About Worrying Cold Test Results of MBs

MTM-MAS Meeting of Thursday 2 March 2006

Outline• Ansaldo MBs

– Splice problems

– Development of HF voltage signals during quenches

• Alstom MBs– Development of voltage signals during quenches with exponential decay

Part I

Splice Problem for Ansaldo MBs (and others ?)

2 March 2006 MTM-MAS Meeting P. Pugnat 3/16

Analysis of Quenches around 4.4 K 1D Model as a 1st approximation

• For x Lkx Sx xxT - H p (T – Tbath) + R I2 / L = 0

For x Lkx Sx xxT - H p (T - Tbath) = 0 (1)kx is the Cu thermal conductivity, H the heat transfer coefficient to liquid helium (H 500-5000 W/m2 K, for normal liquid He) & p is the wetted perimeter of the cable.

• The solutions of the system (1) is : T(x) = Tbath + (1 - e-L/2 cosh(x/)) R I2 / H p L for x LT(x) = Tbath + e-x/ sinh(L/2) R I2 / H p L for x L

where the thermal length = (kx Sx / H p )1/2.

• The maximum of the temperature increase in the splice is given by :T = T(0) - Tbath = (1 - e-L/2) R I2 / H p L

From Pre-Review January 2003, EDMS 369824

2 March 2006 MTM-MAS Meeting P. Pugnat 4/16

Analysis of Quenches around 4.4 K1D Model –

Interpretation

2 109

4 109

6 109

8 109

0.1

0.2

0.3

0.4

0.5

0.01

T R 250( )

T R 500( )

T R 750( )

T R 1000( )

108

109 R

• From the simple 1-D model with He cooling, T = T(0) - Tbath

= (1 - e-L/2) R IQ2 / H p L

• Problem to determine – The cooling term H– If heating or lack of cooling ?

• If the quench did not occurred in the splice an upper estimate of R of internal splices can be given from Tsharing(splice) 0.4 KFrom Roxie Bsplice/Bc 88.8%

From Pre-Review January 2003, EDMS 369824

2 March 2006 MTM-MAS Meeting P. Pugnat 5/16

Analysis of Quenches around 4.4 K Upper Limit of splices R that can be deduced

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1001 1002 1003 1004 1006 1007 1008 1009 1010 1011 1012 1013 1014

Magnet Id

R [

n

]

Assuming 12.5 % of surface cooled with H = 2 kW/m2 K

Specification = 1.2 n

From Pre-Review January 2003, EDMS 369824

2 March 2006 MTM-MAS Meeting P. Pugnat 6/16

Conductor limited quench around 4.5 K

Overview for Ansaldo MBs

• “Past” history (EDMS 402365, LHC-Project-Report-807): – 6/9 MBs identified with a problem at 1 splice, only 2008 with a

Quench Performance limitation detected around 4.5 K; it was accepted.

• Most recent results:– 20/28 MBs identified with a problem at 1 splice, only 2051 with QP

limitation detected around 4.5 K & 1.9 K; it was rejected.

– MB List: 2043 (D2U), 2047 (D1L), 2051 (D1U), 2054 (D1U), 2092 (D2U), 2097 (D2U), 2123 (D1U), 2140 (D1L), 2164 (D2U), 2171 (D2L), 2179 (D2U), 2187 (D2U), 2192 (D1U), 2193 (D1L), 2200 (D1U), 2201 (D1U), 2202 (D2U), 2224 (D2U), 2247 (D2U), 2241 (D2U).

• Splices are the weakest points in the coil.

• What about long term stability ? How many cases not detected ? How many critical cases in the machine with beam losses ?

2 March 2006 MTM-MAS Meeting P. Pugnat 7/16

Summary of Raw Data, need to be filtered

Prepared by Janusz KozakMB File I , A B , T T , K

2043 n01 10294.2 7.26 4.542043_2 n01 10319.0 7.28 4.50

n02 10321.7 7.28 4.50

2047 n01 10123.0 7.14 4.53

2051 n01 8977.7 6.34 4.54n02 9026.2 6.38 4.54

2051_2 n01 8766.6 6.19 4.63n02 8889.2 6.28 4.58n03 8893.9 6.28 4.58n04 8954.8 6.33 4.53

2054_2 n01 10514.4 7.41 4.46

2092 n01 10324.0 7.28 4.58

2097_2 n01 10357.0 7.30 4.53

2123_3 n01 10258.0 7.24 4.56

2140 n01 9381.0 6.62 4.52n02 10228.3 7.22 4.52

2164 n01 9792.9 6.91 4.552164_3 n01 10274.3 7.25 4.55

n02 10273.1 7.25 4.55n03 10350.8 7.30 4.50

MB File I , A B , T T , K2171 n01 10241.1 7.22 4.55

2179_2 n01 5000.4 3.54 2.04n02 10405.9 7.34 4.54

2187_2 n01 9995.7 7.05 4.54

2192 n01 10398 5.07n02 10393 4.54

2193 n01 9397.4 5.06

2200 n01 10301 5.27n02 10300 4.99

2201 n01 10126.7 4.56n02 10275 4.56

2202 n01 10239 4.20n02 10249.3 4.54

2224 10229.2 4.5210386.7 4.54

2247 9971.5 4.5510406.1 4.54

2241 10393 4.57

2 March 2006 MTM-MAS Meeting P. Pugnat 8/16

Case of 2051 Splice limitation at 1.9 K &

4.5 K1.89 K, quench @ 12645 ALQA Localisation:Typical for a quench Localised around a splice

1.89 K,VTaps Signal

Results of quenches at 4.54 K : 8978 A & 9026 A

Results of quenches at 1.89 K : 12643 A - 12657 A

2 March 2006 MTM-MAS Meeting P. Pugnat 9/16

Possible explanation ?

• Visit of September 2005 at Ansaldo; unfortunately only one pole could be visually inspected: Pole #1047 of 2262

• Measurements:– 4.33 mm– 4.37 mm– 4.37 mm– 4.34 mm– 4.35 mm

Specification: 4.34 0.02 mm

Add a tolerance on Max-Min ?

The larger values measured correspond to the splice zone where the solder is not completely melt,…

We will see with the cold tests of 2262,…

2 March 2006 MTM-MAS Meeting P. Pugnat 10/16

Summary on splices

• Not a recent concern,…

• The main reasons to have a quench around a splice can be:– Too high R too much heating,– Cooling inefficiency,– Non-uniformity of R “pathological” current redistribution.

• Even if Ansaldo were pushed to increase its production rate, its interest is also to produce MBs with good splices,– Why 2051 tested a 2nd time in July 2005 not yet open ?– 2262 should be tested asap with anticryostats

• At least one MB from Noell shows a similar problem; 3331 quenched at 10117 A around 4.5 K in D1L, but very poor statistics for this company…

Part II

Development of HF voltage signals during quenches for Ansaldo MBs

2 March 2006 MTM-MAS Meeting P. Pugnat 12/16

Electrical integrity of MBs during quenches: High Frequency V-signals

and the MB seems Ok,…

For other cases, an interturn short develops,…

2 March 2006 MTM-MAS Meeting P. Pugnat 13/16

Electrical integrity of MBs: larger amplitudes observed for Ansaldo MBs

Part III

Development of voltage signals during quenches with exponential

decay for Alstom MBs

2 March 2006 MTM-MAS Meeting P. Pugnat 15/16

Electrical integrity of MBs during quenches: V-jumps with exponential decay

Detected only on Alstom MBs, in particular: 1074, 1188, 1237, 1249, 1261, 1263, 1264, 1266, 1270, 1286, 1289

Looks like capacitor discharge in a gap with ms, where ?

2 March 2006 MTM-MAS Meeting P. Pugnat 16/16

Electrical integrity of MBs during quenches: Actions Taken

• Tune the Alarm system in the Automatic Quench Analysis (collaboration with AB/CO) to the “known” level of precursors

• Training & Daily Support to Test Coordinators and Operators

• Distribution of written doc. like EDMS Id 546522 to Test Coordinators and Operators

i.e. Specification when additional quenches must be performed

• Special investigations & dedicated analysis