To understand the physical mechanism underlying the cross-field transport of mass and energy in magnetoplasmas is a long-standing problem in fusion research. Woods (1987) has recently developed a second-order transport theory which has been used to explain a number of transport-related phenomena observed in tokamaks. Here, we apply second-order transport theory to the reverse field pinch (RFP) and a phenomenon observed in tokamaks known as 'snakes'. Expressions for the mass and energy confinement times in the RFP, Ï<sub>p</sub> and Ï<sub>e</sub>, are deduced and agreement with experimental results from HBTX is found. For typical operating conditions the times Ï<sub>p</sub> ~ 0.1ms and Ï<sub>e</sub> ~ 0.2ms are observed in HBTX. Second-order transport theory predicts Ï<sub>p</sub> ~ 0.4ms and Ï<sub>e</sub> ~ 0.4ms for this machine. Scaling laws for β<sub>p</sub> versus η<sub>e</sub>,β<sub>p</sub> versus I<sub>Ï</sub> and Ï<sub>e</sub> versus I<sub>Ï</sub> are compared with measurements from HBTX and agree well with observation. Snakes are large density perturbations observed in JET after fuel pellet injection. Typical snakes in JET are remarkably stable and are found to have density decay times longer than predictions based on neoclassical theory (Stringer 1987). After their formation, snakes have even been observed to grow (Weller <i>et al.</i> 1987), which suggests the presence of an inward diffusion mechanism. There is also some evidence for a temperature depression in the snakes region. An explanation of the stability and energy balance in snakes based on second-order transport theory is proposed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:670322 |
| Date | January 1989 |
| Creators | Deane, G. B. |
| Contributors | Woods, Leslie Colin |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:c087aa58-7ae2-4f3c-a78e-887f1bca8b76 |
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