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The base plasma heat load on the ITER first wall results from the projection of the plasma scrape off layer power profile onto the shaped surface of the first wall panels. The actual heat load on the first wall is larger than the base heat load, due to enhancement factors such as design approximations, manufacturing and assembly errors, and deviations to the ideally toroidal magnetic field configurations. The heat load increase is accounted for through penalty coefficients, ranging individually from a few percent to 50%. The probabilistic combination of individual penalty coefficients to give a global penalty coefficient is presented in the paper. The global penalty coefficient ranges from 1.37 to 2.44, depending of the first wall row and plasma phase. [ABSTRACT FROM AUTHOR]

Abstract: In magnetic fusion experiments, a simple technique to evaluate the heat flux on first wall components is a key to controlled plasma surface interaction. The heat flux can be characterized by the peaking factor which is the ratio of the peak heat flux to the average heat flux. The peaking factor can be calculated exactly using simple derivations and standard software tools. This analysis is applied to an Iter class experiment for plasma-wall contact during start up phases at 15MW, in idealised, realistic and misaligned situations. Even though the peaking factors are usually above 10, the peak heat load on the wall remains moderate at a few MW/m2. [Copyright &y& Elsevier]

Abstract: A fundamental difference between ITER and present devices is the need to shield against 14MeV neutrons. This has major consequences for plasma start-up/rampdown (su/rd) and also for protecting the first wall from plasma contact. This has led to design decisions: (a) not to place in front of the n-absorbing blanket a separate wall-limiter structure, (b) to modularize the blanket into ∼400 remote handling compatible blanket modules (BM), and (c) to shape the front face of the BMs for plasma contact. Combined protection-su/rd options are considered here for the inner and outer wall with regard to optimal shaping. Unfortunately, the modularity of the BM system (inter-BM gaps and misalignments) requires shaping of the BM faces that increases peak power loads by ∼10× relative to the ideal (continuous, circular) wall-limiter. Fortunately, the level may still be acceptable, ∼2MW/m2, even for su/rd power of 7 MW. [Copyright &y& Elsevier]

Abstract: A precise geometric method is used to calculate the power deposition on the future JET ITER-Like Wall beryllium tiles with particular emphasis on the internal edge loads. If over-heated surfaces are identified, these can be modified before the machining or failing that actively monitored during operations. This paper presents the methodology applied to the assessment of the main chamber beryllium limiters. The detailed analysis of one limiter is described. The conclusion of this study is that operation will not be limited by edges exposed to plasma convective loads. [Copyright &y& Elsevier]

Abstract: The material eroded from the surface of plasma facing components is redeposited partly close to high heat flux areas. At these locations, the deposit is heated by the plasma and the deposition pattern evolves depending on the operation parameters. The mapping of the deposit is still a matter of intense scientific activity, especially during the course of experimental campaigns. A method based on the comparison of surface temperature maps, obtained in situ by infrared cameras and by theoretical modelling is proposed. The difference between the two is attributed to the thermal resistance added by deposited material, and expressed as a deposit thickness. The method benefits of elaborated imaging techniques such as possibility theory and fuzzy logics. The results are consistent with deposit maps obtained by visual inspection during shutdowns. [Copyright &y& Elsevier]

Abstract: Long pulse operation imposes severe constraints on plasma facing components. Tore Supra pioneers this operation mode, with a large area high heat flux limiter technologically representative of next step experiments divertor targets. The failure mode of the individual elements are described, along with the strategies employed to reduce the occurrence of accidents. Two are developed: the knowledge of the heat flux in the scrape off layer and particularly the ability to predict the power density on the component’s surface, and the feed back control of edge diagnostics. Emphasis is set on infrared thermography which delivers 2D+time data, particularly useful for the prevention of accidents. This diagnostic is sensitive to the growth of carbonaceous deposits, which are highly non-uniform in Tore Supra as is presented in the paper. [Copyright &y& Elsevier]

Abstract: Three lagging tiles – over 12054 – are present since 2006 on Tore Supra main limiter, an actively cooled high heat flux plasma-facing component. The deterioration is attributed to progressing cracking of the bond between the tiles and the copper based heat sink. It is observed by an infrared camera: the thermal time constant of the tiles during cool down increased by a factor of three during the experimental campaigns of 2006 where a high level of additional power was used repetitively during long pulses. An element with a defective tile is removed for inspection during the summer shut down of 2007. The bond is cracked on three quarters of the length. Although the defects are important, the defective tiles do not limit the operation. [Copyright &y& Elsevier]

Abstract: The ITER First Wall is being redesigned to address a number of issues identified during the 2007 design review. One of the main improvements concerns the handling of parallel plasma heat loads. The design must be optimised for maximum leading edge protection with acceptable power flux distribution, which is achieved by shaping the First Wall panels. The conceptual design presented in the paper can accommodate both inboard and outboard limiter plasmas for a total power in the discharge of 7.5MW at 7.5MA and allows the abandonment of the original dedicated port limiters. [Copyright &y& Elsevier]

Abstract: During the last Tore Supra campaigns, an anomalous deformation in the near infrared spectrum of radiation has been observed on neutraliser underneath the Toroidal Pumped Limiter (TPL) on which we have observed the growth of carbon layer. The consequence is the difficulty to assess the surface temperature of the components and the power loaded. Laboratory experiment has been performed, using an Electron Cyclotron Resonance (ECR) ions source, to reproduce, characterize and explain this phenomenon. The luminance emitted by Carbon Fibre Composite (CFC) and pyrolytic graphite, have been observed under 95keV of H+ bombardments. The amplitude of the deformation was found to depend on the type of material used and the power density of the incident power loaded. This paper presents the possible hot spots explanation. The experimental luminance deformation is reproduced and these results are validated using a thermal model of dust in radiative equilibrium. [Copyright &y& Elsevier]

Abstract: On the limiter of Tore Supra, the heat loads map computed from deconvolution of IR surface temperatures shows good agreement with calorimetry measurements. This experimental heat pattern allows deducing the heat fluxes in the scrape-off layer using a 3D magnetic calculation and assuming only parallel heat transport along field lines. This calculation leads to an underestimation of the power circulating in the edge plasma according to the power balance, similarly to RFA measurements. The comparison between experimental heat loads on the limiter and modelling also shows a spreading of heat fluxes near the LCFS that cannot be explained only by parallel transport in the SOL. [Copyright &y& Elsevier]

Abstract: The precursors and following sequential events leading to radiative disruptions in Tore Supra have been analysed using infrared imaging, together with visible and ultraviolet spectroscopy of impurity species. A common feature observed prior to the disruptions is the appearance of a small (∼cm2) hot spot on the main plasma facing component, the Toroidal Pumped Limiter (TPL), clearly localised in a zone of thick carbon re-deposition (>100μm). A MARFE (Multifaceted Asymmetric Radiation From the Edge) is often triggered, followed by disruption. Such hot spots have been observed in ∼24% of the analysed disruptions, which is consistent with the fact that only 4/18 (22%) of the total area of the TPL is monitored with infrared cameras. These results suggest that over-heating of thick carbon re-deposition layers may play a role in the operational limits (MARFE, disruption) encountered. [Copyright &y& Elsevier]

Abstract: A spatially resolved calculation of the charge exchange particle and energy fluxes on the Toroidal Pumped Limiter (TPL) of Tore Supra is presented, as a first step towards a better understanding and modelling of carbon erosion, migration, as well as deuterium codeposition and bulk diffusion of deuterium in Tore Supra. The results are obtained with the EIRENE code run in a 3D geometry. Physical and chemical erosion maps on the TPL are calculated, and the contribution of neutrals to erosion, especially in the self-shadowed area, is calculated. [Copyright &y& Elsevier]

Abstract: In the frame of JET’s ITER-like wall project for most of the divertor surface tungsten coatings are intended to be employed on bidirectionally carbon fibre reinforced carbon substrates. Since this is thermomechanically rather mis-matched, a variety of deposition conditions were considered. Mostly in cooperation with industry, five Euratom associations provided 14 different types of samples with respect to production method and coating thickness. In a step-wise selection procedure, these were subjected to a thermal screening test and a thermal cycling test in the ion beam facility GLADIS as well as to an ELM-like thermal shock test in the electron beam facility JUDITH. A general failure mode is crack formation upon cool-down. Coatings with several microns of thickness show a distinct delamination feature in addition. Further analysis included metallographic investigation, X-ray diffraction for film stress assessment, adhesion testing as well as measurements on the contents of light impurities. [Copyright &y& Elsevier]

Abstract: The uniform layer with thickness at least 50–100μm was found on the CFC tiles from the inboard midplane after more than four years of tokamak operation. The upper part of the uniform layer was amorphous, but at the depth of ∼5μm a structure consisting of micro-size regions with aromatic chains located parallel to the surface was found. Gradual transition from uniform layer to underlying CFC structure was observed. The reciprocating material probe was used for installation of CFC samples in the Tore Supra deuterium plasma. The thermal desorptional spectra of these samples are compared with the spectra of the samples irradiated in the laboratory stand and with the spectra of hydrogenated carbon film. The peculiarities of hydrogen isotope trapping under plasma irradiation and at the atmosphere are presented and discussed. [Copyright &y& Elsevier]

Abstract: This paper presents the results of a modelling study conducted to estimate the power crossing the separatrix (P SOL) in the ITER device during a standard start-up sequence. This is used to calculate the power intercepted by the start-up limiters and the resulting power load distribution. The models and methodologies applied to calculate P SOL and the power loads on the limiters are described in detail elsewhere ([e.g., M. Kobayashi et al., Nucl. Fusion. 47 (2) (2007) 61]) and only a brief mention of some of the main results is included here. These assessments show that for the range of conditions analysed, the maximum P SOL intercepted by the two ITER limiter start-up modules during the current ramp-phase is ∼6MW. The peak power load to each limiter is calculated to be ∼5MW/m2, but these values depends on assumptions on physical quantities (e.g., transport coefficients, i.e., D ⊥ and χ ⊥), which are uncertain and still await confirmation by experiments. Recommendations are made for modelling and experiments to extend the study presented here. [Copyright &y& Elsevier]

Abstract: We have re-examined the basic dependences of carbon generation due to physical (D+ and Cn+) sputtering and from thermally dependent sources (chemical erosion) by comparison with a spectroscopic database for carbon emission from localized regions of CIEL. To be able to compare with observations in this complex environment, a model for carbon generation and transport has been created to include contributions from the important, but non-ideal, processes of carbon generation from material in intra-tile gaps and from poorly adherent re-deposited layers. Consistency simulations have been carried out to assess the degree to which the spot observations represent local emission, due to possibly long mean free paths of high-energy emitted particles, or from impurities transported into the spectroscopic field of view from other areas. Model results are compared with the experimental trends in the ratio of CII and Dα emission with power and edge parameters. In the course of the analysis a potentially important vector has been found for transport of re-deposited material to more remote locations and its significance discussed. [Copyright &y& Elsevier]

Abstract: The implementation of actively cooled high heat flux plasma facing components (PFCs) is one of the major ingredients required for operating the Tore Supra tokamak with very long pulses. A pioneering activity has been developed in this field from the very beginning of the device operation that is today culminating with the routine operation of an actively cooled toroidal pumped limiter (TPL) capable to sustain up to 10MW/m2 of nominal convected heat flux. Technical information is drawn from the whole development up to the industrialisation and focuses on a number of critical issues, such as bonding technology analysis, manufacture processes, repair processes, destructive and non-destructive testing. The actual experience in Tore Supra allows to address the question of D retention on carbon walls. Redeposition on surfaces without plasma flux is suspected to cause the final ‘burial’ of about half of the injected gas during long discharges. [Copyright &y& Elsevier]

Abstract: In Tore Supra long pulses, particle balance gives evidence that a constant fraction of the injected gas (typically 50%) is retained in the wall for the duration of the shot, showing no sign of wall saturation after more than 6min of discharge. During the discharge, the retention rate first decreases (phase 1), then remains constant throughout the pulse (phase 2). Phase 1 could be interpreted as implantation of particles combined with a constant codeposition rate, while phase 2 could correspond to codeposition alone, once the implanted surfaces are saturated with deuterium. This paper presents a possible contribution of charge exchange neutrals to the implantation process, based on modelling results with the Eirene neutral transport code. A complex pattern of particle implantation is evidenced, with saturation time constants ranging from less than one to several hundreds seconds, compatible with the experimental behaviour during phase 1. [Copyright &y& Elsevier]

Abstract: The new CIEL (Composantes Internes Et Limiteur) configuration of the Tore Supra tokamak has as its main plasma-facing component (PFC) a Toroidal Pumped Limiter (TPL) [P. Garin et al., in: Proceedings of the 20th Symposium on Fusion Technology, Marseille, vol. 2, 1998, p. 1709], which must sustain the bulk of the energy leaving the plasma. Analysis of the heat deposition pattern on the TPL indicates that perpendicular heat transport may play at least as significant a role as parallel heat transport [F. Saint-Laurent et al., Nucl. Fusion 40 (2000) 1047, R. Mitteau et al., these Proceedings]. We present a new approach for modelling the heat deposited onto the TPL, which follows test ‘heat packet’ trajectories backwards from the TPL towards the hot plasma column. Results are compared with experimental data and trends due to plasma parameters dependencies are described. Because of ripple effects, the limiter is covered by wetted areas with long connection lengths (tens of meters), and shadowed areas with very short connection lengths (centimeters). Sharp transitions between the two are clearly seen in experiment and also reproduced in the model. [Copyright &y& Elsevier]

A pioneering activity has been developed by CEA and the European industry in the field of actively cooled high heat flux plasma facing components in Tore Supra operation, which is today culminating with the routine operation of an actively cooled toroidal pumped limiter (TPL) capable of sustaining up to 10 MW/m2 of nominal convected heat flux. This success is the result of a long lead development and industrialization program (about 10 years) marked out with a number of technical and managerial challenges that were taken up and has allowed us to build up a unique experience feedback database, which is displayed in the paper. [Copyright &y& Elsevier]

Abstract: Budget restrictions have forced the ITER Organization to reconsider the baseline divertor strategy, in which operations would begin with carbon (C) in the high heat flux regions, changing out to a full-tungsten (W) variant before the first nuclear campaigns. Substantial cost reductions can be achieved if one of these two divertors is eliminated. The new strategy implies not only that ITER would start-up on a full-W divertor, but that this component should survive until well into the nuclear phase. This paper considers the risks engendered by such an approach with regard to known W plasma-material interaction issues and briefly presents the current status of a possible full-W divertor design. [Copyright &y& Elsevier]

Abstract: In ITER, as in any tokamak, the first wall and divertor plasma-facing components (PFC) must provide adequate protection of in-vessel structures, sufficient heat exhaust capability and be compatible with the requirements of plasma purity. These functions take on new significance in ITER, which will combine long pulse, high power operation with severe restrictions on permitted core impurity concentrations and which, in addition, will produce transient energy loads on a scale unattainable in today’s devices. The current ITER PFC design has now reached a rather mature stage following the 2007 ITER Design Review. This paper presents the key elements of the design, reviews the physics drivers, essentially thermal load specifications, which have defined the concept and discusses a selection of material and design issues. [Copyright &y& Elsevier]