EBT reactor magnetics and particle confinement

Abstract

Optimization of the vacuum magnetic field of an ELMO Bumpy Torus (EBT) reactor is investigated. Several methods of improving reactor volume utilization and single particle confinement are analyzed. These include the use of (a) a large number of sectors and/or a large mirror ratio, (b) high field Nb3Sn or Nb3Sn/NbTi hybrid mirror coils, (c) split-wedge mirror coils, (d) axis-encircling aspect ratio enhancement (ARE) coils, and (e) recently developed field symmetrizing (SYM) coils. Of these, particle drift orbit and three-dimensional tensor pressure equilibrium calculations show that the use of SYM coils in conjunction with high field mirror magnets offers the most promise of good plasma performance in reactors that are smaller (by up to 50%) than previous reference designs that did not employ supplementary coils. Aspect ratio enhancement coils also offer an attractive alternative for improved confinement, but they do not have many of the advantages of SYM coils, particularly for reactor applications. Split-wedge mirror coils improve volume utilization and trapped particle confinement, but they do not enhance the confinement of transitional and passing particles. High field magnets improve confinement by permitting a larger mirror ratio and a larger plasma radius by virtue of their smaller cross-sectional area and higher current density. The relative merits of each magnetics configuration are discussed, including the effects on single particle confinement, reactor volume utilization, materials requirements, engineering design considerations, and reactor assembly, maintenance, and accessibility.