[en] In this paper, plasma transport at magnetic axis in tokamaks is systematically studied by means of variational principle. The ion thermal conductivity and the bootstrap current at magnetic axis have been derived. The conclusion is that the ion thermal conductivity at magnetic axis is larger than outer part of the plasma and it has weaker dependence on the magnetic field, which is called Bohm-like diffusion. For the long-term operation of tokamak reactor, especially for the low aspect ratio tokamaks, bootstrap current may play an important role. Ten percent of bootstrap current density at magnetic axis could reduce the need of noninductive current drive. High temperature is favourable in confinement in the tokamak reactor scale. The variational principle is proved to be more accurate and effective in evaluation of all neoclassical transport coefficients

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[en] The authors mainly study the vertical displacement instability in a low-aspect-ratio tokamak, and discuss the relation between aspect-ratio and elongation. For low-aspect-ratio tokamaks, it is possible for the magnetic flux surface to have a larger elongation. Meanwhile, the authors also find that the elongation will tend to reduce when A ≤ √2, and the range of the triangular deformation parameter and the aspect-ratio of tokamak are subject to certain restrictions

[en] The quasilinear F-P equation with the toroidal effects is numerically solved by a multiple shooting method. The ratio of plasma current density to unit power density J/Pd is calculated on the basis of the solution obtained above. The numerical results derived from this method are in agreement with those obtained from physical analysis

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[en] Neoclassical transport for the shaped tokamak with X point is investigated using Hamiltonian formalism. For a set of Soloveev's configurations, the neoclassical diffusion coefficient is rigorously derived for the plateau regime which is inversely proportional to the connection length. When an X point appears at plasma boundary, the diffusion coefficient is greatly reduced by the much longer connection length compared with a circular cross-section plasma. Since the formalism is not limited for aspect ratio, for A=1.3, it may be valid in a very narrow range of collisionality, 0.8 < ν*_i < 1.0, at ψ/ψ₀ = 0.95. In the range of collisionality, the detrapping rate is very high. (author)

[en] The physical design of poloidal field coils on SUNIST is described. The main content is the optimum of MHD equilibrium configuration, in the first step of SUNIST operation, it is vertical stable. Only shaping field coils are in series each other. The position of shaping field coils and the distribution of current in it are optimized. Using the regularization method and method of so called blind man climbing mountain, the distribution of current in OH coil is optimized

[en] An ideal current distribution in the air-core transformer coils is obtained using variation principle. Climbing mountain method is utilized for optimizing the dimension and position of the real coils. Not only can the requirement of minimizing the stray field in the plasma region be guaranteed, but also integer turns for the coil can be realized. The latter brings a significant convenience to engineering

[en] The ion orbit loss flux at the plasma edge is calculated, including the squeezing factor. A bifurcation solution is found by balancing the ion loss flux and the anomalous electron flux. At a certain level of anomalous electron flux, the plasma poloidal rotation increases with ion temperature. When the fluctuations are suppressed and the electron confinement is improved, the radial electric field and its shear can increase appreciably at the same ion temperature. The squeezing factor plays an essential role in the L-H mode transition. More negative electric fields and more negative electric shear diminish the anomalous fluxes. The whole picture is in agreement with experimental signatures during the transition. (author). Letter-to-the-editor. 20 refs, 3 figs