Pier Paolo Granieri, TE-CRG Ack.: R. van Weelderen, L. Bottura, D. - - PowerPoint PPT Presentation

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Pier Paolo Granieri, TE-CRG Ack.: R. van Weelderen, L. Bottura, D. - - PowerPoint PPT Presentation

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Collimation Working Group, September 16, 2013 Pier Paolo Granieri, TE-CRG Ack.: R. van Weelderen, L. Bottura, D. Richter, P. Galassi, D. Santandrea and S. Redaelli, R. Bruce, B. Salvachua, F. Cerutti, E. Skordis, A. Lechter, M. Sapinski for

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SLIDE 1

Pier Paolo Granieri, TE-CRG

Ack.: R. van Weelderen, L. Bottura, D. Richter, P. Galassi, D. Santandrea and S. Redaelli, R. Bruce, B. Salvachua, F. Cerutti, E. Skordis, A. Lechter, M. Sapinski for discussing QT results & analysis Collimation Working Group, September 16, 2013

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SLIDE 2
  • Steady-state vs. transient quench limits
  • Deduction of steady-state quench limit for the LHC MB cable
  • Method
  • Results and comparison to collimation quench test
  • Previous quench limit estimations
  • What can we do to improve the quench limit computation?
  • "Near steady-state" cable quench limit

16/9/2013

Outline

P.P. Granieri - Quench limits

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SLIDE 3

16/9/2013

Quench limits

steady-state, mW/cm3 (slow losses, > 1-10 s) transient state, mJ/cm3 (fast losses)

Heat transfer from cable to He bath (through cable electrical insulation) Experiments and modeling ongoing:

  • heat transfer through cable’s

electrical insulation (stack method)

  • The deduced quench limits refer to a

uniform heat deposit over the cable

Local heat transfer from strand to He inside the cable No conclusive experiments (yet)  we rely on numerical codes:

P.P. Granieri - Quench limits

Dominant mechanism

0-D (ZeroDee):

  • uniform heat deposit and

field over cable cross-section

  • no longitudinal direction

1-D (THEA):

  • single strand experiencing a

heat deposit and field variation along its length

  • similar to QP3 (Arjan,

Bernhard)

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SLIDE 4

Deduction of cable steady-state quench limits

  • For steady-state beam losses, a quench occurs if

Tcable exceeds Tcs (4 - 5.5 K for the LHC MB)

  • The cable quench limits depend on
  • Heat extraction:
  • cable cooling within the magnet
  • mechanical pressure, if Nb-Ti coil
  • stack heating configuration
  • Operating conditions:
  • transport current
  • magnetic field, thus cable and

strand considered

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Method reported in: P.P. Granieri and R. van Weelderen, “Deduction of Steady-State Cable Quench Limits for Various Electrical Insulation Schemes with Application to LHC and HL-LHC Magnets”, IEEE Trans. Appl. Supercond. 23 submitted for publication

P.P. Granieri - Quench limits

Raw data:

  • LHC MB and EI4: D. Richter, P.P. Granieri et al.
  • SSC: C. Meuris, B. Baudouy et al.
  • Nb3Sn: P.P. Granieri et al.
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SLIDE 5

Results along the azimuthal direction

16/9/2013 P.P. Granieri - Quench limits

6.5 TeV, 4.5 x 10^11 protons/s Collimator settings (relaxed): TCP7 @ 6.7 σ, TCS7 @ 9.9 σ

Heat deposit comes from simulations by R. Bruce, B. Salvachua, S. Redaelli, L. Skordis, F. Cerutti, A. Lechner, A. Mereghetti

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SLIDE 6

Results as a function of Iop, and comparison to 2013 collimation QT

  • most critical regions considered, i.e. mid-plane for MB
  • in agreement with the LHC collimation quench test performed in 2013

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Experiment: S. Redaelli, B. Salvachua, R. Bruce, W. Hofle, D. Valuch, E. Nebot FLUKA simulations: F. Cerutti, E. Skordis LHC collimation Review 2013: http://indico.cern.ch/conferenceOtherViews.py?vi ew=standard&confId=251588

P.P. Granieri - Quench limits

2013 collimation quench test: 4 TeV, 1.63 x 10^12 protons/s Collimator settings: TCP7 @ 6.1 σ, TCS7 @ 10.1 σ

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SLIDE 7

Current vs. previous estimations of steady-state quench limits

  • Summary of the determined steady-state cable quench limits
  • Previous estimations, at 7 TeV beam energy:
  • Jeanneret, Leroy et al. (Note 44, 1996) : 5 mW/cm3

conservative hypotheses of an insulation “assumed non porous to helium”, and a Tmargin of 1.2 K (8.65 T) “But a real insulation has helium porosities, and a better understanding of heat transfer requires an experimental approach”

  • Bocian et al. (2009 ): 12-17 mW/cm3

some mechanisms of heat transfer were neglected: the He II heat transfer through the insulation micro-channels, and the plateau at the boiling temperature

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Magnet Operating current (kA) Beam energy (TeV) Quench limit (mW/cm3) MB 6.8 4 58 11 6.5 49 11.8 7 47

P.P. Granieri

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SLIDE 8

What can we do to improve the computation

  • f steady-state quench limits?
  • Perform heat transfer measurements at different bath temperatures
  • e.g. for a bath at 2.1 K the steady-state quench limit is nearly half the value at 1.9 K
  • Obtain a deeper insight of the He II heat transport

mechanisms occuring in the inter-layer region

  • Extend the study to the whole coil/magnet, since there might be
  • ther regions saturating before the coil inner layer considered so far
  • Numerical modeling of the coil, in order to simulate

the actual heat deposit profile that cannot be experimentally reproduced in a lab

16/9/2013 P.P. Granieri - Quench limits

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SLIDE 9

"Near steady-state" cable quench limit

16/9/2013 P.P. Granieri - Quench limits

  • Steady-state heat transfer conditions are reached

after a few seconds, depending on cable, heat transfer, He temperature, etc

  • For non steady-state mechanisms we need to rely
  • n numerical codes:
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SLIDE 10

What else can we do to improve the computation of quench limits?

  • Besides what stated few slides ago, perform transient heat transfer

measurements

  • Prelimirary results: 1.5 s to reach 90% of the steady-state temperature
  • More analyses will be performed

16/9/2013 P.P. Granieri - Quench limits

1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5 15:15.8 15:33.1 15:50.4 16:07.7 16:25.0 16:42.2 16:59.5

Temperature [K] Time [min:sec:0]

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SLIDE 11

Conclusion

16/9/2013 P.P. Granieri - Quench limits

  • We presented a general method to determine steady-state quench limits of SC

magnets, by measuring heat transfer on cable stacks while taking into account the cable cooling within the magnet, the coil mechanical and operating conditions

  • The method was successfully applied to the LHC main dipole magnets, providing

an improvement w.r.t. previous steady-state quench limits estimation

  • good agreement with LHC collimation quench test performed in 2013 at 4 TeV
  • Calculations of “near steady-state” quench limits have been presented
  • Recommendations on how to improve the quench limit computation
  • In steady-state conditions
  • In near steady-state conditions
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SLIDE 12

Backup slides

16/9/2013 P.P. Granieri - Quench limits

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SLIDE 13

Deduction of cable steady-state quench limits: the method

1) Experimentally correlate heat extraction and strands temperature

  • heating configuration of the cables: typically heating all the cables
  • as a function of the mechanical pressure (for He II porous Nb-Ti coils)
  • in different positions of the cable (center vs. edge)

2) Scale the heat extraction to the coil geometry

  • nly the innermost cables’ small face is in direct contact with the He II bath
  • the outermost small face can be, depending on the magnet design, in contact with He

3) Compute Tcs (Iop , B)

  • cable location within the coil cross-section
  • strand location within the cable cross-section

4) Compute the heat extracted at Tcs (Iop , B)

  • at the pressure corresponding to the cable location within the coil cross-section
  • LHC dipole (MB): pressure varying btw 50 MPa (mid-plane) to 5 MPa (pole)
  • HL-LHC IR quad (MQXC): pressure varying btw 120 MPa (mid-plane) to 25 MPa (pole)
  • HL-LHC IR quad (MQXF): no pressure

7/19/2013 P.P. Granieri - Steady-state quench limits 13

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SLIDE 14

Heat transfer models

  • Transient heat transfer between strands and He inside the cable
  • From experimental results of each He phase. But the model of the whole process should

be validated

  • Steady-state heat transfer between cable and external He bath
  • From experimental results (see first part of the talk)

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, . . K HeI s h nucl boil film gas

h h h h h h          

lim h h Sat h Sat film gas lat

T T T T T T T E E E E

 

     

He II He I Nucleate Boiling Film Boiling Gas

strands

P.P. Granieri - Quench limits

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SLIDE 15

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Comparison to 2013 ADT-fast loss QT

2013 ADT-fast loss quench test Experiment: D. Valuch, W. Hofle, T. Baer, B. Dehning, A. Priebe,

  • M. Sapinski

Simulations: A. Lechner, N. Shetty, V. Chetvertkova

P.P. Granieri - Quench limits

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SLIDE 16

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Comparison to 2013 Q6 QT

MQM, 4.5 K Heat deposit ~ ns Very good agreement I = 2000 A, no quench Quench limit mid-plane: 23 mJ/cm3 Quench limit pole: 21.8 mJ/cm3 I = 2500 A, quench Quench limit mid-plane: 20 mJ/cm3 Quench limit pole: 18.5 mJ/cm3

2013 Q6 quench test Experiment: C. Bracco, M. Solfaroli, M. Bednarek, W. Bartmann Simulations: A. Lechner, N. Shetty

P.P. Granieri - Quench limits

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SLIDE 17

16/9/2013

Comparison to 2010 wire scanner QT

2013 wire scanner quench test Experiment: B. Dehning, A. Verweij, K. Dahlerup-Petersen, M. Sapinski,

  • J. Emery, A. Guerrero, E.B. Holzer, E. Nebot, J. Steckert,
  • J. Wenninger

Simulations: A. Lechner, F. Cerutti

P.P. Granieri - Quench limits