Comparisons between time dependent simulations and experiments in ion cyclotron heated plasmas in the JET tokamak have been made. A time dependent code, PION-T, has been used to simulate the heating. The scenario that has been analysed is minority heating of hydrogen in a deuterium plasma. Two measured quantities have been compared with the calculations, namely the anisotropic plasma energy content and the 2.4 MeV neutron flux from (D,D) reactions. Two versions of the PION-T code have been used, one with zero banana width and one in which a simplified model for taking the finite width of drift orbits into account is employed. The zero banana width calculations yield good agreement between measurements and calculations for relatively low power levels only. However, with the second version of the code, taking the finite width of the drift orbits into account, good agreement can also be obtained for higher power levels. The non-thermal neutron yield caused by second harmonic absorption by the deuterium is simulated and agreement is found provided the hydrogen concentration, for which no reliable measurements are available, is suitably chosen. Finally, by studying the rapid changes in fast ion energy content in connection with sawtooth instabilities, it is found that about 40% of the fast ions are expelled outside the q=1 surface and that prompt losses are negligible

The onset of a neoclassical tearing mode (NTM) depends on the existence of a large enough seed island. It is shown in the Joint European Torus that NTMs can be readily destabilized by long-period sawteeth, such as obtained by sawtooth stabilization from ion-cyclotron heating or current drive. This has important implications for burning plasma scenarios, as alpha particles strongly stabilize the sawteeth. It is also shown that, by adding heating and current drive just outside the inversion radius, sawteeth are destabilized, resulting in shorter sawtooth periods and larger beta values being obtained without NTMs.

Observations of bulk plasma rotation in radio frequency (RF) heated JET discharges are reported. This study is concentrated on RF heated L-mode plasmas. In particular, the toroidal rotation profiles in plasmas heated by ion cyclotron resonance frequency (ICRF) waves and lower hybrid (LH) waves have been analysed. It is the first time that rotation profiles in JET plasmas with LH waves have been measured in dedicated discharges. It is found that the toroidal plasma rotation in the outer region of the plasmas is in the co-current direction irrespective of the heating scenario. An interesting feature is that the toroidal rotation profile appears to be hollow in many discharges at low plasma current, but a low current in itself does not seem to be a sufficient condition for finding such profiles. Fast ion transport and finite orbit width effects are mechanisms that could explain hollow rotation profiles. This possibility has been investigated by numerical simulations of the torque on the bulk plasma due to fast ICRF accelerated ions. The obtained torque is used in a transport equation for the toroidal momentum density to estimate the effect on the thermal bulk plasma rotation profile.

Third-harmonic ion-cyclotron-resonance heating of 4He-beam ions has produced for the first time on the JET tokamak high-energy populations of 4He ions to simulate 3.5 MeV fusion-born alpha (alpha) particles. Acceleration of 4He ions to the MeV energy range is confirmed by gamma-ray emission from the nuclear reaction 9Be(alpha,ngamma) 12C and excitation of Alfvén eigenmodes. Concomitant electron heating and sawtooth stabilization are observed. The scheme could be used in next-step tokamaks to gain information on trapped alpha particles and to test alpha diagnostics in the early nonactivated phase of operation.