Analysis of the quench tests in S56 in May and July 2011€¦ · Training Delayed quench of a joint During the Chamonix 2011 workshop it was shown that the largest probability to

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.


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.


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


Diode


‘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


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


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



Diode

Joint

Udiode

I

I

Test results Measured magnets Forward voltage over the diodes Propagation into the bus Voltage & resistance in the diode leads


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)



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


Propagation towards the joint at 6 kA magnet quench


Conclusion: Propagation in 5 out of 12 busses. The joint does not quench, but at higher currents many joints will.

Assuming RRR=250


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.


Rcold: resistance measured during cold reception in SM18

Contents:


• Geometry

• Test results

• Simulations

• Open questions

• Conclusion


Comsol output for the final temperature after a 6 kA quench with zero contact resistances (adiabatic conditions)

95 K

60 K 50 K


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


Contents:


• 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


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


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.


Are large resistances dangerous for operation at 12 kA, t=100s?

Cooling to helium is disregarded


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.


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)


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.


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, 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


Upper diode busbar

RB joint

Main RB bus

Lyra


Zoom for B15R5

BB2

BB4

UM2

HM4 HM3

EE015 EE014

Documents

Analysis of the quench tests in S56 in May and July 2011€¦ · Training Delayed quench of a joint During the Chamonix 2011 workshop it was shown that the largest probability to