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 similar to 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 1Hz 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 5-10MA depending on modelling assumptions.

. Results from three-dimensional modeling of plasma edge transport and plasma wall interaction during application of resonant magnetic perturbation for ELM control at ITER are presented. We show a systematic assessment of the impact of RMP application on the divertor fluxes and the plasma edge structure for the ITER standard H-mode scenario. Two perturbation field amplitudes at full and half of the ITER RMP coil current capability are applied in vacuum approximation. The results are compared to a case including plasma response from non-linear MHD modeling and a case at high q 95 . A strong reduction of the thermal confinement is found with vacuum RMP fields applied. The divertor fluxes are redirected into a complex, three-dimensional pattern of helical magnetic fingers. These fingers stretch out as far as 60 cm across the divertor targets yielding a spreading of the heat and particle fluxes with reduced peak heat loads. Opening of the magnetic field lines from inside of the separatrix establishes scrape-off layer like channels of direct parallel flow towards the target plates. This results in a strong convective outflow of particles and energy. The sensitivity of the impact of the RMP fields on the level of plasma response, of the RMP amplitude and q 95 is investigated.

Resonant Magnetic Perturbations (RMPs) are applied with the Dynamic Ergodic Divertor (DED) at TEXTOR to control the plasma edge transport and the plasma surface interaction. This leads to the formation of a three-dimensional (3D) topology of the scrape-off layer (SOL). To quantify the erosion/deposition balance and the material migration in this 3D boundary, spherical test limiters were exposed to plasmas with and without RMP fields applied. Methane doped with 13C as tracer element was injected through a gas inlet in the test limiter. The local gas source was monitored by spatially resolving spectroscopy and the resulting deposition patterns on the limiters were analysed with colourimetry and nuclear reaction analysis. These measurements were compared to simulations of the magnetic field topology simulations. The data provide evidence of a particle migration dominated by an ExB drift within stochastic zones of the 3D plasma boundary.

Ion cyclotron wall conditioning (ICWC) discharges, in pulsed-mode operation, were carried out in the limiter tokamak TEXTOR to explore safe operational regimes for the experimental parameters for possible ICWC-discharge cleaning in International Thermonuclear Experimental Reactor (ITER) at half field. Antenna coupling properties obtained during the ion cyclotron range of frequencies (ICRF) wall conditioning experiments performed in helium–hydrogen mixture in TEXTOR were analysed in relation to the obtained ICWC-plasma characterization results. Satisfactory antenna coupling in the mode conversion scenario along with reproducible generation of ICRF plasmas for wall conditioning, were achieved by coupling radio frequency (RF) power from one or two ICRF antennas. The plasma breakdown results obtained in the TEXTOR tokamak have been compared with the predictions of a zero-dimensional RF plasma production model. The present study of ICWC emphasizes the beneficial effect of application of an additional (along with toroidal magnetic field) stationary vertical (B V ≪ B T) or oscillating poloidal magnetic field (B P ≪ B T) on antenna coupling and relevant plasma parameters.

This paper focuses on encouraging results obtained on the characterization of RF produced plasmas during pulsed-mode wall conditioning discharges in ion cyclotron resonance frequency (ICRF) regime in the limiter tokamak TEXTOR. Recent Ion Cyclotron Wall Conditioning (ICWC) experiment carried out in TEXTOR tokamak, lead to the identification of various dependences of the antenna-plasma coupling efficiency on the plasma parameters for possible ICWC-discharge cleaning in ITER at half field. Our ICWC experiments emphasize on (i) study of antenna coupling during the mode conversion scenario, (ii) reproducible generation of ICRF plasmas for wall conditioning, by coupling RF power from one or two ICRF antennas and (iii) effect of application of an additional (along with toroidal magnetic field) stationary vertical (BV≪BT) or oscillating poloidal magnetic field (Bp≪BT) on antenna coupling and relevant plasma parameters.

First results from three-dimensional modeling of the divertor heat and particle flux pattern during application of resonant magnetic perturbation fields as ELM control scheme in ITER with the EMC3-Eirene fluid plasma and kinetic neutral transport code are discussed. The formation of a helical magnetic footprint breaks the toroidal symmetry of the heat and particle fluxes. Expansion of the flux pattern as far as 60 cm away from the unperturbed strike line is seen with vacuum RMP fields, resulting in a preferable heat flux spreading. Inclusion of plasma response reduces the radial extension of the heat and particle fluxes and results in a heat flux peaking closer to the unperturbed level. A strong reduction of the particle confinement is found. 3D flow channels are identified as a consistent reason due to direct parallel outflow from inside of the separatrix. Their radial inward expansion and hence the level of particle pump out is shown to be dependent on the perturbation level.

In this paper, results of a direct comparison of TEXTOR and DIII-D experiments with resonant magnetic perturbation (RMP) fields are presented. This comparison of resistive L-mode plasmas at TEXTOR with highly conductive H-mode plasmas at DIII-D is useful to identify generic physics mechanisms during application of RMP fields with a strong field line pitch angle alignment in the plasma edge.A reduction in the pedestal electron pressure pe with increasing extension of the vacuum modelled stochastic layer and pe recovery with decreasing layer width is found caused by a q95 resonant reduction in the edge (0.8 < ΨN < 0.95) electron temperature Te(q95) on both devices. For RMP edge-localized mode (ELM) suppressed H-mode plasmas at DIII-D, the gradients ∇Te and nominal values of Te are reduced in this edge region while increasing in the pedestal (0.95 < ΨN < 1.0) with RMP field applied and both are highly dependent on q95. In contrast, an increase in the central ion temperature with strong steepening of the ion temperature profile at mid-radius is found—again being highly dependent on q95. However, these resonant thermal transport effects are only seen in high triangularity plasmas revealing a strong shape dependence of the thermal transport. In contrast to the highly q95 dependent thermal transport features, the reduction of ne—known as density pump out—shows a much weaker dependence on q95. We show the potential to reduce the RMP induced particle pump out by fine tuning of the RMP spectral properties. At low resonant field amplitudes enhanced particle confinement is seen in high-field side limited L-mode discharges on both devices while higher resonant field amplitudes yield particle pumps out.

In this contribution, we report on the application of Li beam emission spectroscopy to determine electron density and temperature in ion cyclotron wall conditioning plasmas with the help of a collisional-radiative model. Intensity ratios of atomic line emission at 670nm, 610nm and 460nm have been chosen. The overall range of ne and Te in ICWC plasmas measured with the Li beam is 1016m−3 to a few 1017m−3 for the electron density and 1.5–15eV for the electron temperature. With the application of oscillating vertical and horizontal magnetic fields in the range of 0.01T the plasma extends towards the bottom of the TEXTOR vessel, providing a wider distribution of particle fluxes to the vessel walls.

The three-dimensional (3D) features of plasma edge profiles and wall interaction patterns induced by edge resonant magnetic perturbation fields (RMP) are discussed comparing TEXTOR and DIII-D. We show that the scrape-off layer (SOL) profiles and decay lengths depend the edge safety factor, the RMP base mode as well as on the plasma rotation during RMP application indicating modification of SOL transport by the 3D perturbation fields. This is compatible with channelling of particle and heat efflux along open perturbed field lines in the very edge of the plasma boundary into a completely re-arranged, helically striated 3D divertor footprint. The distribution of the measured divertor heat and particle fluxes at DIII-D match the vacuum modelled magnetic footprint topology in L-mode while in H-mode the striation width exceeds the modelled footprint width by 15–30%. This 3D structure of the measured heat and particle fluxes results in a new situation for the material erosion properties and initial quantification of the net-erosion within the 3D footprint shows in L-mode a 50% decrease of the chemical erosion yield and evidence for a comparably small 15-20% increase in physical sputtering. Extrapolation of these findings to ITER by vacuum modelling of the magnetic footprint for the actual ELM control coils shows a similar vacuum magnetic footprint topology as found at DIII-D during RMP ELM suppression. However, the open field lines escape the CFC covered ITER divertor area potentially transferring net-erosion characteristics from the CFC domain onto the Tungsten including so far unconsidered heat and particle loads on this sensitive material.

As shown on DIII-D edge localized modes (ELMs) can be either completely eliminated or mitigated with resonant magnetic perturbation (RMP) fields. Two infrared cameras, separated 105° toroidally, were used to make simultaneous measurements of ELM heat loads with high frame rates. Without the RMP fields ELMs display a variety of different heat load dynamics and a range of toroidal variability that is characteristic of their 3D structure. Comparing radial averages there is no asymmetry between two toroidal locations. With RMP-mitigated ELMs, the variability in the radially averaged power loads is significantly reduced and toroidal asymmetries in power loads are introduced. In addition to RMP ELM suppression scenarios an RMP scenario with only very small ELMs and very good confinement has been achieved.

The Porous Plug Injector (PPI) has proven to be an invaluable diagnostic for in situ characterization and quantification of erosion phenomena in DIII-D. Previous work has led to derivation of three primary figures of merit for chemical erosion (CE) in attached and cold divertor conditions: relative intensity of C+ chemical and physical sources, the CE yield (Ychem), and effective photon efficiencies for chemically eroded products. Application of these figures for accounting of observed absolutely calibrated CI and CII emission intensities is demonstrated to produce a self-consistent solution at the DIII-D targets. Reinterpretation of the CI (C0) spectral lineshape profile supports the relative roles of local chemical versus physical sputtering as previously determined for CII (C+). Comparison of calculated in situ Ychem to that measured ex situ suggests a tokamak-specific lower energy threshold for CE and has potentially major implications for prediction of tritium co-deposition near the divertor targets in ITER.

In this paper key results of a comparison of TEXTOR and DIII-D experiments with external resonant magnetic perturbation (RMP) fields are presented. These comparisons of resistive L-mode plasmas at TEXTOR to highly conductive H-mode plasmas at DIII-D identify generic physics mechanisms of the application of RMP fields with a strong field line pitch angle alignment in the plasma edge. We show evidence that a stochastic edge layer in both very different plasma regimes is induced with at least a thin layer of open field lines in the plasma edge breaking the axis-symmetry of the tokamak introducing a new three-dimensional plasma boundary. In both plasma regimes a reduction of the electron pressure pe with increasing extension of the vacuum modeled stochastic layer and pe recovery with decreasing layer width is found caused by a q95 resonant reduction of the electron temperature Te(q95). The potential to reduce the RMP induced particle pump out by fine tuning of the RMP spectral properties is shown. At low resonant field amplitudes enhanced particle confinement is found in high field side limited L-mode discharges on both devices while higher resonant field amplitude yield particle pump out.

Wall conditioning techniques applicable in the presence of permanent toroidal magnetic field will be required for the operation of ITER, in particular for recovery from disruptions, vent and air leak, isotopic ratio control, recycling control and mitigation of the tritium inventory build-up. Ion Cyclotron Wall Conditioning (ICWC) is one of the most promising options and has been the subject of considerable recent study on current tokamaks. This paper reports on the findings of such studies performed on European tokamaks, covering a range of plasma-facing materials: TORE SUPRA, TEXTOR, ASDEX Upgrade and JET.

Ion Cyclotron Wall Conditioning (ICWC) discharges, in pulsed-mode operation, were carried out in TEXTOR to simulate a scenario of ITER wall conditioning at half-field. The ICWC discharges were performed in a continuous Helium flow with adjunction of molecular Hydrogen, puffed after the ICRF ignition thus achieving better antenna coupling in the Mode Conversion scenario with improved ICWC performance. Reproducible generation of ICRF plasmas and reliable wall conditioning, after proper wall preloading with Deuterium glow, were achieved by coupling the RF power at 29MHz from one or two ICRF antennas at different toroidal magnetic fields (different cyclotron harmonics). The antenna coupling properties were analyzed in relation to wall conditioning output (removal rates) for selected marker masses. Present study of ICWC at low and high power density per particles (at different gas pressures) emphasizes on the efficiency of the application of stationary, oscillating or rotating poloidal magnetic field. These experimental results will be compared with the predictions of a 0-D RF plasma production model.

ITER and future superconducting fusion machines need efficient wall conditioning techniques for routine operation in between shots in the presence of permanent high magnetic field for wall cleaning, surface isotope exchange and to control the in-vessel long term tritium retention. Ion Cyclotron Wall Conditioning (ICWC) based on the ICRF discharge is fully compatible and needs the presence of the magnetic field. The present paper focuses on the principal aspects of the ICWC discharge performance in large-size fusion machines: (i) neutral gas RF breakdown with conventional ICRF heating antennas, (ii) antenna coupling with low density (similar to 10(17) m(-3)) RF plasmas and (iii) ICWC scenarios with improved RF plasma homogeneity in the radial and poloidal directions. All these factors were identified as crucial to achieve an enhanced conditioning effect (e.g. removal rates of selected "marker" masses). All the observed effects are analyzed in terms of RF plasma wave excitation/absorption and compared with the predictions from I-D RF full wave and 0-D RF plasma codes. Numerical modeling and empirical extrapolation from the existing machines give good evidence for the feasibility of using ICWC in ITER with the main ICRF antenna.