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Control of a Tokamak requires operating many sophisticated control loops in a dynamic sequence of activities. To take appropriate actions in case technical or physics conditions occur unexpectedly, the continuous control must be backed up by Exception Handling (EH) logic. To mature the Conceptual Design of the ITER Plasma Control System (PCS) with such logic for the Preliminary Design, we studied, in a formal process, how the plasma will be controlled during the 1 st plasma and early operation phases of ITER and analysed the required control and EH functions and dependencies: Three classes of Exception Handling were identified which cover all use cases: modification of the control behaviour of a single control function, modification of the control structure of connected controllers, and change of the control goal which modifies the overall control system. The three classes form a EH hierarchy from low to high impact responses that can be implemented as local EH in the Pulse Continuous Control layer and as central EH in the Pulse Supervision layer of the PCS.

Local beryllium (Be) I and Be II line intensities were measured in the plasma–wall interaction region near an ICRH antenna in JET. The intent was to use these intensities as a measure of the formation of local Radio Frequency (RF) sheath potentials, through RF sheath rectification and potential build up at the end of field lines passing in front of the antenna. Experimentally, it was found that the Be I and Be II emission increase when using the antenna local to the spectroscopic measurement, and increase even more when using a remote antenna that is magnetically connected to the observation point. Magnetic field mapping indicates a magnetic connection between the observation location and the top corner region of the remote antenna and/or its protection limiter. These measurements can be used in support of RF sheath modeling that is an important part of the optimization of antenna design for next generation fusion energy devices, including ITER.

A specific experiment was performed in Tore Supra, dedicated to the search for consistency between wall inventories estimated from gas balance and post-mortem analysis and to the characterization of the D-retention mechanism. More than 160 similar discharges were performed, representing a cumulative time of 18 000 s of plasma with no intermediate conditioning procedure. The only significant operational issue was linked to the ejection of flakes from the plasma facing components, whose frequency increased dramatically during the campaign, triggering a plasma detachment phase followed by a disruption in number of cases. In-vessel inventory was increased by ∼3.1 × 1024 D, and constant retention rate (∼2.3 × 1020 D/s averaged over discharge duration) was measured, with no indication of wall saturation. First measurements on dismantled tiles of the Toroidal Pump Limiter (TPL) show [D]/[C] ratios ranging from 0.04 to 0.20, on a typical thickness of 15–20 μm. Extrapolated to the whole TPL, this yields an amount of ∼(1.5 ± 0.3) × 1024 D, i.e. ∼50% of the estimated in-vessel inventory.

A prototype of ICRF antenna based on the load-resilient electrical layout anticipated for ITER has been built at CEA-Cadarache. It consists of two toroidally adjacent resonant double loops (RDLs) based on the conjugate-T concept proposed for the ITER ICRF array. This prototype has been recently validated in Tore Supra plasmas exhibiting fast density perturbations in front of the antenna. This paper reports on the load resilience properties of the antenna prototype, as well as the RF modeling and the commissioning. Significant effort on modeling, coupled to an extensive low power campaign, has allowed characterization of the antenna in both vacuum and plasma loading conditions. Plasma load modelings computed with the code TOPICA – very helpful to set up the matching points on plasmas – are found to be in good agreement with the experimental results. The main studies focus on load resilience properties have been carried out in L-mode plasmas. Supersonic molecular beam injection (SMBI), able to launch a series of very short/dense gas jets at Mach number up to 5, was used to mimic the sudden increases of the antenna coupling provoked by ELMs. The results are found to be in good agreement with RF circuit calculations that include 3D modeling.