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Author(s):
M. Yokoyama et al.
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Title:
Core Electron-Root Confinement (CERC) in Helical Plasmas
Date of publication:
Oct. 2006
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Key words:
21 IAEA Fusion Energy Conference , EX/5-3
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Abstract:
The improvement of core electron heat confinement has been realized in a wide range of helical devices such as CHS, LHD, TJ-II and W7-AS. Strongly peaked electron temperature profiles and large positive radial electric field, E_r, in the core region are common features for this improved confinement. Such observations are consistent with a transition to the “electron-root” solution of the ambipolarity condition for E_r in the context of the neoclassical transport, which is unique to non-axisymmetric configurations. Based on this background, this improved confinement has been collectively dubbed “core electron-root confinement” (CERC). The electron heat diffusivity is much reduced due to the electron-root E_r compared to that with E_r=0 assumed, which clearly demonstrates that 1/nu ripple diffusion (nu being the collision frequency) in low-collisional helical plasmas could be overcome. The magnetic configuration properties play important roles in this transition, and thresholds are found for the collisionality and electron cyclotron heating (ECH) power.
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