In the course of the Preliminary Tritium Experiment in JET, where combined deuterium and tritium neutral beam injection generated a DT fusion power of 1.7 MW, ion cyclotron emission (ICE) was measured in the frequency range Y I 180 MHz. The ICE spectra contain superthermal, narrow, equally spaced emission lines, which correspond to successive cyclotron harmonics of deuterons or alpha particles at the outer midplane, close to the last closed flux surface at major radius R -4.0 m. Above about 100 MHz the lines merge into a relatively intense continuum. The ICE signal fluctuates rapidly in time, and is extinguished whenever a large amplitude edge localized mode (ELM) occurs.In pure deuterium and mixed DT discharges ICE spectra are similar in form, but on changing from pure D to mixed D + T neutral beam injection at constant power, the intensity of the ICE rises in proportion to the increased neutron flux: this indicates that fusion alpha particlesand not beam ionsprovide the free energy to generate ICE. The JET ICE database, which now extends over a range of six decades in signal intensity, shows that the time averaged ICE power increases almost linearly with total neutron flux. The rise and fall of the neutron flux during a single discharge is closely followed by that of the ICE signal, which is delayed by a time of the order of the fusion product slowing down time. This feature is well modelled by a TRANSP code simulation of the density of deeply trapped fusion products reaching the plasma edge. Calculations reveal a class of fusion products, born in the core, which make orbital excursions of sufficient size to reach the outer midplane edge. There, the velocity distribution has a ring structure, which is found to be linearly unstable to relaxation to obliquely propagating waves on the fast Alfv6n-ion Bernstein branch at all ion cyclotron harmonics. The paper shows how ICE provides a unique diagnostic for fusion alpha particles.

When an ion cyclotron resonance heating (ICRH) antenna array is phased (A$ # 0 or T), the excited asymmetric k,, spectrum can drive non-inductive currents by interaction of fast waves both with electrons (transit time magnetic pumping (e-TTMP) and Landau damping (e-LD)) and with ions at minority (fundamental) or harmonic cyclotron resonances, depending upon the scenario. On the basis of earlier theories, a simplified description is presented that includes the minority ion and electron current drive effects simultaneously in a 3-D ray tracing calculation in the tokamak geometry. The experimental results of sawtooth stabilization or destabilization in JET using the minority ion current drive scheme are presented. This scheme allows a modification of the local current density gradient (or the magnetic shear) at the q = 1 surface resulting in a control of sawteeth. The predictions of the above model of current drive and its effects on sawtooth period calculated in conjunction with a model of stability of internal resistive kink modes, that encompasses the effects of both the fast particle pressure and the local (q = 1) magnetic shear, are found to be qualitatively in good agreement with the experimental results. Further, the results are discussed of our model of fast wave current drive scenarios of magnetic shear reversal with a view to achieving long duration high confinement regimes in the forthcoming experimental campaign on JET. Finally, the results are presented of minority current drive for sawtooth control in next step devices such as the International Thermonuclear Experimental Reactor (ITER).

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A number of experiments with heating of deuterium-tritium (D-T) plasmas using waves in the ion cyclotron range of frequencies (ICRF) have been carried out at the Joint European Torus (JET). The results of these experiments have been analysed by comparing experimentally measured quantities with results of numerical simulations. In particular, four scenarios have been examined: (1) heating of minority (~5−20%) deuterons at the fundamental ion cyclotron frequency, ω ω = cD ; (2) second harmonic heating of tritium, ω ω = 2 cT ; (3) fundamental minority heating of 3 He with a few percent of 3He, and (4) second harmonic heating of deuterium, ω ω = 2 cD . An important aim of the analysis is to assess if the present understanding of the ICRF physics is adequate for predicting the performance of ICRF in D-T plasmas. In general good agreement between experimental results and simulations is found which increases the confidence in predictions of the impact of ICRF heating in future reactors. However, when a relatively high deuterium concentration was used in the ω ω = cD scenario, discrepancies are observed. In order to increase confidence in the simulations, we have studied the sensitivity of the simulation results to various plasma parameters.