[en] Effects of particle and energy losses on the velocity distribution function of minority ions heated by ICRH are considered. An approximate model, including such losses, is derived for the stationary pitch angle averaged distribution function. Energy losses are shown to be important when the energy confinement time is of the same order or smaller than the slowing down time for ion-electron collisions. The criterion for when particle losses are important is shown down time but also, among other things, on the applied RF-power. Effects of a velocity dependent particle confinement time are also studied. (author)

[en] An investigation is made of the influence of toroidal effects, in the form of trapped particles, on ion velocity distributions in the presence of ICRH. The analysis is based on a bounced averaged Fokker-Planck equation including RF-driven quasi-linear velocity space diffusion. A pitch angle averaged distribution, suitable for calculating weighted velocity space averages of the distribution, is derived under the assumption that the influence of anisotropy can be neglected. For a given absorbed power, this pitch angle averaged distribution is found to be independent of the aspect ratio. (author)

[en] The kinetic theory of runaway electron avalanches caused by close Coulomb collisions is extended to account for radial diffusion. This is found to slow down the growth of avalanches. An approximate analytical formula for the growth rate is derived and is verified by a three-dimensional Monte Carlo code constructed for this purpose. As the poloidal magnetic flux that is available to induce an electric field in a tokamak is limited, avalanches can be prevented altogether by sufficiently strong radial diffusion. The requisite magnetic fluctuation level is sensitive to the mode structure and the speed of the disruption. It is estimated to be δB/B ∼ 10^-3 for parameters typical of large tokamaks. (author)

[en] The time of the distribution function of the beam injected particles in the presence of ICRH in a two component plasma is determined. Consideration is restricted to the time development during two complementary time periods: (i) the early time period i.e. 0 < t << /tav/sb(s), and (ii) the quasi-steady-state, i.e. t > /tav/sb(s), where /tav/sb(s) is the slowing-down time for beam ion-electron collisions. Explicit analytical solutions are obtained for anisotropic as well as isotropic beam injection. (authors)

[en] Modelling of interaction between RF waves and fast ions has been developed. As an application, a steady-state ITER scenario with Q = 5 has been simulated to study the absorption of LH (lower hybrid) wave power by alpha particles. The absorption, for an LH frequency of 3.7 GHz, has been found to be of the order of 3% for realistic alpha particle density profiles, including finite orbit width effects. Assuming that an acceptable level of parasitic absorption is below 10%, the results of the SPOT/DELPHINE coupling indicate that the use of 3.7 GHz klystrons for LH waves in ITER cannot be ruled out. However, higher frequencies will give a greater margin. It should also be kept in mind that there are uncertainties in the modelling. For instance, it is based on simulated plasma quantities, such as the density and temperature, and one cannot be sure how ITER will perform in reality. Moreover, we have not considered alpha particle transport induced by magnetic field ripple or Toroidal Alfven Eigenmodes, which could have an influence on the alpha particle distribution in the outer part of the plasma (this should be the subject of a future study). The modelling would also benefit from benchmarking against JET experiments with LH heating and a detectable presence of fast particles

[en] The present report summarizes the work performed within the contract JT4/9008, the aim of which is to derive analytical models for ion velocity distributions resulting from ICRF heating on JET. The work has been performed over a two-year-period ending in August 1986 and has involved a total effort of 2.4 man years. (author)

[en] Absorption of lower hybrid (LH) waves by alpha particles may reduce significantly the current drive efficiency of the waves in a reactor or burning plasma experiment. This absorption is quantified for ITER using the ray-tracing+2D relativistic Fokker-Planck code Delphine. The absorption is calculated as a function of the superthermal alpha particle density, which is constant in these simulations, for two candidate frequencies for the LH system of ITER. Negligible absorption by alpha particles at 3.7 GHz requires n(alpha,supra) = 7.5 10¹⁶ m^-3, while no significant impact on the driven current is found at 5 GHz, even if n(alpha,supra) = 1.5 10¹⁸ m^-3. (authors)

[en] The effect of bulk ion heating in Tore Supra has been investigated by studying discharges with varying concentrations of minority ions during ICRF hydrogen minority heating in Deuterium/⁴He plasmas. As expected, the level of bulk ion heating is found to increase with the minority concentration. Higher levels of ion heating are shown to be accompanied by two significant effects: an improved energy confinement and a strong influence on the plasma rotation. (author)

[en] The recent successful certification and opening of a first-of-a-kind, deep geological repository for safe disposal of long-lived, transuranic radioactive waste (TRUW) at the Waste Isolation Pilot Plant (WIPP) site, New Mexico, United States of America (USA), embody both long-standing local and wide-spread, gradually achieved, scientific, institutional, regulatory, political, and public acceptance. The related historical background and development are outlined and the main contributors to the successful siting, certification, and acceptance of the WIPP TRUW repository, which may also serve as a model to success for other radioactive waste disposal programs, are described. (author)

[en] The predictive transport code CRONOS has been augmented by an orbit following Monte Carlo code, SPOT (Simulation of Particle Orbits in a Tokamak). The SPOT code simulates the dynamics of nonthermal particles, and takes into account effects of finite orbit width and collisional transport of fast ions. Recent developments indicate that it might be difficult to avoid, at least transiently, current holes in a reactor. They occur already on existing tokamaks during advanced tokamak scenarios. The SPOT code has been used to study the alpha particle behaviour in the presence of current holes for both JET and ITER relevant parameters. (authors)