Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR

Relationship of edge localized mode burst times with divertor flux loop signal phase in JET

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 the Be II emission at the divertor. The ELMs analysed arise from intrinsic ELMing, in that there is no deliberate intent to control the ELMing process by external means. We use ELM timings derived from the Be II signal to perform direct time domain analysis of the full flux loop VLD2 and VLD3 signals, which provide a high cadence global measurement proportional to the voltage induced by changes in poloidal magnetic flux. Specifically, we examine how the time interval between pairs of successive ELMs is linked to the time-evolving phase of the full flux loop signals. Each ELM produces a clear early pulse in the full flux loop signals, whose peak time is used to condition our analysis. The arrival time of the following ELM, relative to this pulse, is found to fall into one of two categories: (i) prompt ELMs, which are directly paced by the initial response seen in the flux loop signals; and (ii) all other ELMs, which occur after the initial response of the full flux loop signals has decayed in amplitude. The times at which ELMs in category (ii) occur, relative to the first ELM of the pair, are clustered at times when the instantaneous phase of the full flux loop signal is close to its value at the time of the first ELM

Erosion and transport of Sn and In in the SOL of MAST plasmas

A satisfactory method for monitoring the erosion of vessel wall tiles in a fusion power plant remains an important missing diagnostic in the fusion program. Spectroscopic observation of embedded impurity layers may provide such a capability. In a preliminary experiment, Sn and In have been introduced to the scrape off layer of MAST plasmas by erosion from a target mounted on the reciprocating probe system, and have been successfully observed spectroscopically in the core and at the edge. The atomic transitions corresponding to each observed spectral line and feature have been predicted and then identified, with those in the visible region being used to estimate the erosion/influx rate. The confined plasma emission has been measured and modelled using the impurity transport code UTC-SANCO. The results show that eroded Sn and In emission is observable and distinguishable in MAST, and shows that the technique has promise for use in future devices. (c) 2007 A.R. Foster. Published by Elsevier B.V. All rights reserved

The removal of co-deposited hydrocarbon films from plasma facing components using high-power pulsed flashlamp irradiation

The use of carbon-based materials for first wall components in tokamaks results in the formation of hydrocarbon deposits on divertor components that could lead to a high level of tritium retention in future fusion devices. Experiments at UMIST have demonstrated that photonic cleaning using high power Xenon flashlamp sources is an efficient method for removing such films and represents a good candidate technology for international thermonuclear experimental reactor (ITER) operations. Studies have shown that effective film removal occurs at a fluence threshold of between 1.9 and 2.5 J/cm2. The by-products of the cleaning process, both particulates and gases, have been characterised using particle sizing spectrometry and quadrupole mass spectrometry respectively. It is found that hydrogen, methane, acetylene, ethylene, ethane and carbon dioxide are the principal gaseous products produced during the cleaning process, which also produces a significant fraction of particulates in the size range 2–20 μm

Changes in regional planning A new opportunity for sustainable development

Period of award: 01 Jan 2000 to 31 Dec 2002. Includes bibliographical referencesAvailable from British Library Document Supply Centre- DSC:3739. 0605(000238368-A) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Interpretive modelling of scrape-off plasmas on the MAST tokamak

Electrical currents in the scrape-off layer (SOL) of MAST are modelled using an interpretive Onion-Skin Model (OSM) constrained with experimental data from MAST diagnostics. The model was extended to include the effects of the magnetic mirror force, which has a strong influence on the particle and momentum balance in spherical tokamaks, such as MAST [1]. These modifications serve to more accurately model the parallel electric fields present in the MAST SOL, which can alter plasma dynamics via the E x B drift. Simulations show that the electrical current at the divertor targets is predominantly thermoelectric, whereas Pfirsch-Schluter currents have a greater contribution to the total current in the bulk of the SOL plasma. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved

Spatial and Temporal Structure of Edge-Localized Modes

This Letter provides information on the spatial and temporal structure of periodic eruptions observed in magnetically confined laboratory fusion plasmas, called edge-localized modes (ELMs), and highlights similarities with solar eruptions. Taken together, the observations presented in this Letter provide strong evidence for ELMs being associated with a filamentlike structure. These filaments are extended along a field line, are generated on a 100   μs time scale, erupt from the outboard side, and connect back into the plasma. Such structures are predicted by a theoretical model based on the “ballooning” instability, developed for both solar and tokamak applications