CERN TE-MPE-EP, RD, 09-April Quench Protection Systems (QPS) for the LHC R. Denz, TE-MPE-EP Acknowledgements: K. Dahlerup-Petersen, A. Siemko, J. Steckert

CERN TE-MPE-EP, RD, 09-April Organization of QPS Quench detection electronics Data acquisition systems & low level supervision Powering interlocks Software tools Energy extraction systems Quench heater power supplies Electrical QA Performance analysis Quench calculations Electronics production

CERN TE-MPE-EP, RD, 09-April QPS - protection of superconducting elements in the LHC Circuit typeQuantity Main bends and quads24 Inner triplets8 Insertion region magnets94 Corrector circuits 600 A418 Total544 Protection system typeQuantity Quench detection systems7568 Quench heater discharge power supplies6076 Energy extraction systems 13 kA32 Energy extraction systems 600 A202 Data acquisition systems2532 System interlocks (hardwired)13722 The size of the system is the principal problem as it asks for very low failure rates not always easily to achieve. Due to the same reason mitigation and consolidation measures are normally not straightforward to implement.

CERN TE-MPE-EP, RD, 09-April QPS performance and operational experience LHC run 1  QPS system exploitation started in 2007 with the early commissioning phase of LHC –Major system upgrade in 2009 extending significantly the diagnostic and protection capabilities (so called nQPS extension) –Upgrade with respect to the new requirements stipulated after the 2008 incident Detection of aperture symmetric quenches in LHC main circuits Dedicated bus-bar splice protection and diagnostics  QPS systems rarely challenged during LHC run 1 but nevertheless mandatory for safe LHC exploitation –So far no magnet quenches above injection current level –Very few quenches of HTS current leads at high current due to cooling problems Potential equipment damage without protection  A part the LHC main circuits all superconducting LHC circuits have been qualified for 7 TeV operation –Challenging time for QPS as many training quenches observed

CERN TE-MPE-EP, RD, 09-April QPS performance and operational experience LHC run 1  Commissioning and early operational phase quite tedious with some bad surprises –Self-destructive switches in quench heater power supplies (6600 units to be repaired!) –Circuit breakers incompatible with some types of power supplies –…  Smooth running in 2011 and 2012 –Majority of spurious system triggers related to radiation induced effects (Single Event Upsets) Consolidation measures to be completed during LS1 System updates not easy to deploy during LHC operation  Other lessons learned –Connectors, cables, electro-mechanical components (not magnets!) are by default problematic and need to be tested very carefully. –Dependency of QPS systems on human interaction to be further reduced as principal cause for near misses during LHC run 1.

CERN TE-MPE-EP, RD, 09-April QPS upgrade during LHC long shut down 1 (LS1)  Major upgrades can only be smoothly implemented during long shutdowns –Re-furbished / upgraded systems should be able to run without major overhaul at least for 3 to 4 years  No principal change of the protection functionality required for the LHC after LS1 –Some protection settings to be adapted to higher energy  Several requests for enhanced supervision & diagnostic capabilities by equipment owners, experts and users –Requested for LHC operation as for hardware commissioning –Enhanced remote control options, less accesses, more automatic analysis and maintenance tools, configuration databases –Major project is the enhanced quench heater supervision system for LHC main dipole magnets  Radiation to electronics (R2E) consolidation to be completed  General system overhaul

CERN TE-MPE-EP, RD, 09-April R2E consolidation  Mandatory upgrade to cope with increased luminosity after LS1  Majority of QPS equipment is already radiation tolerant –200 Gy total integrated dose, 2 x ncm -2  Relocation of QPS equipment (the best you can do …) –Concerns the inner triplet protection systems installed in UJ14, UJ16 and UJ56 (12/35 dumps in 2012)  Deployment of radiation tolerant hardware for exposed areas where relocation is not (yet) feasible –Insertion region magnet protection (IPQ & IPD) –600 A protection Development to be completed upgrade is mandatory  Enhanced power-cycle options for data acquisition systems –Includes automatic re-start of stalled field-bus couplers –Intermediate solution until next generation of radiation tolerant DAQ systems is available

CERN TE-MPE-EP, RD, 09-April Enhanced quench heater supervision  The upgrade is driven by the intention to reduce the risk of damage to the quench heater circuits –The present system monitoring only the discharge voltage is not sensitive enough to detect all fault states of the quench heater circuits especially failures of the heater strips. –All of the few quench heater faults observed so far during LHC operation could be mitigated by disabling the respective heater circuit and switching to a low field heater. –There is however a risk of a quench heater fault requiring at least an exchange of the magnet (short to coil, compromised electrical integrity of the magnet) –The enhanced quench heater supervision is supposed to reveal precursor states of a potential failure –The newly developed system records simultaneously the discharge voltage and current (sampling rates up to 192 kHz, 16 Bit resolution)

CERN TE-MPE-EP, RD, 09-April Future developments - introduction & motivation  Classical superconducting NbTi based accelerator magnets can normally be protected with a fixed set of detection settings allowing as well the use of robust but less flexible technology such as analog bridge detectors. –Example MB and MQ protection in LHC  In case saturation effects are significant, also classical magnets may require dynamic, current depending detection settings especially in case of limited instrumentation. This approach normally requires the use of a digital detection system. In addition such a system needs a dedicated current sensor. –Example 600 A corrector magnet circuit protection in LHC  Future Nb 3 Sn based accelerator magnets by default require dynamic detection settings in order to cope with the specific physics of these magnets. –Implementation of this functionality requires a digital system –Required user input: threshold voltages, maximum permitted reaction times … Reasonable baseline: ±200 mV detection threshold, 10 ms evaluation time –Base on past experience it is strongly recommended to develop and test the quench detection systems at an early stage of the magnet testing (as now ) Quench detection settings to be assessed for each case and to be optimized on the system integration level Requirements for the protected element (safe protection, minimized stress) Compatibility with accelerator operation (e.g. tune feedback …) Capabilities of detection systems (physical limits) Example: 10 ms evaluation time does not allow to filter 50/60Hz noise  requires adapted instrumentation (bridge configuration)

CERN TE-MPE-EP, RD, 09-April Digital quench detection systems  The first deployment of digital quench detection systems based on micro-processors dates meanwhile 30 years back (R. Flora et FNAL 1982) –The majority of the LHC quench detection systems are digital –Digital systems provide functionalities, which cannot be realized with classical electronics Examples are the protection of 600 A corrector magnet circuits and the aperture symmetric quench protection for LHC main magnets MB and MQ  Digital quench detection systems are actually mixed signal systems, where the final decision whether a signal is regarded as a quench or not is taken by a micro-controller or processor, a digital signal processor DSP or in more recent developments by a field programmable gate array FPGA. –Detection algorithm is implemented in the device firmware  computer code typically written in C, VHDL (not a programming but a hardware description language)  Basic construction elements are the analog input stage, the analog to digital converter, the digital core and the interfaces to interlocks and supervision.  The isolation barrier in modern systems is always in the digital signal path. –Supersedes designs based on isolation amplifiers A part the actual detection electronics, the data acquisition systems (DAQ) become more an more important and sophisticated. Some of the QPS DAQ systems installed in the LHC (splice supervision, enhanced quench heater supervision) are of higher performance than those used on the magnet test benches.

CERN TE-MPE-EP, RD, 09-April Detection systems for Nb 3 Sn magnets  Proposed solution is a multi-channel digital detection system –Two magnet voltages + current –Dedicated current sensor required; for accelerator operation this sensor should be redundant (detection system by itself is always redundant) –Systems for inner triplet upgrade can be installed in “radiation free” areas Relocation of present protection systems during LS1 Expected radiation levels during HiLumi runs to be verified  Multi-channel digital detection systems are already used in the LHC for the aperture symmetric quench detection of the LHC main magnets (type DQQDS) –System has four isolated input channels and can be easily re-configured –System configuration can be change remotely –Exploitation requires dedicated supervision application Default for LHC, to be adapted for test bench

CERN TE-MPE-EP, RD, 09-April Test & deployment strategy  Deployment of the first digital detection systems for Nb 3 Sn magnets started in March 2013 (project engineer in charge is J. Steckert) –In the initial phase system will be installed in parallel to the existing systems and be adapted to the respective interlocks –A supervision application for the new detection system will be delivered and the test bench operators will be trained accordingly  On the mid term the system must be upgraded to an LHC like configuration –Separation of protection functionality from test bench DAQ systems –Installation of a powering interlock controller (PIC) –Deployment of full PIC and QPS supervision layer  With the new approach the development of the detection electronics and DAQ systems will be in line with magnet R&D; the transition from test to accelerator environment should be smooth and straightforward