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Progress in the definition of the requirements for edge localized mode (ELM) control and the application of ELM control methods both for high fusion performance DT operation and non-active low-current operation in ITER is described. Evaluation of the power fluxes for low plasma current H-modes in ITER shows that uncontrolled ELMs will not lead to damage to the tungsten (W) divertor target, unlike for high-current H-modes in which divertor damage by uncontrolled ELMs is expected. Despite the lack of divertor damage at lower currents, ELM control is found to be required in ITER under these conditions to prevent an excessive contamination of the plasma by W, which could eventually lead to an increased disruptivity. Modelling with the non-linear MHD code JOREK of the physics processes determining the flow of energy from the confined plasma onto the plasma-facing components during ELMs at the ITER scale shows that the relative contribution of conductive and convective losses is intrinsically linked to the magnitude of the ELM energy loss. Modelling of the triggering of ELMs by pellet injection for DIII-D and ITER has identified the minimum pellet size required to trigger ELMs and, from this, the required fuel throughput for the application of this technique to ITER is evaluated and shown to be compatible with the installed fuelling and tritium re-processing capabilities in ITER. The evaluation of the capabilities of the ELM control coil system in ITER for ELM suppression is carried out (in the vacuum approximation) and found to have a factor of ∼2 margin in terms of coil current to achieve its design criterion, although such a margin could be substantially reduced when plasma shielding effects are taken into account. The consequences for the spatial distribution of the power fluxes at the divertor of ELM control by three-dimensional (3D) fields are evaluated and found to lead to substantial toroidal asymmetries in zones of the divertor target away from the separatrix. Therefore, specifications for the rotation of the 3D perturbation applied for ELM control in order to avoid excessive localized erosion of the ITER divertor target are derived. It is shown that a rotation frequency in excess of 1 Hz for the whole toroidally asymmetric divertor power flux pattern is required (corresponding to n Hz frequency in the variation of currents in the coils, where n is the toroidal symmetry of the perturbation applied) in order to avoid unacceptable thermal cycling of the divertor target for the highest power fluxes and worst toroidal power flux asymmetries expected. The possible use of the in-vessel vertical stability coils for ELM control as a back-up to the main ELM control systems in ITER is described and the feasibility of its application to control ELMs in low plasma current H-modes, foreseen for initial ITER operation, is evaluated and found to be viable for plasma currents up to 5–10 MA depending on modelling assumptions. [ABSTRACT FROM AUTHOR]

The application of resonant magnetic perturbations results in a non-axisymmetric striation pattern of magnetic field lines from the plasma interior which intersect the divertor targets. The impact on related particle and heat fluxes is investigated by three dimensional computer simulations for two different recycling conditions (controlled via neutral gas pumping). It is demonstrated that a mismatch between the particle and heat flux striation pattern (splitting vs. no splitting), as is repeatedly observed in ITER similar shape H-mode plasmas at DIII-D, can be reproduced by the simulations for high recycling conditions at the onset of partial detachment. These results indicate that a detailed knowledge of the particle and energy balance is at least as important for realistic simulations as the consideration of a change in the magnetic field structure by plasma response effects. [ABSTRACT FROM AUTHOR]

Pumping of neutral gas and re-fuelling in other locations (e.g. neutral beam injection or gas puffing) are key ingredients in divertor physics. However, these have not been included in previous 3D edge plasma transport simulations with the EMC3-EIRENE code. Including these effects brings the simulations closer to reality and we demonstrate that this has a significant impact on divertor parameters. In particular, we study the impact of the pumping efficiency on ITER similar shape plasmas at the DIII-D tokamak in the presence of resonant magnetic perturbations. Further, we investigate the so-called 'particle pump-out effect'. We show that in the present transport model and for given pumping and re-fuelling rates, the density at the transition to the core region decreases with increasing perturbation current and also the temperature. The striation patterns in the target particle and heat fluxes are extended into the regular scrape-off layer, which is caused by cross-field transport into a thin layer around the perturbed separatrix. [ABSTRACT FROM AUTHOR]

The TEXTOR helical divertor is a magnetic configuration created by the application of external resonant magnetic perturbations with the intention to control plasma edge transport and the resulting particle and heat fluxes to the divertor target. It is confirmed by 3D computer simulations that no high-recycling-like regime is established under TEXTOR relevant conditions, despite the fact that a transition to detachment (i.e. a saturation or even a roll-over of the recycling flux) is observed at high densities. The driving mechanisms are, distinct from apparently similar observations in poloidal divertors and stellarator divertors, a combination of volumetric power losses and enhanced upstream-to-downstream heat transport, but with no significant role of the momentum balance. [ABSTRACT FROM AUTHOR]

Measurements of the plasma edge electron density ne and temperature Te fields during application of a fast rotating, resonant magnetic perturbation (RMP) field show a characteristic modulation of both, ne and Te coherent to the rotation frequency of the RMP field. A phase delay [uppercase_phi_synonym] between the ne(t) and Te(t) waveforms is observed and it is demonstrated that this phase delay [uppercase_phi_synonym] is a function of the radius with [uppercase_phi_synonym](r) depending on the relative rotation of the RMP field and the toroidal plasma rotation. This provides for the first time direct experimental evidence for a rotation dependent damping of the external RMP field in the edge layer of a resistive high-temperature plasma which breaks down at low rotation and high resonant field amplitudes. [ABSTRACT FROM AUTHOR]

Interpretation of spectroscopic measurements in the edge region of high-temperature plasmas can be a challenge since line of sight integration effects make direct interpretation in terms of quantitative, local emission strengths often impossible. The EMC3-EIRENE code--a 3D fluid edge plasma and kinetic neutral gas transport code--is a suitable tool for full 3D reconstruction of such signals. A versatile synthetic diagnostic module has been developed recently which allows the realistic 3D setup of various plasma edge diagnostics to be captured.We highlight these capabilities with two examples for Wendelstein 7-X (W7-X): a visible camera for the analysis of recycling, and a coherent-imaging system for velocity measurements. [ABSTRACT FROM AUTHOR]

This paper overviews recent progress on the experimental identification and physics interpretation of 3D effects of magnetic field geometry on divertor transport. The 3D effects are elucidated as a consequence of competition between transports parallel (||) and perpendicular (⊥) to magnetic field, in open field lines cut by divertor plates, or in magnetic islands. The competition has strong impacts on divertor functions, such as determination of density regime, impurity screening, and detachment control. The effects of magnetic perturbation on the edge electric field and turbulent transport are also discussed. Based on the experiments and numerical simulations, key parameters governing the 3D transport physics for the individual divertor functions, e.g. pumping efficiency through divertor density regime, impurity screening and detachment control, are discussed. [ABSTRACT FROM AUTHOR]