Study On Quench Process And Quench Protection Of MICE Superconducting Coupling Magnet

International Muon Ionization Cooling Experiment– MICE is one of the advanced research tasks on key technology to verify the feasibility of neutrino factory and muon collider. The superconducting coupling solenoid magnet, as one of the key components in the MICE equipment, is to produce a magnetic field about 2.6T along the beam center line to control the muon beam in the RF cavity located inside them. Quench of superconducting magnet will induce over heating and over voltage in the coil of the magnet and result in permanent damage to the magnet, so the study on quench process and design of the quench protection system are both key aspects for the superconducting magnet design. The coupling magnet wound with commercial copper matrix NbTi conductor and impregnated with epoxy resin is designed to be passivly quench protected by coil subdivision combined with quench-back effect of the mandrel. This dissertation takes the MICE superconducting coupling solenoid magnet as the research object, built its quench process numerical simulation model, studied the variation of its main parameters during quench process in detail and designed its reasonable and feasible quench protection system. The research results of this dissertation will provide theoretical and practical application guidance for the quench protection system design of the coupling magnet and similar solenoid magnets. The main research contents in this dissertation are as follows:In order to design reasonable quench protection circuit for the coupling magnet, the quench process of the coupling magnet was studied by semi-empirical numerical simulation. Considering the quench-back effect from mandrel in the classical quench simulation method based on quench propagation method, a semi-empirical numerical model for simulation of the quench process of the coupling magnet was built. According to the experimental results of the quench process of a successfully operated experimental superconducting magnet, compared with the calculated results of the model, the model was verified. The model was applied to study the effect of subdivision number, protection resistance, material of banding on the quench process of the coupling magnet, and a reasonable quench protection circuit was designed for the coupling magnet. In order to throughly understand the quench process of the coupling magnet, the eddy current in the mandrel and the quench-back effect induced, the quench process of the coupling magnet was further studied by finite element simulation. Based on the coupled field analysis function of ANSYS, considering quench-back effect of the mandrel, a transient coupled thermal and electromagnetic finite element model for the quench process was build. The model was applied to calculate the quench process of the coupling magnet, the calculated results by the finite element model were compared with the calculated results by the semi-empirical model and the finite element model was verified. The quench-back effect of mandrel was further studied by this model, and the advantage and disadvantage of the finite element model and the semi-empirical model were pointed out.The calculation results of the over heating in the magnet is roughly accurate by the open quench simulation methods, but that of the over voltage is very conservative,and a more accurate calculation method for the over voltage in the sub-divided solenoid during quench process is presented in this dissertation. The accurate calculation of the over voltage needs to analyze the voltage distribution in the magnet. The magnet is treated as a circuit comprised of turn unit, and each turn has property of resistance and inductance simultaneously. During quench process the inductance of each turn does not vary and the resistance of each turn varies with the temperature of the turn. According to the transient temperature and current of each turn, the distribution of the resistive voltage, inductive voltage and resultant voltage along the conductor in the magnet were calculated. The more accurate calculation method for the maximum internal voltage, layer-to-layer voltage and turn-to-turn voltage in the sub-divided solenoid during quench process was presented. This method was applied to study the over voltage in the sub-divided solenoid during quench process and the effect of the subdivision number on the over voltage.Cold diode assembly is a key component of the quench protection system for the coupling magnet, and it works in the temperature range of 4.2~4.8K and at the magnetic field of 1.5~2.5T. All the simulation, analysis and design of the charging, discharging and quench protection circuit of the coupling magnet must be based on the cryogenic performance of the cold diode assembly. A set of cryogenic test system for the diode assembly was built. The forward and the reverse electrifying characteristic of the diode at room temperature and liquid nitrogen temperature, as well as the cryogenic performance of the cold diode assembly under larger forward current condition were measured. Utilizing the measurement and control system of the prototype coil for the coupling magnet, the cryogenic performance of the cold diode at ~10K was tested as well.