Self-consistent determination of the ion thermalization rate at the plasma boundary of TJ-II by the supersonic He beam diagnostic

A method for measuring the thermalization rate of He ions injected into the edge of a magnetically confined plasma, free from calibration and photon-to-ion ratio uncertainties, has been deduced for the first time. He+ ions are introduced into a plasma boundary by means of a supersonic He beam and the radial distribution of neutral He and He+ emissions along the beam propagation path through the plasma is analysed. The new technique allows for the determination of local ion temperature profiles in non-rotating edge plasmas if the impurity composition at the edge is known, thus extending the application of the He beam diagnostic to Ti edge profile measurements. Methods to disentangle rotation and thermalization losses are also proposed, thus further extending the technique to plasma rotation measurements near the last closed flux surface.