Parallel electron temperature and density gradients measured in the JET MkI divertor using thermal helium beams

This paper describes the first application of a thermal helium beam diagnostic to a divertor. The helium beam is used to determine spectroscopically the electron temperature and density from the inner and outer strike paints up to the X-point, using helium line ratios which are primarily sensitive to electron density and temperature, as reported by Schweer et al. [J. Nucl. Mater. 196-198 (1992) 174]. Measurement of the neutral helium line intensities in the outer divertor target were performed under attached, high recycling and detached plasma conditions in Ohmic and L-mode discharges. An interpretative model has been developed using the DIVIMP code at JET which incorporates the helium injection point, the nozzle divergence and the viewing arrangement of the periscope for a particular equilibrium.