Analysis of the quench tests in S56 in May and July 2011
Arjan Verweij, TE-MPE
On behalf of all persons involved in the tests
Contents
- Motivation for these tests
- Geometry
- Test results
- Simulations
- Open questions
- Conclusion
A. Verweij, CMAC, 22 Aug 2011
During the Chamonix 2009 workshop it was pointed out that a 13 kA joint could burn-out in case of a quench, if there would be a bad bonding between the cable and the copper bus coinciding with a discontinuity in the copper stabiliser.
Motivation
Since then, resistance measurements and -ray pictures have shown the presence of many of such defective joints in the machine, limiting the safe operating current to about 6 kA.
A. Verweij, CMAC, 22 Aug 2011
Prompt quench of a joint
Beam losses
Resistive losses in the splice
Burn-out of the joint
Cable/bus movement
Quench of a magnet
Thermal propagation through the bus
Thermal propagation through GHe
Spurious trips/heater firings, ….
Training
Delayed quench of a joint
During the Chamonix 2011 workshop it was shown that the largest probability to quench a joint was caused by thermal propagation of the heat developed in the magnet and the diode by-pass. It was therefore concluded to remain at 3.5 TeV in 2011. It was also recommended to measure this propagation in the machine.
A. Verweij, CMAC, 22 Aug 2011
Magnet (1.8 MJ @ 6 kA)
Diode
Joint
Typical powers at 6 kA: Diode: 6 kW Diode busbars: 2x25 W Contacts: 200 W (assuming 2x3 mW)
Geometry
I
I
Magnet (1.8 MJ @ 6 kA)
Diode
A. Verweij, CMAC, 22 Aug 2011
‘half moon’ contacts
‘heat sink’ contacts
RB joint
Upper diode busbar (partially flexible) ‘Half moon’ contact
Main busbars
towards diode
Geometry
21 cm
The diode
Rc,moon
Rc,hs
Diode box, Helium contents : 5 liter
Lower diode busbar
Rc,diode Lower heat sink
Upper heat sink
A. Verweij, CMAC, 22 Aug 2011
Reception tests in FRASCATI: Endurance tests: 10 current cycles with 13 kA, t=120 s. The diode voltage and Rc,diode were measured. Rc,hs has only been checked a few times. Cold reception tests (in SM18): Each diode has only experienced one current pulse below 1 kA for less than 1 s. Rc,hs+Rc,moon has been measured during this transient and was always below 5 mW.
Contents:
• Motivation for these tests
• Geometry
• Test results
Measured magnets
Forward voltage over the diodes
Propagation into the bus
Voltage & resistance in the diode leads
• Simulations
• Open questions
• Conclusion
A. Verweij, CMAC, 22 Aug 2011
Measured magnets
Magnet ID
Training quenches in SM18
Training quenches in
the LHC
Secondary quenches in
the LHC
Test quenches May 2011
Test quenches July 2011
A15R5-3188 12.3 12.4 10.5 5.2 4.6 2 6
B15R5-3353 12.2 6.3 7.4 6.8 2 6 2 5 0.76 4 6 6 3
C15R5-3338 12.2 12.7 10.9 10.7 2.4 2 6
A16R5-3204 11.6 12.2 11.2 2 0.76 4 6 3 5
B16R5-3361 12.5 12.4 7.4 2 2 5 0.76 6 3 4
C16R5-2246 11.5 11.8 12.4 12.8
0.6 5.2 2 6 4
All numbers in kA
Total: 28 heater induced quenches
3 magnets with training 3 magnets without training
6 magnets from stable part of production
A. Verweij, CMAC, 22 Aug 2011
Magnet (1.8 MJ @ 6 kA)
Diode
Joint
Udiode
I
I
Test results Measured magnets Forward voltage over the diodes Propagation into the bus Voltage & resistance in the diode leads
A. Verweij, CMAC, 22 Aug 2011
Diode voltages for 6 kA quenches
Magnet not yet fully s.c., all current in magnet
Magnet s.c., all current in magnet, U=L*dI/dt
Diode blocks
Diode cooling down
Conclusion: Forward voltage (and hence the heating) over the 6 diodes is very uniform. (s<10 mV)
A. Verweij, CMAC, 22 Aug 2011
Magnet (1.8 MJ @ 6 kA)
Diode
Joint
Ubus
Ubus To next magnet
To next magnet
I
I
Test results Measured magnets Forward voltage over the diodes Propagation into the bus Voltage & resistance in the diode leads
A. Verweij, CMAC, 22 Aug 2011
Propagation towards the joint at 6 kA magnet quench
A. Verweij, CMAC, 22 Aug 2011
Conclusion: Propagation in 5 out of 12 busses. The joint does not quench, but at higher currents many joints will.
Assuming RRR=250
Magnet (1.8 MJ @ 6 kA)
Diode
Joint
Ulead,A
Ulead,C
I
I
Test results Measured magnets Propagation into the bus Forward voltage over the diodes Voltage & resistance in the diode leads
Diode lead ‘resistances’ for 6 kA quenches
Conclusion: Large spread among the 12 leads. ‘Steps’ occurring in first 15 s.
5 mW: maximum measured at reception in SM18 13 mW: specification during reception in SM18
Diode lead ‘resistances’ for B15R5 Anode Conclusion: Inductive signal is small. Results indicate the presence of one or more irregular contacts. The three 6 kA curves differ a factor 2.
Summary
A15R5 B15R5 C15R5 A16R5 B16R5 C16R5
C A C A C A C A C A C A
Rcold 3 3 2 2.7 3 2.9 3 1.8 3.6 3.2 3.1 2.4
Rmin 1.5 2.3 2.6 1.8 3.2 1.8 5 2.2 1.6 2.2 1.6 2.2
Rmax 2.2 9 24 22 7.9 5.3 48 21 6 11 4.2 15
Prop. in bus
No 10 cm No No 11 cm 10 cm 16 cm 9 cm No No No No
C=Cathode, A=Anode, Resistances in mW
Conclusion: There is no correlation between diode lead resistance and propagation into the bus.
A. Verweij, CMAC, 22 Aug 2011
Rcold: resistance measured during cold reception in SM18
Contents:
• Motivation for these tests
• Geometry
• Test results
• Simulations
• Open questions
• Conclusion
A. Verweij, CMAC, 22 Aug 2011
Comsol output for the final temperature after a 6 kA quench with zero contact resistances (adiabatic conditions)
95 K
60 K 50 K
A. Verweij, CMAC, 22 Aug 2011
Simulations are performed using the codes Comsol and QP3, giving very similar results.
Simulations
Comsol output for the final temperature after a 6 kA quench with Rc,moon=40 mW (adiabatic conditions)
95 K
90 K
180 K
A. Verweij, CMAC, 22 Aug 2011
Contents:
• Motivation for these tests
• Geometry
• Test results
• Simulations
• Open questions concerning the high resistances in the diode leads:
1) Do the resistances increase/decrease with the number of current pulses?
2) Is there a correlation with current?
3) Are these values dangerous for 12 kA operation?
3) Where is this large contact resistance?
• Conclusion
A. Verweij, CMAC, 22 Aug 2011
Do the resistances increase/decrease with the number of current pulses?
0
10
20
30
40
50
0 2 4 6 8 10
Dio
de
lead
re
sist
ance
[u
Oh
m]
Test number
A15R5, cathode
A15R5, anode
B15R5, cathode
B15R5, anode
A16R5, cathode
A16R5, anode
B16R5, cathode
B16R5, anode
C16R5, cathode
C16R5, anode
Conclusion: The behaviour with number of current pulses is irregular
A. Verweij, CMAC, 22 Aug 2011
Is there a correlation with the current?
0
10
20
30
40
50
0 1000 2000 3000 4000 5000 6000 7000
Dio
de
lead
re
sist
ance
[u
Oh
m]
Current [A]
A15R5, cathode
A15R5, anode
B15R5, cathode
B15R5, anode
A16R5, cathode
A16R5, anode
B16R5, cathode
B16R5, anode
C16R5, cathode
C16R5, anode
Conclusion: There is an average trend that the resistance increases with current.
A. Verweij, CMAC, 22 Aug 2011
Are large resistances dangerous for operation at 12 kA, t=100s?
Cooling to helium is disregarded
A. Verweij, CMAC, 22 Aug 2011
Conclusion: Resistances above 20 mW are worrying, especially if the resistance is in the half moon.
0
100
200
300
400
500
600
700
800
0 20 40 60 80 100
Max
te
mp
era
ture
[K]
Half moon resistance [uOhm]
6 kA, tau=50 s
9 kA, tau=68 s
12 kA, tau=100 s
The maximum temperatures are lower if the excess resistance is located at the bolted
contact with the heat sink.
Rc,moon
Rc,hs
Rc,diode
Where is the large contact resistance?
Simulations show that a large Rc,moon should cause thermal propagation into the main bus. However the measurements do not show a correlation between the diode lead voltage and the propagation.
This contact was accurately monitored during the reception tests in FRASCATI, and was very small and became even smaller with number of current pulses.
A. Verweij, CMAC, 22 Aug 2011
Conclusion: the largest contribution is most likely located at Rc,hs, but more tests are needed to validate this.
Several tests are planned to find out what is happening
Cold tests in SM18 on several diodes (end 2011) As similar as possible to the machine but with additional instrumentation. Currents up to 12 kA.
3rd series of quench tests in the machine (Sept 2011)
Quenches at 2-6 kA on 4 quadrupole apertures. Warm tests on a few diodes (Aug 2011)
Small current (10-100 A). Applying a force on the diode bus bar simulating the Lorentz force in the machine.
Tests in SM18 on a dipole + diode (2012)
A. Verweij, CMAC, 22 Aug 2011
Conclusion (1/2)
Diode voltages:
As expected.
Opening and forward voltages among the diodes are very uniform. Propagation into the bus:
Observed at 6 kA for 5 out of the 12 leads. At 5 kA for 1 out of 6.
Running at 3.5 TeV is a bit more safe than presented in Chamonix 2011.
It is rather sure that at currents >7 kA a magnet quench will almost always propagate to the closest 13 kA joint.
No quenches in the bus have been observed at 6 kA due to propagation of ‘warm’ helium gas.
A. Verweij, CMAC, 22 Aug 2011
Conclusion (2/2) Diode lead voltages/resistances:
The measured resistances (up to 50 mW) are much larger than measured during the cold reception in SM18 (<5 mW) and in many cases much larger than specified during production (<13 mW). The results suggest the presence of irregular contacts.
The variation among the 12 measured diode leads is very large, and even larger resistances may be present in the other 4000 diode leads of the LHC.
Resistances >20 mW are worrying for safe operation at 12 kA, t=100 s especially if this resistance is in the ‘half moon’. The large excess resistance measured is probably at the heat sink, since no correlation is observed between propagation and the voltage in the diode lead. Note also that we have not experienced any problem with the high current training quenches during the 2008 hardware commissioning.
Several experiments are proposed to better understand the origin of the large increase in resistance and the correlation with current.
The CSCM (see next talk) during the X-mas shut-down could offer a unique occasion to map the resistance of all the diode leads at 6 kA.
A. Verweij, CMAC, 22 Aug 2011
A. Verweij, TE-TM, 16 Aug 2011
Annex slides if needed
Resistance of the heat sink at 10 K with RRR=100 0.001 mW
Resistance of the lower diode bus at 10 K with RRR=100 (upper heat sink) 0.17 mW
Resistance of the lower diode bus at 10 K with RRR=100 (lower heat sink) 0.28 mW
Resistance of the upper diode bus at 10 K with RRR=100 0.23 mW
Power in a diode at 2 kA About 2.4 kW
Power in a diode at 6 kA About 6.6 kW
Energy needed to warm up the helium inside the diode from 1.9 to 2.17 K 1.4 kJ
Energy needed to warm up the helium inside the diode from 2.17 to 4.3 K 5.1 kJ
Energy needed to evaporate the helium inside the diode 14 kJ
Energy needed to warm up both heat sinks from 1.9 to 4.3 K 4 J (see next plot)
Temperature rise of the diode lead (RRR=100, adiab.) for 6 kA, t=50 s decay 1.9 K to 31.3 K
Resistance rise of the diode lead (RRR=100, adiab.) for 6 kA, t=50 s decay 0.59 to 0.86 mW
Resistance of the lower diode lead at 110 K 4.6 to 7.7 mW
Temperature rise of the heat sink (adiab.) for 6 kA, t=50 s decay 1.9 K to 110 K
Some numbers
Temperature increase heat sink (6 kA, tau=50 s, no cooling)
0
60000
120000
180000
240000
300000
360000
0
20
40
60
80
100
120
0 20 40 60 80 100
Dis
sip
ate
d e
ne
rgy
[J]
Tem
per
atu
re [
K]
Time [s]
Temperature heat sink
Dissipated energy diode
RC,diode (Contact resistance between diode and heat sink. Spec.: <5 mW)
Lorentz force between the diode leads at 6 kA
20 N
70 N
30 N
10 N
A. Verweij, CMAC, 22 Aug 2011
Upper diode busbar
RB joint
Main RB bus
Lyra
A. Verweij, CMAC, 22 Aug 2011
Zoom for B15R5
BB2
BB4
UM2
HM4 HM3
EE015 EE014