FTU plasma discharges with an extremely high amount of Li injection have been performed using a poloidal liquid lithium limiter acting as the principal Li source in the shadow of the main TZN toroidal limiter. Very peculiar of these discharges is the formation of a ‘virtual’ toroidal lithium limiter that redistributes the energy flux to the tokamak vessel first wall by radiative processes and therefore decreases the heat load onto the Mo limiter. These experiments contribute to the investigation of a more complex scenario that will possibly be faced by a project of a liquid lithium divertor in a tokamak with high additional power (or high power load on to the targets).

The fundamental mechanisms responsible for the interplay and synergy between the absorption dynamics of extraordinary-mode electron cyclotron waves at two different harmonic resonances (the 2nd and 3rd) are investigated in the TCV tokamak. An enhanced 3rd harmonic absorption in the presence of suprathermal electrons generated by 2nd harmonic heating is predicted by Fokker–Planck simulations, subject to complex alignment requirements in both physical space and momentum space. The experimental signature for the 2nd/3rd harmonic synergy is sought through the suprathermal bremsstrahlung emission in the hard x-ray range of photon energy. Using a synthetic diagnostic, the emission variation due to synergy is calculated as a function of the injected power and of the radial transport of suprathermal electrons. It is concluded that in the present experimental setup a synergy signature has not been unambiguously detected. The detectability of the synergy is then discussed with respect to v...

In large hot tokamaks like JET, the width of the reconnecting layer for resistive modes is determined by semi-collisional electron dynamics and is much less than the ion Larmor radius. Firstly a dispersion relation valid in this regime is derived which provides a unified description of drift-tearing modes, kinetic Alfvén waves and the internal kink mode at low beta. Tearing mode stability is investigated analytically recovering the stabilizing ion orbit effect, obtained previously by Cowley et al (1986 Phys. Fluids 29 3230), which implies large values of the tearing mode stability parameter Δ′ are required for instability. Secondly, at high beta it is shown that the tearing mode interacts with the kinetic Alfvén wave and that there is an absolute stabilization for all Δ′ due to the shielding effects of the electron temperature gradients, extending the result of Drake et al (1983 Phys. Fluids 26 2509) to large ion orbits. The nature of the...

We report correlated observations of enhanced whistler waves and energetic electron acceleration collected by multiple satellites specifically near the geostationary orbit during the 7–10 November 2004 superstorms, together with multi-site observations of ULF wave power measured on the ground. Energetic (>0.6 MeV) electron fluxes are found to increase significantly during the recovery phase, reaching a peak value by ∼100 higher than the prestorm level. In particular, such high electron flux corresponds to intensified whistler wave activities but to the weak ULF wave power. This result suggests that wave–particle interaction appears to be more important than inward radial diffusion in acceleration of outer radiation belt energetic electrons in this event, assisting to better understand the acceleration mechanism.

In this paper, we present a study on D–H ( ⁷Li) plasmas with moderate hydrogen concentration (∼15%) on the HT-7 tokamak. Enhanced density fluctuation induced by ion cyclotron range of frequencies (ICRF) at the centre of the plasma is observed by a continuous wave CO ₂ (λ = 10.6 µm) collective scattering system. At the same time, the Doppler shift V _D due to plasma rotation in the mode-converted ICRF D–H ( ⁷Li) plasmas is observed experimentally for the first time on the HT-7 tokamak, and the Doppler shift V _D is approximately linear versus the change in plasma stored energy Δ W.

We consider wave propagation in a cold and isotropic relativistic plasma, in the presence of a moving density perturbation, which can be created by a particle bunch or by an intense laser pulse. We derive the space and time reflection coefficients and discuss the associated frequency shifts. This work could be useful for the development of radiation sources and new diagnostic techniques for laser and plasma acceleration experiments.

During hydrogen pellet injection experiments in the Large Helical Device (LHD), over-ablation caused by fast ions (due to tangential neutral beam injection (NBI) heating at 150–180 keV beam energy) is shown to dominate the measured penetration depths. The neutral gas and plasma shielding model, including the interaction of the pellet with fast ions, is applied, and its predictions are shown to agree well with the measured H _α emission profiles. The toroidal deflection of the pellet trajectories observed in the direction of beam injection is reproduced by the model when unbalanced ablation on the two sides of the pellet is included. The attenuation of the fast-ion and electron heat fluxes entering the ablation cloud is examined, showing that the high-energy part of the fast-ion distribution function is responsible for the high ablation rates, and that the thermal electron population is not the dominant ablating species. An analytical scaling for the balanced NBI conditio...

Based on the one-dimensional analytical theory of radial correlation reflectometry (RCR), numerical models of RCR experiments have been built. Computations are carried out for O-mode at a simple linear plasma density profile under conditions relevant to experiments. The turbulence spectrum and cross correlation function reconstruction procedure is applied and its feasibility is demonstrated while the assumptions of the model are fulfilled. The limitations of the method are discussed. The numerical models of the RCR experiments, targeted at the reconstruction of the turbulence spectrum in tokamaks where the plasma density profile can be approximated by a linear density profile, are performed and show in most of the cases that the wave number spectra can be extracted. The RCR capabilities and dependences on the main experimental parameters are also studied.

Arcing is a long standing plasma–surface interaction issue in nuclear fusion research, and the issue has been revived recently from new points of view. In this study, arcing under fusion relevant conditions is demonstrated in a linear plasma device using a pulsed laser to mimic the transient heat load. Ignition conditions of arcing were investigated systematically by changing the laser power, plasma conditions, surface nature and so on. Moreover, the cross-sectional view of arc trail was observed by transmission electron microscope, and the erosion of nanostructured tungsten due to arcing was estimated. It was found that more than half of the nanostructured tungsten still remained after an arc spot run on the nanostructure.

Three-dimensional modulated electrostatic ion-acoustic wave packet in magnetized plasma with electrons obeying kappa distribution is investigated. The standard reductive perturbation theory is used to derive the corresponding three-dimensional nonlinear Schrödinger (3D-NLS) equation which governs the dynamics, as well as the slow modulation of the ion-acoustic wave packets. Both the dispersive and the nonlinear coefficients of the 3D-NLS equation are modified by the inclusion of the transverse velocity perturbations, as well as the external magnetic field. New instability regimes arise when the ion to electron temperature ratio σ _i, the spectral index κ (i.e. measuring deviation from Maxwellian equilibrium), and the ion gyrofrequency ω _ci are presented. Importantly, the latter establishes new instability regimes that are not presented in an unmagnetized plasma.