Expected Quench Levels of the Machine without Beam: Starting at 7 TeV ? P. Pugnat CERN, Geneva,...

Expected Quench Levels of the Machine without Beam: Starting at 7

TeV ?

P. PugnatCERN, Geneva, Switzerland

LHC Project Workshop Chamonix XV,

Tuesday 24 January 2006

23-27 January 2006

Chamonix XV - Expected quench levels of the machine without beam: starting at 7 TeV ? P. Pugnat 2/15

Introduction

Abstract (revised)

The quench training performance of about 900 LHC main dipoles and 200 main quadrupoles cold tested to date will be presented and commented. From these results an estimate of the number of quenches that could be required to operate the whole machine at nominal energy will be presented without considering beam loss effects. The energy level at which the machine could be operated without being disturbed by training quenches at the early phase of the commissioning will also be addressed. The missing and required information necessary to improve these predictions will be pointed out.

23-27 January 2006


Outline

• Introduction• Quench training performance of MBs

– After the 1st cool-down– After the 2nd cool-down

• Extrapolation for the LHC operation– Estimate of the number of Training Quenches of MBs before

reaching nominal energy– Estimate of the current level from which Training Quench will

occur

• Case of MQs – Quench training performance– Estimate of the number of Training Quenches before reaching

nominal energy– How to improve the reliability of the predictions ?

• Conclusion

23-27 January 2006


Reminder of the “jargon” used Training Quenches, Detraining, Memory Effect,…

• Only Training Quenches will be considered;

• Quench due to cryogenic problem or wrong electrical connections are not considered but can also be present; importance of diagnoses,…

• No beam.

7.5

8.0

8.5

9.0

9.5

0 2 4 6 8 10 12 14 16 18 20 22 24

Quench Number

Mag

netic

Fie

ld a

t Que

nch

B (T

)

MBP2O1 LHC Prototype dipole

No Quench

50 ms/div, 1 mV/div

Example of mechanical activity 0.5 s before a quench

23-27 January 2006


Histogram of the number of quenches to reach 8.33 T (11850 A) for the 1st 908 LHC Main

Dipoles cold tested

Result on test benches: 38.1 % of MBs reached the nominal field during their 1st powering without Training Quenches

Rejected

1104 3117 1005

23-27 January 2006


Histogram for MBs of the number of quenches to reach 8.33 T (11850 A) after the 2nd cool down & Direct Extrapolation

Rejected

TC performed on 115 MBs ( 12.7 %);From a direct Extrapolation & the Hypotheses No detraining + MBs with TC will not quench, the number of quenches that can be expected:

(1232 - 115) x (0.17 + 2 x 0.03 + 3 x 0.01) 300 i.e. 40 / octant

But problem with the representativity of the sample that contains the weakest MBs, a sort of worst case scenario ?…

23-27 January 2006


Reminder of the Algorithms used for the Cold Test Program

• From MARIC 2004-85 (streamline of the test program 2 Quench rule)

• From MARIC 2005-112 (correction the test program proposed by QWU 3 Quench rule)

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Extrapolation for the LHC operation MBs Sample bias correction

Magnet 1st Q level

2nd Q level

N° of Q's to 8.33 T (11.85 kA)

N° of Q's to 8.4 T (12 kA)

N° of Q's to 9 T Bmax 1st run

Th. Cycle

1st Q level ATC

2nd Q level ATC

N° of Q's to 8.33 T ATC (11.85 kA)

N° of Q's to 8.4 T ATC (12

kA)TCAverage 7.70 8.22 1.82 2.26 3.62 8.90 8.44 8.66 0.33 0.46STDEV 0.66 0.46 1.35 1.57 2.33 0.14 0.35 0.27 0.78 0.73

# 113 108 115 115 42 115 100 84 113 110NoTCAverage 8.06 8.54 1 1 3 8.90STDEV 0.65 0.37 1 1 2 0.15

# 785.00 643.00 791 791 420 791.00?

• From {TC}, the reduction of the average number of quenches to reach ATC 8.33 Tis reduced by 82 % ; assuming the same reduction for the sample {NoTC}, Average number of Training Quenches by octant to start at 8.33 T:

(1232 - 115) x 0.181 / 8 25

With Hypotheses: No nasty MBs, No Performance Drift for future MBs, No long time Relaxation of the trained magnets, No detraining ? Estimation for detraining ATC: 0.04 x 3 x 25 < 5 additional Quenches / octant

To start at 8.33T, in average a Total 25-30 Quenches / octant

• Same approach to estimate the dispersion: 1 6 Training Quenches

23-27 January 2006


Cumulative Statistics for MBs

0.000.100.200.300.400.500.600.700.800.901.001.10

6.00 6.50 7.00 7.50 8.00 8.50 9.00

Field Level (T)

Cu

mu

lati

ve

Fra

cti

on

of

MB

s

TC, 1st Q

No TC, 1st Q

TC, 1st Q ATC

TC_2nd QNo TC, 2nd Q

TC, MaxB

No TC, MaxB

TC, 2nd Q ATC

23-27 January 2006


Training Quench Probability versus B for MBs

Probability of a MB quench

0.0010

0.0100

0.1000

1.0000

6.00 6.50 7.00 7.50 8.00 8.50 9.00

B (T)

• For field below 7.3 T, Prob {MB-Q} 1% • If the field is reduced by 1 T from 8.33 T, Prob {MB-Q} 0.18 0.009

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Histogram of the number of quenches to reach 11850 A for the 1st 196 LHC Main Quadrupoles cold tested

SSS277Under investigation

Result on test benches: 56.1 % of dipoles reached the nominal field gradient during their 1st powering without Training Quenches

23-27 January 2006


Case of MQs

• Poor Statistics for the Memory Effect:– 9 SSS with a TC (4.6 %)– ATC, 3/9 quenched above

nominal

• With the same method as for MBs & the same hypotheses:0.17 x 360 60 Quenches i.e. 8/octant as a very rough estimate due to the lack of data,…

• As a low Memory Effect was observed on test benches Some MQs will also exhibit Training Quenches in the tunnel.

TC

0.170.58{NoTC}

# 186

0.6672.33{TC}

# 9

# Quench to reach 223 T/m

# Quench to reach 223 T/m

Reduction of 71 %

With the same reduction

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Conclusion 1/2

• From a first estimate & extrapolations of present data, 25-30 ± 6 Training Quenches/octant for MBs + 8/octant for MQs are expected before to reach the 7 TeV requirements.

• At the level Proba few %, Training Quenches will start typically at current value in MBs 11 kA (6.5 TeV) and probably at a close level for MQs.

• To improve the estimations for MQs, the Memory Effect needs to be study and more statistics is required.

• When all main magnets will be cold tested, these numbers can be reassessed, octant by octant.

23-27 January 2006


Conclusion 2/2

• Expected quench Levels of the Machine without Beam: Starting at 7 TeV ?– It depends on the time available for Training Quenches but this

objective should be maintained as much as possible,…– Strategy: Any “spare” time must be dedicated to the training of

magnets, all octants in parallel; this is a part of the commissioning. Dedicated analysis after each Training Quench to give the green light for the next powering; Need of a safe powering flag for each electrical circuit? Same approach as cold tests on the benches: Postmortem Tools should be available and trained Experts for the analysis.

– Training Quenches could arise from magnets other than MBs and MQs but also many other problems to look at before to train the LHC,…

23-27 January 2006


Acknowledgments to

• The OP Team for providing the results,• The EQ Support Team for providing the validation

of results,• N. Smirnov for providing the statistical results of

SSSs,• M. Pojer to regularly update statistical results of

MBs,• A. Siemko for fruitful discussions.

Expected Quench Levels of the Machine without Beam: Starting at 7 TeV ? P. Pugnat CERN, Geneva,...

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