UKAEA Papers

Showing 1881 - 1890 of 1902 UKAEA Paper Results
1991

The purpose of this paper is to investigate the possible relationships between transport properties such as thermal diffusivity and resistivity on the one hand, and the magnetic properties such as q profile and toroidal flux change on the other, in tokamaks that exist under macroscopically quasistationary conditions. It is experimentally well estab…

Published
1991

The question of the influence of nonaxisymmetric field perturbations on tokamaks is investigated. Recent experiments in the COMPASS-C tokamak [in Proceedings of the 15th Symposium on Fusion Technology, Utrecht (North-Holland, Amsterdam, 1989), Vol. 1, p. 3611 with externally applied helical fields reveal that magnetic islands do not appear until th…

Published
1991

The gyrokinetic theory of ion cyclotron resonance is extended to include propagation at arbitrary angles to a straight equilibrium magnetic field with a linear perpendicular gradient in strength. The case of the compressional Alfvén wave propagating in a D(3He) plasma is analyzed in detail. A self-consistent local dispersion relation is obtained u…

Published
1991

In a cylindrical plasma, tearing modes can be calculated by asymptotic matching of ideal magnetohydrodynamic (MHD) solutions across a critical layer. This requires a quantity that represents the “discontinuity*’ in the ideal solution across the layer. In a torus, poloidal harmonics are coupled and there are many critical surfaces for each toroi…

Published
1990

Two designs of electron suppressor have been tested in a volume negative ion source operating dc with a large extraction aperture diameter (16 mm). Both suppressors employ magnetic fields to divert the electrons near the extraction aperture onto collector electrodes. However, while one suppressor uses a fixed field produced by permanent magnets, th…

Published
1990

One problem inherent in the use of small planar Langmuir probes to analyze low-density plasma is expansion of the space-charge sheath with increased probe potential due to the departure from planarity caused by a nonnegligible sheath edge. Experimental evidence showing the existence of significant edge effects in the ion saturation region of the ch…

Published
1990

A tangentially viewing pinhole camera has been used to image the COMPASS-C plasma in the vacuum ultraviolet and soft x-ray spectral regions with framing rates up to 330 Hz. The PC-based system acquires up to 256 128 X 128 pixel images per shot and incorporates an array processor to allow on-line tomographic reconstructions. Data compression is used…

Published
1990

Local extrema in the equilibrium magnetic field strength can occur in tokamak plasmas when the plasma beta is increased. Furthermore, the magnetic field strength experienced by an electromagnetic wave propagating along a vertical chord in lower-beta tokamak plasmas may also pass through an extremum. For both these reasons, it is of interest to calc…

Published