between opposite halves • for alignment and acceptance • cool down: -25 < Toperate < +10 oC • come as close as possible to LHC beams • minimise material between vertex and • first hit on Si  put detectors in vacuum • large outgas rates of detector components •  separate detectors from LHC vacuum retract by  3 cm during beam filling/tuning detector prototype

3. Detector module FEE power input: 128 channels/chip 16 chips/sensor 2 sensors/module 50 modules  204’800 channels at 6 mW/channel  1.2 kW from chips + radiation  0.3 kW Mock-up for thermal tests silicon sensor FE chip cooling interface

4. VELO mechanical design (v5.0) • Decouple access to silicon detectors • from access to primary vacuum • Baking up to 150 oC is possible • Use ultrapure neon venting • VELO and NEGs need not be rebaked • after access to Si detector Openings for feedthrough flanges (22’000 pins) Vertex detector half 120 cm 25 cm RF/Vacuum thin shield Exit window 1.5-2 mm thick Al Cooled Si sensors in secondary vacuum

5. Mixed-phase CO2 Cooling system Phase diagram CO2 • Advantages: • Radiation hard (used in nuclear power plants) • Non toxic (conc. < 5%), non flammable • Low pressure drop in microchannel tubes • Good thermodynamic properties • Widely available at low cost • No need to recover or recycle • Principle of operation: • CO2 is used in a two-phase cooling system. • The coolant is supplied as a liquid, the heat is taken away by evaporation. • LHCb VELO: in total, ~ 54  40 W of heat, each cooled by a pipe of OD=1.1/ID=0.9 mm. • Tested at NIKHEF: See LHCb 99-046/VELO • capacity of cooling pipe > 50 W • heat transfer coefficient between pipe and coolant > 2 W cm-2 K-1 critical point 100 solid liquid gas Pressure [bar] 10 vapor triple point 1 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 Temperature [°C]