DIFFER: Publications
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Overview of JET results for optimising ITER operation
No full textThe 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 upgrade providing record power in 2019–2020, and tested the technical and 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 (α) 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 and 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
Evidence on the effects of main-chamber neutrals on density shoulder broadening
No full textEvidence that density shoulder broadening is dependent on high main-chamber neutral density is presented. Shoulder broadening does not occur when the sources for main-chamber neutrals are minimized using divertor baffles and wide gaps to the first wall (∼3× the density decay length). Removing the baffles or reducing the gap to the inner wall both act to increase the density shoulder amplitude in otherwise identical TCV discharges. Radial turbulent transport is correlated with shoulder amplitude.
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ChemPlot, a Python Library for Chemical Space Visualization
No full textVisualizing chemical spaces streamlines the analysis of molecular datasets by reducing the information to human perception level, hence it forms an integral piece of molecular engineering, including chemical library design, high-throughput screening, diversity analysis, and outlier detection. We present here ChemPlot, which enables users to visualize the chemical space of molecular datasets in both static and interactive ways. ChemPlot features structural and tailored similarity methods, together with three different dimensionality reduction methods: PCA, t-SNE, and UMAP. ChemPlot is the first visualization software that tackles the activity/property cliff problem by incorporating tailored similarity. With tailored similarity, the chemical space is constructed in a supervised manner considering target properties. Additionally, we propose a metric, the Distance Property Relationship score, to quantify the property difference of similar (i. e. close) molecules in the visualized chemical space. ChemPlot can be installed via Conda or PyPI (pip) and a web application is freely accessible at https://www.amdlab.nl/chemplot/.
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Power-to-X: On the development of a KEROGREEN reactor module for sustainable CO production and the challenges in CO2 plasmolysis and gas separation
Full text linkEnergy partitioning in N-2 microwave discharges: integrated Fokker-Planck approach to vibrational kinetics and comparison with experiments
No full textThis work investigates energy transfers between electrons, vibrational and translational degrees of freedom and their effect on dissociation mechanisms in a N2 microwave plasma in the pressure range between 50 and 400 mbar. A novel self-consistent 0D plasma chemistry model describing vibrational kinetics via the vibrational energy equation and the Fokker-Planck approach is developed. It is used to simulate conditions achieved experimentally, providing good agreement with measured values of vibrational and gas temperature and electron density. Above 100 mbar, energy efficiency of dissociation increases with power density, due to the significant contribution of collisions between vibrationally excited N2 and electronically excited molecules. Energy transfer to vibrations is maximum at low power density and low pressure due to reduced gas heating.</p
Concept for a multi-purpose EU-DEMO pellet launching system
No full textPellets - mm-size solid bodies produced from frozen fuel - are mainly destined for fuelling purposes in the fusion reactor EU-DEMO. However, pellets have been proven capable tools for further tasks too, e.g. ELM frequency control and the efficient delivery of seeding gases have been already demonstrated. Here, a concept is presented for a single pellet launcher based on a stop-cylinder centrifuge accelerator equipped with multiple pellet sources. The sources can deliver pellets with different sizes and composition, finally combined into one single compound pellet train. Thus, the pellet launching system (PLS) is capable to control simultaneously different plasma parameters with a minimized cross talk between these different actuations. Currently, a new PLS is under development for the new large superconducting tokamak device JT-60SA which can be potentially regarded as a prototype for the envisaged EU-DEMO system. Its initial configuration will be capable to control plasma density and ELM pacing simultaneously; optionally a source for doped pellets can be added. Status and recent achievements of this systems are reported. At the full metal wall mid-size tokamak ASDEX Upgrade (AUG), work is ongoing developing a versatile control strategy and corresponding tools. Capable to inject pellets with high speed through a guiding tube from the torus inboard side, AUG represents a fully reactor relevant configuration. While all demonstrations have been performed with a single pellet source hence bound to actuation prioritizing one actuation parameter, all tools developed can be expanded straightforwardly to multi-purpose control. For example, one novel tool optimizes real-time feedback pellet flux control taking into account the discrete nature of the pellets. As well, a solution is worked to handle the issue of missed-out pellets. Such failed pellets are considered unavoidable due to the fragile nature of the solid fuel but identified as significant hazard for reactor burn control
Use of machine learning for a helium line intensity ratio method in Magnum-PSI
No full textOptical emission spectroscopy (OES) of helium (He) line intensities has been used to measure the electron density, n e, and temperature, T e, in various plasma devices. In this study, a neural network with five hidden layers is introduced to model the relation between the OES data and n e/T e from laser Thomson scattering in the linear plasma device Magnum-PSI and compared to multiple regression analysis. It is shown that the neural network reduces the residual errors of prediction values (n e and T e) less than half those of the multiple regression analysis in the ranges of 2 × 10 18<n e<8×10 20m−3 and 0.1<T e<4 eV. We checked two different data splitting methods for training and validation data, i.e., with and without considering the unit of discharge. A comparison of the splitting methods suggests that the residual error will decrease to ∼10% even for a new discharge data when accumulating a sufficient data set.</p
Performance of liquid-lithium-filled 3D-printed tungsten divertor targets under deuterium loading with ELM-like pulses in Magnum-PSI
No full textA fusion reactor divertor must withstand heat flux densities <10 MW m−2. Additionally, it may have to withstand millisecond pulses on the order of 0.5 to 30 MJ m−2 due to (mitigated) edge-localized modes (ELM) occurring with 30 to 60 Hz. We investigate if these requirements can be met by capillary porous system (CPS) liquid lithium divertors (LLD). 3D-printed tungsten CPS targets were exposed in the linear plasma device Magnum-PSI, to deuterium plasma discharges lasting 15 s, generating 1.5 to 16 MW m−2, and Te ~ 1.5 eV. Additionally, ELM-like pulses were superimposed on top of the steady state for 3 s with a frequency of 2 and 100 Hz, power flux densities of 0.3 to 1 GW m−2, and Te up to ~14 eV. All Li targets survived without damage. The surface temperature (Ts) was locked at ~850 °C, which was attributed to power dissipation via vapor shielding. Meanwhile, unfilled reference targets melted during the severest pulsed loading. A blue grayish layer of presumably LiD formed when Ts < 500 °C, but disappeared when the locking temperature was reached. This implies that LiD formation can be avoided, but that it may require a surface temperature at which Li evaporation excessively contaminates the core plasma in a tokamak. During pulsed loading the plasma facing surface remained wetted in all conditions. Bolometry indicated that, only during pulses, there was a large increase in radiative power dissipation compared to targets without Li. A high speed camera with a Li-I filter showed that strong Li evaporation continued up to 5 ms after a pulse. Overall, the liquid-lithium-filled 3D-printed tungsten targets were found to be highly robust, and 3D-printing can be considered as a promising manufacturing technique for LLDs. Further research is needed particularly on the formation of LiD and the associated tritium retention, as well as the impact of enhanced evaporation during and after ELMs on the core plasma
Minimizing carbon deposition in plasma-induced methane coupling with structured hydrogenation catalysts
No full textThe effect of temperature and hydrogen addition on undesired carbonaceous deposit formation during methane coupling was studied in DBD-plasma catalytic-wall reactors with Pd/Al2O3, using electrical power to drive the reaction. Experiments with thin catalyst layers allowed comparison of the performance of empty reactors and catalytic wall reactors without significantly influencing the plasma properties. The product distribution varies strongly in the temperature window between 25 and 200 °C. Minimal formation of deposits is found at an optimal temperature around 75 °C in the catalytic-wall reactors. The selectivity to deposits was c.a. 10% with only 9 mg of catalyst loading instead of 45% in the blank reactor, while decreasing methane conversion only mildly. Co-feeding H2 to an empty reactor causes a similar decrease in selectivity to deposits, but in this case methane conversion also decreased significantly. Suppression of deposits formation in the catalytic-wall reactor at 75 °C is due to catalytic hydrogenation of mainly acetylene to ethylene. In the empty reactor, H2 co-feed decreases conversion but does not change the product distribution. The catalytic-wall reactors can be regenerated with H2-plasma at room temperature, which produces more added-value hydrocarbons