The Helically Symmetric Perspective

• The Tokamak possesses desirable physics attributes for a fusion reactor based on its axisymmetric nature
  • good single-particle confinement
  • can be designed for low aspect ratio
  • simple coil-set

• The lack of symmetry in the magnetic fields in conventional stellarators results in large deviations of particle orbits from magnetic surfaces and direct loss orbits - enhanced low-collisionality transport and poor low-collisionality confinement

• Stellarator with helically symmetric field inherently possesses solutions to many problems currently being examined in tokamak research and in conventional stellarator research
  • intrinsically steady-state devices
  • no observed density limit
  • no required plasma current for confinement
  • |B| is independent of a helical-like angle variable
  • neoclassical transport is directly analogous to, and reduced, as compared to an equivalent axisymmetric system (Tokamak)
  • 1/ν regime suppressed
  • no superbanana orbits
  • no direct loss orbits
  • good collisionless alpha particle confinement

HSX is the only device in the world that has a magnetic field structure that has been termed Quasi-Helically Symmetric (QHS). Quasi-helically symmetric stellarators, to a good approximation, possess a direction of symmetry and are therefore topologically equivalent to a tokamak without plasma current. They achieve this near-symmetry by having virtually no toroidal curvature that a conventional toroidal device would have if it had an aspect ratio greater than 400.

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File last modified Friday, 17-Nov-2006 12:11:57 CST