T. Fülöp P. Helander
The theory of neoclassical transport in an impure toroidal plasma is extended to allow for larger pressure and temperature gradients and faster toroidal rotation than are usually considered. Under these conditions, the density of heavy impurities is not constant on flux surfaces, and the neoclassical transport becomes a nonlinear function of the gr…
PublishedC. N. Lashmore-Davies J. A. Wesson C. G. Gimblett
A uniform compressible plasma with a uniform flow along the magnetic field in the presence of a resistive wall is shown to be subject to two instabilities. For the first instability, the flow velocity is required to exceed the Alfve´n speed, whereas for the second it need only exceed the sound speed. For a sufficiently high ion temperature, ion La…
PublishedS. C. Chapman R. O. Dendy G. Rowlands
There is increasing evidence that the Earth’s magnetosphere, like other macroscopic confined plasma systems (magnetic fusion plasmas, astrophysical accretion discs), displays sandpile-type phenomenology so that energy dissipation is by means of avalanches which do not have an intrinsic scale. This may in turn imply that these systems evolve via s…
PublishedT. Fülöp Peter J. Catto P. Helander
Bulk ion flow can be modified by ion–neutral interactions in the edge region of tokamaks where neutral atoms are abundant. In this region, the standard neoclassical expression for the ion flow is not consistent with the experimental observations. Previous work in the plateau regime [Valanju et al., Phys. Fluids B 4, 2675 (1992)] suggests that the…
PublishedPeter 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…
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…
PublishedParag Vyas Denis Mustafa A. William Morris
Theoretical and experimental work on the vertical position control system on the COMPASS-D tokamak is described. An analog proportional 1 derivative (P 1 D) system is currently used, and two important sources of disturbance are observed in the system. One source is 600-Hz noise from thyristor power supplies, and the other is impulselike disturbance…
Published