Practical Design Aspects for Superconducting Magnets Cooled with Pool Boiling He-I
The combined stored energy and current density obtainable with pool boiling magnets is constrained by a maximum stress limit, a quench adiabatic temperature rise limit, and a cryostable heat flux limit. The temperature rise and cryostability constraints can be combined to yield a relationship between practical maximum current densities and stored energies. The resulting curve, which bounds the realm of applicability for pool boiling design, is presented and compared with the requirements of several magnet applications. The ratio of maximum stored energy to current density is proportional to the square of the design heat flux. This, in turn, is determined by the choice of stability criterion and the available heat transfer within the winding. As the stability criterion becomes more liberal, the disturbance energies for which the conductor will recover become smaller. This performance/risk tradeoff is discussed in relation to the “training” phenomenon of pool boiling magnets and to the increase in resistivity of copper in magnets subjected to neutron radiation. Finally, it is known that cooling channel geometry and the amount of vapor present within the winding affect the available heat transfer. The relationship between the pool boiling curve for helium and the winding configuration is discussed. Strategies for limiting the degradation of heat transfer caused by excessive vapor in the winding are presented. Some closing remarks are made concerning the potential for further improved performance of pool boiling magnets, and areas for additional research of pool boiling/ ventilation in magnet windings are suggested.
KeywordsHeat Transfer Heat Flux Stability Criterion Boiling Heat Transfer Cooling Channel
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