What Caused the Lead burn-out in Spectrometer Magnet 2B

Abstract

MICE Note 324 What Caused the Lead burn-out in Spectrometer Magnet 2B Michael A. Green Lawrence Berkeley National Laboratory 29 November 2010 Abstract The spectrometer solenoids are supposed to be the first magnets installed in the MICE Cooling Channel [1] to [7]. The results of the test of Spectrometer Magnet 2B are reported in a previous MICE Note [8], [9]. Magnet 2B was tested with all five coils connected in series. The magnet failed because a lead to coil M2 failed before it could be trained to its full design current of 275 A. First, this report describes the condition of the magnet when the lead failure occurred. The lead that failed was between the cold mass feed-through and the heavy lead that connected to coil M2 and the quench protection diodes. It is believed that the lead failed because the minimum propagation zone (MPZ) length was too short. The quench was probably triggered by lead motion in the field external to the magnet center coil. The effect of heat transfer on quench propagation and MPZ length is discussed. The MPZ length is compared for a number of cases that apply to the spectrometer solenoid 2B as built and as it has been repaired. The required heat transfer coefficient for cryogenic stability and the quench propagation velocity along the leads are compared for various parts of the Magnet leads inside the cold mass cryostat. The effect of the insulation on leads on heat transfer is and stability is discussed. Table of Contents Abstract Table of Contents Conditions that may have led to the M2 Coil Lead Break The Break in the M2 Lead in Spectrometer Solenoid 2B Adiabatic MPZ Length for Various Leads inside the Cold Mass Adiabatic Burn-out Time and Solder Melt time for Various Leads The effect of Transverse Heat Transfer on MPZ Length The Transverse Heat Transfer Coefficient needed for Cryogenic Stability The Effect of Lead Insulation on the Transverse Heat Transfer Adiabatic Quench Propagation Velocity along the Leads Changes made on the Magnet Leads and their Effect on Stability Other Issues found when the Magnet was Disassembled Coil Voltage and Current Measurements, and Other Issues Concluding Comments Acknowledgment References Second revision on 27 February 2011