Overview of the recommendation on LHC Splices Consolidation Frederick Bordry, head of the CERN Technology Department, has called for a series of three reviews with the general mandate “to review CERN’s plans and consolidation actions concerning the superconducting splices in the LHC machine for 7 TeV operation”. –all splices… not only RB and RQF/D The first of the three reviews, intended to focus on the design of the repairs of the superconducting splices for the main 13 kA bus bars, was held at CERN on October The review committee consists of Daniel Bresson (Alstom), George Ganetis (BNL), Toru Ogitsu (KEK), Frédéric Savary (ITER & CERN), Jim Strait (Fermilab, Chair), and Pierre Vedrine (CEA Saclay).

From the executive summary… Most of the executive summary is dedicate to the consolidation of the RB and RQF/D splices….not discussed here Part is related to other circuits… A systematic risk assessment has begun, that is surveying all of the superconducting circuits, and which is planned to develop into a more complete risk analysis of the higher risks identified. This is a very important activity, which seems to be well launched, and which needs to be well supported to ensure that it is completed in a timely fashion. We look forward to seeing the results of the risk analysis when the committee meets next.

Recommendation II.2. Ensure that an integrated, systems approach is being followed, covering both electrical and mechanical issues, neighboring systems, operations,. Need to develop electrical diagrams that shows information of the circuit that integrates both mechanical and electrical information in a single document. Use detailed electrical circuit models to analyze the peak voltages that could develop during quench and fault conditions. What are the difference in voltages is between components of different circuits during various conditions. Emphasis was put on the potential causes of electrical arcs due to high voltage breakdowns in the circuits. It was also mentioned that over-temperature of components can also cause electrical arcs due to conductor melting and or damaging conductor insulation. On the low current spool circuits there is only a ground fault current interlock that is alarmed if it goes above a pre-set value. The current is not recorded in the control system.

Comments to recommendation II.2. Integrated electrical/mechanical circuits diagrams along with circuit analysis models are an important tool needed for performing a comprehensive risk analysis. It is important to do a comprehensive survey of mechanical components in the circuits to assess the potential for voltage break- down risk. (e.g. the spider on dipole and quad busses) It is a very good idea to use independent experts to analyze the systems, which gives a new set of eyes to look for potential issues. There is a lack information on the maximum temperature rise due to a quench on the lower current circuits. This information can be very useful in determining how much margin is in the maximum temperature attained during a quench.

contd. We note that the previous comment concerning the lack of information about maximum temperatures might not need to have been made had a related recommendation from the LHC Enhanced Quench Protection System Review, February 2009, been carried out. It stated, “Collect and review existing MIITs limit calculation documentations for all components in all circuits and generate a summary document for design and reference. Use it to verify existing circuit protection designs.” The monitoring and recording of ground leakage currents during operations and electrical high potential testing is needed to allow the tracking of performance of the electrical isolation for the various circuits.

My comments A lot of simulation work and comparison with measurements was done in the past (more than 10years ago). This activity was stopped around the year A lot of information is still available, but scattered in notes, reports, …. The circuit models (done in SABER) are still available, but nobody works with them, and it would take time to re-activate these activities What questions do we have today? –can we damage a magnet during operation, with and without beam? taking into account realistic operational currents…. –can we avoid tripping of circuits? –can we relax the QPS threshold, and under what circumstances? –do we need to consolidate circuits during the long shutdown? Needed… –requires calculation of maximum voltage hot spot temperature in magnets and bus bars as a function of current –cross-talk between circuits

My comments Not all possible question can be addressed in finite time Priorities need to be defined My priority: develop circuit drawings and models together Have the tools to reply to the above questions Use the tools for some case studies … and to address question coming up during operation

Reports I Quench Simulations for the LHC Undulator / Hilaire, A (CERN) ; Völlinger, C (CERN), LHC-PROJECT-NOTE Geneva 2003 Principles developed for the construction of the high performance, low-cost superconducting LHC corrector magnets / Ijspeert, Albert ; et al., IEEE Trans. Appl. Supercond. 12 (2002) 90-93, 17th International Conference on Magnet Technology, CERN, Geneva, Switzerland, Sep 2001, pp.90-3 Simulation of the Effect of a Series of Superconducting Magnets on a Quenching Magnet using a Controlled Current Pulse / A.Hilaire et al. LHC-Project-Report- 527; CERN-LHC-Project-Report-527, 2002 Protection of the Superconducting Corrector Magnets for the LHC / R.Schmidt, et al., LHC-Project-Report-419; CERN-LHC-Project-Report-419, CERN, 2000 Quench propagation and heating in the superconducting 600 a auxiliary busbars of the LHC / R.Herzog, R et al. Joint Cryogenic Engineering Conference And International Cryogenic Materials Conference, Madison, WI, USA, Jul 2001 Quench Propagation and Heating in the Superconducting 600 A Auxiliary Busbars of the LHC / M.Calvi et al., LHC-Project-Report-511; CERN, 2004 Resistive transition and protection of LHC superconducting cables and magnets / F.Sonnemann, CERN-THESIS , CERN, p.

Reports II Protection of the MCS Sextupole Corrector Magnets / Schmidt, R (CERN), LHC- Project-Note-85: CERN, 1997 Protection of LHC superconducting corrector magnets / D.Hagedorn, et al., LHC- Project-Report-63; CERN, p. ….there are more