This document presents the packaging completion and storage setup of the MITICA Cryopumps performed at NBTF site on October 5th, 2023 just after the completion of the SAT.

This document presents the packaging completion and storage setup of the MITICA Cryopumps performed at NBTF site on October 5th, 2023 just after the completion of the SAT.

The Divertor Tokamak Test (DTT) [1],[2] is a superconducting device under construction in Frascati, Italy. DTT was proposed to assess the performance of a conventional ITER divertor and address the power exhaust issue that will affect future fusion devices as DEMO. DTT will be equipped with three auxiliary heating systems, including a Neutral Beam Injection (NBI) system. DTT NBI is a high-energy and high-power neutral beam system (ENBI = 250-510 keV, PNBI <= 10 MW) that generates a population of suprathermal particles, known as Energetic Particles (EPs). EP confinement is crucial to improve plasma performances and avoid EP losses to the machine first wall. In this contribution, we characterize the beam-plasma interaction in axisymmetric magnetic field for different planned DTT plasma scenarios. The aim of the present investigation is to explore beam EP confinement in DTT plasmas, extending previous analyses [3] of the reference plasma scenario [4] to configurations at reduced toroidal magnetic field or current, taking into account the possibility of reducing NBI energy and power. The orbit-following Monte Carlo ASCOT suite of codes [5] is used. In particular, BBNBI [6] is used to evaluate the fraction of shine-through losses, i.e. beam particles lost to the first wall before ionization occurs. Through BBNBI we also obtain the information on newly-born fast ions required to populate the topological map built in the Constant of Motion (CoM) phase space [7]. This topological map is used to predict initial EP orbits and prompt losses, i.e. losses happening before collisions with background plasma occur. The ASCOT code is instead used to simulate the full slowing down collisional process and in order to gather information about EP distribution functions, beam contribution to the plasma in terms of power, current and momentum, and possible additional loss channels, e.g. orbit losses. Predictive beam-plasma interaction modelling is essential to explore the use of the NBI system on DTT plasmas, defining its operability. This contribution presents a further step to optimize future DTT operations by contributing to the understanding of beam EP behavior in DTT.

To reach fusion conditions and control plasma configuration in ITER, a suitable combination of additional heating and current drive systems is required, which includes two Neutral Beam Injectors (NBI) providing a total of 33MW hydrogen/deuterium particles electrostatically accelerated to 1MeV; efficient gas-cell neutralisation at such beam energy needs negative ions, obtained by plasma-assisted caesium-catalysed surface conversion. The source plasma is generated by 8 inductively-coupled drivers (typical electron density of the order of 1018m-3 and electron temperature of 10-20eV at 0.3Pa filling pressure), expanding into a single 2m tall chamber by diffusing through a magnetic filter. Such a filter lowers the electron temperature and density, creating the conditions for the existence of an ion-ion plasma in front of the apertures of the plasma electrode. The beam features depend on the parameters of this plasma. As ITER NBI requirements have never been simultaneously attained, a Neutral Beam Test Facility (NBTF) was set up at Consorzio RFX (Italy), hosting two devices, which integrate the experience of several research groups worldwide. MITICA will represent the full-scale NBI prototype with 1MeV particle energy obtained by five 200 kV stages in series. SPIDER, with 100keV particle energy, started testing and optimising the full-scale ion source: extracted beam uniformity >90%, negative ion current density (for one hour) and beam optics (beam divergence <7mrad; beam aiming direction within 2mrad).

SPIDER (Source for Production of Ion of Deuterium Extracted from Radio Frequency plasma), has been operating in Padova since May 2018, with the aim to test and develop the ITER-scale radio-frequency negative ion source, to study the beam characteristics and to verify the source operation. The source produces more than 500 gigabyte per operational day. Extracting as much information as possible from a set of selected signals (plasma light, voltages and currents of power supplies, cameras, tomography, beam emission spectroscopy, caesium oven parameters and others) during an experimental day allows a more efficient use of the largest neutral beam operating source. The simultaneous visualization of signals, related to pre-defined times of interest arrays, monitors the state of the beam and source features from quite different points of view. However, the time evolution of signals of interest often does not represent the expected format for data analysis. The experimental pulse can be divided in phases called 'blips', which correspond to a given experimental configuration typically lasting 40 s. Blips are separated by time periods, required for changing the experiment settings to different configurations. Some punctual information is required for visualization, while derived information is then stored in a relational database for subsequent analysis. The derivation of punctual values was performed offline, with the disadvantage of not being able to derive results of interest during the experiment itself. The new tool derives blip-related information during the pulse, as soon as required data have been stored in the pulse file. The availability of such tool represents a big improvement in the exploitation of the scientific results of SPIDER that can be used in this way during the experimental session itself. Furthermore new features are being developed regarding the addition of other signals including secondary ones and the access to the database from multiple platforms.

We compute reconstructions of 4D and 5D fast-ion phase-space distribution functions in fusion plasmas from synthetic projections of these functions. The fast-ion phase-space distribution functions originating from neutral beam injection (NBI) at TCV and Wendelstein 7-X (W7-X) at full, half, and one-third injection energies can be distinguished and particle densities of each component inferred based on 20 synthetic spectra of projected velocities at TCV and 680 at W7-X. Further, we demonstrate that an expansion into a basis of slowing-down distribution functions is equivalent to regularization using slowing-down physics as prior information. Using this technique in a Tikhonov formulation, we infer the particle density fractions for each NBI energy for each NBI beam from synthetic measurements, resulting in six unknowns at TCV and 24 unknowns at W7-X. Additionally, we show that installing 40 LOS in each of 17 ports at W7-X, providing full beam coverage and almost full angle coverage, produces the highest quality reconstructions.

SPIDER is the full-scale prototype of the plasma source of the negative-ion driven neutral beam injector for the heating and current drive of the ITER plasma. The uniqueness and complexity of the system requested this ad hoc test stand aiming at optimizing the performance of the RF inductively generated plasma, negative ion production and extraction, electron filtering, and robustness and controllability of all systems required to work together. After about three years of operation, presently SPIDER is in a long shutdown, in which the whole plasma source and accelerator were dismounted. In this phase, additional modifications with respect to the original design will be introduced to improve the system performance, driven by the experience acquired in the last years. These include the addition of further sets of permanent magnets in the plasma source expansion chamber and around the RF drivers, with the aim of improving the plasma confinement and consequently its density and possibly its uniformity. The present paper reports the study and the analyses behind this modification, which impacts on the original already complex magnetic configuration, made particularly difficult by the limited space available and the high voltages. The use of ferromagnetic shields, necessary to limit stray fields possibly increasing the breakdown probability, make the design particularly complex because of the greater impact on the previous configuration. An iterative process between analyses to determine the ideal configuration and CAD verifications was required. The analyses had to take into account the new magnetic configuration to be created in the particular area of interest, and the overall configuration in order to not compromise its efficacy.

The Beam Driven Plasma Neutralizer (BDPN) has been proposed as a more efficient alternative to the gas neutralizer for negative-ion based Neutral Beam Injection (NNBI). In this paper we model the performance of an entire NNBI beamline with a BDPN. We simultaneously consider all the relevant physics and engineering aspects, the most important being the plasma density and degree of ionization inside the BDPN as a function of its geometry and feed gas flow, the geometrical transmission of the beamline, the dependence of the neutral gas distribution in the beamline on the geometry of the beamline components and gas flows, and the species evolution of the extracted D- beam through this neutral and charged particle distribution. Furthermore, we calculate the heat loads expected on the BDPN parts and on the NBI components located downstream of it and study the effect of the magnetic cusp field across the BDPN entrance on beamline transmission. While our results constitute an optimization only under the applied boundary conditions, we find that the beamline with a BDPN increases the system's wall plug efficiency by about 13% to 0.34 from the 0.30 estimated for a gas neutralizer.

The Divertor Tokamak Test (DTT) is a new experimental facility whose construction is starting in Frascati, Rome, Italy; its main goals are improving the understanding of plasma-wall interactions and supporting the development of ITER and DEMO. DTT will be equipped with a Neutral Beam Injector (NBI) based on negative deuterium ions, designed to inject 10 MW of power to the tokamak. A fundamental system for the good operations of the DTT NBI will be its Gas injection and Vacuum System (GVS). Indeed, the efficiency of the entire NBI strongly depends on the good performance of its GVS. The GVS for DTT NBI will be composed of two systems working in parallel: a grounded section connected to the main vacuum vessel, and a high voltage part connected to the ion source vessel and working at -510 kV voltage. The grounded part will feature a fore vacuum system (given by screw and roots pumps) plus a high vacuum system based on turbo-molecular pumps located on the side walls of the vessel and Non-Evaporable Getter (NEG) pumps located inside the vessel on the upper and lower surfaces. On the other hand, the high voltage part will feature a fore vacuum system (given by two compact screw pumps mounted on the external surface for the ion source vessel) plus a high vacuum system based on turbo-molecular pumps also located on the sidewalls of the ion source vessel. A dedicated deuterium gas injection will feed the process gas to the ion source and the neutralizer. This paper gives a description of the conceptual design of the GVS for DTT NBI, and of the procedure followed to optimize this system considering the operational requirements and the other constraints of the DTT NBI.

SPIDER is the full-scale prototype of the ion source of the ITER Heating Neutral Beam Injector, where negative ions of Hydrogen or Deuterium are produced by a RF generated plasma and accelerated with a set of grids up to ~100 keV. SPIDER Beam Source design complies with the ITER specific requirements, being fully installed within a vacuum vessel, and with the electrical circuits operating at the residual background pressure. The Power Supply System is composed of high voltage dc power supplies capable of handling frequent grid breakdowns, high current dc generators for the magnetic filter field and RF generators for the plasma generation. During the first 3 years of SPIDER operation different electrical issues were discovered, understood and addressed thanks to deep analyses of the experimental results supported by modeling activities. One of the main issues encountered was the presence of RF discharges on the RF circuit on the backside of the beam source, limiting the operating pressure within the source. The self-excited RF oscillators showed frequency instabilities that were found to be intrinsic limits of the application of this technology to the resonant loads of Neutral Beam Injectors; their understanding allowed assessing the technical basis for the final decision to replace the RF generators in SPIDER and MITICA and change the current ITER baseline to solid-state amplifier technology. Other issues faced regard the effect of the mutual coupling between the RF circuits on board the source, various electromagnetic compatibility problems, the limitation in the operational space to be mitigated improving the SPIDER operating strategies, the revision of the configuration of the magnetic filter field layout to avoid plasma quench. The paper gives an overview on the observed phenomena and relevant analyses to understand them, on the effectiveness of the short-term modifications provided to SPIDER to face the encountered issues and on the design principle of long-term solutions to be introduced during the currently ongoing long shutdown.

The Divertor Tokamak Test (DTT) is a new, super-conducting device, being constructed in Frascati, Italy. DTT will be capable of plasma operations at high density and high heating power, in conditions relevant to address the power exhaust issue in support of ITER operation and DEMO design. DTT foresees the installation of a mix of auxiliary heating systems to couple up to 45 MW to the plasma, including Neutral Beam Injection (NBI). The neutral beam injector is currently being designed, aiming at delivering tangentially to the plasma neutral particles at energy of 510 keV, with a total power of ~10 MW. In the present work, we apply for the first time the orbit-following Monte Carlo code ASCOT to DTT, in order to analyse with more details the interaction of the high-energy beam, described in real geometry beamlet by beamlet, and the plasma. The results of the simulation give an insight of the behaviour of beam energetic particles in DTT. Thanks to the flexibility of DTT, different plasmas can be generated, e.g. in terms of plasma shape due to different divertor concepts. We present the comparison of two cases with different plasma vertical positions and we analyse the effect on beam absorption in the plasma. We then present a sensitivity scan on plasma density, to verify the coupling of beam power at densities lower than the reference target scenario. These investigations are crucial to provide feedback and suggestions to DTT design and to assess the beam fast ion physics for plasma scenario developments.

This Inspection Report describes the BLCs box dimensions as-installed on-site in its final position. The assembly of the pipe-bellow connecting the BLC box to the Mitica Beam Line Vessel is not performed at this stage due to constrains of the Mitica overall schedule, however the dimensions included in this document show the assemblability of this component that will be done at a later stage.

SPIDER is the 100 keV full-size Negative Ion Source prototype of the ITER Neutral Beam Injector, operating at Consorzio RFX in Padova, Italy. The largest Negative Ion Source in the world, SPIDER generates an RF driven plasma from which Deuterium or Hydrogen negative ions are produced and extracted. At the end of 2021, a scheduled long-term shutdown started to introduce major modifications and improvements aiming to solve issues and drawbacks identified during the first three years of SPIDER operations. The first action of the shutdown period was the disassembly and characterization of the SPIDER beam source after removal from the vacuum vessel and its placement inside the clean room. Each component was carefully assessed and catalogued, following a documented procedure. Some source components, i.e., the Plasma Grid, Extraction Grid and Bias Plate, revealed the presence of different and non-uniform red, white and green coatings that might be correlated to back-streaming positive ions impinging on grid surfaces, electrical discharges and caesium evaporation. Thus, several analyses have been carried out to understand the nature of such coatings, with the study still ongoing. The evidence of caesium evaporation and deposition on molybdenum-coated SPIDER components, such as the formation of oxides and hydroxides, is demonstrated through surface characterization analyses with the use of the Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS).

Final report of activities performed during 2020 and 2021 under Specific Order Contract F4E-OFC-1007-01-01.

This report concern the activities performed on the OFC-582-03 from 01 December 2021 till 30 September 2022.

To characterize the SPIDER negative ion beam in terms of beam uniformity and divergence during short pulse operations, an instrumented calorimeter named short-time retractable instrumented kalorimeter experiment (STRIKE) has been designed and operated. STRIKE is made of 16 1D carbon fiber-carbon composite (CFC) tiles, intercepting the whole beam and observed on the rear side by two infrared (IR) cameras. To know the energy flux profile hitting the front surface and then the beam parameters, it is necessary to solve an inverse non-linear problem, mathematically ill-posed, upon knowing the non-linear characteristics of the tiles and the 2-D temperature pattern measured on the rear side of the tiles themselves. Most of the conventional methods used to solve this inverse problem are unbearably time-consuming; when fully operative STRIKE receives 1280 beamlets, each one characterized by at least five features, a ready-to-go tool to determine the beam condition is highly recommended. In this work, the inverse problem in stationary conditions is faced by using a neural network (NN) model, pursuing different training approaches. The NN is trained by associating features extracted from the 2-D temperature profile, obtained by a fitting process to the heat flux profile parameters. The proposed method is then applied to experimental STRIKE data from the beam campaigns.

These technical specifications are the basis for the procurement of the new thermocouples to be installed on the Plasma Driver Plate, Rear Driver Plate and the lateral wall of the source case of SPIDER. These new sensors are required to replace the TCs damaged in the late 2018 due to a breakdown. The lengths of the sensors have been adjusted to the new layout of the source after the change of the bias bus bars.

This document contains the preliminary design for the MITICA Central Safety System.