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Quench statistics

Quench statistics . Outline: Reminder of the facts about natural quenches in the main dipole circuit in sectors 4-5 and 5-6 observed quench characteristics and propagation of quenches quench behaviour in the tunnel vs . SM18 quench data symmetric quench propagation phenomenon

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Quench statistics

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  1. Quench statistics Outline: Reminder of the facts about natural quenches in the main dipole circuit in sectors 4-5 and 5-6 observed quench characteristics and propagation of quenches quench behaviour in the tunnel vs. SM18 quench data symmetric quench propagation phenomenon What can be done to speed up the quench training in the machine A. Siemko and E. Todesco

  2. Reminder of the “jargon” used • Quench Training, Retraining, Memory Effect,…

  3. Quench Training in Sectors 4-5 and 5-6

  4. Training quench characteristics • Typical current decay curve +10A/s • dI/dt -100 A/s

  5. HYDRAULIC BEHAVIOUR DURING A QUENCH 18 bar Pressure build-up 2 min. Pressure discharge 3 h

  6. Example of a training quench and quench propagation • Natural quench in A22R4 at 9859 A (magnet name 3176) • 4 magnets quenched (3 after quench propagation) • Sequence of events:

  7. during 1st powering38 % of MB magnets has reached the nominal field without quench 42 % of MB magnets has required 1 quench to reached the nominal field What can be expected from series tests in SM18 • Powering to Nominal Field of 8.33 T

  8. What can be expected from series tests in SM18 • Thermal Cycle performed on ~10 % of MB magnets The number of quenches that can be expected in the tunnel can be estimated although the sample is not “entirely” random A. Siemko and P. Pugnat

  9. What can be expected from series tests in SM18 • Retraining data for magnets submitted to a TC in Sector 4-5

  10. Magnets tested after Magnets tested virgin thermal cycle 1232 115 115 ~ 82% reduction of number of quenches to go to nominal Extrapolation method • From thermally cycled magnet sample {TC} the reduction of the average number of quenches to reach I nominal (11850A) and I commissioning (12000A) is equal to ~ 82% • Assuming the same reduction for other magnets {NoTC}  Average number of Training Quenchesper sector can be calculated ?

  11. Extrapolation method • Additional hypotheses: • No “problematic” MBs in the machine after series tests in SM18 • No long time relaxation of the trained magnets • No retraining for magnets submitted in SM18 to a thermal cycle • No important detraining ?  Estimation for detraining: 0.04 x 3 x 22 < 3 additional Quenches/Sector ?

  12. Estimated number of quenches per sector • * calculations were based on a sample of 115 MBs submitted to a TC • ** assuming two quenches per working day

  13. MONTECARLO ANALYSIS • Aim: critically review the quench data taken at SM18 to see if they partially justify the 5-6 results • Montecarlo analysis with pessimistic hypotheses, more than what used the previous method • A method based on extrapolation: • We take the first virgin quench of all magnets of 5-6 (available for all magnets) • We sum the correlation between 1st quench after thermal cycle and 1st virgin quench measured in 136 magnets, split per firm • We take the correlations that are available, i.e. that ones of poorly quenching magnets (pessimistic hypothesis) • This correlation is affected by a random part that must be taken into account  one needs a MonteCarlo • The method gives only the first quench for each magnet • Up to now, all 5-6 quenches were in different magnets

  14. MONTECARLO ANALYSIS • MonteCarlo results versus sector 5-6 HC data • Qualitatively is fine: a lot of Noell, a few Ansaldo, no Alstom • Now, after 27 Noell quenches, we are below of around 400-600 A

  15. MOTECARLO ANALYSIS • Noell magnets lost some memory, but not completely

  16. TRAINING EFFECT MEASURED IN SM18 • In general magnets gain current from 1st virgin quench to 1st quench after thermal cycle • The gain the larger when the virgin quench is lower • Noell shows some anomalousbehavior • It is the only manufacturer that has some magnets with a detraining loss

  17. TRAINING IN SM18 VS. TRAINING IN SECTOR 5-6 • … the detraining loss looks worse in the sector 5-6 data

  18. Phenomenon of Symmetric Quenches • In sector 5-6 five symmetric quenches were observed after quench propagation caused by a thermo-hydraulic wave • One quench (in B16.R5 at ~7.4 kA) has developed the high “MIITs” and resulting high hot spot temperature • There is a weakness in the magnet protection.

  19. ANALYSIS AND FUTURE STRATEGY • Development of “tools” to speed-up training is undergoing • Overshooting with current to have more training quenches at the same time • Requires development of dedicated electronics to prevent diodes overheating and to control maximum number of quenching magnets • Forced quench training • Tried on 4th June (3 quenches at the same time) and on 5th June (4 quenches) but not conclusion yet

  20. Conclusions • During the high current quenches in MB magnets of RB45 and RB56 circuits: • all individual systems (PC, PIC, QPS, EE and CRYO) performed as designed • typical quench propagation time from magnet to magnet was observed to be in the rage of 40-60 seconds – slightly slower as compare to the initial estimates (better). • Statistical analysis of the quench data taken at SM18 do not explain the quench behavoiur of dipoles in sectors 4-5 and 5-6 • Much more pronounced than expected detraining effect was observed in a lot of Noell magnets. • Critical review the production data of the magnets can help to understand the quench behaviour observed in sector 5-6

  21. Conclusions • There is a weakness in the magnet protection in case of symmetric quenches • Remedy is under study • Much more pronounced than expected detraining effect was observed in a lot of Noell magnets. • Critical review the production data of the magnets can help to understand the quench behaviour observed in sector 5-6 • “Tools” to speed-up training of magnets in the machine are under development

  22. Additional information (quench data)

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