Coil Design for a Mirror Based Fusion-Fission Reactor

Abstract: The SFLM Hybrid project aims to show that it is probable that a fusion-fission reactor can be constructed with a single-cell minimum B mirror machine as a neutron source. In this licentiate thesis, theoretical work has been done with the magnetic coil system of such a device and also with the overall concept. The magnetic mirror field is based on the Straight Field Line Mirror field and the device has a mirror cell length of 25 m. A fission mantle surrounds the mirror cell, catching almost all fusion neutrons. The energy multiplication of fission to fusion energy is about 150 with keff = 0.97, implying that almost all the produced energy comes from fission. Beyond each mirror end, a magnetic expander is added to the mirror cell. The expanders increase the plasma receiving “divertor” area to an almost arbitrary size, which provides tolerable average heat load on the wall materials. They also add to MHD stability and may be a mean to increase the electron temperature. The device is heated with ion cyclotron radio frequency heating and the fission mantle is cooled using liquid lead or a liquid lead-bismuth eutectic. The device is self-sufficient in tritium. The magnetic field has been optimized for flute stability, low ellipticity and low field gradients in the long-thin approximation. The optimization of the magnetic field components has been made with a local optimizer. A coil set has been calculated which reproduces the selected optimized magnetic field with satisfactory accuracy and within the preliminary geometric constraints imposed by the fission mantle and coolant influx/outflux. Circular coils produce the axisymmetric field component and quadrupolar coils similar to baseball coils produce the quadrupolar field component. The proposed device does not suffer from severe material problems (to our knowledge) or a pulsed mode of operation such as for the ITER project. The main remaining question to be answered seems to be the electron temperature in the plasma, which need to reach about 500 eV for efficient power production.