1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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
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8. 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

9. 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

10. 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

11. 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

12. 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 ms
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

13. 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

14. 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

15. 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
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16. 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… …
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17. 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.
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18. 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
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19. 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.
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20. 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

21. 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

22. 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……
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23. 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
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24. 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
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25. 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
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26. 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)
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27. 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