Introduction, Andrzej Siemko Objectives of the event CSCM project motivations Started in 2009, and discussed in Chamonix and with CERN-MAC Initially primary goal was to determine “safe” energy for 2012 Issue of resistance in bypass diodes came up Other topics related to CSCM to be discussed in later TE-TM draft R.Schmidt

Actual status and knowhow of the LHC, M Koratzinos Status of interconnects Non-perfect joints, lack of continuity, limit LHC energy Some data from measurements Together with simulations determine energy, conservative approach Types of quenches Prompt from beam (not observed, unlikely) Bus bar propagation quenches, above 4 TeV in a few seconds after a quench (for dipoles, not for quadrupoles) Warm helium quenches, more than 20s after magnet quench Question: do we need to do tests of RQF/D to go to higher energy? This year only one unintentional quench at top current Prompt quenches versus bus-bar quenches Magnets will quench significantly earlier (about a factor 10e3 to 10e4 from beam losses) Should be updated Limits on safe energy Detailed simulations were done, for rather complex geometry Results for RB, 5TeV requires less than 45uOhm, and tau=68s (results for prompt quenches very similar) At low energy, 4TeV with respect to last Chamonix improved (several changes) R.Schmidt

Actual status and knowhow of the LHC, M Koratzinos Quench propagation tests Propagation in 5 out of 12 busses At 3.5TeV, 15cm propagation, 21cm to reach interconnects 2mm bad joint, no propagation, with 40mm bad joint, there will be propagation No tests were done with bad joints – therefore no quench propagation observed… does not exclude propagation in case of bad joints RQ tests needed for higher energy? If only prompt quenches then no need for thermal amplifier? Degradation? Actual energy limit versus circuits, knowledge and assumptions With a probabilistic approach, sector 45 limits to 3.6TeV, other sectors either higher energy, or not known. Warning: approach is probabilistic, and there might be a degradation with time Does the resistance increase with current? No known. Alternative method that had been used to determine energy: for a small amount of interconnects (144 oo 10000) accurate measurement were done, and concluded to operate up to 3.5TeV (recent analysis give a value close to 4TeV) Can we measure less than 8 sectors: for 5TeV 7 sectors, for 4TeV and 4.5TeV four sectors to be measured RRR measurements RRR is between 200 and 300, average about 250 (assumed at some stage 100) R.Schmidt

Actual status and knowhow of the LHC, M Koratzinos Other limitations – no showstoppers RB in 78: limited to 1.6kV, and be used RQ4.L8: quench heater issue RQX.R1: heater issue Energy extraction For 4.5TeV and 5TeV, 68 seconds for RB is required For 4TeV, just ok, no changes Reconnection time is 0.5days For RQ, new chimneys allow to stay at 10s for all energies, will be delivered in February / March R.Schmidt

Actual status and knowhow of the LHC, M Koratzinos Discussions What about the RRR of the cable? Not clear. Conservative number used for simulation. If we do not measure sector 45, no increase of energy is possible. Focus on tests for one sector (maximum two). Would be good to measure a sector we already know. Second priority would be sector 78. Sector 34 and 45 there are problems with leaktightness R.Schmidt

Diode interconnection tests , Arjan Verweij Diode resistance issue Large resistances of the diodes were observed, not clear where it comes from. Bus bars have very little resistances, rather issues with the contact resistance. Screws appear to be somehow weak. Early production of half moon resistance was not acceptable. Half moon design was changed to obtain acceptable values for the contact resistances, all below 5 uOhm. Frascati: 8-10 endurance test of 13kA, no contact resistance was measured between heat sink and bus bar. CERN measurement RB diodes: warm measurements of 691 diodes, average of 2.5 uOhm, at cold average of 3.3uOhm (AS: some doubts about these numbers, to be further investigated, on-going). Recent tests in LHC tunnel: 28 heater induced quenches for RB Large differences of voltages, not reproducible. For 2kA, resistance between 1 and 10uOhm For 6kA, resistance between a few and 30-40uOhm In general, the higher the current, the higher the resistance Can also become smaller with current cycles? R.Schmidt

Diode interconnection tests, Arjan Verweij Summary RB Maximum 48 uOhm Changes from quench to quench Recent tests in LHC tunnel: 9 heater induced quenches for RQ Different parameters for connections, more bolted connections For low current (up to 3kA) initially low resistance, increases with current Maximum resistance for a few cases at 5kA: 45 uOhm Could be a “movement” of the bolted connection? Why? Some ideas…. Micro contacts go to very high temperature Resistance changes with temperature Simulations Only macroscopic simulation, cannot deal with such effects… Investigation on-going Summary Never any problems seem during quench tests in 2008 CSCM can address this issue There could be permanent degradation from CSCM, should be no issue for 6kA R.Schmidt

Diode interconnection tests, Arjan Verweij Discussion During Frascati tests, about a factor of 10 improvement from first to last current cycle (13kA, 130s time constant) Now conditions for diodes are different (storage, installation into magnets, time, …) Could be a systematic design issue, proposal to remove few diodes from LHC for investigation during Xmas stop Diodes from sector 34 can be tested -this is underway Tests in SM18 on the way, should clarify the origin Proposals “Official” task force on diodes is suggested, to be defined by TE management Presentation by Marta Bajko in TE-TM R.Schmidt

CSCM tests description, Arjan Verweij Calculation of the “safe” current is very indirect We might be too conservative, tail of the resistance distribution has not been observed, and defects might be on two sides of interconnects We might have a margin of a few kA, depending on the assumptions Might be different at cold with respect to measurements at warm Tests with CSCM will remove uncertainties Done as for e real current decay during energy extraction All elements in “safety circuit – parallel to magnet” are tested, but only worst defects are measured Diode leads resistances are all measured Stored energy in circuit very small, if anything goes wrong, limited damage For cryogenics, total dissipated energy is 66MJ for a 1minute test at 6kA in a sector Description of the tests Current cycle is proposed, first opening all diodes In case of thermal runaway, switch off current R.Schmidt

CSCM tests description, Arjan Verweij Plateau time, plateau current, didt, protection threshold, etc. Details of current cycle was worked out 300 A/s ramp for RQ, 1000 A/s for RB (possibly also 300 A/s) Some arguments for higher current Some arguments for lower current … to be worked out Thermal runaway T increase very quickly when, say, 50 K are reached, takes a few seconds Thresholds have to be established (from SM18 tests), very critical Time at the plateau will define the “safe” energy, will obtain “safe current” as function of thermal runaway time QPS thresholds Board A: below 100 mV, for dV/dt about 20-50mV/s Board B: more difficult, but can be done Temperature should be within a few K (16K…22K) Current cycles Several current cycles are proposed (about 7 cycles, from 500A to 5kA or 6kA), possibly some intermediate currents. Time on flat top will also be changed. R.Schmidt

CSCM tests description, Arjan Verweij SM18 tests Validate the method, the extrapolation to 1.9K, test hardware, learn about required thresholds values Defect is slightly longer than 40 mm, lot of diagnostics present, heaters to trigger quench installed Should be done during next two weeks… Summary Circuit analysis: done, for normal functioning and some failures (such as over voltages), to be extended Leads to be considered Detection time will be at least 60ms, possibly up to 100ms (seems to be not critical) What about the design of the clamping of the lead to the bus? Similar to diodes? To be addressed… R.Schmidt

CSCM test implementation, Jens Steckert Protection against thermal runaway Two different mechanisms for detecting the runaway are implemented dV/dt trigger only active when V above 100mV, and after the ramp is finished mBS (mDQQBS) boards developments Board had to be developed, could be derived from existing boards Detection within about 70-100ms Testing in LHC: good results, very low noise, 16 Hz seems to be a good frequency (…or 32Hz, to be checked?) Test electronics installed for SM18 tests DAQ Local storage of data, and then transmission to computer system (Timber) Protection of the CL and magnets Current leads protected with existing system Symmetric quench detection board will remain active EE system shorted out For short part of the circuit, no redundancy If not all diodes open, circuit will be switched off Spread between diode opening below 800mV (todays threshold) R.Schmidt

CSCM test implementation, Jens Steckert Implementation and impact on the actual protection system Quench heaters will be off DQQBS to be replaced by mDQQBS (DQQBS board to be stored in tunnel) oOPS off Validation tests before CSCM powering test Procedure for testing will be written up Recovery Go back to initial situation (procedure will be written up) Recommissioning after recovery Full test on QPS Heater firing required? Pyramid? Discussion Some points in the DAQ will be lost (should not compromise data taking) 800mV for symmetric quench detection might not be sufficient, but can be changed Current leads: could it be lowered to 1mV? Might be possible… Consolidation of interconnects in the DFB: open issue, to be discussed… R.Schmidt

Powering implementation, Hugues Thiesen Voltage and current requirements and power converter Requires 4-6kA and up to 300V, in total up to 2 MW Modify existing RB converter and use it for RB and RQF/D (hardware intervention required between tests) Tests were performed in P Hall, using 4Ohm load Implementation and impact on the powering systems Short circuit of EE for RB, limiting voltage to 300V Time constant to discharge in about 0.3s (EE system would not help to reduce the time constant) Quadrupole RQF and RQD circuit tests can be done in series Use only one EE system for RQ (other is shorted) DC connection at level of the power converter Earth fault detection system needs to be modified PIC Power permit required, global abort and cryo signals to be disabled UPS should remain operational For tests, modifications are required, somewhat complex, must be done correctly R.Schmidt

Powering implementation, Hugues Thiesen Other systems Water and electricity needed Validation tests before CSCM powering tests Test converter in short circuit or with 4Ohm, including tests of interlock loops Preparation time is estimated to 2 weeks + 1 day Powering tests have some unknown, circuit parameters are not precisely known Recovery Need to redo all the steps Re-commissioning after recovery Summary Main open issue is the power converter control with special load Specialists required Procedures to be written Discussion Unbalance of the circuit needs to be addressed Voltage ripple, what kind of noise is expected R.Schmidt

ELQA, Giorgio D'Angelo Before CSCM tests During CSCM tests Usual conditions as for all tests Modified QPS boards should be installed During CSCM tests Temperature of 20K, pressure of 5.5bar in magnets and 1.8bar in DFB RB to earth max 400V, RQF+D to earth max 300V is expected For CSCM, RB 600V and RQF+D 360V, leakage current 50 (20)uA After CSCM tests Nominal conditions, as all tests after X mas stop No impact of these tests on schedule Issues What about non conformities? E.g. with the pressure that is required in sector 34 and 45? Discussion Maybe 4bar would be acceptable, not yet clear. Depends on density of helium. Pressure during tests also required? Yes… … R.Schmidt

Cryogenic implementation, Krysztof Brodzinski CSCM – assumptions T= 20K (+- 10K), 5bars DFBs lower part stabilised to 50K LHC cryogenics architecture Do not need 1.8K units, 4.5K units with reduced number of sub-systems to provide 20K Will use several cooling circuits Small part of superconductor can be at a different temperature (close to DFB) Difficult to have 4.5K in DFB, and 20K in adjacent cell Temperature in the DFB for bus bars expected to be between 20K and 50K with a temperature gradient. Could we reduce TT891A to 30-40K? Some margin exists, possibly 40K? To be discussed and analysed. AV: should be ok. Whole sector can be stabilised to +-1K, recovering about 3-4h. However, T at diode might take longer to be stabilised. Impact on vacuum to be addressed related to beam screen cooling loop. R.Schmidt

Cryogenic implementation, Krysztof Brodzinski Impact on planning Sectors become available after week 3 or 4, for three sectors tests would be transparent to planning Sector 45 no pressurisation to 5bar Safety aspect No liquid helium, 2200 kg/sector, 10 times less than nominal operation Discussion What temperatures can be used? 20K is easier than others… Can we accept some parts of the circuit at higher temperature? Yes… During cool-down we have to watch out, to optimise beam operation, might risk to have an inversion of temperatures between cold bore and beam screen R.Schmidt

Measurements and Analysis, Zinur Charifoulline How to measure the splices and diode interconnections 0.5-1kA safe: new HW and SW has to be tested 4kA-6kA unsafe 1st segment requires more attention Thresholds at every channel needs to be set, required recording of data for every ramp Operator needs to start the test, could this be done automatically? By the sequencer? Time structure needs to be constructed JAVA application and ORACLE DB under development Needs to be very reliable… Discussion Why to measure RRR? Does not cost anything… What consequences if we measure with 30 Hz? Little difference…but buffer reading out takes longer How to avoid systematic errors? Inductive voltages….? Should be ok. R.Schmidt

Implementation and Safety, Andrzej Siemko Energy and risk Energy stored in the circuits: 70kJ to 130kJ, very little compared to nominal powering, but enough to make a hole in the stainless steel sleeves Risk assessment Before CSCM, during CSCM and after CSCM Important modification of all protection systems Failure modes and risks Risks related to different subsystems that are all affected: PC, PC,EE and QPS Most important failure modes were addressed using a risk matrix Catastrophic risk identified only after CSCM tests… great care to go back to standard operation Mitigation reduces risk to acceptable level by: procedures for reconfiguration, test and (re-)commissioning This allows to reduce the risk to low, but dedicated procedures step-by-step are required R.Schmidt

Implementation and Safety, Andrzej Siemko Discussion Re-commissioning is similar to initial commissioning For some issues we do not know (e.g. diodes) there can be hidden risks What is the objective for this measurement? What is the gain, what is the risk to perform these tests? There are other risks … maybe also of NOT DOING the tests R.Schmidt

Sequence and detailed planning, Matteo Solfaroli Camillocci Preparation timeline for CSCM RB-PC configuration tests two weeks Other activities (QPS etc.) in the shadow Tests minimum time 6-7 days (first sector longer) IST for QPS, PCC, current ramps, establish thresholds Three days per circuit, one day change over from RB to RQ Strategy to test the 8 sectors Global tests would take at least 8 weeks (e.g. before LS1), assuming that 2-3 weeks are required for 20K stabilisation, without considering recovery Initial strategy Showed this would take long, only type test to be done during Xmas stop Realistic planning for one sector with re-commissioning Tests of sector 34 (36uOhm) would be the best option, in the shadow Safety Recall powering phase I and II (above 100kJ) He in magnets is 10 times less, therefore phase I is proposed Who is finally responsible for safety? EN department head? Who lead the tests? OP? Project? Needs to be defined…… R.Schmidt

Sequence and detailed planning, Matteo Solfaroli Camillocci Discussion Impact of relocation of cryo PLCs in sector 34 Sector 56 might be warmed up If only RB should be measured… how much less time? Few days… Seven days seem to be a little short… at least for the first sector R.Schmidt

Impact of tests and beam commissioning after Xmas break, Mirko Pojer Do we need to measure the diodes in all sectors? Different options… measure zero to eight sectors Re-commissioning after CSCM tests For main circuits and spool pieces full ELQA and re-commissioning Similar to 2011, possibly some more tests to be done (pyramids?) No big impact Time required to go to higher energy, also required to go to 4TeV Extra tests for powering system (e.g. EE tests, splice mapping, ..) If E>4TeV, EE time constant modification QPS thresholds need to be considered – to be changed? No quench issues up to 5TeV RB in sector 78 – breakdown at 1.6kV, what above 4Tev? IPQ/D no problem to increase current up to 5TeV IT.R1 quench heaters to be reconfigured with high capacitance heater PS Correctors: there area few issues, in particular one corrector R.Schmidt

Impact of tests and beam commissioning after Xmas break, Mirko Pojer Impact on LHC beam operation Need to modify functions Protection validation Understanding of beam operation at higher current Possible issues for optics to be addressed… Unexpected issues? Impact on LHC other systems BLM thresholds, other instruments Increase heat load on cryogenics (sector 45 critical?) Vacuum Experiments (Van der Meer scan) Commissioning Possibly one week more to go to higher energy With higher energy we might learn about new issues All sectors begin 2012, about 2 months more End of 2012 (before LS1) all sectors, could be reduced to about one week delay R.Schmidt

Impact of tests and beam commissioning after Xmas break, Mirko Pojer Discussion At the end, 6 weeks (??) more physics when tests done at the end, this needs further consideration Collimators need to adjusted (but this will be done anyway) R.Schmidt

For some issues we do not know (e.g. diodes) there can be hidden risks Discussion Re-commissioning after the CSCM is similar to initial commissioning of the RB / RQ circuits For some issues we do not know (e.g. diodes) there can be hidden risks What is the objective for this measurement? What is the gain, what is the risk to perform these tests? There are other risks … maybe also of NOT DOING the tests More info from SM18 tests, and more info from studies on diodes before the Xmas shutdown… R.Schmidt