Hydrogen minority ion cyclotron resonance heating in presence of the iter-like wall in jet

The most recent JET campaign has focused on characterizing operation with the "ITER-like" wall. One of the questions that needed to be answered is whether the auxiliary heating methods do not lead to unacceptably high levels of impurity influx, preventing fusion-relevant operation. In view of its high single pass absorption, hydrogen minority fundamental cyclotron heating in a deuterium plasma was chosen as the reference wave heating scheme in the ion cyclotron domain of frequencies. The present paper discusses the plasma behavior as a function of the minority concentration X[H] in L-mode with up to 4MW of RF power. It was found that the tungsten concentration decreases by a factor of 4 when the minority concentration is increased from X[H] ≈ 5% to X[H] % 20% and that it remains at a similar level when X[H] is further increased to 30%; a monotonic decrease in Beryllium emission is simultaneously observed. The radiated power drops by a factor of 2 and reaches a minimum at X[H] ≈ 20%. It is discussed that poor single pass absorption at too high minority concentrations ultimately tailors the avoidance of the RF induced impurity influx. The edge density being different for different minority concentrations, it is argued that the impact ICRH has on the fate of heavy ions is not only a result of core (wave and transport) physics but also of edge dynamics and fueling

Fishbone-like instability at the edge of ELM-free quiescent H-modes in DIII-D

Quiescent H-modes (QH-mode) are characterized by edge MHD activity known as the Edge Harmonic Oscillations (EHO). This paper reports the observation of EHOs in the form of chirping modes that resemble fishbone activity

Spatially resolved plasma rotation profiles with ICRF on JET

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Fishbone-like instability at the edge of ELM-free quiescent H-modes in DIII-D

Quiescent H-modes (QH-mode) are characterized by edge MHD activity known as the Edge Harmonic Oscillations (EHO). This paper reports the observation of EHOs in the form of chirping modes that resemble fishbone activity

Plasma current dependence of the edge pedestal height in JET ELM-free H-modes

Some models for the suppression of turbulence in the L to H transition, suggest that the width of the H-mode edge barrier is either proportional or is of the order of the thermal or the fast-ion poloidal Larmor radius. This would require that the width of the edge barrier should depend on the plasma current. This dependence has been clearly verified at JET in experiments designed to control the edge MHD stability of ELM-free hot-ion H-mode plasmas. The effects of isotopic mass and the applicability of several edge barrier models to the hot-ion H-mode plasmas were analysed in (Guo H Y et al 2000 Edge transport barrier in JET hot-ion H-modes Nucl. Fusion 40 69) using a large database containing both deuterium-only and deuterium-tritium plasmas. This database has now been enlarged to include discharges from a plasma shape scan, allowing one to study the dependence of the pedestal height on the edge shear. In addition, the range of plasma currents was extended up to 6 MA. It is shown that the edge data are best described by a model where the edge barrier width is determined by the fast ions weighted towards the components with largest poloidal Larmor radii. However, it is not possible to conclusively eliminate the thermal ion model

Application of ICRF waves in tokamaks beyond heating

Interaction of waves in the ion cyclotron range of frequencies (ICRF) with a plasma has a number of key properties that make them attractive beyond pure heating. First, the waves can interact resonantly with either the plasma ions or electrons. In the case of ion cyclotron damping, a small number of resonant ions are often accelerated to high energies. These ions, apart from heating the bulk plasma via Coulomb collisions, can increase fusion reactivity, affect plasma stability and drive current. They have also been invaluable in diagnostic applications and simulations of fusion-born 3.5 MeV alpha-particles. The second key property of ICRF waves is the transfer of wave momentum to the plasma. This allows one to drive current, affect plasma rotation and induce radial transport of the fast-ions with toroidally directed waves. Finally, ICRF power deposition is rather narrow and its location can be externally controlled, which has important applications in improving the plasma performance, affecting the local plasma transport and providing a tool for plasma transport studies. Representative examples from present-day tokamak experiments are reviewed to highlight the available capabilities

Observation of Alpha Heating in JET DT Plasmas

An experiment at the Joint European Torus (JET) has demonstrated clear self-heating of a deuterium-tritium plasma by alpha particles produced in fusion reactions. The alpha heating was identified by scanning the plasma and neutral beam mixtures together from pure deuterium to nearly pure tritium in a 10.5 MW hot ion H mode. At an optimum mixture of $60+/-20$% T, the fusion gain ( = Pfusion/Pabsorbed) was 0.65 and the alpha heating showed clearly as a maximum in electron temperature. The change in temperature produced by alpha heating was Te$0$ = 1.3+/-0.23 keV in 12.2 keV. The effect of the heating could also be seen in the ion temperature and energy content