•The Lorentz force acting on the toroidal field coil of a tokamak are minimized using an ad-hoc numerical code which finds the optimal tilting angles in the toroidal direction.•The result of the ...optimization is a coil whose various regions are tilted with different angles.•The optimization has been carried out for the entire coil perimeter, or restricted to the inner leg.•The tilting of the inner leg creates a second central solenoid generating poloidal flux.•The additional central solenoid can be employed to increase the duration of plasma discharges.
The implications of the adoption of a tokamak's toroidal field coil characterized by differential tilting in the azimuthal direction are investigated. From an engineering point of view, the major advantage introduced by such coils is a drastic reduction of some components of the electromagnetic forces in certain areas. As a beneficial side-effect, they generate poloidal field, in addition to toroidal field. The former advantage allows for a partial relaxation of the reinforcing structural material required in the machine design, while the poloidal flux generated during the current rise, when used in conjunction with the conventional central solenoid, would allow for discharges of longer duration. This paper presents results obtained by applying the tilting optimization procedure to circular and D-shaped coils, and characterized by geometrical and physical parameters proper of high-field compact tokamaks, since the issue of electromagnetic force reduction is most relevant in these devices.
We report on the results achieved by installing two Chemical Vapor Deposition (CVD) single crystal diamond detectors in one of the equatorial ports of the Frascati Tokamak Upgrade (FTU) tokamak, ...during the last six months of operation of the machine. The devices were fabricated at the University of Rome “Tor Vergata” in a metal/instrinsic/p-type diamond layered structure, allowing them to be used as Schottky photodiodes for VUV and Soft-X ray detection. Both detectors were placed inside the machine and operated in current mode under high vacuum conditions.
The fast response capabilities of diamond detectors allowed to observe several plasma events, like the so-called Anomalous Doppler instabilities, the pellet injection and ablation, and Multifaceted Asymmetric Radiation From the Edge (MARFE). Diamond detectors often but not always followed the Magnetohydrodynamics (MHD) activity, depending on their localization relative to the emitting region. Core temperature oscillations following Electron Cyclotron Heating system (ECH) modulation were also observed. In addition, the diamond signals were compared to selected channels of the FTU bolometry system with similar line-of-sight: the encouraging results have launched an R&D program for the development of diamond-based bolometers.
•Effective core fueling in DEMO requires launching pellets from the High Field Side.•Injection speeds not less than 1km/s will be necessary, even from the HFS.•Guiding tracks with a bend radius ≥6m ...are envisaged to deliver intact pellets.•Injection of high-speed pellets from the HFS along free-flight paths, is proposed.•Outboard high-speed injection is still being considered, instead, for JT-60SA.
Core fuelling of DEMO tokamak fusion reactor is under investigation within the EUROfusion Work Package “Tritium, Fuelling and Vacuum”. An extensive analysis of fuelling requirements and technologies, suggests that pellet injection still represents, to date, the most realistic option. Modelling of both pellet penetration and fuel deposition profiles for different injection locations, assuming a specific plasma reference scenario and the ITER reference pellet mass (6×1021 atoms), indicates that: 1) Low Field Side (LFS) injection is inadequate; 2) Vertical injection may be effective only provided that pellets are injected at ∼ 10km/s from a radial position ≤∼8m; 3) effective core fuelling can be achieved launching pellets from the High Field Side (HFS) at ∼1km/s. HFS injection was therefore selected as the reference scheme, though scenarios featuring less steep density and temperature gradients at the plasma edge could induce to reconsider vertical injection at speeds in the range of 4–5km/s. To deliver intact pellets at 1km/s from the HFS, the use of guide tubes with a bend radius ≥6m is envisaged. The results of above simulations rely on the hypothesis that pellets are delivered at the plasma edge with the desired mass and speed. However, mass erosion and fracturing of pellets inside the guide tube (severely limiting the transfer speed), as well as pressure build up and speed losses at relevant injection rates, might hamper the use of curved guide tubes. An additional innovative approach, aimed at identifying inboard straight “free flight” injection paths, to inject pellets from the HFS at significantly higher speeds, is proposed and discussed as a backup solution. Outboard high-speed injection is still being considered, instead, for JT-60SA.
•Core fuelling of EU-DEMO tokamak requires pellet injection from the HFS at ≳1 km/s.•Two complementary approaches are being pursued to achieve this goal.•Guide tubes with bend radii ≥6 m to try ...delivering intact pellets at ∼1 km/s.•High-speed (∼3 km/s) pellet injection along DLS paths from the HFS or vertical port.•Scatter cone of free-flight high-speed pellets measured and neutron flux estimated.
Pellet injection represents, to date, the most promising option for core fuelling of the EU-DEMO tokamak. Simulations with the HPI2 pellet ablation/deposition code indicate, however, that sufficiently deep fuel deposition requires injection from the High Field Side (HFS) at velocities ≳1 km/s. Two complementary inboard injection schemes are being explored: one makes use of guide tubes with curvature radii ≥6 m in the attempt of preserving pellet integrity at speeds of ˜1 km/s, the other is investigating the feasibility of injecting high-speed (˜3 km/s) pellets along “direct line of sight” (DLS) trajectories, from either the HFS or a vertical port. Options using quasi-vertical DLS paths routed across the upper vertical port have been explored first, as they can be more easily integrated, Unfortunately, the radial position of the available vertical access (≳9 m from the machine axis) turns out to be unfavorable; further simulations with the HPI2 code predict indeed that vertical injection may be effective only if pellets trajectories are well inboard the magnetic axis. High-speed injection through oblique inboard “DLS” paths, not interfering with the Central Solenoid (CS), are instead predicted to yield good performance, provided that the injection location is ≲2.5 m from the equatorial mid-plane. The angular spread of high-speed free-flight pellets, recently measured using an existing facility, turns out to be enclosed within ˜ 0.7°. This scatter cone may require significant cut off volume of the Breeding Blanket (BB). Moreover, DLS in-vessel conical penetrations may increase the neutron flux outside of the bio-shield, and also result in a significant heat load in the cryogenic pellet source. These issues are being investigated, to identify suitable shielding strategies; preliminary results are reported. The suitability of straight guide tubes to reduce the scatter cone, and hence the corresponding open cross section on BB penetration and the neutron streaming, will be explored as a further step.
•The radiological impact of Ignitor in the TRINITI site in Russia is negligible.•Ignitor could be easily licensed in Russia from safety and radiological viewpoints.•TRINITI is a fully characterized ...nuclear site, apt to host the Ignitor experiment.•The maximum accidental dose is far below any limit for emergency countermeasures.•The Ignitor plant does not need any further containment building.
A safety analysis study has been applied to the Ignitor machine. Deterministic evaluations of radioactive environmental releases have been performed. The preliminary radiological impact analysis for the normal operation and the main accidental sequences of Ignitor, in case of its localization in the TRINITI site in Russia are presented. The site of TRINITI, hosting since decades nuclear installations, is well characterized, both from the meteorological and population aspects: many data have been collected over the years.
The Ignitor machine, both during routine functioning and accidental sequences, presents a negligible radiological impact. Ignitor does not need any concrete primary containment, like those used in fission nuclear power plants. There is no need of people evacuation or emergency countermeasures even in presence of the worst accident.
•Remote control of a pellet facility has been proved repeatable and reliable.•E3S platform has been successfully tested in remote control of a pellet injector.•Performance tests indicate that, for ...massive I/O data flow, E3S should be scaled-up.
The four-barrel, two-stage gun Ignitor Pellet Injector (IPI) was developed in collaboration between ENEA and ORNL. The prototype injector is presently located at Oak Ridge (TN, USA), and is normally operated locally through a control and data acquisition system developed in LabVIEW. More recently, a remote-control system has been set up, based on RealVNC®, which allows to operate the IPI from a control room in Italy. Tools for data transfer and storage into ENEA ICT area have also been provided. A Staging, Storage and Sharing system, named E3S, developed using OwnCloud as architectural component, is used for file synchronization and sharing of the data acquired by the diagnostic systems. It provides a homogeneous platform able to store and share heterogeneous data produced by many data acquisition systems in large nuclear fusion experiments. This paper reports about the implementation of the IPI remote control, and presents the application of E3S to this specific case, allowing easy storage and sharing of experimental data onto a wide-area distributed file-system, as well as remote data access via web-services based on MDS+ tool, integrated with MySQL metadata. A performance analysis of the architectural components is also introduced.
•Larger and hotter fusion devices require high speed pellets for fuelling and density profile tailoring.•Long plasma pulses require repetitive pellet injector.•A R&D program is outlined to build on ...existing expertise by ENEA and ORNL to build a fast and repetitive injector suitable for future fusion devices.
The injection of cryogenic pellets from the low field side (LFS) has long been in use for core fuelling of fusion devices, but injection from the high field side (HFS) has proved to provide a more effective core particle deposition, despite the severe limitations imposed to the pellet speed (≤300m/s) by inboard accessibility. In the future, an alternative approach may be that of injecting high-speed pellets from the HFS, through suitable “free-flight” paths, eliminating curved transfer systems. Furthermore, the expected length of the plasma discharges will require steady-state repetitive systems. ORNL and ENEA have been collaborating on high-speed injectors since 1990; they successfully realized a high-speed repeating pellet injector (2.55km/s at 1Hz). Since then, good progress has been achieved on both fronts of steady-state extruders, and operation and reliability of two-stage guns. A comprehensive R&D program is therefore proposed to investigate how far speed limits and repetition rates of combined two-stage guns and steady-state extruders technologies can be extended. Simulations results are presented showing pellet penetration for several injection locations on a tokamak under construction such as JT60-SA, on the basis of one set of design plasma parameters.
Objectives
To evaluate a new material containing tantalum oxide as an alternative radiopacifier, and a water-based gel for hydration, in comparison with two calcium silicate–based cement: ProRoot MTA ...and Biodentine.
Materials and methods
ProRoot MTA (Dentsply), Biodentine (Septodont), and a new hydraulic calcium silicate cement White-MTAFlow (Ultradent) (in ‘thin’ consistency) were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The interaction with dentin was also assessed using SEM and EDS. Physical and chemical properties radiopacity, setting time, linear flow, volumetric central filling, and lateral flow, pH, and volume change were investigated together with the color luminosity (L) and color change (ΔE). The agar diffusion and direct contact antimicrobial activity, and methylthiazolyldiphenyl-tetrazolium-bromide (MTT) cytotoxicity using human fibroblast cells were also evaluated. Data were statistically analyzed at a 5% significance level.
Results
All materials were composed of tricalcium and dicalcium silicate but had different radiopacifiers, and calcium hydroxide (portlandite) deposition was detected in XRD analysis. White-MTAFlow exhibited radiopacity values in accordance with ISO standard, and the longest setting time. The water-based gel provided the highest linear flow, a comparable cavity central filling, and the highest groove-lateral flow in the volumetric flow analysis. White-MTAFlow exhibited an alkalinity reduction, and Biodentine, a progressive increase of pH values after 28 days. However, similar volume loss for White-MTAFlow was assessed in comparison to Biodentine after the 28-day immersion. White-MTAFlow showed the highest L value (91.5), and ProRoot MTA the lowest (78.1) due to dentin staining caused by bismuth migration. None of the materials exhibited inhibition halos against the tested bacteria, and similar turbidity values were obtained after 48 h in direct contact with
E. faecalis
, indicating an upregulation to bacterial growth. White-MTAFlow showed MTT cytocompatibility similarly to the control group.
Conclusions
White-MTAFlow in ‘thin’ consistency presents comparable physicochemical, biological, and antimicrobial properties to ProRoot MTA and Biodentine, and does not cause color alteration in dentin.
Clinical relevance
White-MTAFlow is a suitable material for use as reparative endodontic cement. Further studies considering its biocompatibility are necessary.
Ignitor is a tokamak project aimed at achieving ignition. In the reference scenario, plasma-surface interactions are controlled by a Mo first-wall/limiter, which constitutes a simple engineering ...solution but, at the same time, a special challenge for edge plasma modelling. Here the ASPOEL plasma fluid code, already applied to Ignitor in the recent past, is coupled with the neutral Monte Carlo code EIRENE. We study the effects of the neutrals on the plasma density and temperature profiles in the Ignitor scrape-off layer, and compute the particle and heat loads onto the Ignitor first-wall limiter.
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