1 - Nuclear Sciences and Applications - IAEA

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IAEA-CN-50/A-VII-2 379
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warm core residue
FIG. 2. Reconstructions of successor oscillations after a full sawtooth collapse using electron cyclotron
emission (ECE) and soft X-ray tomography (SXR). The bar on the time axis indicates the interval over
which ECE measurements are used to reconstruct the contour plot. The SXR contour plot is a 'snapshot'
at one instant during this period.
energy, resulting in a flattening of the central temperature profile on a
timescale of lOO^s. This picture of the collapse, obtained by soft X—ray
tomography, is supported by reconstructions of successor oscillations using
ECE measurements (the former employs measurements from two
perpendicular cameras, the latter exploits the plasma rotation to
reconstruct two-dimensional images from measurements along a single line
of sight through the plasma). Figure 2 compares reconstructions of
successor oscillations of the same collapse by the two techniques. Although
the ECE reconstructions have lower time resolution, they are in agreement
with the soft X—ray results. More detailed analysis confirms the conclusion
[1,2] that the collapse resembles a broad convective flow rather than a
resistive reconnection in a narrow layer.
Certain subordinate relaxations ('fast* partial sawteeth) share some aspects
of the full sawtooth collapse: they occur on a rapid timescale and are
accompanied by large successor oscillations. However, there are important
differences. Whereas the full collapse leads to a convective flow of the hot
plasma centre and the formation of a cold bubble in the plasma core, soft
X—ray tomography and fast ECE temperature measurements reveal that