Enhanced Diagnostics & Supervision for Quench Heater Circuits

1. Enhanced Diagnostics & Supervision for Quench Heater Circuits R. Denz TE-MPE-CP

2. Outline • Introduction • Quench Heater Discharge Power Supply exploitation • Enhanced quench heater diagnostics • System integration • Cost estimate and timeline • Hardware – status of development  Vincent’s talk

3. Introduction • 6076 quench heater circuits in LHC used for active magnet protection • 4928 x MB, 784 x MQ, 364 x IPQ, IPD, IT • Quench heater power supply type DQHDS performance in principal good but spoiled to a certain extent by one faulty component (see next slide) • At present the quench heater circuits are hardly used and stressed but this will change significantly once LHC increases energy • Magnet training campaigns, more beam induced quenches • In most cases the loss of a quench heater circuit would be acceptable but there is a risk of serious (non acceptable) collateral damage, i.e. a short to coil, which could require an exchange of a magnet • QPS supervision should indicate a potential failure of a quench heater circuit • Enhanced diagnostics must be properly integrated into existing system • Sufficient resources must be provided (material cost + manpower)

4. Quench Heater Discharge Power Supply (DQHDS) exploitation • Failure rate of DQHDS basically determined by one component, the infamous main switch • Material analysis performed by CERN specialists confirmed wrong ratio of components (overshoot of hardener) in a moulded plastic part • Replacement campaign launched in 2010 (~1600 / 6076 switches so far exchanged) • Additional software interlock to take into account quench heater redundancy of the MB protection • QPS_OK flag to be corrected accordingly (deployment started ~20% done together within radiation upgrade) • MTBF currently ~ 1 Mh (1.16 Mh in 2010) • MTBF_MQ > 4 Mh (all updated, no faults so far), MTBF_MB ~ 0.8 Mh • Discharge tests during QPS-IST at lower energy • Successfully tested (U_HDS ~ 100 V) with IPQs during winter shutdown • Software application for fully automatic execution and analysis still to be developed

5. Enhanced quench heater diagnostics - motivation • Increase diagnostic capabilities for qualification and possible fault detection of the LHC main dipole quench heater circuits • Present system monitors quench heater voltage – sufficient for healthy heater circuits and DQHDS integrity check • Some dipole magnets are equipped with quench heaters which may show problems during LHC exploitation • Magnet expert wish list: • Monitor discharge current • Check electrical continuity of quench heater after discharge • Check quench heater sanity (if possible) • Check for eventual earth faults • Perform discharge tests with lower energy  see exploitation • Extension to other magnet types, e.g. MQ? • This needs to be clarified quickly as system integration is quite different for MB, MQ, IT, IPQ and IPD

6. Enhanced quench heater diagnostics - constraints • Significant but successful effort from 2009 through 2011 to stabilize QPS • System is now working correctly and reliable • Any modification must minimize impact on existing systems • At this level it is by far easier to get it wrong than to get it right • Modification of existing electronics, i.e. Local Protection Unit and Quench Heater Discharge Power Supplies, not wishful: • Potentially radioactive material  special workshop etc. • High risk of collateral damage • ALARA principle • LS01 2013/2014 is one of the few occasions to perform this upgrade • Major work in the LHC tunnel due to splice consolidation • Collateral damage expected • Extensive re-testing of equipment required in any case

7. Enhanced quench heater diagnostics – possible upgrades

8. Enhanced quench heater diagnostics – feasibility studies I • Monitoring of discharge voltage and current • Feasible if installed as separate new data acquisition system • Data acquisition at significantly higher sample rates (~20 kHz) • Current measurement by dedicated tailor-made current transformer • Affordable resolution is one per mil  100 mA • Two different technical solutions elaborated • Microcontroller based (integrated 12 Bit ADC) • 12 Bit  25 mA / 250 mV resolution • FPGA based with external 16 Bit ADC • Both solutions have already been tested for radiation tolerance in previous projects • Only useful if combined with powerful analysis software • Implicates as well a change of the QPS supervision • 3 PM data blocks instead of one: the selected board, the other board, heater supervision

9. Enhanced quench heater diagnostics – feasibility studies II • Electrical continuity and heater sanity • Old almost discarded approach of DC resistance measurements has been re-evaluated recently R0 = 4.907 mΩ ΔR = 1.782 mΩ w0 = 15 mm Δw = 14.7 mm Measurements performed by Joaquim Mourao

10. Enhanced quench heater diagnostics – feasibility studies II • Test results indicate that an ohmmeter with ~100 µΩ resolution should be able to detect the onset of a potential rupture of the quench heater strip • Bipolar measurements required in order to compensate thermals • I = ± 100 mA U = ± 1.2 V (RHeater ~ 12 Ω) • Measurement system must only be used with unpowered magnets • Radiation tolerance not required as system can be switched off during operation with beam • One system per protection system sufficient • Also wishful in order to compare better the different heater circuits of a magnet • Design of such a system seems to be feasible at “moderate” cost (but not for free!) • Type testing of hardware ongoing  more news from Vincent

11. System integration I • System integration will strongly depend on the magnet type • MB, MQ systems are different • IT, IPQ and IPD systems similar but quite different from the other two • Very long cables  difficult for resistance measurement • All new systems must communicate with QPS supervision through the DAQ systems of the magnet protection • Local communication bus to be extended  new measurement electronics has to be integrated into a new protection crate • For MB (1232) and MQ (392) new crates are required • Power supplies and quench detectors can be re-used • Fieldbus coupler (DQAMC) must be able to address 6 clients • Present controller used for MB and MQ can only address 4 clients new fieldbus couplers for MQ required • IT, IPD and IPQ: integration into old crates feasible • Should be done within nQPS upgrade of these systems

12. System integration II • Electrical distribution boxes for racks type DYPB and DYPQ (“Crawford boxes”) to be modified as well • Necessary manipulations to be indentified and to be checked with RP whether this work can be performed on systems currently installed in the tunnel (see Vincent’s presentation) • Purchase of new boxes is most probably not significantly more expansive than the modification of the old boxes • QPS fieldbus network in the tunnel should be reconfigured in order to increase the maximum data transmission rate • Current network is loaded already up to 90% • To be done anyhow for the exploitation of the NanoFip boards • QPS supervision to be upgraded as well • New signals to be defined etc. (straight forward but tedious ...) • Post mortem data transmission to be modified • QPS-IST for main circuits to be revised and extended

13. Cost estimate & timeline • Table shows a first price estimate (hardware only) for the update of MB and MQ protection systems • Manpower not yet included but significant (also a lot of “donkey work”) • Time constraints • Specification and R&D phase to be completed in 2011 • Type testing early 2012 (including tests in LHC) • Purchasing procedures to be launched as well early 2012 (potential bottleneck, especially for orders > 200 kCHF) • Production 2nd half 2012, 2013 • Test & installation during LS01 2013/2014