Showing papers by "Richard D. Gill published in 1987"
TL;DR: In the Joint European Torus the ablation of injected pellets produces a striking resonance effect when the pellets reach surfaces with q values 1 and (3/2), and structures with mode numbers m = 1,n = 1 and m = 3, n = 2 are observed with the soft-x-ray cameras as compact snakelike perturbations.
Abstract: In the Joint European Torus the ablation of injected pellets produces a striking resonance effect when the pellets reach surfaces with q values 1 and (3/2. Subsequently, structures with mode numbers m=1,n=1 and m=3,n=2 are observed with the soft-x-ray cameras for up to 2 s as compact snakelike perturbations. These structures, which persist through several sawtooth collapses, give information on the radii of the q=1 and q=(3/2 surfaces and the q-profile evolution. The observations can be explained by the formation of magnetic islands.
170 citations
TL;DR: A new test of the proportional hazards assumption for two-sample censored data is presented in this paper, which is based on a comparison of different generalized rank estimators of the relative risk.
Abstract: SUMMARY A new test of the proportional hazards assumption for two-sample censored data is presented. The test is based on a comparison of different generalized rank estimators of the relative risk. Asymptotic normality and consistency against alternatives with monotone hazard ratio are shown and relationships to other proposals are pointed out. A related graphical method is presented and recommendations for the choice of appropriate weight functions are given. The strengths and weaknesses of the test procedure proposed are illustrated by four examples featuring various situations which are of practical importance in clinical research.
163 citations
TL;DR: In this article, magnetic separatrix configurations have been produced in JET for plasma currents of up to 3 MA, and experimental results obtained with these configurations show that some features can be achieved that are common to divertor tokamaks.
Abstract: Magnetic separatrix configurations have been produced in JET for plasma currents of up to 3 MA. Experimental results obtained with these configurations show that some features can be achieved that are common to divertor tokamaks. In Ohmic discharges, high recycling regimes can be produced. In neutral beam heated discharges, substantial improvement of the energy confinement time is achieved together with the characteristic signatures of an H-mode. These characteristics include improved particle confinement, flatter density profile, and an increase in electron temperature especially at the edge, leading to a characteristic pedestal feature. At higher neutral beam power, higher plasma densities are reached, with deterioration of beam penetration and strong radiation losses in the outer region of the plasma. The global energy confinement time in the H-mode is observed to degrade with additional power. However, results of radial power balance analysis suggest that in the central region, where the radiation is not important, the degradation of confinement is small.
67 citations
TL;DR: The appearance and disappearance of H-mode behaviour in JET Tokamak discharges is associated with characteristic instabilities detected by edge magnetic probes, arrays of soft X-ray diodes and reflectometry as mentioned in this paper.
Abstract: The appearance and disappearance of H-mode behaviour in JET Tokamak discharges is associated with characteristic instabilities detected by edge magnetic probes, arrays of soft X-ray diodes and reflectometry: edge disruptive-like modes are observed before L-H transitions whereas H-L transitions are accompanied by large bursts of broad-band activity. Other observed fluctuations, shown to be resonant in the central region of the discharge, are not affected by the transitions. The importance of edge fluctuations and induced transport in a magnetic separatrix configuration is thus emphasised.
13 citations