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The PRIMA project aims at the construction of two ITER-NBI facilities in Padova (Italy). The first one is called SPIDER which is negative H/D 100 keV RF source, while the second one (MITICA) will be a full scale 1 MeV deuterium beam injector as the one that will be used in ITER. In order to resolve the horizontal beam intensity profile in MITICA and one of the eight beamlets groups in SPIDER, the Close-contact Neutron Emission Surface Mapping (CNESM) system is being developed. The goal of this device is to reconstruct the D− beam evaluating the map of the neutron emission due to interaction of the deuterium beam with the deuterons implanted in the beam dump surface. For this reason, the CNESM diagnostic, which is based on nGEM detectors for fast neutrons, will be placed right behind the SPIDER and MITICA beam dump, i.e. in an UHV (Ultra High Vacuum) environment. Since the nGEM detectors need to operate at atmospheric pressure a vacuum sealed detector box has been designed to be installed inside the vacuum vessel and able to sustain atmospheric pressure inside. This paper describes the status of the CNESM diagnostic and underlines the different phases followed during the realization and installation of the diagnostic on the SPIDER beam dump as well as its imaging performances.

SPIDER is the prototype ion source for ITER Heating and Diagnostic Neutral Beams. To investigate the phase-space distribution of its beamlets, an Allison type emittance scanner was developed. This kind of diagnostic is widely used in ion sources for high-energy accelerators, but has never been employed in fusion-relevant ion sources. Its measurements will assess the optics properties of the beamlets of a large negative ion source, providing a local measurement of their phase-space structure, and they will be useful to validate numerical models. This paper presents the experimental setup of the diagnostic, describing the detector, its integration in SPIDER, the handling system and the control electronics. The effectiveness of the design of the detector Faraday cup to repel secondary electrons is experimentally proven. Finally, the emittance measurements obtained in a dedicated test facility are also reported and compared with ray tracing simulations.

Magnetic fields in negative ion driven Neutral Beam Injectors (NBIs) are essential to reduce the electron temperature and density in the extraction region, along with filtering out the otherwise unavoidably co-extracted electrons. In SPIDER, the full scale ion source and extractor of the ITER NBI, a horizontal magnetic field up to 8 mT inside the plasma source is produced by a current of up to 5 kA flowing through the plasma-facing electrode and additional bus-bars. First SPIDER experimental campaigns showed an influence on the plasma generation when the magnetic field is increased beyond a threshold. This effect has been ascribed to the particular topology of the field in the plasma volume inside the 8 inductively-coupled radio-frequency drivers that generate the plasma. The paper describes the experiments aimed at identifying the problem and the design process for a new layout of bus-bars capable of creating an optimized magnetic field topology within the RF driver, while keeping it almost unchanged in the other regions where the required performances were already achieved. Particular attention was given for a design leaving the possibility of easily modifying the new topology, so as to significantly expand the operating margin of the experimental activity.

In large multi-aperture, multi-grid negative-ion accelerator for fusion application, the background gas density in the electrostatic accelerator causes a loss of negative-ion current and the formation of dangerous stray particles. In addition, to sustain in dynamic equilibrium a sufficient gas pressure in the plasma ion-source, a very large pumping speed is typically necessary. This paper presents and compare simulations and measurements of gas flows and background pressure profiles, through the electrostatic accelerator of the SPIDER beam source, the full-size prototype source of the ITER neutral beam injectors. The gas pressure profiles through the ion accelerator were measured by multiple movable capacitive pressure gauges, mapping the uniformity of the profiles along nine beamlets at three different filling pressures. The gas flow simulations in molecular flow regime were performed with a large-scale view-factor model, and with a single-aperture periodic test particle Monte Carlo model. The models reproduced the measured pressure profiles but additionally, provided also the profiles of local gas density. The gas conductance and the profiles calculated with the full-scale gas flow model correctly reproduce the measured profiles, and the transversal non-uniformities over the 1.6 m × 0.6 m cross section. The calculated gas density profile is also verified by comparing the two different numerical approaches. The gas flow model validated at room temperature can be used to simulate the pressure profile during operation, in presence of gas heating and dissociation by the source plasma.

The ITER Neutral Beam Test Facility, in an advanced construction in Padova, includes the installation, tests, and optimization of the full prototype of the ITER Heating Neutral Beams injectors (HNBs), named MITICA. The MITICA Neutral Beam Injector will host its main items in a SS304L vacuum vessel composed of two modules, connected between them on site: the Beam Source Vessel (cubic of 5 m side and 67 tons weight) containing the ion Beam Source and the Beam Line Vessel (section 4.5 m x 4.5 m, length 11 m and 76 tons weight) containing the Beam Line Components and the Cryopumps. The project requirements were transferred in the manufacturing design and in the fabrication process of these large vessels produced through welding and machining. The following steps were in particular carried out before and during manufacturing: o FE analyses to assess the structural integrity and limited deformations under vacuum loading conditions (leading to ribs reinforcement) o materials selection suitable for the specific application o qualification of special processes (welding and NDE) to ensure control of welding distortions and leak tight joints o implementation of double barrier sealings for the most critical connections o control of deformations under vacuum loads comparing displacement measurements with results of FE analyses. The Factory Acceptance Tests of the individual vessels are presented, including their Helium Leak Tests. The two vessels have been assembled on-site inside the MITICA bio-shield. They have been connected through a double sealing barrier composed of elastomer and a leak tight welded flange connection, previously qualified at the factory. The main outcomes of on-site final assembly and Site Acceptance Tests are described. Both vessels have been manufactured, installed and tested by De Pretto Industrie; the design and the technical support were provided by Consorzio RFX, while the procurement was managed by F4E.

SPIDER experiment is operating at the PRIMA site in Padova (I) since June 2018, with the aim of testing and optimizing the negative ion source prototype for ITER Heating Neutral Beam Injectors. In the first operational phase it was discovered that, as the in-vessel hydrogen pressure exceeds the design requirements, discharges occur on the back of the radio frequency source. A specific operational campaign allowed defining a threshold below which the discharge probability is strongly reduced. In order to extend the operational range of the source pressure above the nominal value, while a significant upgrade of the vacuum pumping system is designed and realized, it was decided to proceed with the SPIDER operations by applying a temporary solution. A mask was installed on the beam source plasma grid, closing most of its apertures, in order to reduce the gas conductance between the inside of the radio frequency source and the surrounding volume. At first only 80 over 1280 apertures are left open, with a specific layout properly arranged so as to guarantee the possibility to diagnose the beam characteristics and to evaluate its uniformity. In the paper the plasma grid masking system will be described in detail, together with the main design choices, the thermal and structural analyses and the tests that were carried out to get a validation of the whole system design. Finally, an overview of the behavior of plasma grid mask during SPIDER operations will be given.

The SPIDER Beam Source (BS), the first prototype of a full scale ion source for the ITER Heating Neutral Beam injector, was delivered to the Neutral Beam Test Facility (NBTF) site in Padova (Italy) after about five years procurement phase. A huge effort was devoted during the procurement for quality controls and testing at the supplier’s workshops. Several activities were also carried out on NBTF site for verification/adjustment of interfaces, solution of still open issues, as well as final tests before and after installation inside the vacuum vessel. The NBTF Team undertook the BS site acceptance tests including: pressure and leak tests of the hydraulic circuits; electrical tests; measurement of magnetic field profiles; functionality tests of diagnostics installed on the BS; checks of grids alignment by means of laser tracker. Accurate positioning of the BS inside the vacuum vessel was performed and various service lines were connected in a tight space. Several improvements were undertaken in order to guarantee reliability and reduce the risks during the commissioning and experimental campaign in 2018. After installation, the integrated commissioning phase was initiated, powering the RF and high voltage circuits, followed by the first operation in vacuum.

For ITER operations, additional heating systems are required. One of these systems is the neutral beam injector (NBI). The SPIDER experiment, a small-scale NBI, is going to be built with the aim to optimize the beam source. For this reason it is provided with several diagnostics, among which the Short-Time Retractable Instrumented Kalorimeter Experiment (STRIKE). In this contribution, a characterization of the Carbon Fiber Composite (CFC) tiles, which are the main component of the diagnostic, is presented. Such analyses include tests with a power laser, exposure to particle beams and thermal stress tests. The results are discussed, which will drive the definition of the acceptance tests of the final supply of CFC tiles.

This paper describes the final design of the Short-Time Retractable Instrumented Kalorimeter Experiment (STRIKE) for the SPIDER experiment (Source for Production of Ions of Deuterium Extracted from Radio frequency plasma) under construction at the Consorzio RFX premises. The STRIKE diagnostic will be used to characterise the SPIDER beam during short pulse operation (several seconds) to verify the degree of attainment of ITER requirements about the maximum allowed beam non-uniformity. After a preliminary design developed in the last few years, the complete STRIKE diagnostic system has been recently subjected to a final review and is now ready for construction. The main components of the system are: an array of 16 tiles made of Carbon Fibre Composite, which will be exposed to the high power density beam (of the order of 20 MW/m22) exiting from the SPIDER Beam Source; a supporting and positioning system, based on a set of structures made of stainless steel, with controlled moving systems, to be installed within the SPIDER vacuum vessel; a set of thermal, electric and thermo-graphic sensors to properly detect the operating conditions. The paper will focus in particular on the development of the engineering design of the supporting and positioning system, with a description of the relevant CAD and FEM analyses, and will give an overview of the complete system, with reference to the manufacture of CFC tile prototypes and to the choice of the complete set of sensors.

The TPE-RX Neutral Beam Injector, which provides a 25 keV positive ion beam energy with a maximum current of 50 A for a pulse duration of 30 ms, will be installed on RFX-mod thanks to the agreement with the AIST Institute of Tsukuba (Japan). The main scientific objective is the study of the behavior of the fast ions, which in the RFP helical equilibrium have exhibited very long confinement times. The integration of TPE-RX NBI on RFX-mod requires the development of several new components: a mechanical interface between the RFX-mod vacuum vessel and neutralizer; a Magnetic Residual Ion Dump; a new vacuum pumping system designed to maximize pumping and minimize beam stopping due to reionization. As regards the power supplies the compliance of the Japanese equipment to the Italian safety rules has been considered and layout studies have been carried out; the integration of the NBI control system in the RFX timing sequence has been studied as well.

The SPIDER experiment (Source for the Production of Ions of Deuterium Extracted from an RF plasma) aims to qualify and optimize the full size prototype of the negative ion source foreseen for MITICA (full size ITER injector prototype) and the ITER Heating and Current Drive Injectors to be installed at ITER site. Both SPIDER and MITICA experiments are presently under construction at Consorzio RFX in Padova, with financial support from IO (ITER Organization), Fusion for Energy, italian research institutions and contributions from Japan and India Domestic Agencies. The vacuum vessel hosting the SPIDER beam source has been manufactured, tested and assembled on site during the last two years 2013-2014. The cylindrical vessel, about 6 m long and 4 m in diameter, is composed of two cylindrical modules and two torispherical lids at the ends. All the parts are made by AISI 304 stainless steel. The possibility of opening/closing the vessel for monitoring, maintenance or modifications of internal components is guaranteed by bolted junctions and suitable movable support structures running on rails fixed to the building floor. A large number of ports, about one hundred, are present on the vessel shell for diagnostic and service purposes. The main working steps for construction and specific technological issues encountered and solved for production are presented in the paper. Assembly sequences and tests on site (vacuum and functional tests) are furthermore described in detail, highlighting all the criteria and requirements for correct positioning and testing performances.

The ITER neutral beam test facility under construction in Padova will host two experimental devices: SPIDER, a 100 kV negative H/D RF source, and MITICA, a full scale, 1MeV deuterium beam injector. A detection system called Close - contact Neutron Emission Surface Mapping (CNESM) is under development with the aim to resolve the horizontal beam intensity profile in MITICA and one of the eight beamlet groups in S PIDER, with a spatial resolution of 3 and 5 cm2 respectively. This is achieved by the evaluation of the map of the neutron emission due to interaction of the deuterium beam with the deuterons implanted in the beam dump surface. CNESM uses nGEM detectors, i .e. GEM detectors equipped with a cathode that also serves as neutron - proton converter foil. The diagnostic will be placed right behind the SPIDER and MITICA beam dump, i.e. in an UHV environment, but the nGEM detectors need to operate at atmospheric press ure, so to contain the detector a vacuum sealed box has been designed to be installed inside the vacuum vessel and at atmospheric pressure inside. The box design was driven by the need to minimize the neutron attenuation and the distance between the beam d ump surface and the detector active area. This paper presents the status of the CNSESM diagnostics and describes the design of the detectors and of the sealed box (in particular the analysis carried out to define its parameters, the necessary pumping and l eak test procedures to ensure the compatibility of the box with the UHV environment and the proposed installation/removal procedure ). Also the general layout of the diagnostic as part of the SPIDER experiment will be discussed. Finally the preliminary des ign of MITICA CNESM diagnostic will be introduced. This work was set up in collaboration and financial support of Fusion for Energy.

The ITER heating neutral beam injector, based on 1 MV D − ions, will be tested and optimized in the SPIDER source and MITICA full injector prototypes, using a set of diagnostics not available on ITER. Beam intensity uniformity is required to stay within ±10%, thus beam profile is measured with a complementary set of diagnostics. Among them, visible tomography measures the line of sight (LOS) integrated H α or D α radiation generated by the collisions between fast particles and neutral background molecules, and emitted on a plane perpendicular to the beam. A sufficient number of well arranged LOSs allows a tomographic reconstruction of the 2D beam emission profile, which is proportional to the beam density. On SPIDER the system is equipped with about 3000 LOSs, grouped in 15 fans, and the tomographic algorithm is based on the pixel method. The design of the diagnostic is presented, with description of layout and main components and test of the prototype linear CCD camera.

In the framework of the activities foreseen for PRIMA (Padova Research on Injector Megavolt Accelerated) the SPIDER experiment plays an essential role with respect to the goal of extracting from an ITER size negative ion source an ion beam aiming to reach 70 A H-, 50 A D- and 100 keV of acceleration energy. The SPIDER ion source, the 100 keV accelerator, a Short Pulse Calorimeter and a beam dump will be housed inside a vacuum vessel purposely designed for this scope, given the high number of internal and external interfaces between the vessel and the other auxiliary subsystems as diagnostics, pumping, inspection, power supply and cooling. The SPIDER vacuum vessel is a cylindrical vessel made of AISI 304 L stainless steel and composed of four main components: two cylindrical modules (beam source module and pumping module) and two torispherical lids (rear lid and front lid). The whole vessel is approximately 6 m long and the internal diameter is 4 m. The two cylindrical modules are connected by means of a bolted flange vacuum sealed with Viton ® o-rings. The two lids are connected to the relevant cylindrical module by means of bolted clamps. All the vessel modules and lids feature a large number of ports to interface the vessel and the internally hosted systems with the auxiliary subsystems. In particular three large vertical electrical bushings (internal diameter of about 700 mm) have been positioned on the beam source module. Each bushing consists of a ceramic ring closed by a metallic flange able to assure vacuum tightness and polarized at −112 kV. The bushing positioned on the top of the vessel houses the feedthroughs for power supply and signal cables; the other two positioned on the bottom are dedicated to the inlet/outlet of beam source cooling and gas injection systems. All the vessel modules are mounted on a rail system to facilitate installation and maintenance operations inside the experiment hall. The most important design issues and solutions are presented in this paper together with analyses descriptions and results.

The ITER Neutral Beam Test Facility (PRIMA - Padova Research on Injector Megavolt Accelerated) is planned to be built at Consorzio RFX (Padova, Italy). PRIMA includes two experimental devices: a full size plasma source with low voltage extraction called SPIDER (Source for Production of Ion of Deuterium Extracted from RF plasma) and a full size neutral beam injector at full beam power called MITICA (Megavolt ITER Injector Concept Advancement). SPIDER is the first experimental device to be built and operated, aiming at testing the extraction of a negative ion beam (made of H and in a later stage D ions) from an ITER size ion source. The main requirements of this experiment are a H / D current of approximately 70 A / 50 A and an energy of 100 keV. This paper presents an overview of the SPIDER Beam Source design, with a particular focus on the main design choices, aiming at reaching the best compromise between physics, optics, thermo-mechanical, cooling, assembly and electrical requirements.