Ultra Low Aspect Ratio Stellarator or Hybrid Configurations

Novel concepts of an ultra-low-aspect-ratio stellarator system, called a Spherical Stellarator (SS), or a stellarator-tokamak hybrid system, called SMARTH (Small Aspect Ratio Toroidal Hybrid) are discussed for high-β regimes of operation. Self-consistent analysis of the three-dimensional MHD equilibria with inductively driven plasma current or bootstrap current is presented. It is stressed that the bootstrap current in SS can be large and is flowing in such a direction that the rotational transform produced enhances the vacuum rotational transform. This feature increases the equilibrium β-limit. The high-β equilibria in SS and SMARTH (β(0) > 30%, β ⋍ 8-9%) are demonstrated, correspondingly, with the bootstrap current and the ohmic current. Possible experiments and scalings, including those for reactor parameters, are outlined.