Anthony J. Webster
During plasma instabilities, “surface currents” can flow at the interface between the plasma and the surrounding vacuum, and in most cases, they are a harmless symptom of the instability that is causing them. Large instabilities can lead to “disruptions,” an abrupt termination of the plasma with the potential to damage the machine in which …
PublishedAnthony Webster
The edge of a Tokamak plasma is interesting due to its geometrical structure that is difficult to model either analytically or computationally, its tendency to form "transport barriers" with increased confinement of energy and momentum, and the edge-localised instabilities associated with transport barriers that threaten the lifetime of components …
PublishedAnthony J. Webster
The surface or “skin” current that can flow at a perturbed interface between plasma and vacuum is considered in the approximation where a surface marks a sharp transition from plasma to vacuum. A short magnetohydrodynamic calculation gives an exact and general expression for the component perpendicular to the average of the magnetic field eithe…
PublishedA. J. Webster C. G. Gimblett
Large tokamaks capable of fusion power production such as ITER, should avoid large edge localized modes (ELMs), thought to be triggered by an ideal magnetohydrodynamic instability due to current at the plasma’s separatrix boundary. Unlike analytical work in a cylindrical approximation, numerical work finds the modes are stable. The plasma’s sep…
PublishedA. J. Webster
It was shown in the first part to this paper how a simple magnetohydrodynamic model can be used to determine the stability of a tokamak plasma’s edge to peeling external kink modes. It was found that stability is determined by the value of , a normalized measure of the discontinuity in the radial derivative of the radial perturbation to the magne…
PublishedA. J. Webster C. G. Gimblett
A potentially serious impediment to the production of energy by nuclear fusion in large tokamaks, such as ITER [R. Aymar, V. A. Chuyanov, M. Huguet, Y. Shimomura, ITER Joint Central Team, and ITER Home Teams, Nucl. Fusion 41, 1301 (2001)]and DEMO [D. Maisonner, I. Cook, S. Pierre, B. Lorenzo, D. Luigi, G. Luciano, N. Prachai, and P. Aldo, Fusion En…
PublishedAnthony J. Webster
This paper describes physically and mathematically how the plasma-vacuum boundary of a tokamak plasma equilibrium can be perturbed to form a separatrix with an X-point, while having an otherwise negligible affect on the plasma equilibrium. A deliberate consequence of the technique is that the radial and poloidal extent of the perturbed region may b…
PublishedJ. W. Connor R. J. Hastie A. J. Webster
The destabilization of ideal magnetohydrodynamic ballooning modes at finite rotation shear is demonstrated for the model s - equilibrium by exploiting low magnetic shear, s , to simplify the two-dimensional stability problem to a one-dimensional eigenvalue problem. This simpler calculation captures the same features as exhibited by a full two-dimen…
PublishedA. J. Webster D. J. Szwer H. R. Wilson
Modern tokamaks can produce transport barriers TBs—localized regions with an increased energy confinement. Previous studies have been unable to examine the stability of internal TBs to radially extended short-wavelength magnetohydrodynamic instabilities “ballooning modes”, for the usual case with a sheared plasma flow and a magnetic shear tha…
Published