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LAr at Point 1 : Power supplies

LAr at Point 1 : Power supplies. LVPS supplies electronics to a Front End crate 2*16 in Barrel, 2*13 in Endcaps LVPS takes 280V (from USA15) and makes +-4, 6, +-7, 11V up to 180A (total ~3kW) Modular : N module contributing to current. N+1 modules available for each voltage (27 modules/PS)

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LAr at Point 1 : Power supplies

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  1. LAr at Point 1 : Power supplies • LVPS supplies electronics to a Front End crate • 2*16 in Barrel, 2*13 in Endcaps • LVPS takes 280V (from USA15) and makes +-4, 6, +-7, 11V up to 180A (total ~3kW) • Modular : N module contributing to current. N+1 modules available for each voltage (27 modules/PS) • Radiation tolerant, Redundant, very tightly packed • Long story of failing manufacturing going back to year 2003 • Recurring problems lead to frequent exchanges during installation phase in pit • 2006: Task force (ATLAS, BNL, expert consultants) identified problems • Design issues • Fabrication issues • Proposed a complete reworking of the parts • 2007 Refurbishment: components, connectors, screws…. (~50 modifications/module) • During operation 2008 all LVPS worked OK but • 2 in redundant mode • 2 identified a “new” failure possibility not addressed in 2007 Campaign 2008-09 : new retrofitting campaign (all 58 LVPS from point 1 to US and back)

  2. LAr at Point 1 : LVPS To come • One [known] unsolved issue (Capacitor damage “C26”) we could not find a better replacement • 58 LVPS in operation since April 09, no failures, no redundant mode • If one “C26” fails, that voltage goes into redundant mode. LVPS can operate OK. • Would need to have a new failure in one of the other ~4 modules of that voltage. • Conclusion: we have fixed all we could • LVPS in good shape, redundancy should work • Medium term: producing a new set of LVPS • 2 Vendors contacted • Phase 1: Single voltages modules of correct size, done OK • Currently making full prototypes (delivery ~September09) • Choice of vendor End 2009 • Production 1st half 2010 • Prove reliability of series off detector (?) • Installation when access permits

  3. LAr at Point 1 : OTx • OTx is the optical transmitter sending off the serialized data of one FEB to the ROD. • Mezzanine : little circuit + Laser emitter (VCSEL) coupling onto fiber with ST connector • 1 OTx / FEB (Tiles has 2!) • Reliable devices were difficult to obtain in 2005 at the time of FEB production • After QC and other improvements devices were acceptable • Extra steps of QC … • Problems seemed solved • No failures during ~1.5 years

  4. LAr at Point 1 : OTx • In 2008 operation ~8 devices failed • Abruptly • Not correlated to anything obvious (B, power on, humidity) • All replaced during shutdown • In 2009 they keep failing, ~1/week (out of the 1600) • By now (since detector closed in May) 5 dead • Happen anywhere (now 4 Front, 1 Middle) • Always : VCSEL is the element failing • Task force analyzing the causes and preparing actions • No root cause yet • Also failed efforts to estimate the size of problem • ESD damage at the time of fabrication is main suspect • Expect some results from FA experts starting now • Preparing backup device • Other VCSEL, similar circuit, similar mezzanine, produced under best conditions • Double VCSEL, but would need two fibers. Difficult installation (eg. in EC chains) • Replacing all OTx’s is a BIG operation • Unclear when it could take place • Effects can be mitigated with L1 Trigger readout

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