Electron density, n_e, and temperature, T_e, in the MkIIa divertor have been measured using neutral helium line ratios. Experimental evidence indicates that the spectroscopic sugnal for helium injected from the vertical target is dominated by recycling. When helium is injected from the horizontal target it is possible to differentiate between injected and recycled spectral sources. To determine the spatial location of the neutral helium emission, and hence of the n_e, T_e measurements, an interpretative model hass been developed which uses the impurity/neutral codes, DIVIMP/NIMBUS, the atomic database ADAS and the diagnostic lines of sight. Measurements and simulations have been performed using the various injection points over a range of target conditions. Comparisons with other divertor diagnostics, such as the divertor interferometer and target Langmuir probes are presented.
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