Confinement and transport in stellarators

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Abstract
A model of particle transport has been incorporated in the equilibrium and stability code beta. From the Clebsch potentials of Boozer’s theory a first‐order partial differential equation with constant coefficients is derived relating a guiding center step size λ∥/‖∇s‖ to the parallel gyroradius ρ∥. In terms of the Fourier coefficients of ρ∥, a formal solution for λ∥ is found that exhibits the resonance at rational values of the rotational transform explicitly. Phenomenological reasoning leads to a transport coefficient for both circulating and trapped particles that involves integrals of λ2∥ analogous to a term in the Mercier stability criterion depending on the square of the Pfirsch–Schlüter current. Good correlation has been established between plateau values of this transport coefficient and Monte Carlo calculations performed by H. Wobig for the Wendelstein VII‐AS experiment, for a typical Heliac, and for reference l=2 stellarators.

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