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EuCARD-WP7-HFM Nb 3 Sn dipole protection

EuCARD-WP7-HFM Nb 3 Sn dipole protection. Author: Philippe Fazilleau CEA/ iRFU /SACM/LEAS September, 2012 @ INFN. Outline. Recall of the 2D computations (presented at the last TDR, march 2012), 2D computations with a varying protection resistance ,

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EuCARD-WP7-HFM Nb 3 Sn dipole protection

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  1. EuCARD-WP7-HFMNb3Sn dipole protection Author: Philippe Fazilleau CEA/iRFU/SACM/LEAS September, 2012 @INFN

  2. Outline • Recall of the 2D computations (presented at the last TDR, march 2012), • 2D computations with a varying protection resistance, • 3D computations preliminaryresults: • Benchmark (Minimum Propagating Zone) • Propagation in the low-field zone • Conclusions and TBD

  3. TDR of march, 20122D computations results The 2D FEM study gives the evolution of the current decrease vs time for t > tdet. The maximal temperature of the hot spot can then be calculated directly by taking into account the detection time (nominal current during tdet) and the curve mentionned (current decrease for for t > tdet). Curve (t > t det) determined by 2D FEM computations Heaters are activated and the code computes the quench propagation, the current decrase and the temperature distribution within the dipole. The use of 2D model decreases notably computation time. Heaters power: 50 W/cm² and 50 % coverage Time constant (I/e) of 520 ms.

  4. TDR of march, 20122D computations results The following figure gives the hot spot temperature in the dipole, taking into account the detection time tdet. The detection must be lower than 40 msif we want a maximal temperature below 150 K (4 heaters case). Nevertheless, we expect a tdet of 100 ms: the maximal temperature is 203 K for 4 heaters. The maximale temperature difference is around 30 K between 2 and 4 heaters. The use of 4 heaters decreases the maximal temperature in the dipole and helps to distribute more uniformely the temperature (lower temperatures gradients).

  5. 2D results: varying resistance As developed for the HTS insert, we studied the effects of a varying protection resistance, switching each time the voltage at its terminals goes below 800 V. Ldipole 186,8 mW 742,7 mW 596,6 mW 474,8 mW

  6. 2D results: varying resistanceCurrent and temperature The current decrease is faster: the MIITs are then smaller and the maximal temperature within the conductor is reduced by 12 K.  This should remains as an option as the gain is low compared to the complexity of the electrical circuit.

  7. 3D computations benchmark of our FEM code CAST3M* The heat equation for the 1D static case without helium cooling leads to the MPZ formula : • High-Field Zone (B = 13,5 T) lMPZ = 5 mm • Low Field Zone (B = 0,5 T) lMPZ = 26,5 mm  Results of simulation are consistent with the formula (less than 10 % deviation) * P. Verpeaux, T. Charras, A. Millard, “CASTEM 2000 uneapprochemoderne du calcul des structures”, Calcul des structures et intelligence artificielle (Fouet J.M., Ladevèze P., Ohayon R., Eds), Pluralis, 1988, p. 261-271.

  8. 3D computations propagation in the low field zone • We simulate the 3D propagation of a quench in the low field region by injecting in an unitary volume an energy larger than the MQE (so that the quenched zone extends more than the MPZ computed). • We have access to several parameters during the first instants of the propagation : • Resistive voltage, • Temperature within the conductor, • Quenched length, • Propagation velocity.

  9. 3D computationsvoltage and temperature It takes 159 msto reach a resistive voltage of 10 mV. The maximal temperature within the conductor is then 31 K. By injecting this value in our hot spot calculation ,we can estimate the maximal hot spot temperature within the conductor: the value is 131 K.

  10. Conclusions • 2D computations • The varying resistance helps to decrease the maximal temperature within the conductor; nevertheless it makes the electrical circuit more complex and has only a slight effect on the temperature gradients, • This should remain as an option in case the detection system is not able to detect low voltages (# 10 mV). • 3D conclusions • Our code has been benchmarked with good approximation of the MPZ, • The 3D computations in the low field zone show that the propagation is slow (vlongi = 0,7 m/s) but so is the temperature elevation; with a detection threshold of 10 mV, the magnet is not endangered (maximal temperature of 131 K). • The computations will be performed on a longer time to check that a higher detection threshold (30 mV ? 50 mV ?) could be used without any issue.

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