| Summary: | Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. === Includes bibliographical references (leaves 89-90). === Quenching is a thermal failure mechanism encountered with superconducting magnets. When a section of conductor is driven normal by an external heat input, the magnet transport current flows through a resistance, causing joule dissipation. If heat is not conducted away from the normal region faster than it is dissipated, the normal region will grow and the temperature will increase indefinitely. Growth of the normal region is commonly refereed to as normal zone propagation(NZP). A reliable NZP model is necessary for designing protection systems because a quench may cause irreparable damage if a section of the winding is over-heated. This thesis develops a numerical NZP model for a three dimensional, dry-wound, BSSCO- 2223 superconducting magnet. The test magnet operates under quasi-adiabatic conditions at 20 K and above, in zero background field. It is contained in a stainless steel cryostat and cooled by a Daikin cryocooler. The NZP model is based on the two-dimensional transient heat diffusion equation. Quenches arc simulated by a numerical code using the finite-difference method. Agreement between voltage traces obtained in the test magnet during heater-induced quenching events and those computed by the numerical NZP model is reasonable. The model indicates that thermal contact resistance has a dominant effect on propagation in the azimuthal direction(across layers). The model is also used to simulate quenching in persistent-mode magnets similar in construction with the test magnet. Specifically studied were effects of magnet inductance, for a given set of operating current and temperature, on the maximum temperature reached in one full turn of the conductor located at the magnet outermost layer driven normal with a heater. The simulation demonstrates that there is an operating current limit for a given magnet inductance and operating temperature below which the magnet can be considered self-protecting. The simulation also demonstrates that shunted subdivision lowers the maximum temperature. === by Benjamin J. Haid. === S.M.
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