The JET 2019-2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major Neutral Beam Injection (NBI) upgrade providing record power in 2019-2020, and tested the technical & procedural preparation for safe operation with tritium. Research along three complementary axes yielded a wealth of new results. Firstly, the JET plasma programme delivered scenarios suitable for high fusion power and alpha particle physics in the coming D-T campaign (DTE2), with record sustained neutron rates, as well as plasmas for clarifying the impact of isotope mass on plasma core, edge and plasma-wall interactions, and for ITER pre-fusion power operation. The efficacy of the newly installed Shattered Pellet Injector for mitigating disruption forces and runaway electrons was demonstrated. Secondly, research on the consequences of long-term exposure to JET-ILW plasma was completed, with emphasis on wall damage and fuel retention, and with analyses of wall materials and dust particles that will help validate assumptions and codes for design & operation of ITER and DEMO. Thirdly, the nuclear technology programme aiming to deliver maximum technological return from operations in D, T and D-T benefited from the highest D-D neutron yield in years, securing results for validating radiation transport and activation codes, and nuclear data for ITER.

In this paper, laser-induced breakdown spectroscopy (LIBS) under magnetic field condition has been studied in laboratory and EAST tokamak. The experimental results reveal that in helium ambient gas, the magnetic field significantly enhances the LIBS signal intensity (~ 3 times). The effect of time delay and laser fluence on the intensity of LIBS has been investigated for optimizing the signal to background ratio (S/B). The developed LIBS approach has been applied to monitor the cleaning performance of the first wall in the fusion device of EAST using the ion cyclotron range of frequency (ICRF). The experimental results demonstrate that the cleaning performance for Li/D co-deposition layer is effective under helium ambient gas. The removing rate of Li on the surface of W tile is faster than that on Mo tile in He-ICRF cleaning and the D/(D+H) ratio on Mo tile is higher by ~ 1.2 times than that on W tile. This work would indicate the feasibility of using LIBS to monitor the wall cleaning processes in EAST tokamak.

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In this work, laser-induced breakdown spectroscopy (LIBS) approach was applied to Experimental Advanced Superconducting Tokamak (EAST) device for in situ diagnosing the lithium-wall conditioning processes and the Li-H/D co-deposition on the inner board of the first wall of EAST. The fuel of D and the co-deposition impurities, such as H, Li, Ca, Na and Mo were clearly observed on the surface of the first wall. During the processes of Li-wall conditioning, the Li signal intensity increases with the increase of the time of Li-wall conditioning, and the average deposited rate of Li was about 0.522 μm h -1 . The study of Li-coating layer indicates that LIBS technique can be used to assess the degree of re-deposition on the first wall. The variation of H/(H+D) as a function of the days of D-discharge demonstrates that Li-wall conditioning technique can significantly reduce the H/(H+D) ratio in the vacuum vessel due to the strong H/D adsorption capability of Li and enhance long-pulse H-mode plasma operation. The results indicate that LIBS technique can be used for in situ analysis of co-deposition and D retention on the first wall of EAST.