Coil Design for the Straight Field Line Mirror

The Straight Field Line Mirror (SFLM) concept relies on a quadrupolar magnetic field providing a minimum B field. That is known to provide a pronounced effect on plasma stability. A threat for a non-axisymmetric magnetic field is enhanced neoclassical transport. However, a magnetic field which is connected with a radial constant of motion has been derived, which practically eliminates such neoclassical effects. The geometry of the device seems suitable for efficient plasma heating by ion and electron cyclotron heating. Neutron computations predict efficient ways to generate power in a hybrid reactor, with a high-power amplification from fission reactions in an annular layer surrounding the plasma confinement region. Reactor safety issues studied so far are favourable, although these studies need to be deepened for reliable predictions. Recent magnetic coil design suggests that a mirror ratio exceeding 10 is possible for the vacuum field. Even higher mirror ratios could be possible with finite beta effects, without violating the minimum B stability criterion or enhancing the flux tube ellipticity. A 'fish bone coil design' is developed to enable a convenient stacking of baseball coils on a cylindrical surface, which reproduces the targeted field with a high precision. The coil design is consistent with expanding flux tubes on the two opposite sides beyond the confinement region. A circular shape of the flux surfaces at the end tank facilitates a control of plasma rotation by biasing ring-shaped end plates. Even very small electric potential gradients from the end plates could enhance radial confinement properties substantially. A plan for the near future is to investigate stronger radial electric fields aimed at centrifugal confinement. (author)