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Abstract: Future fusion experiments will rely on tungsten armour tile for their plasma facing components. In order to sustain steady state operation, the components need to be cooled through an attachment to a heat sink. All current reference concepts rely on contact bonds, unfavourable for long-term application (high temperature service, cycle fatigue, thermal shocks). Three routes toward the development of thick tungsten bonds are presented here, namely functionally graded tungsten copper assembly, electron beam welding of tungsten, and coating processes. All present favourable prospects, and tend to indicate that a thick bond is possible with tungsten. Dedicated programs as well as industrial implication are however required if such concepts are to be used actually for the fabrication of large components series. [Copyright &y& Elsevier]

• Active wall monitoring systems are an increasingly important asset for safe operation of metallic wall steady state magnetic fusion experiments. • Wall Infrared diagnostic connection to plasma control system enables wall monitoring. • WEST operates the C4 experimental campaign in 2019 with an ITER relevant wall monitoring system (soft control plus hard interlock). • The control activates on 63 occurrences, principally on an upper divertor pipe being heated by particles losses. • It facilitated WEST path to high power operation during C4 campaign, by effectively managing the technical risks to critical wall components. A real time Wall Monitoring System (WMS) is used on the WEST tokamak during the C4 experimental campaign. The WMS uses the wall surface temperatures from 6 fields of view of the Infrared viewing system. It extracts the raw digital data from selected areas, converts it to temperatures using the calibration and write it on the shared memory network being used by the Plasma Control System (PCS). The PCS feeds back to actuators, namely the injected power from 5 antennae's of the lower hybrid and ion cyclotron resonance radiofrequency (RF) heating systems. WMS activates feed back control 63 times during C4, which is 14 % of the plasma discharges. It activates mainly as the result of a direct RF loss to the upper divertor pipes. The feedback control maintains the wall temperature within the operation envelope during 97 % of the occurrences, while enabling plasma discharge continuation. The false positive rate establishes at 0.2 %. WMS significantly facilitated the operation path to high power operation during C4, by managing the technical risks to critical wall components. [ABSTRACT FROM AUTHOR]

Nitrogen (N2) will be used in ITER to enhance the radiative fraction to ∼90%, thereby cooling the edge plasma and preventing damage to the plasma-facing components. However, the reactivity of N2 with hydrogen isotopes can lead to the formation of tritiated ammonia (NT3). This should be considered in terms of the in-vessel tritium inventory, the regeneration of the cryo pumps, and the processes in the ITER de-tritiation plant. In the 'W' Environment in Steady-state Tokamak (WEST), a series of long L-mode discharges (∼50 s), with a constant N2 seeding from the outer strike point region has been performed on the upper actively cooled divertor. In the absence of active pumping, the N2 balance shows steady-state retention during plasma discharge, and is partially (∼35%) released in between discharges. Although a significant amount of N2(18.65 Pa m3) has been injected, the wall still exhibited N2 pumping capabilities. Under these conditions, as long as this N2 reservoir is not saturated, there is not enough N available for the detectable threshold of ND3 formation to be reached. In these WEST experiments, no ammonia is detected during the pulse or after the pulse in the outgassing phase. These results are consistent with and complementary to the N2 seeded experiments performed in the Joint European Torus (JET) with its ITER-like wall and in the Axially Symmetric Divertor Experiment (ASDEX) upgrade. [ABSTRACT FROM AUTHOR]

Highlights: [•] Detailed design development plan for the ITER tungsten divertor. [•] Latest status of the ITER tungsten divertor design. [•] Brief overview of qualification program for the ITER tungsten divertor and status of R&D activity. [Copyright &y& Elsevier]

Abstract: The ITER reference materials have been tested separately in tokamaks, plasma simulators, ion beams and high heat flux test beds. In order to perform a fully integrated material test JET has launched the ITER-like Wall Project with the aim of installing a full metal wall during the next major shutdown. As a result of R&D projects in 2005–2006, bulk tungsten tiles are foreseen at the outer horizontal target and tungsten coating at the other divertor tiles. In some regions of the main chamber, beryllium coated Inconel tiles and bulk beryllium tiles are utilised which include marker tiles as erosion diagnostics. This paper gives an overview of the R&D carried out in the frame of the ITER-like Wall Project on the development of an inertially cooled bulk tungsten tile design and the characterization of tungsten and beryllium coating technologies. [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: 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]