Estimates of neoclassical transport

• A particle orbit deviates from the magnetic surfaces, to the extent that the electrostatic potential varies on the surface (since the particle does not feel the pressure gradient force), and because of the ?B and curvature drifts.

• In the zero temperature limit, the particle orbits are in the surface, and confinement must be excellent.

• For finite temperature, the deviation sets the step size for random walk diffusion driven by particle collisions - ‘neoclassical’ transport

• Diffusive confinement time:

  • D=(?r)2/?e
  • ?p=a2/D= ?e a2/(?r)2

• We will estimate (?r)2 to get to particle confinement time

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