Consequences of a hypothetical incident for different sectors

(with beam energy up to 5 TeV)  

Laurent Tavian

Thanks to contribution and helpful discussions withM. Jimenez, V. Parma, F. Bertinelli, J.Ph. Tock,

R. van weelderen, S. Claudet, A. Perin, C. Garion, R. Schmidt

Chamonix 2011 LHC Performance Workshop,Session 04: Beam Energy

 

Content

• Introduction– Recall of the 19th Sept’08 fault tree– Recall of sector consolidation status for 2011/12 operation

• Updated fault trees and consequences in case of:– A hypothetical electrical arc in a cryo-magnet interconnect

for beam energy up to 5 TeV– A hypothetical electrical arc in a magnet cold-mass for

beam energy up to 5 TeV• Conclusion

Fault tree of 19 Sept 2008 incident at the LHC Cryogenic effects [1/2]

Electrical arc

Beam pipe perforation

He vessel perforation Soot

He discharge in insulation vacuum

Contamination by soot

Inadequate sizing of relief devices

(MCI)

Pressurization of vacuum enclosures

Mechanical damage to MLI

Contamination by MLI

ODH in tunnel

Blast

Trip AUG

Loss of beam vacuum

Break vent door

Ph. Lebrun

Fault tree of 19 Sept 2008 incident at the LHC Cryogenic effects [2/2]

Pressurization of vacuum enclosures

Pressure forces on vacuum barriers

Plastic deformation of shells

Buckling of bellows

Rupture of supports and ground anchors

Displacement of magnets

Mechanical damage to interconnects Secondary electrical

arcs

Damage to tunnel floor

Ph. Lebrun

Sub-sector inventory(Ref. CERN ATS Note 2010-057)

Q1_R Q7_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L Q3_L--> --> --> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q3_R Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q7_L Q1_L

D1 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D2

Q1_R Q7_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L--> --> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q3_R Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q7_L

D1 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D2 D5

Q7_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L--> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q7_L

D5 D1 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D2

Q7_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L Q3_L--> --> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q7_L Q1_L

D1 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D2

Q1_R Q7_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L--> --> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q3_R Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q8_L

D1 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D3

Q8_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L--> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q7_L

D4 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D2 D5

Q7_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L Q3_L--> --> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q7_L Q1_L

D5 D1 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D2

Q1_R Q7_R Q11_R Q15_R Q19_R Q23_R Q27_R Q31_R Q33_R Q31_L Q27_L Q23_L Q19_L Q15_L Q11_L Q3_L--> --> --> --> --> --> --> --> --> --> --> --> --> --> --> -->

Q3_R Q10_R Q14_R Q18_R Q22_R Q26_R Q30_R Q32_R Q32_L Q28_L Q24_L Q20_L Q16_L Q12_L Q7_L Q1_L

D1 A1 A1 A1 A1 A1 A2 A1 A1 A1 A1 A1 A1 D2

DFB

X

I2 M3 M1 M1 D6 D6 M4 I1

DFB

A

DFB

A

DFB

L

Q6_

L

Q5_

L

Q4D

2_L

S8-1

DFB

X

D1_

R

D2Q

4_R

DFB

M

DFB

M

Q5_

R

DFB

M

Q6_

R

DFB

X

M2 D7 M1 M3 I2

Q6_

L

DFB

M

Q5_

L

DFB

M

Q4D

2_L

D1_

L

S7-8

DFB

M

Q6_

R

DFB

A

DFB

AD

FBA

DFB

M

Q6_

L

M1 M1 D6 M2

S6-7

DFB

M

Q4_

R

DFB

M

Q5_

R

DFB

A

I1 M4 D6 D6 M1 M1

DFB

A

DFB

A

DFB

M

Q5_

L

DFB

M

Q4_

L

S5-6

DFB

X

D2Q

4_R

Q5_

R

Q6_

R

DFB

L

I1M1 M3 M1 D6 D6 M4

DFB

A

DFB

L

Q6_

L

Q5_

L

Q4D

2_L

DFB

X

S4-5

DFB

M

D3_

R

D4Q

5_R

DFB

M

DFB

M

Q6_

R

DFB

A

D3_

L

M2 D8 D6 M1 M3 M1

DFB

A

DFB

M

Q6_

L

DFB

M

Q5D

4_L

DFB

M

S3-4

DFB

M

Q6_

R

DFB

LC

DS

LC

DFB

A

DFB

A

Q6_

L

DFB

M

I2 M3 M1 D7 M2

S2-3

DFB

X

D1_

R

D2Q

4_R

DFB

M

DFB

M

Q5_

R

Q6_

R

DFB

A

Q4D

2_L

D1_

L

DFB

X

I1 M4 D6 D7 M1 M3 I2

DFB

A

DFB

A

Q6_

L

DFB

M

Q5_

L

DFB

M

S1-2

DFB

X

D2Q

4_R

Q5_

R

Q6_

R

DFB

L

Inner tripletInner triplet Maching sectionDispersion suppressor Arc

Dispersion suppressor Matching section

MCI in case of electrical arc in an interconnect

080919 accident (~ 5 TeV)

With “smaller” electrical arc (i.e. lower magnetic stored energy and/or lower discharge time constant), perforation of the beam pipe can not be excluded with the present consolidation status. (Electrical insulation of the beam pipe interconnect foreseen in 2013/12)

Discharge conditions through safety devices vs beam energy

• Mass flow MCI flow (already at 3.5 TeV, an electrical arc is able to create the MCI breaches ( 2 x 60 cm2)), e.g. 30 kg/s in the continuous cryostat.

0

10

20

30

40

50

60

70

80

90

100

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6 7 8

Disc

harg

ed h

eliu

m te

mpe

ratu

re [K

]

Stor

ed m

agne

tic e

nerg

y [M

J]

Beam energy [TeV]

Stored energy

Discharge temperature• Temperature of helium heated by

the electrical arc power and discharged through the safety devices depends on:• the stored magnetic energy• The current discharge time

constant• The heat transferred by

convection from the environment.

Maximum pressure build-upin vacuum enclosure

Q6R

2Li

nk Q

6R2

DFBA

Mid

-arc

sub-

sect

orDS

& D

FBA

DFBA

Mid

-arc

sub-

sect

orDS

& D

FBA

Link

Q6L

8Q

6L8

DFBA

Mid

-arc

sub-

sect

orDS

& D

FBA

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

S1-2 S2-3 S3-4 S4-5 S5-6 S6-7 S7-8 S8-1

Max

imum

vac

uum

-enc

losu

re p

ress

ure

[bar

]

3.5 TeV

5 TeV

Maximum pressure of re-enforced fixed points

Vacuum-enclosure design pressure

Off-design remaining cases

Vacuum sub-sectorP max [bar]

Remarks3.5 TeV 5 TeV

Link Q6R2 & Q6L8 5.1 5.1 Compatible with vacuum enclosure design margin (DN200 link)

Q6R2 & Q6L8 1.8 1.8 Compatible with vacuum enclosure design margin

Mid-arc S2-3, S7-8 & S8-1 1.8 2.3* Compatible with vacuum enclosure design margin and re-enforced fixed points on SSS

DFBA HCM R2, L3, R7 & L8 1.6 2.0 Compatible with vacuum enclosure design margin and re-enforced fixed points on DFBA

DFBA HCM R8 & L1 1.4 1.7 Compatible with vacuum enclosure design margin and re-enforced fixed points on DFBA

DS L3, L8 & L1 1.4 1.6 Compatible with vacuum enclosure design margin and re-enforced fixed points on SSS and DFBA

Conclusion: Up to 5 TeV, no longer mechanical collateral damages in adjacent sub-sectors!

*: Above 1.9 bar, plastic deformation of SSS vacuum barrier could occur(pressure test under preparation)

Updated fault tree up to 5 TeV

Electrical arc

Beam pipe perforation

He vessel perforation Soot

He discharge in insulation vacuum

Contamination by soot

Inadequate sizing of relief devices

(MCI)

Pressurization of vacuum enclosures

Mechanical damage to MLI

Contamination by MLI

ODH in tunnel

Blast

Trip AUG

Loss of beam vacuum

Break vent door

Ph. LebrunInstrumentation flange opening

on temporary consolidated sectors

Mechanical damage of instrumentation

cabling

Damages in case of a hypothetical electrical arc in an interconnect

(up to 5 TeV)• Sept’08 damages which are mitigated by the 2009 consolidations:

– Plastic deformation of shells– Buckling of bellows– Rupture of supports and ground anchors– Damage to tunnel floor– Mechanical damage to interconnects– Secondary electrical arcs

• Damages still present up to 5 TeV– He vessel and beam pipe perforation– Mechanical damage of MLI– Contamination by soot of MLI and beam pipes– Contamination by MLI of vacuum enclosure and beam pipes– Mechanical damage of BPM cabling

Expected damages in case of a hypothetical incident

PTQVQV QVQV SVSV

Cold-massVacuum vesselLine ECold support postWarm JackCompensator/BellowsVacuum barrier

Q D D QD D D QD D D QD D D QD

PTQVQV SV

Q D D QD D D QD

He vessel perforationMechanical damage of MLI

Contamination of MLI by soot & of vacuum enclosure by MLIContamination of beam pipe(s) by soot

BD

Contamination of beam pipe(s) by MLI(over the whole continuous cryostat length)Length to be removed and re-installed (~12 dipoles + ~4 SSS)

BDBD BD BD BD BD BD BD BD BD BD BD BD BD BD BD BD

PTQVQV QVQV SVSV

Q D D QD D D QD D D QD D D QD

PTQVQV SV

Q D D QD D D QD

He vessel perforationMechanical damage of MLIContamination of MLI by soot & of vacuum enclosure by MLI

Contamination of beam pipe(s) by soot

BD

Contamination of beam pipe(s) by MLI(over the whole continuous cryostat length) Length to be removed and re-installed (~14 dipoles + ~4 SSS)

BDBD BD BD BD BD BD BD BD BD BD BD BD BD BD BD BD

To be exchanged or repaired (surface) before operation restart

To be repaired in-situ before operation restart

Consolidation can wait the next long shut-down

Electrical arc position

Electrical arc in the middle of a subsector

Electrical arc closed to a vacuum barrier

Mechanical damage of instrumentation cabling

Mechanical damage of instrumentation cabling

Mechanical damage of MLI (1)• Without MLI, cold mass enclosure are not protected against pressure

build-up in case of break of the insulation vacuum with air.Heat transfer by condensation of air on cold wall

• From a calculation by Nusselt– h ≈ 0.943 (r2 g k3 Lv/h x DT)0.25

• Assimilating air to nitrogen– h ≈ 680 W/m2 K– heat flux h DT ≈ 50’000 W/m2

– average thickness of film ≈ 0.2 mm

• Multi-layer insulation– take e = 10 mm

• Conduction in solid nitrogen– conductivity integral from 77 to 4 K

≈ 50 W/m– Heat flux h DT ≈ 5’000 W/m2

LHe Air

Liquid air film, fallingx

Heat transport limited by conduction across falling film

LHe Air

Liquid air film, falling

Solid air trapped between MLI layers

e

Heat transport limited by conduction across solid air

Bare wall with MLI

Not compatible with the cold-mass pressure relief system !

Ph. Lebrun

Mechanical damage of MLI (2)Affected length?

• S3-4 incident: ~ 2/3 of the total affected length (22 cryo-magnets over 2 sub-sectors)

• New incident ?:– MLI damage goes with rv2 or m2/r or m2T/P

• S3-4 incident 30 kg/s – 6 bar – 70 K• New incident 3.5 TeV: 30 kg/s – 1.1 to 1.3 bar – 40 K factor 3 to 2.6• New incident 5 TeV: 30 kg/s – 1.1 to 1.5 bar – 60 K factor 4.5 to 3.5

– But the distribution of the safety devices allows a faster decrease of the flow along the length

– Let’s assume the same damage ratio (2/3) for a new incident i.e.: • ~ 10/16 cryo-magnets to be repaired use of spares for dipoles re-cryostating of SSS (no spare)

– Question: Can we safely operate with only missing MLI on SSS? (if yes, the heavy SSS re-cryostating could wait the next long shutdown!)

Contamination by soot of beam pipes: Affected length?

• Experience return from S3-4– V1 more representative (not burst disk opening)– In V1 about 600 m contaminated with soot– Pressurization: up to 3.5 bar

V1V2

~600 m

~400 m

• New incident expectation: Affected length is assumed to be proportional to the quantity of soot introduced:• For most sub-sectors, pressurization limited to 1.1-1.5 bar:

quantity of soot introduced in the beam pipes divided by 2.3 to 3 250 to 200 m of magnet could be affected

• For the specific mid-arc subsectors (3/8), pressurization limited to 1.8 -2.3 bar: quantity of soot introduced in the beam pipe divided by 2 to 1.5 300 to 400 m of magnet could be affected

M. Jimenez

Repair schedule following a hypothetical interconnect electrical arc

monthsweeks 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Sector warm-up (4 weeks)

Prepare spare dipoles (12 to 14) (1 week of preparation + 2 dipoles per week)

removal of SSS (4) (2 weeks of preparation + 2 SSS per week)

removal of dipole (12 to 14) (3 dipoles per week)

Recryostating of SSS for MLI(2 to 3) (4 weeks per SSS with overlap of 2 weeks)

Beam tube and BS cleaning of SSS (3 to 4) (1 SSS per week)

New SSS assembly (0 to 1) (2 weeks of preparation + 3 months)

Reinstallation (12-14 dipoles + 4 SSS) (3 months)

Opening of IC and PIMS (sector wide) (4 weeks)

BS MLI cleaning (1 shift) (3 months)

Reclosing of IC (sector wide) (4 weeks)

Sector recooldown (including cryo-tunning) (6 weeks)

Sector ELQA and HWC (4 weeks)

New DFBA assembly

7 81 2 3 4 5 6

Remark: In case of a hypothetical electrical arc in an Inner Triplet, soot contamination of the detector beam pipe cannot be excluded (Fast shutter valves installation only in 2013/12 long shutdown) Long and heavy repair work if NEG coatings are damaged! (4 to 6 months)

Fault tree of an electrical arc in magnet coil (caused by a short circuit or by a catastrophic beam loss)

Electrical arc in a magnet cold mass

Beam pipe perforation

Magnet quench Soot ?*

Pressurization of CM

Contamination by soot ?*

ODH in tunnel

Pressurization of beam vacuum

Beam pipe rupture disk

opening

Mechanical damage of bellows (Nested &

PIMs)*Not seen during the “Noell 4”Incident in SM18

Damage due to a hypothetical electrical arc in a magnet coil

Complementary solutions to improve the beam vacuum protection and to protect sensitive equipments (RF, kickers, experiments,…) J.M. Jimenez – LHC MAC April’10.

Mitigation solutionsRupture disks (3/4)

Max. pressure (quench valve)

Adjusted level at 10 bars (quench valve)

Nested bellows buckling

PIM bellows buckling

C. Garion

Maximum pressure following a dipole quench (measurements)

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5

Max

imum

pre

ssur

e [ba

r]

Beam energy [TeV]

tc - 100 stc - 50 sNested bellows buckling

PIM bellows buckling

Working line ?

KC. WuR. van Weelderen

S. Claudet

Damages in case of a hypothetical electrical arc in a magnet coil

• Beam pipe perforation of a single magnet (Reminder: the downtime for a single dipole exchange is about 4 months)

• Plastic deformation (rupture ?) of nested & PIM bellows:– No damage at 3.5 TeV (with 50 s time constant)– Could become critical above 3.5 TeV especially if we

increase the discharge time constant.• PIMs can be repaired in-situ• Nested bellow repair requires magnet removal.

Conclusion• Electrical arc in an interconnect:

– The present consolidation, up to 5 TeV, will suppress mechanical collateral damages in adjacent sub-sectors.

– Nevertheless, mechanical damage of the MLI in the concerned sub-sector as well as contamination of the beam pipe(s) could require heavy repair work.

– With the present consolidation status, a new incident will still have big impact on the machine down time (8 to 12 months)

• Electrical arc in a dipole coil:– Limited impact at 3.5 TeV (but at least 4 months of downtime to exchange one

dipole)– Could be more critical above 3.5 TeV (damage of bellows over several sub-sectors)

• A hypothetical incident caused by an electrical arc during the 2011/12 operation could seriously impact the LHC physics program: Corresponding risks must be carefully assessed.