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2011
The overall phenomenology of plasmas emerges from multiple couplings between processes on many different lengthscales and timescales, creating innumerable feedback loops. For example, overall energy confinement – the central emergent property for fusion – is governed by a selfconsistent loop involving: temperature, density, and current profiles…
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2011
The sawtooth instability in tokamak plasmas results in a periodic reorganization of the core plasma. A typical sawtooth cycle consists of a quiescent period, during which the plasma density and temperature increase, followed by the growth of a helical magnetic perturbation, which in turn is followed by a rapid collapse of the central pressure. The …
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2011
The behaviour of the turbulence in magnetic fusion plasmas is discussed in the framework of dimensional analysis. Three main dimensionless parameters are identified, which directly affect the adiabatic response of the plasma and hence control the electron response. They were originally introduced by Scott [B. Scott, Plasma Phys Control. Fusion, 39,…
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2011
The edge of a Tokamak plasma is interesting due to its geometrical structure that is difficult to model either analytically or computationally, its tendency to form "transport barriers" with increased confinement of energy and momentum, and the edge-localised instabilities associated with transport barriers that threaten the lifetime of components …
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2010
A new Thomson scattering diagnostic system has been designed and is being built now on the COMPASS tokamak at the Institute of Plasma Physics ASCR in Prague IPP Prague in the Czech Republic. This contribution focuses on design, development, and installation of the light collection and detection system. High spatial resolution of 3 mm will be achiev…
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2010
A Thomson scattering diagnostic designed to measure both edge and core physics has been implemented on MAST. The system uses eight Nd:YAG lasers, each with a repetition rate of 30 Hz. The relative and absolute timing of the lasers may be set arbitrarily to produce fast bursts of measurements to suit the time evolution of the physics being studied. …
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2010
Thomson scattering measurements with subcentimeter spatial resolution have been made during a sawtooth crash in a Mega Ampere Spherical Tokamak fusion plasma. The unparalleled resolution of the temperature profile has shed new light on the mechanisms that underlie the sawtooth. As magnetic reconnection occurs, the temperature gradient at the island…
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2010
Plasma rotation in tokamaks is of special interest for its potential stabilising effect on micro- and macro instabilities, leading to increased confinement. In MAST, the torque from Neutral Beam Injection (NBI) can spin the plasma to a core velocity ~ 300km.s -1 (Alfven Mach number ~ 0.3). Low density plasmas often exhibit a weakly non-monotonic sa…
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2010
In this contribution, we report on experiments performed in MAST to investigate dust creation, transport and influence on plasma performance. The exceptional diagnostic access of MAST allows stereoscopic imaging of dust particles motion in both the divertor and the main chamber, utilising fast infrared cameras. This technique allows the 3D trajecto…
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2009
This paper describes the interferometer systems on the Large Helical Device (LHD). LHD is equipped with five interferometer systems, each of which has a different operational purpose and measurable electron density range. A single-channel millimeter-wave interferometer is mainly used for low-density plasmas along a horizontal line of sight on the e…
Showing 221 - 230 of 266 UKAEA Paper Results