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) over tilde perpendicular t o of minority ion cyclotron range of frequencies (ICRF) heated protons in the Joint European Torus (JET). A relation is established between (T) over tilde perpendicular to and the perpendicular proton temperatu re T perpendicular to(0) at the position of maximum power deposition. At energies E much greater than T perpendicular to(0), the value of (T ) over tilde perpendicular to inferred from the NPA is nearly equal to T perpendicular to(0). In the opposite limit E much less than T perpe ndicular to(0), it is shown that (T) over tilde perpendicular to much less than T perpendicular to(0). Applying this model to NPA measuremen ts from a JET pulse with varying ICRF power P-RF, it is found that the scaling of T perpendicular to(0) with P-RF in the 2 to 10 MW range is almost linear, as expected. Moreover, calculated values of the ICRF h eated proton energy content, based on deduced values of T perpendicula r to(0), agree with diamagnetic measurements. The NPA measurements thu s give access to a fundamental property of the heated proton energy di stribution, which plays a crucial role in sawtooth stabilization.