Closed flux surface EBT

The EBT device uses magnetic mirror sectors to provide equilibrium. the plasma is stabilized in a toroidal confinement system with high beta electron rings in the mirrors. Conventional EBT's have a planar magnetic axis and hence closed magnetic field lines. Cancellation of the toroidal drifts is provided by poloidal drifts in the mirror sectors. Transport scaling can be greatly improved by twisting the magnetic axis out of the plane and providing closed, nested flux surfaces. Confinement can be further improved by putting all the mirror sectors in straight sectors, making them axisymmetric and providing uniform toroidal field in the non-planar connecting sectors. Two devices have been examined in some detail, a twisted racetrack device with geometry similar to the figure ''8'' stellerator and a device in which the straight mirror segments are connected by sections of a more general helical axis stellerator. Both devices appear to have equilibria at significant beta and exhibit quite favorable neoclassical transport scaling. For example, neoclassical confinement in a twisted racetrack reactor with a perimeter equal to that of a 20 m major radius conventional EBT is equivalent to that in a 35 m major radius conventional EBT with ARE coils