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The RFX-mod Reversed Field Pinch device passive boundary is being improved: - Drastic reduction of resistivity of first shell surrounding the plasma; - Reduction of plasma-stabilizing conductor distance from b/a=1.11 to b/a=1.04. The RFX-mod core upgrades consist of: - Removal of Inconel vacuum vessel; - Modification of the stainless steel Support Structure to ensure Vacuum Tightness (VTSS); - Modification of the copper Passive Stabilizing Shell (PSS); - Installation of upgraded sensors inside the vacuum vessel. Initial main points of investigation in the new device are discussed.

To reach fusion conditions and control the plasma configuration in ITER, the next step in tokamak fusion research, two neutral beam injectors (NBIs) will supply 17MW each, by neutralizing accelerated negative hydrogen or deuterium ions. The requirements of ITER NBIs (40A/1MeV D- ions for

RFX-mod is an experimental fusion device, which contributes to the plasma physics studies both in Reversed Field Pinch (RFP) and tokamak configurations. Its high flexibility, due to an active magnetohydrodynamic (MHD) control system and the modular Coils Power Supply (CPS) system, allowed operating RFX-mod in a wide range of experimental conditions with a plasma current up to 2 MA. Experiments with such high plasma current allowed the study on new promising confinement regimes, dominated by a self-organization process with the generation of a helical structure in the plasma core. Presently RFX-mod is under a significant upgrade (RFX-mod2) to extend the operational scenarios increasing the proximity between the conductive shell and the plasma. This main modification of the magnetic front-end, together with other main improvements, are expected to increase the performance of the machine in both magnetic configurations. In the frame of the studies to exploit the new potential of RFX-mod2 achieving a higher plasma current and longer flat-top duration, a solution based on additional magnetic energy storage has already been proposed. The study of RFP physics at higher plasma current could be crucial to confirm positive trends, like electron temperature and persistence of Quasi Single Helicity states with the plasma current, and to explore and achieve improved confinement states. This paper presents an alternative reconfiguration of the poloidal power supply system of RFX-mod2 based on a combined resistor-capacitor energy transfer system. This system allows to store energy in capacitor banks during the first phase of the plasma current ramp-up and release it to the plasma when the magnetizing current change polarity, driving the plasma current over 2.5 MA. The proposed upgrade does not involve radical poloidal CPS modifications, maintaining the present converters number and ratings and remaining within the power limits of the main power transformers (300 MVA).

At the ITER Neutral Beam Test Facility in Padua (Italy), the ion source full scale prototype SPIDER has been in operation since June 2018. SPIDER is designed for an acceleration voltage of -100 kV, however early operation has taken place with a limit of -30 kV. As of March 2021, the limitation has been lifted and the experiment begun to explore the range of beam energies exceeding 30 keV. This has revealed a number of novel issues with the power supplies of ion source and extractor, mainly associated to grid breakdowns. Those power supplies include a set of high current single quadrant resonant converters, known as Source Support power supplies and a high voltage pulse step modulator feeding the extraction gap. The Source support power supplies perform a variety of functions, ranging from providing magnetic filter field current to polarising electrodes for minimization of the co-extracted electrons, from heating of the filaments to polarising the magnetic cores for protection from grid breakdowns. The Extraction Grid power supply extracts a negative ion and electron beam from the source, by applying a high voltage down to -12 kV dc to the gap between Plasma Grid and Extraction Grid. Grid breakdowns at beam energies exceeding 30 keV have shown the capability to upset the output measurements of the Source Support power supplies, limiting operation and reducing reliability of the whole system. The paper describes work undertaken firstly to identify the issues, found to belong to two distinct categories, general failures of all Source Support power supplies measurements and trips from the output voltage measurements of a well-defined subset of power supplies. Further investigation has associated the events to specific experimental conditions, pointing out weak points of the design and suggesting remedial actions. A number of modifications could be deployed quickly and tested in June 2021, before the stop to SPIDER operation for a planned major shutdown. The results of those tests are reported, along with the plan of future modifications for achieving immunity of the Source Support power supplies to the adverse effects of grid breakdowns at full acceleration voltage.

A critical point for the use of the superconducting magnets in Reversed Field Pinch (RFP) fusion reactors is represented by their limitations in the allowed magnetic field derivative, which poses constraints in the maximum induced loop voltage for the gas breakdown and the initial rise of the plasma current. Also in Tokamaks the losses in the superconducting coils related to magnetic field variation need to be carefully considered. On the other hand the use of superconductors for the poloidal field magnets is mandatory in a fusion reactor due to the high volt-seconds required for plasma current rise, the flat-top in pulsed machine and to guarantee the plasma equilibrium. A new concept is proposed for a RFP reactor with a mixed use of different coils: some made with superconductors and others with conventional copper coils operating at low temperature (about 80- 100 K). The proposed solution allows to obtain high loop voltage in the start-up phase, followed by a reduced voltage in the following rise and flat-top plasma current maintaining the level of magnetic field derivative in the superconductors within the allowed limits. The basic principle is firstly discussed on the basis of a simplified model that allows to understand the coils - plasma operation and the evolution of the magnetic field into the superconducting coils. This new concept is then utilized for a feasibility study of the poloidal magnetic system of a pilot neutron source based on a Reversed Field Pinch (RFP) as fusion core. The preliminary design shows the feasibility of this mixed solution for the poloidal field coils of a RFP machine (R=4, a=0.8) with a plasma current of 12 MA, with a high initial loop voltage (100-200 V for about half second) for a fast rise of the plasma current with a reduced magnetic field derivative in the superconductors, less than 2 T/s.

Fusion-Fission Hybrid Reactor (FFHR), neutron-producing fusion core surrounded by a fission blanket, benefits from a renovated interest because of (i) its potentiality to address energy production before the availability of pure fusion reactors, (ii) its capability of fission fuel fertilization and (iii) waste management. The core fusion reactor of a FFHR requires less stringent performances respect to DEMO or the fusion power plants: it has to produce less than a hundred of MW of fusion power with Q = 1-5 and comes with a reduced fast neutron wall load, sustainable by the available nuclear material. While the Reversed Field Pinch (RFP) has yet an energy confinement too low for a high Q reactor, it is an alternative configuration to tokamak and stellarator for this application. Its disruption-free configuration, the need of a much weaker toroidal magnetic field coils and the capability of reaching thermonuclear temperatures without additional heating, but only by ohmic heating (due to no intrinsic plasma current limit and the strong winding of current lines due to the low q values), are significant advantages. New studies are in progress in order to revisit the status and the potentiality of the RFP as a fusion core in FFHR, taking into account the recent progress and expected improvement in RFP physics brought by the results of the RFX-mod experiment (R=2, a=0.46, Ip=2MA) and its underway upgrade. Scaling from the obtained experimental results opens the possibility, with increased machine size and plasma current, to realize a more robust and simple fusion neutron source respect to the other considered solutions; starting from these result, the possibility to realize a preliminary pilot experiment with a RFP (R=4m, a=0.8m, Ip=12-14MA) as a simplified neutron fusion source is in progress.

Fusion-fission hybrid reactors (FFHR), which consist of a neutron-producing fusion core surrounded by a fission blanket, keep a sustained interest because of their potential to address energy production before the availability of pure fusion reactors and also because of their capability of fuel supply and waste management. The U.S. Department of Energy (DOE) sponsored a workshop in 2009 in order to assess the potentiality of fusion-fission reactors and, among the others alternative to the Tokamak as fusion core, the Reversed Field Pinch (RFP) was considered, even if not on the same timeline of the Tokamak. On the other hand, the interest in the RFP as fusion core resides, inter alia, in its possibility to reach ignition in a pure ohmic way with a "light" toroidal field winding, which simplifies significantly the hybrid reactor layout and operation and strongly decreases costs with respect to other fusion core solutions. New studies are now in progress in order to revisit the status and the potentiality of the RFP as fusion core in FFHR, taking into account (i) the recent progress in RFP physics brought by the results of the RFX-mod experiment (R=2, a=0.46, Ip=2MA), mainly about MHD modes control, (ii) the expected performance improvements resulting from the ongoing upgrade of the machine. Starting from RFX-mod results and scaling laws, and considering the estimated improvements of the performances derived from the machine enhancements underway, the possibility to realize a preliminary pilot experiment in which a RFP is the neutron fusion source is analysed. The research needs for this advanced solution are updated with respect to the 2009 workshop.

DEMO represents a fundamental step between ITER and a commercial reactor. Its main aim is to demonstrate the capability of producing electricity and operate with a closed fuel-cycle. In parallel tothe studies to explore the technology feasibility of key parts, there is also the need of others addressed at improving the plant RAMI and contributing to the overall assessment of the technical and economic viability of commercial fusion. With specific reference to the electrical power plant, the design solutions mainly adopted in the last decades need to be reconsidered now at least for two main reasons; the first is that the requirements for DEMO are more demanding, because the power peaks envisaged are significantly higher than in ITER and the handling of the generated and recirculated power poses issues not experienced in previous experimental devices, neither they will be in ITER. The other reason is that the continuous progress in the field of power semiconductors and converter topologies together with the decreasing of their cost could make more attractive, in perspective, different design solutions with respect to traditional ones. In DEMO, the Plant Electrical System (PES) is one of the largest systems; its scope covers the electrical power generation and the Power Supply (PS) systems necessary for supplying all the plant loads. The studies conducted so far have been addressed to well understand, on the one hand the specific design challenges with respect to an equivalent system for a fission power plant and on the other hand the additional issues with respect to the ITER electrical system. In order to satisfy the power needs for the DEMO operation, minimizing the request of contribution from the electrical grid, and in particular high peaks of active power and huge amount of reactive power, R&D has been launched to explore suitable electrical/magnetic energy storage systems and advanced power converter topologies to maximize the energy exchange within the plant. This talk will give an overview of the DEMO PES main requirements and system architecture, of the progress of the studies conducted so far, highlighting the main issues to be faced, the paths taken to address them and thepreliminary results achieved.

Si anticipano qui alcuni interventi del IV Seminario di Bertinoro svoltosi il 17 ottobre 2008 sul tema Tecnica e politica delle citazioni: l’Introduzione di Franco Carinci, nonchè la relazione della Prof.ssa Fiorella Lunardon e l’intervento della Prof.ssa Marina Brollo. La relazione e l’intervento evidenziano i due aspetti rilevanti delle citazioni, quali supporto e rispettivamente quali elementi di valutazione della ricerca ai fini della ripartizione dei Fondi. Gli atti sono in corso di pubblicazione su Quaderni di Argomenti di Diritto del Lavoro, con premessa di Mattia Persiani e Franco Carinci, e, oltre alla relazione di Fiorella Lunardon e all’intervento di Marina Brollo, con contributi di Alessandro Bellavista, Laura Castelvetri, Vito Leccese, Marco Marazza, Antonio Viscomi, Roberto Pessi, Mariella Magnani

An overview of the recent operations and the main results of cesium injection in the Source for the Production of Ions of Deuterium Extracted from Rf plasma (SPIDER) negative ion source are described in this contribution. In experiments without cesium injection, all SPIDER plants were tested to verify the basic expectations on the operational parameters (e.g., electron cooling effectiveness of magnetic filter field) and to determine its operational region. For beam properties, it was shown that the current density varies across the beam in the vertical direction. In preliminary cesium experiments, the expected increase of negative ion current and simultaneous decrease of co-extracted electrons were found, along with the influence of the control parameters (polarization of the plasma electrodes, magnetic filter field) on the SPIDER beam uniformity in the horizontal and vertical directions. It was shown that non-Gaussian tails can be identified in the angular distribution on the plane perpendicular to the beam propagation direction. Stray particles, nonhomogeneous beam and large divergence might result in unexpected heat and particle loads over ITER neutral beam injector (NBI) accelerator grids; it is the goal of SPIDER to assess and possibly to identify suitable methods for controlling these beam features. A major shutdown, planned for late 2021, to solve the issues identified during the operation and to carry out scheduled modifications, is outlined. Such improvements are expected to allow SPIDER to pursue the ITER requirements in terms of negative ion current, electron-to-ion ratio, and beam duration.

Ricostruzione sistematica e organica della disciplina dell'informazione e consultazione dei lavoratori introdotta nell'ordinamento italiano con il d.lgs. 6 febbraio 2007, n. 25. Le autrici, in particolare, esaminano l'art. 4 del decreto attuativo della direttiva comunitaria, dedicato alla forma, contenuti, modalità ed effetti delle forme partecipative.