Peter J. Catto P. Helander J. W. Connor R. D. Hazeltine
The edge plasma of a tokamak is affected by atomic physics processes and can have density and temperature variations along the magnetic field that strongly modify edge transport. A closed system of equations in the Pfirsch–Schluter regime is presented that can be solved for the radial and poloidal variation of the plasma density, electron and ion…
PublishedT. Fülöp Peter J. Catto P. Helander
Ion plasma flow and flow shear just inside the last closed flux surface of a tokamak can be strongly altered by neutral atoms and anomalous effects. For a collisional edge, neutrals modify the standard Pfirsch–Schluter expression for the parallel ion flow through the strong coupling provided by ion–neutral collisions. Even for rather small neut…
PublishedP. Helander
The theory of neoclassical transport in an impure, toroidal plasma is extended to allow for steeper pressure and temperature gradients than are usually considered. It is found that the ion particle flux is a nonmonotonic function of these gradients for plasma parameters typical of the tokamak edge. A sudden transition between states of low and high…
PublishedR. O. Dendy P. Helander
Self-organized criticality ~SOC! often features in sandpile-type modeling of complex systems such as magnetic fusion plasmas, but its observed role in real sandpiles is equivocal. Here, a probabilistic model displaying some of the observed phenomenology of real sandpiles is proposed. It generates avalanches involving particle loss that, like most e…
PublishedD. C. Mcdonald R. A. Cairns C. N. Lashmore-Davies G. Le Clair
Detailed ray tracing, of wave propagation in a plasma near electron cyclotron resonances, suggests that refraction can lead to reduced absorption, in some cases. By studying the full wave equation for the ordinary wave near the fundamental, in a slab model, it is shown that such refraction does indeed reduce absorption, for this particular case, bu…
PublishedC D Warrick B Lloyd M R O’Brien
Electron cyclotron (EC) waves can perform a variety of roles in ITER including start-up assist, heating to ignition, on and off-axis current drive and instability control. EC wave absorption is robust and well understood producing highly localised heating with total absorption anticipated for almost all parameters foreseen in ITER. Other advantages…
PublishedR. D. Hazeltine P. Helander Peter J. Catto
The simplest nontrivial model of transport across a magnetic island chain in the presence of collisionless streaming along the magnetic field is solved by a Wiener–Hopf procedure. The solution found is valid provided the boundary layer about the island separatrix is narrow compared to the island width. The result demonstrates that when this assum…
PublishedR. A. Cairns V. Fuchs C. N. Lashmore-Davies
We apply a fast wave approximation to the propagation of the fast wave across the magnetic field. This approximation involves replacing the hot plasma conductivity tensor by an approximation which reduces the problem to a second order differential equation. Such a procedure is particularly useful in the high harmonic regime, where many terms with t…
PublishedColin George Windsor Thomas Noel Todd David Leonard Trotman Michael Edward Underhill Smith
The plasma position and shape on the COMPASS-D tokamak have been controlled simultaneously with a 75- kHz bandwidth, hard-wired, real-time neural network. The primary network operates with up to 48 selected magnetic inputs and has been used in the vertical position control loop to control the position of the upper edge of the plasma at the radius o…
Published