Fast ion density measurements using high energy neutral particle analysis in JET

In the JET tokamak the perpendicular velocity distribution function of ICRF heated ions is inferred in the energy range 0.3 £ E (MeV) £ 1.5 from neutral particle analyser measurements of the emitted high energy atomic flux. The measurements are integrated along a vertical line of sight through the plasma centre, with a finite viewing solid angle. A method is presented to deduce the ICRF heated minority ion density in the plasma centre taking into full consideration the geometry of the measurements. The results are verified against independent measurements of fast ion density and perpendicular energy content, and quantitative agreement is obtained. These results further validate the model of impurity induced neutralization, which was developed to interpret the high energy atomic flux measurements in JET. They give access to fundamental properties of the ICRF heated ion distribution function, and provide improved tools for understanding the behaviour of fast ion populations in forthcoming fusion plasma experiments.