Effect of toroidal field ripple on plasma rotation in JET

Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude (3) from an average value of M = 0.40-0.55 for operations at the standard JET ripple of 6 = 0.08% to M = 0.25-0.40 for 6 = 0.5% and M = 0.1-0.3 for delta = 1%. TF ripple effects should be considered when estimating the plasma rotation in ITER. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes (delta similar to 1%) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation. The edge counter rotation was found to depend, besides on the TF ripple amplitude, on the edge temperature. The observed reduction of toroidal plasma rotation with increasing TF ripple could partly be explained by TF ripple induced losses of energetic ions, injected by NBI. However, the calculated torque due to these losses was insufficient to explain the observed counter rotation and its scaling with edge parameters. It is suggested that additional TF ripple induced losses of thermal ions contribute to this effect

IShTAR: a test facility to study the interaction between RF wave and edge plasmas

International audienceExistence of high electric fields near an RF antenna launcher causes a number of parasitic phenomena, such as arcing and impurity release, which seriously deteriorate the performance of an ICRF heating scheme in fusion devices. Limited accessibility of the near antenna region in large-scale fusion experiments significantly complicates the associated experimental studies. The IShTAR (Ion Sheath Test Arrangement) test facility has been developed with the requirement to provide a better accessibility and diagnosability of plasmas in the direct vicinity of an ICRF antenna. The purpose of this work is to give a detailed description on the experimental setup and the available diagnostics. Furthermore the paper will demonstrate the capability of the experiment to study phenomena near an ICRF antenna launcher which are relevant for large-scale fusion ICRH systems

Characterization of ion cyclotron resonance heating in presence of the ITER-like wall in JET

Carbon is not compatible with the long term use required for plasma facing components in future fusion reactors of the tokamak type e.g. from the point of view of erosion and tritium retention.Wand Be were chosen as plasma facing materials for ITER. JET was equipped with beryllium (as opposed to C or C-coated) walls in the shutdown of 2010-2011. To sustain the very high heat loads inevitably falling on it and thus excluding the use of metals with a low melting point such as Be and in spite of the fact that its radiation is significant because of its large Z, a Tungsten (W) orW-coated divertor was simultaneously installed. The recent JET campaign has focused on characterizing high density high temperature operation with this "ITER-like" wall (ILW). One of the questions that needed to be answered is whether the auxiliary heating methods do not lead to unacceptable high levels of impurity influx preventing fusion-relevant operation. This paper briefly reports on two aspects of the present understanding of ion cyclotron resonance heating (ICRH) or radio frequency (RF) heating in presence of the ILW: ICRH-specific impurity influx and heating performance. They are complementing related discussions on heat loads, and on plasmaWcontent and possible sources. A much more extensive study will be published elsewhere

Fernando SEBASTIÁN AGUILAR, Nueva Evangelización. Fe, cultura y política en la España de hoy, Ed. Encuentro, Madrid 1991, 302 pp. [RECENSIÓN]

\u3cp\u3eThe 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.\u3c/p\u3