ECR EDMS Doc Nr 944765 Change of Interlock

ECR EDMS Doc. Nr 944765 Change of Interlock functionality for 60 A orbit Improvement of transmission dependability corrector circuits in the LHC for the 60 A Power Permit MPP, 12 th August 2008 M. Zerlauth, CO-MI Acknowledgements: Amalia, Rudiger, Gianluigi, Stephen, Julian 1

Introduction – Motivation for ECR è Introduction of additional Power Permit for 60 A correctors in Nov 2007 in addition to existing overvoltage protection proven very useful, especially during early operation and to avoid activations of the HW interlock and unnecessary quenches (PP in FGC previously set to 1 by default) è Due to absence of hardware interfaces with PIC, SW solution has been chosen for the transmission of these conditions to the 752 FGCs (8 * 94 correctors) MPP, 12 th August 2008 è During HWC and early beam operation, unintentional removals of the PP 60 A have been observed (due to server reboots, SW updates, etc. . ), leading to the simultaneous ramp down of all 94 correctors è Dangerous failure case with circulating beam, as resulting in fast loss of beam with BLM as sole protection è ECR addresses a proposal to increase the dependability of this SW link whilst maintaining the existing equipment protection (magnets, current leads, …) 2

What circuit types does this ECR concern? è Interlock functionality = f (interfaces with PIC, circuit type, location of CL) è Main protection scheme of the 60 A orbit corrector circuits is based on an overvoltage detection on the current leads of the circuit. This main protection has never changed. MPP, 12 th August 2008 PIC DFB-CL SSS-CL CS/CM è RB, RQD/RQF X X X è IPQ X X X è IPD X X X è IT X X X è 600 A (all) X X X è 80 -120 A X X è 60 A X X PP 60 A ECR: 886005 EDMS: 368927 3

What circuit types does this ECR concern? MPP, 12 th August 2008 è ECR concerns the 60 A orbit corrector circuits, since early 2008 the 80 -120 A correctors are part of the ‚global‘ CRYO_MAINTAIN and CRYO_START condition 4

Current Transmission of PP 60 A è In it’s current state, the PP 60 A has functionality of a run-time interlock (CRYO_MAINTAIN) è Complicated SW link susceptible to failures, which during beam operation leads to fast loss of the beam and potential equipment damage MPP, 12 th August 2008 è Proposed to transform the PP 60 A to a start-up interlock while beam is present is in the machine (by forcing PP 60 A to TRUE at 2 levels) è To achieve circulating beam, all 8 arc cryostats must be at nominal operating conditions, thus less stringent cryogenic conditions for 60 A correctors are assured by the global CRYO_MAINTAIN & START of the arc è CRYO operation will merge for beam operation all cryo conditions into single interlock (Arc, PP 60 A, …) 5

Conclusion è ECR addresses a proposal to increase the dependability of a recently added SW link whilst the existing equipment protection (magnets, current leads, …) is maintained and untouched è Its implementation will help avoiding a potentially dangerous failure case in the machine è The functionality of the PP 60 A will remain the one of a run-time interlock when no beam is present, while it will become a start-up interlock when beam is present in the machine è While beam is present, the necessary cryogenic conditions for the 60 A circuits are assured by the more stringent CRYO_MAINTAIN & START of the arc cryostats MPP, 12 th August 2008 è For beam operation, all cryo conditions (60 A, arc magnets, DFBs, cryo plants, . . ) will be merged into a single interlock / sector è If proposal approved by this body, the ECR shall be re-written to better clarify its impact and extent and re-circulated for approval 6

MPP, 12 th August 2008 Thanks a lot for your attention 7

‘History of changes’ for 60 A orbit corrector circuits è Main protection scheme of the 60 A orbit corrector circuits is based on an overvoltage detection on the current leads of the circuit. This main protection has never changed. è Feb 2006: Following discussions with AT and MPP, the interlock scheme of sc circuits has been extended by a link towards the cryogenic system (CRYO_MAINTAIN and CRYO_START). Could only be done for circuit with hardwired connections to the powering interlock system, ie all circuits except the 60 A correctors. è Nov 2007: To provide also the necessary cryogenic conditions as a start-up interlock to the 60 A circuits, the transmission of a software signal to the 60 A orbit corrector circuits was agreed and implemented between MPP, PO and the interlock team to avoid unnecessary activations of the HW interlock due to missing operational conditions. è Aug 2008: The ECR in question is an improvement of the implementation done in 2007, and is not modifying nor decreasing the protection of the 60 A orbit corrector circuits, but an improvement of the reliability and availability of said software link. MPP, 12 th August 2008 è 8

‘History of changes’ for 60 A orbit corrector circuits è The proposed modification has to our understanding no impact on the safety of the 60 A circuits, as it is only effective when beam is already present in the machine. Beam presence in the machine is only possible if all powering subsectors are operating at their nominal cryogenic conditions, which is assured by the CRYO_MAINTAIN and CRYO_START functionality of the eight arcs (ie that all main magnets are below 2 K and the beam screen is at nominal operating conditions). Thus, the less stringent conditions for the 60 A orbit correctors, ie that all main magnets <4 K and the beam screen at nominal are always met when beam is present in the LHC. MPP, 12 th August 2008 è 9

Thermal screen è Note: è It was decided not to include an interlock for thermal screen temperature in the CRYO_MAINTAIN signal for several reasons: è The minimum possible temperature of thermal screen is fixed by the corresponding output of the turbine at 35 K, thus cannot drop below this point (in sector 78 this temperature was seen to be around 42 -43 K most of the time). Two alarms are set for the surveillance of the nominal operating range of 50 K<T<75 K (as specified by Andrzej and Amalia), which will automatically trigger an on-call intervention of a cryogenic operator. To avoid a continuously active alarm, the Alarm threshold will be lowered to 40 K. è Powering outside the nominal range (lower temperature with risk of ice and humidity and temperatures > 75 K) does not endanger equipments safety (no risk of quenches). This mode of operation is also identical to the once chosen for all other current leads (where this condition is no direct input to the CRYO_MAINTAIN but surveyed with specific MPP, 12 th August 2008 Alarms). 10