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[en] Full text: In the framework of the EUROfusion work package “Heating and current drive”, a conceptual design of the neutral beam injector (NBI) for DEMO, has been developed by Consorzio RFX in collaboration with other European institutes. High efficiency is a fundamental requirement for DEMO, this has been taken into great consideration for the DEMO NBI, as a fundamental part of the maximization of RAMI performance. To increase the efficiency of the system, innovative solutions have been introduced for the neutralizer and the vacuum pumping systems. In particular, the design of a neutralizer based on the “closed recirculating cavity with nonlinear gating” (RING) photoneutralizer concept, using the second harmonic of a laser trapped in cavity through which the beam passes, has been implemented in the DEMO NBI conceptual design. The DEMO NBI has been designed to be also compatible with a gas neutralizer. Non-evaporable getter (NEG) pumps are foreseen to provide the required vacuum pumping inside the vessel. Compared to cryopumps, NEG pumps present numerous advantages: they are more resistant to neutron radiation and they do not need any continuous energy supply system for the operation. In order to increase the reliability and availability of the beam source, the DEMO NBI features a beam source composed of 20 subsources (two adjacent columns of 10 subsources each), following a modular design concept. Each subsource features its radio frequency driver. Such a modular solution is capable to provide a better alignment among the corresponding apertures of the accelerator grids, because the modules have a significantly smaller size than the whole accelerator, hence the horizontal and vertical deformations are also reduced compared with a nonmodular solution. To increase the maintainability of the system, the DEMO NBI has been designed in such a way that all the main components can be substituted without removing other components. For example, the beam source can be removed from the lateral opening of the beam source vessel, the neutralizer and the residual ion dump from dedicated upper flanges, the duct from the equatorial port close to the NBI port. Several analyzes have been carried out to investigate and optimize this conceptual design, namely optics, electrostatics, magnetics, neutronics and thermo-mechanics assessments. (author)
[en] The prototype cryoline (PTCL) for ITER is a representative cryoline from the complex network of all cryolines for the project. PTCL consist of six process pipes (of which four are operating at 4 K temperature level while two are operating at 80 K temperature level), thermal shield and outer vacuum jacket. PTCL will be tested for its thermal performance, mechanical integrity, leak tightness and functioning of components at cryogenic temperatures. The test infrastructure requirements for testing of PTCL have been identified based on the optimized test methodology. The best suited infrastructure option to test PTCL involves 80K system with helium compressor, test boxes, liquid helium Dewar, liquid nitrogen Dewar and interconnecting cryolines. Process study and various analyses have been performed to finalize the specifications of test infrastructure. The present work describes study on global thermo-hydraulic analysis of PTCL test infrastructure. Preliminary process simulation using the ASPEN HYSYS® has been performed to study the dynamic behavior of 80K system. (author)
[en] Highlights: • In-plasma dust-surface impacts recorded with unprecedented resolution. • Experimental determination of the normal and tangential restitution coefficients. • Validation of the dominance of plastic/adhesive work over frictional dissipation. • Calibration of the analytical impact model of the MIGRAINe dust-dynamics code. - Abstract: Mechanical dust-wall collisions are unavoidable in fusion devices and their accurate modeling is essential for the understanding of dust transport. The MIGRAINe dust dynamics code features analytical models addressing all facets of dust-surface impacts, some aspects of which have not been experimentally validated thus far. Dedicated dust injection experiments have been carried out in Pilot-PSI resulting to the visualization of in-plasma tungsten dust-surface impacts with an unprecedented resolution. They allowed for a calibration of key quantities of the MIGRAINe impact model.
[en] An overview of theoretical understanding of edge plasma physics in fusion devices is presented. The effect of grazing angle on solid surface (divertor) erosion due to ion sputtering is studied by 1D-3V fluid approach. For an oblique magnetic field, there exists a different kind of region in front of the solid surface named as Chodura sheath (CS). It is assumed that the CS is additive to the Debye sheath (DS). For a certain value of the grazing angle, it has been observed that the DS vanishes and the entire potential drop occurs across the CS. This new analysis of the event provides some facts of pragmatic importance. These will improve the solutions of edge impurity codes. Important factors like ion energy and impact angle for physical sputtering are highlighted. The dependence of these two parameters on grazing angle is also investigated in detail. (author)
[en] Full text: Plasma exhaust is a critical aspect of DEMO-class devices, so there needs to be confidence that it will work. This paper considers the methodology to establish confidence in potential solutions, drawing on approaches inside and outside fusion, including evolving high power computing tools — these approaches could also help find improved solutions, possibly where all the plasma and materials ingredients operate in known regimes, reducing uncertainty. Crucially, the elements need to be integrated into an overall solution that can meet the demanding performance requirements and constraints of a fusion plant yet also accommodate significant uncertainties in plasma, materials and component behaviour. A prior full scale test of a DEMO exhaust solution is not feasible, almost by definition. The reference approach is to take the best available design, with various uncertainties and unknowns, and use margins and risk mitigation tools to address these. We explore a complementary approach based on models for the final step to give more confidence in the performance and uncertainty range of the design. The two approaches could be combined. For the plasma aspects, qualification will be eased if solutions have resilience to uncertainties and variations, ideally with natural “springiness”, or damping of transients. These can be tested with integrated models containing all relevant mechanisms and interactions, suitably validated. Materials and components have comparable modelling and integration challenges, in particular predicting the effects of combined loads (e.g., neutron, thermal, mechanical). A possible strategy is to combine measured and predicted materials properties and failure mechanisms (such as crack propagation, deformation) into a hierarchical multiscale model from atom-scale up. Such a modelling workflow would be well suited to high levels of parallelization and would improve over use of average material properties. In-silico qualification of such a large and complex system is very challenging, but has large potential benefits in cost, time, flexibility and optimization. Fortunately essentially all science issues are being addressed in the community (e.g., in EUROfusion). The computational demands are excessive today, but the rapid development of both computing power and numerical techniques is likely to transform the situation in the next 10–20 years. (author)
[en] This paper intends to overview the status of fusion activities and to present emerging issues related to the management of resources and knowledge in fusion projects; they can be better addressed by looking at appropriate methodologies and tools in the thematic areas of knowledge management. After a short introduction outlining the present transition phase of the worldwide fusion activity, I will present a preliminary analysis of emerging requirements and challenges, which create the foundations for knowledge management practices for the Fusion Sector. Differences between the fusion and the fission sector will also be discussed, and appropriate practices for some selected challenges will be proposed and analysed. (author)
[en] A room temperature bore superconducting (SC) solenoid magnet has been developed at Control Instrumentation Division (CnID) for carrying out liquid PbLi Magneto Hydro Dynamic (MHD) and corrosion experimental studies for ITER TBM. The SC solenoid magnet is designed to generate central bore magnetic field of 4 Tesla in a bore diameter of 300 mm and length of 800 mm with a field uniformity of 0.5% or better. The SC magnet is made up of low temperature NbTi copper composite wire whose critical temperature (Tc) is 9.8 K. The SC magnet needs to be cooled to liquid helium temperature (4.2 K) for its stable operation. Considering the operational requirement, an adiabatically stable SC magnet is under development. The adiabatically cooled SC magnet is completely immersed inside the liquid helium vessel. As the latent heat of vaporisation of liquid helium is less, heat load on liquid helium vessel needs to be reduced. In this paper we discuss about the liquid helium cryostat developed with conduction cooled thermal shield. Various heat loads on the liquid helium cryostat is calculated. Design modification of the existing cryostat to reduce the heat load and improved thermal performance is discussed. (author)
[en] Recent developments in different areas of edge plasma physics, including plasma transport, atomic physics effects, plasma-wall interactions and other wall-related issues, are highlighted and reviewed.
[en] The research and development activities on inductively coupled plasma (ICP) based ion source for neutral Beam Injectors (NBI) are getting popular in Fusion application due to its reduced maintenance requirement. However, it is also well known that ICPs are also widely used in many other fields like: semiconductor processing, plasma based bio medical application, space propulsion etc. In the present report, a detailed study of power loss contributions due to different power loss mechanisms from different RF components in the circuit is carried out in light of efficient source operation and correspondingly loss contributions for IPR ROBIN Test bed. It is observed that, power reflection due to impedance mismatch constitutes a major part of uncoupled power to plasma. Power loss in the antenna, isolation transformer and in the Faraday shield is also significant. Some calculations are benchmarked with ROBIN experiment
[en] In 2018 75 projects of new fusion machines and fission reactors were reported. Concerning thermonuclear fusion, there are 2 kinds of projects, those that revisit concepts that were left aside by national laboratories and those that intend to complete present works on ITER by proposing innovating technologies. The discovery in 2015 of a new alloy allowing the construction of superconducting coils operating at higher temperatures and generating more intense magnetic fields has opened the way to more compact machines than ITER. Commonwealth Fusion Systems (CFS), Lockheed Martin and Tokamak Fusion are enterprises working on such machines. To illustrate the second type of projects, there is the Canadian start-up General Fusion that is studying a concept that relies on the use of an array of pistons driving a pressure wave to compress liquid metal rotating around a 3 million degrees plasma. The compression of the liquid metal heats the plasma triggering the fusion of hydrogen nuclei. Most of the projects are financed by the private sector. (A.C.)