The aim of this study is to compare two methods of interpolation, namely Kriging (a standard algorithm), mainly used in geostatistics, and the Experimental Probabilistic Hypersurface (developed by ...SCM SA). We study several technical points, such as their ability to take uncertainties into account, to return an uncertainty on the interpolation, the quality of the numerical procedures, etc. The Experimental Probabilistic Hypersurface (EPH) is a minimal information model, which only uses the existing data and makes as less artificial hypothesis on the data as possible. The Kriging, on the contrary, relies on an estimation of the variability of the data using a variogram.
Abstract
In this paper we present a method to compute spatial and time evolution of electromagnetic forces in magnetic confinement fusion devices based on a combination of signal analysis of magnetic ...measurements with a simple electromagnetic modelling. The method allows analyzing the whole plasma discharge including fast transient phenomena such as fast terminations or disruptions. It has been tested and verified on RFX-mod, an experiment equipped with a non-continuous toroidal passive stabilizing shell, but it can be applied to cases with continuous wall such as tokamak devices, as well. An experimental plasma discharge, with a fast termination phenomenon at the end of the flat-top phase, has been analyzed and the related forces have been computed by using two different sets of data: synthetic magnetic field measurements provided by ANSYS simulation and real experimental ones. The results are in good agreement in all the phases of the plasma discharge. Moreover, because of the very low-computational requirements, it is shown that the presented method can be used as a tool for real-time monitoring of the electromagnetic forces on the shell to be integrated in the protection system of the future RFX-mod2 experiment.
•RFX-mod upgrade is proposed for studies in both RFP and Tokamak configuration.•RFX-mod2 design implies a major change of the components of the machine assembly.•High-performance polymers will be ...used for in-vessel support structure.•Thermo-mechanical FEM verification of the RFX-mod2 shell has been completed.
An upgrade of RFX-mod toroidal machine assembly is under development, aimed at widening the explored operational scenarios both in RFP and Tokamak configuration. The main design driver for this machine upgrade, named RFX-mod2, is the enhancement of the ‘shell-plasma proximity’, which is expected to provide a significant improvement in the plasma magnetic confinement. In order to achieve this goal, the existing Passive Stabilizing Shell will be adapted in order to be enclosed in the new vacuum vessel. This reconfiguration of the internal components of the experiment requires the design of a new structure aimed at supporting both the shell and the plasma facing components. The paper describes the design aspects of the shell assembly, with particular focus on the thermo-mechanical FEM analyses performed to verify the design of the components at the expected operating conditions.
Abstract
SPIDER, an RF-driven negative ion source in the Neutral Beam Test Facility (NBTF), serves as the prototype for ITER's neutral beam injector (NBI). It is composed of 8 drivers powered by 4 RF ...generators, aiming to accelerate 50 A of negative hydrogen ions to 100 KeV with a beam uniformity target of 10%. The experiment, launched in 2018, tested negative ion production using caesium. Results match those of similar facilities, but SPIDER faces challenges due to its size, multiple drivers, and non-uniform plasma expansion. These issues impact beam uniformity, preventing the machine from reaching expected performance. To address this, SPIDER initiated a significant shutdown at the end of 2021 for improvements.
One the most important aspects studied during the first experimental campaign is source uniformity, addressed both in terms of plasma and of caesium distribution. The latter is particularly relevant since its quality is directly related to the beam uniformity and divergence. To have more insight about these issues, monitoring the plasma properties in the extraction region is crucial, hence in the present contribution, the design and development of two new diagnostic systems are described: a movable Langmuir probe and a Retarding Field Energy Analyser (RFEA).
The first can provide a vertical scan of the main plasma parameters close to the plasma grid. The spatial resolution would improve with respect to the already installed set of fixed Langmuir probes embedded in the grid system, and the newly installed diagnostic could interact with other sensors to produce complementary measurements (namely, electron photo-detachment).
The latter, instead, allows the monitoring of the positive ion energy distribution: positive ions, in fact, can be precursors of the negative ones produced at the caesiated surface, but also influence the energy of negative ion and their extraction probability and thus collecting information about their energy distribution allows inferring details about the extracted negative ion beam.
The two diagnostics are designed focusing on the experimental constraint of integrating the diagnostics in a harsh and complex environment such as SPIDER plasma: a preliminary study of the placement inside the source is carried out, then the electrode of the movable probe and the RFEA sensor are sized according to the spatial and energy resolution requested by the system.
•An upgrade of RFX-mod is proposed for studies in both RFP and Tokamak configuration.•RFX-mod2 design implies a major change of the components of the machine assembly.•Vacuum-tight ...electrical-insulated crossed joints of the new vessel will be realized.•High-performance polymers and surface coatings will be used for in-vessel components.
The design of RFX-mod2 experiment implies a major change and reconfiguration of the internal components of the present machine assembly. Critical aspects of the design regard the technical solutions needed to fulfil geometrical, vacuum and electrical requirements imposed by interface with existing components and by specific operating conditions. The paper presents an overview of the design choices and the proposed implementations, assessed by means of engineering analyses and experimental tests performed on mock-ups of the new components.
Src-family kinases (SFKs) regulate different granulocyte and monocyte/macrophage responses. Accumulating evidence suggests that members of this family are implicated in signal transduction pathways ...regulating phagocytic cell migration and recruitment into inflammatory sites. Macrophages with a genetic deficiency of SFKs display marked alterations in cytoskeleton dynamics, polarization and migration. This same phenotype is found in cells with either a lack of SFK substrates and/or interacting proteins such as Pyk2/FAK, c-Cbl and p190RhoGAP. Notably, SFKs and their downstream targets also regulate monocyte recruitment into inflammatory sites. Depending on the type of assay used, neutrophil migration in vitro may be either dependent on or independent of SFKs. Also neutrophil recruitment in in vivo models of inflammation may be regulated differently by SFKs depending on the tissue involved. In this review we will discuss possible mechanisms by which SFKs may regulate phagocytic cell migratory abilities.
Abstract
The experimental fusion reactor ITER will feature two (or three) heating neutral beam injectors (NBI) capable of delivering 33(or 50) MW of power into the plasma. A NBI consists of a plasma ...source for production of negative ions (extracted negative ion current up to 329 A/m
2
in H and 285 A/m
2
in D) then accelerated up to 1 MeV for one hour. The negative ion beam is neutralized, and the residual ions are electrostatically removed before injection. The beamline was designed for a beam divergence between 3 and 7 mrad.
The ion source in ITER NBIs relies on RF-driven, Inductively-Coupled Plasmas (ICP), based on the prototypes developed at IPP Garching; RF-driven negative-ion beam sources have never been employed in fusion devices up to now. The recent results of SPIDER, the full size ITER NBI ion source operating at NBTF in Consorzio RFX, Padova, measure a beamlet divergence minimum of 12mrad and highlighted beam spatial non-uniformity. SPIDER results confirmed the experimental divergence found in smaller prototype sources, which is larger compared to filament-arc ion sources. Although prototype experiments have shown that the extracted current requirement can be achieved with minor design improvements, the beamlet divergence is expected to marginally achieve the design value of 7 mrad, which in multi-grid long accelerators results in unexpected heat loads over the accelerator grids. A contributor to the beam divergence is the energy/temperature of the extracted negative ions, so it is believed that plasma differences between the two source types play a role. Research is focused on the plasma parameters in the ion source.
One RF driver, identical to the ones used in SPIDER, installed in a relatively small-scale experimental set-up, inherently more flexible than large devices, is starting operations devoted to the investigation of the properties of RF-generated plasmas, so as to contribute to the assessment of negative ion precursors, and of their relationship with the plasma parameters, particularly when enhancing plasma confinement. The scientific questions, that have arisen from the preliminary results of SPIDER, guided the design of the test stand, which are described in this contribution, together with the diagnostic systems and related simulation tools. The test stand, which shares with the larger experiment all the geometrical features and constraints, will allow technological developments and optimized engineering solutions related to the ICP design for the ITER NBIs.
Abstract
Three years of experiments on SPIDER allowed characterization of the main features of the source plasma and of the negative ion beam, in the original design configuration. For the large ...dimensions of the source chamber, and of the extraction area, the investigation of the single-beamlet currents and of the source plasma uniformity had to be carried out to extend the knowledge gained in smaller prototype sources. The configuration of the multiple RF drivers and filter field topologies were found to cause a peculiar behavior in the plasma confinement in the drivers, creating left-right asymmetries which were also visible in the extracted negative ion currents, even after the early implementation of a new scheme of plasma-grid current send and return busbars that greatly improved performance at high filter fields. The plasma properties in the driver and expansion region as well as the positive ion energy at the extraction region were studied in different experimental conditions, and interpreted also with the support of numerical models, suggesting that an improved plasma confinement could contribute to the increase of the plasma density, and to a certain extent to a lowering of the plasma potential profile; both effects shall contribute to increase the presence of cold negative ions for the formation of low-divergence beamlets. Early results related to unwanted RF discharges on the back of the plasma source and the gas conductance of the beam source suggested the reduction of the vessel pressure as mitigation, leading to the definition of a new pumping system. The difficulties related to the simultaneous operation, stable control and high-power operation of multiple RF self-oscillating vacuum tube based RF generators were an unambiguous obstruction to the experimentation, calling for the implementation of RF solid-state amplifiers. The initial tests related to caesium management, the non-uniform plasma properties at different locations across the plasma grid, and the challenges in the measurement of the current and divergence of the accelerated beamlet, unambiguously resulted in the need of new diagnostic systems to investigate with better resolution the spatial uniformities. This contribution summarises how the main experimental findings in the previous experimental campaigns are driving modifications to the SPIDER experiment, during the present shut down, in view of future operations.
This paper summarizes the results of preliminary insulation tests performed on copper samples covered with a Al 2 O 3 (aluminum oxide, commonly called alumina) film, deposited using the Atmospheric ...Plasma Spray (APS) technique.The electrical insulation tests were conducted in a vacuum chamber in the presence of weakly ionized plasma, in order to simulate the operating conditions that are expected in the plasma edge region in the RFX-mod2 experiment, in particular in the region included between the first wall and the copper passive stabilization shell.A minimum thickness of alumina deposit is required in order to ensure the dielectric rigidity required by the conditions of use in RFX-mod2. From electromagnetic simulations, it is estimated that the dielectric thickness must be such as to withstand a voltage greater than 1.5 kV.The experiments were carried out by applying a potential difference, generated by a bank of capacitors, between the sample and a copper pin placed in front of the alumina covered surface. The results of the tests conducted show that an alumina thickness of about 0.1 mm is sufficient to guarantee electrical insulation, up to a voltage of about 2.5kV.
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