Modelling ohmic confinement experiments on the START tokamak

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Abstract
Ohmic confinement data from the tight aspect ratio tokamak START have been compared with transport simulations carried out with the ASTRA code. Neoclassical expressions have been modified to describe tight aspect ratio configurations and the comparison between START data and models of anomalous transport has been made quantitative using the standard test from statistics. Four confinement models (T11 model, Rebut - Lallia - Watkins model, Lackner - Gottardi model and Taroni et al's Bohm model) have been compared with the START data. Three of the models are found to simulate START's electron temperature data moderately well, while Taroni et al's Bohm model overestimates electron temperatures in START by an order of magnitude. Thus, comparison with START data tends to discriminate against the validity of Bohm models at tight aspect ratio; Bohm models are pessimistic for ITER.