Confinement and power balance in the S-1 spheromak

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Abstract
The confinement and scaling features of the S-1 spheromak have been investigated using magnetic, spectroscopic and Thomson scattering data in conjunction with numerical modelling. Results from the multi-point Thomson scattering diagnostic show that the central beta remains constant (βt0 ~ 5%) as the plasma current density increases from 0.68 to 2.1 MAm−2. The density is observed to increase slowly over this range, while the central electron temperature increases much more rapidly. Analysis of the global plasma parameters shows a decrease in the volume average beta and the energy confinement as the total current is increased. The power balance has been modelled numerically with a zero-dimensional non-equilibrium time dependent coronal model and is consistent with the experimental observations. In addition to energy losses from radiation, the model includes convection and conduction. The conduction includes magnetic field fluctuation induced energy loss.