Interpretation of measurements of ICRF heated minority proton distributions in JET

Neutral particle analyser (NPA) measurements of emitted hydrogen flux, integrated along a chord through the plasma centre, have been used to infer a perpendicular tail temperature T ⊥ of minority ion cyclotron range of frequencies (ICRF) heated protons in the Joint European Torus (JET). A relation is established between T ⊥ and the perpendicular proton temperature T ⊥ (0) at the position of maximum power deposition. At energies E >> T ⊥ (0), the value of T ⊥ inferred from the NPA is nearly equal to T ⊥ (0). In the opposite limit E << T ⊥ (0), it is shown that T ⊥ << T ⊥ (0). Applying this model to NPA measurements from a JET pulse with varying ICRF power P RF , it is found that the scaling of T ⊥ (0) with P RF in the 2 to 10 MW range is almost linear, as expected. Moreover, calculated values of the ICRF heated proton energy content, based on deduced values of T ⊥ (0), agree with diamagnetic measurements. The NPA measurements thus give access to a fundamental property of the heated proton energy distribution, which plays a crucial role in sawtooth stabilization