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The standard neoclassical theory of the impurity transport in tokamak plasma is improved by including the plasma elongation effect. The neoclassical up/down asymmetry of the impurity density is largely enhanced by the plasma elongation and is under-predicted by the neoclassical theory with the circular cross section assumption. Accordingly, the impurity Pfirsch–Schlüter neoclassical transport is also enhanced by the plasma elongation.

The Hollow cathode z-pinch is designed and operated to investigate the ejected plasma through the hollow cathode. The hollow cathode is simulated using the snow plow model. The model uses three phases: the radial inward phase, the reflected shock phase and expansion phase. The differential equation of plasma motion and its electric circuit equation are derived and solved numerically using the code. The snow plow model suggested that the plasma radius decreases to zero, so this problem was solved adding the effect of the internal kinetic pressure and the shock wave into the general equation of motion using β factor. The effect of β factor (ratio of the kinetic pressure of plasma to magnetic pressure) is studied on plasma temperature, plasma radii, plasma velocity, pinching time and plasma elongation distance. The simulated results illustrate that the β factor varies from 0 to 0.79. The data illustrate that the elongation velocity of plasma is increased by decreasing the β factor, while the elongation displacement of the plasma is increased by increasing of the ring radii of the hollow cathode. The code illustrates that a multi-pinch of the CS could be appeared at high energy. [ABSTRACT FROM AUTHOR]

Abstract: In the vast majority of tokamaks, the high confinement mode (H mode) has been systematically achieved and studied. The transition to the H-mode is a very complex phenomenon but it can be represented by the relation between a limited number of macroscopic quantities. The predicted power (P Thresh) for accessing the H-mode is generally estimated by statistical analysis of multi-machine experimental data and typically presented in terms of equations in power law monomial form. Even if the positive effects of the plasma shape on the confinement time have been clearly documented, the dependence of the P Thresh on elongation and triangularity is still an aspect no completely clarified. The objective of this paper is to assess whether the P Thresh dependency on the shape of the plasma can be derived by a statistical approach using a recent version of ITPA International Global Threshold Data Base (IGDBTHv6b). A statistical method to select relevant macroscopic quantities in the candidate models for the scaling of P Thresh is presented and a multi-machine scaling law, using non-linear regression techniques, is derived. [Copyright &y& Elsevier]