UKAEA Journals

Showing 1 - 10 of 20 Journals Results
2015

A unique sequence of 120 almost identical plasmas in the Joint European Torus (JET) recently provided two orders of magnitude more statistically equivalent data than ever previously available. The purpose was to study movement of eroded plasma-facing material from JET’s new Beryllium wall, but it has allowed the statistical detection of otherwise…

Published
2014

During July 2012, 150 almost identical H-mode plasmas were consecutively created in the Joint European Torus, providing a combined total of approximately 8 minutes of steady-state plasma with 15 000 Edge Localised Modes (ELMs). In principle, each of those 15 000 ELMs are statisti- cally equivalent. Here, the changes in edge density and plasma energ…

Published
2014

A phase relationship is identified between sequential edge localized modes (ELMs) occurrence times in a set of H-mode tokamak plasmas to the voltage measured in full flux azimuthal loops in the divertor region. We focus on plasmas in the Joint European Torus where a steady H-mode is sustained over several seconds, during which ELMs are observed in …

Published
2014

For a two week period during the Joint European Torus (JET) 2012 experimental campaign, the same high confinement plasma was repeated 151 times. The dataset was analysed to produce a probability density function (pdf) for the waiting times between edge-localised plasma instabilities (“ELMs”). The result was entirely unexpected. Instead of a smo…

Published
2014

The generic question is considered: How can we determine the probability of an otherwise quasirandom event, having been triggered by an external influence? A specific problem is the quantification of the success of techniques to trigger, and hence control, plasma instabilities in magnetically confined fusion (MCF) experiments. The successful develo…

Published
2013

The mark-recapture method was devised by Petersen in 1896 to estimate the number of fish migrating into the Limfjord, and independently by Lincoln in 1930 to estimate waterfowl abundance. The technique can be applied to any search for a finite number of items by two or more people or agents, allowing the number of searched-for items to be estimated…

Published
2013

The statistics of edge-localized plasma instabilities (ELMs) in toroidal magnetically confined fusion plasmas are considered. From first principles, standard experimentally motivated assumptions are shown to determine a specific probability distribution for the waiting times between ELMs: the Weibull distribution. This is confirmed empirically by a…

Published
2013

Edge localised mode (ELM) measurements from reproducibly similar plasmas in the Joint European Torus (JET) tokamak, which differ only in their gas puffing rate, are analysed in terms of the pattern in the sequence of inter-ELM time intervals. It is found that the category of ELM defined empirically as type I—typically more regular, less frequent,…

Published
2012

This paper reconsiders the problem of calculating the expected set of probabilities hpii, given the observed set of items {mi}, that are distributed among n bins with an (unknown) set of probabilities {pi} for being placed in the ith bin. The problem is often formulated using Bayes theorem and the multinomial distribution, that with a constant prio…

Published
2011

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 …

Published