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The SPIDER experiment, part of the Neutral Beam Test Facility (NBTF) at Consorzio RFX (Padua, Italy), is the prototype of the negative ion source for the ITER neutral beam injectors; the source is coupled to a 100 kV three-grid acceleration system. A Beam Emission Spectroscopy (BES) diagnostic was installed in SPIDER to study and optimize energy distribution, aiming, uniformity and divergence of the H-/D- beam extracted from the source. The diagnostic is based on the analysis of the Doppler shifted H{\alpha}/D{\alpha} light emitted in the interaction between the beam particles and the H2/D2 molecules of the background. In 2019 the BES diagnostic in SPIDER was installed and calibrated, and it allowed to characterize the first hydrogen beams extracted from the SPIDER source, in cesium free conditions. The number of active beamlets composing the beam was reduced from 1280 to 80, affecting the BES diagnostic capabilities. This paper presents the BES diagnostic setup and discusses the first collected results. Under limited extracted current density ($\sim$ 10 A/m^2) and ion energy ($\leq$35 keV), no significant vertical beam deflection caused by the magnetic filter field in the source was detected. In some cases the beamlets were observed to be elongated in horizontal direction; beamlet divergence values down to 20 mrad and 30 mrad e-folding were measured in vertical and horizontal direction, respectively; the intensity of the Doppler shifted radiation was found to be strongly correlated to the beam current and to the beam divergence. The progressive compensation of beamlet deflections (caused by electron suppression filter fields) with increasing voltage in the extraction gap was studied., Comment: 21 pages, 8 figures. Accepted manuscript of a published paper

The NIO1 experiment hosts a flexible RF H- ion source, developed by INFN-LNL and Consorzio RFX to improve the present concepts for the production and acceleration of negative ions. The source is also used to benchmark the instrumentation dedicated to the ITER neutral beam test facility. Many diagnostics are installed in NIO1 to characterize the source and the extracted negative ion beam. Among them, Beam Emission Spectroscopy (BES) has been used in NIO1 to measure the divergence and the uniformity of the beam, together with the fraction of beam ions which was neutralized inside the acceleration system. The diagnostic method is based on the analysis of the Doppler shifted $H_\alpha$ photons emitted by the fast beam particles and collected along a line of sight. The article presents the experimental setup and the analysis algorithms of the BES diagnostic, together with a discussion of the first measurements and of their correlation with the operational parameters., Comment: 3 pages, 2 figures. Contributed paper for the ICIS 2017 conference. Accepted manuscript of a published paper

The SPIDER H-/D- ion source is currently in operation in the Neutral Beam Test facility (NBTF) at Consorzio RFX (Padova, Italy) to prove the possibility of generating up to 40 A of negative ions, with a maximum extracted current density of 350 A/m2 (H)/285 A/m2 (D) and a fraction of co-extracted electrons not greater than 0.5 (H)/1 (D). These performances are required for the realization of the ITER Neutral Beam Injector (NBI), which should deliver 16.7 MW to the plasma by means of negative ions accelerated up to 1 MeV and neutralized before being injected into the ITER tokamak. In order to obtain such high extracted current densities and low co-extracted electron fractions it is necessary to lower the work function of the surface of the acceleration system grid facing the source; this will be accomplished by coating the surfaces with Cs, routinely evaporated by three ovens. The functionality of the ovens has been tested at the CAesium oven Test Stand (CATS), hosted at NBTF. The test stand is equipped with several diagnostics, among which a Laser Absorption Spectroscopy (LAS) diagnostic. Using a tunable laser diode, the LAS diagnostic gets the high resolution absorption spectrum of the Cs 852 nm D2 line along a line of sight to measure Cs density at ground state. The paper describes the test stand and the LAS diagnostic, together with the characterization of the ovens to be installed in SPIDER. The paper will also study the systematic density underestimation effect caused by Cs ground state depopulation, as a function of laser intensity and of Cs density, in the perspective of correcting the density evaluation., 8 pages, 4 figures. Contribution to the LAPD 2019 conference. Accepted manuscript of a published paper (embargo expired)

NIO1 is a compact and flexible radiofrequency H- ion source, developed by Consorzio RFX and INFN-LNL. Aim of the experimentation on NIO1 is the optimization of both the production of negative ions and their extraction and beam optics. In the initial phase of its commissioning, NIO1 was operated with nitrogen, but now the source is regularly operated also with hydrogen. To evaluate the source performances an optical emission spectroscopy diagnostic was installed. The system includes a low resolution spectrometer in the spectral range of 300-850 nm and a high resolution (50 pm) one, to study respectively the atomic and the molecular emissions in the visible range. The spectroscopic data have been interpreted also by means of a collisional-radiative model developed at IPP Garching. Besides the diagnostic hardware and the data analysis methods, the paper presents the first plasma measurements across a transition to the full H mode, in a hydrogen discharge. The characteristic signatures of this transition in the plasma parameters are described, in particular the sudden increase of the light emitted from the plasma above a certain power threshold., 3 pages, 2 figures. Contributed paper for the ICIS 2015 conference. Accepted manuscript

Counterintuitive experimental evidences have been observed during High Voltage Direct Current (HVDC) tests of two concave, axial-symmetric, electrodes insulated by large vacuum gaps of 3 and 7 cm with voltages from 150 to 370 kVdc. The dissipation of microdischarge power during the conditioning procedure occurs mostly on the anodic side in a region close to the axis of the system where the electric field is at a minimum, far from the positions where the breakdowns have been observed. The analyses of the phenomena are carried out by comparing the temporal evolution of voltages, currents, pressure, measurements of x-ray energy spectra, and images from infrared and visible light cameras. Numerical simulations, based on ray-tracing algorithm, correctly identify the positions where the power dissipation of microdischarges occurs. A mutual exchange of charged particles in the electrostatic field between electrodes seems a reasonable physical mechanism to interpret the observations. These findings suggest a new perspective to review the current literature and interpret new results considering geometric details which were so far omitted: the areas with the most intense electric field, typically located on the surfaces of the electrodes under test, are not necessarily the sole surfaces involved in the HVDC conditioning in high vacuum.

The SPIDER experiment is the full size prototype of ITER heating neutral beam. It is equipped with two bi-dimensional arrays of Langmuir probes, covering the Plasma Grid (PG) surface and the Bias Plate (BP). These sets of diagnostics are routinely used during SPIDER operation and allow to investigate the properties of the plasma in the expansion region. The measurements are typically influenced by RF induced source oscillations, and a technique to extract average values is described. The dependencies of plasma parameters on power, pressure, magnetic filter field, plasma grid and bias plate biases are reported and used to assess the uniformity of the plasma, showing the presence of plasma drifts due to the magnetic field.

The ITER Heating Neutral Beam (HNB) injector RF plasma source is required to generate a 40A D- or 46A H- ion current, with low electron/ion ratio (

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.

The ITER Heating Neutral Beam (HNB) injector is required to deliver 16.7 MW power into the plasma from a neutralised beam of H-/D- negative ions, produced by an RF source and accelerated up to 1 MeV. To enhance the H-/D- production, the surface of the acceleration system grid facing the source (the plasma grid) will be coated with Cs because of its low work function. Cs will be routinely evaporated in the source by means of specific ovens. Monitoring the evaporation rate and the distribution of Cs inside the source is fundamental to get the desired performances on the ITER HNB. In order to proper design the source of the ITER HNB and to identify the best operation practices for it, the prototype RF negative ion source SPIDER has been developed and built in the Neutral Beam Test Facility at Consorzio RFX. A Laser Absorption Spectroscopy diagnostic will be installed in SPIDER for a quantitative estimation of Cs density. By using a wavelength tunable laser, the diagnostic will measure the absorption spectrum of the 852 nm line along 4 lines of sight, parallel to the plasma grid surface and close to it. From the absorption spectra the line-integrated density of Cs at ground state will be measured. The design of this diagnostic for SPIDER is presented, with details of the layout and of the key components. A preliminary installation of the diagnostic on the test stand for Cs ovens is also described, together with its first experimental results; the effect of ground state depopulation on collected measurements is discussed and partially corrected., Comment: 6 pages, 5 figures. Contributed paper for the SOFT 2018 conference. Accepted manuscript (embargo expired)

A state-of-the-art EJ276 plastic scintillator-based detector for neutron spectroscopy has undergone detailed characterization both in a controlled laboratory and on-site at the SPIDER negative ion source facility in Padua. The device will be used for the spectroscopy of 2.5 MeV neutrons produced from Deuterium-Deuterium fusion reactions occurring inside the SPIDER beam dump. A plastic based scintillator with neutron/gamma discrimination has some key advantages over the commonly used organic liquid scintillators with regards economic cost and handling safety. The purpose of this characterization is to determine the operational functionality and reliability of this new breed of detector material. Several tests were performed to verify expected operation with regards to signal reproducibility, long-term stability, and pulse shape discrimination (PSD) capabilities. It was found that the detector system (EJ276 scintillator + photomultiplier tube) performed well in terms of reproducibility and PSD, however the long-term stability of the scintillator light output was seen to diminish considerably over time (>50% decrease) and must be consistently monitored in order to have an accurate conversion scale needed for energy spectroscopy.

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.

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 16.5 MW each, by neutralizing accelerated negative hydrogen or deuterium ions. The requirements of ITER NBIs (40A/1 MeV D- ions for ≤1 h, 46A/870 keV H- ions for ≤1000 s) have never been simultaneously attained. So in the Neutral Beam Test Facility (NBTF, Consorzio RFX, Italy) the operation of the full-scale ITER NBI prototype (MITICA) will be tested and optimised up to full performances, focussing on accelerator (including voltage holding), beam optics, neutralisation, residual ion removal. The NBTF includes also the full-scale prototype of the ITER NBI source with 100 keV particle energy (SPIDER), for early investigation of: negative ion production and extraction, source uniformity, negative ion current density and beam optics. This paper will describe the main results of the first two years of SPIDER operation, devoted to characterizing plasma and beam parameters, including investigation of RF-plasma coupling efficiency and magnetic filter field effectiveness in reducing co-extracted electrons. SPIDER is progressing towards the first caesium injection, which aims at increasing the negative ion density. A major shutdown, planned for 2021, to solve the issues identified during the operation and to carry out programmed modifications, will be outlined. The installation of each MITICA power supply and auxiliary system is completed; in-vessel mechanical components are under procurement by Fusion for Energy (F4E). Integration, commissioning and test of the power supplies, procured by F4E and QST, as the Japanese Domestic Agency (JADA), will be presented. In particular, 1.0MV insulating tests were carried out step-by-step and successfully completed. In 2020 integrated tests of the power supplies on the accelerator dummy load started, including the assessment of their resilience to accelerator grid breakdowns using a short-circuit device located in vacuum. The aggressive programme, to validate the NBI design at NBTF and to meet ITER schedule (requiring NBIs in operation in 2032), will be outlined. Unfortunately, in 2020 the coronavirus disease infection affected the NBTF activities. A solution to proceed with integrated power tests despite the coronavirus is presented.

SPIDER, the full-size prototype of the negative ion source for future ITER Heating and Current Drive, is equipped with a tomographic diagnostic to characterize the negative hydrogen (and deuterium) beam. The main goal of the tomographic system is the reconstruction of the beam emission pattern, which is proportional to the beam density, by assuming a uniform background gas, through the measurement of the beam emitted light along a sufficiently large number of lines-of-sight (LoSs), to study the beam homogeneity and divergence. Currently, 11 2D visible cameras observe the beam on a plane at a distance of 400 mm from the last grid of the accelerator, all around the beam; sensors of different sizes with different lenses are used, to maximize the resolution despite the limited number of points of view. The cameras are calibrated both in intensity and spatially and their fans of LoSs have been reconstructed. Once calibrated, the experimental data are compared with the simulated ones, simultaneously for all the cameras in order to have a complete profile of the extracted beam. Simultaneous Algebraic Reconstruction Technique (SART) algorithm as inversion technique is used to reconstruct for the first time the 2D beam emissivity profile, and it is applied to study the spatial uniformity of the beam as a function of the filter field and the extraction voltage.

A novel method for the path combination of two lasers with very similar wavelengths has been implemented to enable the evaluation of a dual-laser calibration Thomson scattering (TS) technique. The first experimental test of this TS technique has been performed in a RFX-mod plasma device, where, due to experimental constraints, the combination of a Nd:YAG (λ = 1064 nm) and a Nd:YLF (λ = 1053 nm) laser system was the only viable choice available. The method requires that the beam path of both lasers be combined into a single path with the same polarization. This presents a unique challenge due to the small difference between the two laser wavelengths. In this paper, we describe two methods for beam combination: first via a prism, eventually dismissed as unpractical, and second via a polarizing beam splitter in reverse with a dual-wavelength waveplate. We detail the optical setup, waveplate design, and successful implementation of this second method.

MITICA is the full-scale prototype of ITER Neutral Beam Injector (NBI), currently under construction in Padova, Italy. In this facility, a 40 A beam of negative deuterium ions will be accelerated to 1 MeV and then neutralized. The emerging beam, after the removal of residual ions, will be dumped onto the calorimeter (up to 17 MW are expected). In each component of the beam-line, monitoring of the presence of plasma and its parameters is crucial: with this aim, various types of electrostatic probes will be installed along the MITICA beam-line. The Neutralizer and the Electric Residual Ion Dump (ERID) panels will be equipped with pairs of Langmuir probes at different vertical and axial positions, with the possibility to be set in single or double probe configurations and to provide local floating potential, ion density and electron temperature measurements. In the neutralizer, the probes will provide information about the beam collisional processes, in view of a neutral fraction optimization. In the ERID, the objective of the probes is to confirm the absence of plasma, which otherwise might invalidate the deflection properties of the device. In the calorimeter, biased electrodes will collect the secondary emission electrons produced by the beam collisions with the cooling tube surfaces. The electrodes will provide vertical and horizontal profiles of the beam at the calorimeter, to study its horizontal steering, divergence and uniformity. Four different probe designs have been developed to fulfill specific scientific and mechanical constrains at the different positions. In this contribution, the realization of the four prototypes, one for each probe, together with a mock-up of the relative housing panel, is described. Problems or difficulties emerged during the manufacturing of specific elements or during the assembly of the probes have been identified and fixed and the prototypes tested. The final design is, thus, presented.

Abstarct The negative ion source SPIDER produces a beam power that has to be absorbed by a beam dump component made of stacked hypervapotrons. The manufacturing process produced dimension errors that have given rise to a possible shine-through issue. Finite volume models were developed to carry out transient thermal analyses aiming at validating the design of a system made of copper screens to shield the heat loads passing through the beam dump. The evaluation of the best solution was conducted by looking both at the thermal performances and the technical feasibility. The results show the capability of the system to safely withstand the heat power up to one hour.

Optical Emission Spectroscopy (OES) on the SPIDER negative ion source has been collecting data since the beginning of operation in Summer 2018. The first few months were devoted to complete the diagnostic commissioning and its integration with the SPIDER control and data acquisition system. Consistent sets of spectroscopic data have been acquired under different experimental conditions, not only varying the plasma source filling pressure and injected power but also changing the RF generator frequencies and the strength of the magnetic field acting as a filter in front of the plasma grid. The main results of OES data analysis are presented in this work. SPIDER optical emission diagnostic comprises a set of 66 channels wavelength resolved and 36 single line channels by means of interference filtering. Some of them collect the photons along line of sight (LOS) perpendicular to the grids through the 8 RF drivers and others along LOS parallel to and near the grids, both horizontally and vertically. Since the starting of extraction experiments, 22 channels have been dedicated to collect the extracted beam emission. The LOS layout allows tracing two 9-point vertical profiles of the source plasma in the extraction region at 35 and 5 mm from the Plasma Grid (PG) and four 4-point horizontal profiles spanning the 65 mm region before the PG. It is also possible to collect spectra from LOS looking in between the grids. Both Balmer series and Fulcher band between 600 nm and 640 nm were routinely collected. Their intensities are very sensitive to the plasma parameters and when coupled to a collisional radiative model can give an estimation of the electron density and gas dissociation. It has been found that the Balmer emission and gas dissociation inside the drivers scale linearly with the RF power, the latter reaching a value up to 20% at high power and low pressure. Rotational gas temperature has also been evaluated; it ranged between 900 K and 1400 K, where higher values were reached for higher pressures and RF powers.

High voltage (HV) insulation across a single gap in vacuum and low-pressure gas is a critical issue in relation to the development and realization of the electrostatic accelerator for the ITER neutral beam injector (NBI) (Toigo et al 2017 New J. Phys. 19 085004). The present paper describes and analyzes the recent experimental results obtained at the High Voltage Padova Test Facility (HVPTF), the laboratory aimed at supporting the development of the prototype for the ITER NBI (De Lorenzi et al 2011 Fusion Eng. Des. 86 742-5). A voltage up to 800kV(DC) was achieved in the HVPTF during the experimental campaigns with a sphere-plane configurations having variable gap length (from 30 to 150 mm) and pressure ranging from high vacuum (10(-7) mbar) to 10(-3) mbar in argon. Such an experimental campaign represents one of the few examples where voltages higher than 500-550 kV DC are sustained by a single vacuum gap between electrodes (Rohrbach 1971 CERN Report 71-5) and therefore constitutes additional experience to improve the knowledge of voltage holding across large vacuum gaps. The results in high vacuum indicate that at the beginning of voltage conditioning the breakdown events occur at the same cathodic electric field irrespective of the electrode geometry. However, after sufficient conditioning time, the breakdown voltage distribution seems to depend also on the electric field at the anode and on the total voltage between electrodes. A benchmark between a numerical tool previously developed to predict the voltage holding in high vacuum (voltage holding prediction model, VHPM (Pilan et al 2011 Fusion Eng. Des. 86 742-5)) and the experimental results is also reported and discussed.

The SPIDER ion source has been designed to generate a current of H- ions up to 60 A and accelerate them up to 100 keV. In addition, the ratio between the co-extracted electrons and negative ions has to be below 1, and a beam inhomogeneity within 10 % has to be attained. A magnetic filter field is produced by a current flowing through the plasma electrode in the vertical direction with the aim of reducing electron temperature and density in the extraction region, so as to enhance the survival probability of H- ions while reducing the co-extracted electrons. Another strategy to reduce the co-extracted electrons is to apply a small bias voltage to the plasma grid with respect to the ion source body. In addition to this, a so-called bias plate is installed in the vicinity of the plasma grid, which can also be biased with respect to source body. However, the application of a bias voltage affects the beam inhomogeneity by modifying the ExB plasma drift within the ion source. Recently, the filter field configuration of SPIDER was modified so as to improve the plasma diffusion towards the extraction region. In addition, the voltage ratings of the bias power supplies were increased. Both these modifications permit to efficiently lower the electron co-extracted current. The present contribution describes such improvements while focusing on the effects they have on the beam inhomogeneity.

The Neutral Beam Injectors of the ITER experiment will rely on negative ion sources to produce 16.7 MW beams of H/D particles accelerated at 1 MeV. The prototype of these sources was built and is currently operated in the SPIDER experiment (Source for the Production of Ions o Deuterium Extracted from an RF plasma), part of the Neutral Beam Test Facility of Consorzio RFX, Padua. In SPIDER, the H-/D- ion source is coupled to a three grids 100 kV acceleration system. One of the main targets of the experimentation in SPIDER is to uniformly maximize the extracted current density; to achieve this it is important to study the density of negative ions available in proximity of the ion acceleration system. In SPIDER, line-integrated measurements of negative ion density are performed by a Cavity Ring Down Spectroscopy (CRDS) diagnostic. Its principle of operation is based on the absorption of the photons of a laser beam pulse by H-/D- photo-detachment; the absorption detection is enhanced by trapping the laser pulse in an optical cavity, containing the absorbing medium (i.e. negative ions). The paper presents and discusses the CRDS diagnostic setup in SPIDER, including the first measurements of negative ion density, correlated to the main source parameters., Comment: 5 pages, 7 figures. Contributer paper for the HTPD 2020 conference. Accepted manuscript

An incoherent Thomson scattering diagnostic will be installed in the JT-60SA tokamak to measure electron temperature and electron density profiles. The target radial spatial resolution is 25 mm with 46 spatial channels. The accuracy in electron temperature and density is a few percent at ne = 7.5 × 1019 m-3, which is the expected value in the plasma core. This paper presents the designs of collection optics, fibers with their alignment system, and polychromators. The collection optics overcomes unique issues for superconducting fusion devices, i.e., limited design space, high-temperature measurements, and harsh radiation condition. When in several years the more performing plasma will generate intense nuclear radiation, the lens materials of the optics can be replaced by radiation resistant glasses without major changes in the lens holder. It will prevent transmission degradation and keep stable measurement accuracy.

Beam tomography is a non-invasive diagnostic that allows us to reconstruct the beam emission profile by measuring the light emitted by the beam particles interacting with the background gas, along an elevated number of lines of sight, which is related to the beam density by assuming a uniform background gas. In the framework of the heating and current drive of future nuclear fusion reactors, negative ion beams of hydrogen and deuterium are required for neutral beam injectors (NBIs) due to their elevated neutralization efficiency at high energy (in the MeV range). Beside the beam energy, beam divergence and homogeneity are two critical aspects in the design of future NBIs. In this paper, the characterization of the negative ion beam of the negative ion source NIO1 (a small-sized radio-frequency driven negative ion source, with 130 mA of total extracted H - current and 60 kV of maximum acceleration) using the tomographic system composed of two visible cameras is presented. The Simultaneous Algebraic Reconstruction Technique (SART) is used as an inversion technique to reconstruct the 3 × 3 matrix of the extracted beamlets, and the beam divergence and homogeneity are studied. The results are compared with the measurements of the other diagnostics and correlated with the source physics. The suitability of visible cameras as a diagnostics system for the characterization of the NIO1 negative ion beam is a small-scale experimental demonstration of the possibility to reconstruct more complicated multi-beamlet profiles, resulting in a powerful diagnostic for large NBIs.

A small radiofrequency ion source named negative ion optimization phase 1 (NIO1) has been recently installed at Consorzio RFX in Padua. The NIO1 source is capable of producing about 130 mA of negative hydrogen ions accelerated at 60 kV and represents a useful test bench for negative ion source optimization. The exploitation of this device is included in the framework of the activities for SPIDER and MITICA and the prototypes of the negative ion source and of the whole neutral beam injector for international thermonuclear experimental reactor (ITER) experiment, respectively. As in SPIDER and MITICA, thermal measurements are performed in NIO1 by several thermocouples (TCs). These measurements are indeed important for the evaluation of the thermal load distribution, plasma generation, and beam extraction uniformities, for the monitoring of different experimental conditions, and for the verification of the reliability of source and beam-line components in the expected range of temperatures. This paper deals with the development of a new electronic frontend for acquisition and transmission (tx) of the thermal signals from the TCs mounted on the ion beam source, preserving signal integrity. It is the updated version of previous circuits initially developed for optical tx of the thermal measurements from the grounded grid in SPIDER. In particular, two of these circuits were installed in the NIFS Neutral Beam Test Stand in Japan and in BATMAN at IPP Garching, Germany. The system presented here is under test in the NIO1 device to check its reliability in monitoring the temperature of some cooling circuits, like in SPIDER and MITICA.

The ITER neutral beam test facility under construction in Padova will host two experimental devices: SPIDER, a 100 kV negative H/D RF beam source, and MITICA, a full scale, 1 MeV deuterium beam injector . SPIDER will start operations in 2016 while MITICA is expected to start during 2019. Both devices feature a beam dump used to stop the produced deuteron beam. Detection of fusion neutrons produced between beam-deuterons and dump-implanted deuterons will be used as a means to resolve the horizontal beam intensity profile. The neutron detection system will be placed right behind the beam dump, as close to the neutron emitting surface as possible thus providing the map of the neutron emission on the beam dump surface. The system uses nGEM neutron detectors . These are Gas Electron Multiplier detectors equipped with a cathode that also serves as neutron–proton converter foil. The cathode is designed to ensure that most of the detected neutrons at a point of the nGEM surface are emitted from the corresponding beamlet footprint (with dimensions of about 40×22 mm2) on the dump front surface. The size of the nGEM detector for SPIDER is 352 mm×200 mm. Several smaller size prototypes have been successfully made in the last years and the experience gained on these detectors has led to the production of the full size detector for SPIDER during 2014. This nGEM has a read-out board made of 256 pads (arranged in a 16×16 matrix) each with a dimension of 22 mm×13 mm. This paper describes the production of this detector and its tests (in terms of beam profile reconstruction capability, uniformity over the active area, gamma rejection capability and time stability) performed on the ROTAX beam-line at the ISIS spallation source (Didcot-UK).

The ion source NIO1 (Negative Ion Optimization 1) is a versatile multiaperture H− source capable of continuous regime operation, with the plasma generated by a 2 MHz/2.5 kW radiofrequency (rf) power supply and extraction of nine beamlets. It aims to partly reproduce the conditions of much larger ion sources, built or in construction for the neutral beam injectors of fusion devices, in a compact and modular ion source, where effects of individual source components can be rapidly verified and compared to simulation code results. Several modifications of the magnetic configuration (both inside the ion source and the embedded magnets inside the accelerator grids) were investigated. Saturation of beneficial effect of filter field at large strength (>0.01 T) leads us to use softer magnetic filters, and the advantages of a crossed deflection field are noted. The rf system takes full advantage of the generator bandwidth (0/ + 20 kHz used). The result database and the integration of major diagnostic systems with the control system are also summarized, with some details on voltage holding and beam uniformity.

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.

Heating neutral beam (HNB) injectors, necessary to achieve burning conditions and to control plasma instabilities in ITER, are characterized by such demanding parameters that a neutral beam test facility (NBTF) dedicated to their development and optimization is being realized in Padua (Italy) with direct contributions from the Italian government (through Consorzio RFX as the host entity) and the ITER international organization (with kind contributions from the ITER domestic agencies of Europe, Japan and India) and technical and scientific support from various European laboratories and universities. The NBTF hosts two experiments: SPIDER, devoted to ion source optimization for the required source performance, and MITICA, the full-size prototype of the ITER HNB, with an ion source identical to SPIDER. This paper gives an overview of the progress towards NBTF realization, with particular emphasis on issues discovered during this phase of activity and on solutions adopted to minimize the impact on the schedule and maintain the goals of the facilities. The realization of MITICA is well advanced; operation is expected to start in 2023 due to the long procurement time of the in-vessel mechanical components. The beam source power supplies, operating at 1 MV, are in an advanced phase of realization; all high-voltage components have been installed and the complex insulation test phase began in 2018. At the same time, construction and installation of SPIDER plant systems was successfully completed with their integration into the facility. The mechanical components of the SPIDER ion source were installed inside the vessel and connected to the plants. Integrated commissioning with the control, protection and safety systems ended positively and the first experimental phase has begun. The first results of the SPIDER experiment, with data from operational diagnostics, and the plans for the 1 MV insulation tests on the MITICA high-voltage components are presented.

The ITER project requires additional heating by two neutral beam injectors, each accelerating up to 1 MV a 40 A beam of negative deuterium ions for one hour. Such requirements have never been reached, so it was decided to build in Padova a facility (PRIMA) that hosts two experimental devices: SPIDER, a 100 kV negative H/D RF beam source, and MITICA, a full-scale injector for the ITER NBI. SPIDER has begun operation in 2018, while MITICA is expected to start after 2020. In both devices the accelerated deuterium beam impinges on an actively cooled beam dump used to stop the deuterons. Detection of fusion neutrons produced between beam–deuterons and dump-embedded deuterons will be used as a means to resolve the horizontal beam intensity profile. A neutron detection system called Close-contact Neutron Emission Surface Mapping (CNESM) is installed right behind the SPIDER beam dump, with the aim to provide the neutron emission map of the beam dump surface. The core of this diagnostic system is an nGEM (neutron-Gas Electron Multiplier) detector which will be able to reconstruct the fast neutron beam profile with an efficiency of about 10−4. A crucial point in order to correctly reconstruct the profile of the deposited D − power is the directionality discrimination capability of the detector. This paper reports on the results of the characterization of the nGEM directionality capabilities, performed at the Frascati Neutron Generator (FNG) using 2.5 MeV neutrons, before installation of the detector inside the SPIDER vacuum vessel.

The full-size ITER ion source prototype SPIDER (Source for the Production of Ions of Deuterium Extracted from a Radio frequency plasma) has recently started beam operation, whose objective is to produce 100 keV, 60 A hydrogen negative ions for 1 h. The source is presently operated in the volume regime, and the beam power is consequently limited. In such a configuration, the high resolution calorimeter STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment), even though uncooled, may be used instead of the SPIDER beam dump without limiting the beam-on time. STRIKE is formed by unidirectional carbon fiber-carbon matrix (CFC) composite tiles that are exposed to the beam while their temperature is recorded by using two infra-red cameras. This setup, thanks to the moderate broadening of the temperature profile guaranteed by the anisotropy of CFC, allows for the determination of detailed features of the beam current distribution (spatial resolution is about 2 mm). Furthermore, positively biasing the CFC tiles permits a direct electrical measurement of the negative ion beam current. Besides the total beam current and beam uniformity, which can be retrieved both by calorimetry and electrical measurement, beamlet divergence and deflection can be determined by infra-red thermography. This contribution describes the characterization of the SPIDER negative ion beam as a function of the source and accelerator parameters by means of the diagnostic calorimeter STRIKE in the volume regime.

One of the main concerns when working with negative ion beams is collimation during propagation. The beam is composed of like charged particles; therefore they tend to repel each other causing the beam to widen after acceleration. In environments where the beam needs to travel long distances before reaching its target, the compensation of its space charge is necessary; the most straightforward way of achieving this is the creation of a plasma around the beam, created by ionization of the background gas by the beam itself. This effect, called space charge compensation, plays therefore a key role in the beam propagation and a deep understanding of this phenomenon is fundamental when operating negative ion sources. In order to perform measurements of the particles forming such beam-generated plasma, a retarding field energy analyzer (RFEA) can be adopted, which is an indirect non perturbing instrument, analysing the particles emitted radially from the beam plasma, and allowing to estimate the plasma parameters from the energy distribution function of ions and electrons. The paper presents the design and the layout of the system for voltage control and data acquisition of the RFEA, developed at Consorzio RFX and used for the experimental campaigns in NIO1 to study the phenomena that cause space charge compensation.

In June 2018 the SPIDER device, which is the full-size prototype of the negative ion source and extractor for the ITER Heating Neutral Beam has entered the first operation phase at the Neutral Beam Test Facility (NBTF) in Padova, Italy. This paper describes the present status of the device, the experimental plans and the results obtained during the first experimental campaign of the radio-frequency driven plasma source.

The use of caesium vapour is mandatory in plasma sources for negative ion beams to achieve a sufficient negative ion density. In the SPIDER ion source, three caesium ovens will provide a sufficiently high caesium flux to the walls of the ion source, but also a relatively even caesium distribution in the ion source volume. In order to qualify the caesium ovens in terms of repeatability of the evaporated caesium flow, and to characterize the caesium flux emitted from its nozzle, a set of diagnostics was installed in the small test facility CAesium Test Facility (CATS). This paper reports on the present configuration of the diagnostic set-up. Surface ionization probes are installed in front of the nozzle apertures. Movable surface ionization detectors are used to reconstruct the angular distribution of the emission. A quartz microbalance is installed at a fixed position, to provide the cumulated caesium over time. Finally, the laser absorption spectroscopy measures the line-integrated caesium density. An example of combined measurement is presented.

Localized heating has been observed in unexpected positions on anodic surfaces in a multi-electrode device insulated by vacuum gaps. In double polarity experiments, a counter-intuitive behavior of current-voltage characteristic has also been observed. The phenomena could depend on a cascade effect of charged particles exchanged between electrodes and on a mutual correlation of particle trajectories between electrode surfaces occurring during the high voltage conditioning phase. Attractors regions ascribed to regenerative processes of charged particles between cathode and anode have been identi fi ed thanks to numerical simulations The position of the attractors depends only on electrode shape and the ratios of applied voltages. This fi nding suggests new perspectives in neutrons sources applications, where recurrent impacts of focused high energy hydrogen isotopes take place on solid hydride targets supported by metallic electrodes insulated by vacuum gaps.

Unidirectional carbon fiber–carbon matrix (CFC) composite tiles, which are proposed to be employed in thermal imaging diagnostic of powerful particle beams, have been designed, manufactured, and tested. The particle beam is intercepted by the tiles, which erodes the carbon surface producing debris, while a plasma forms in front of the tiles due to beam–gas interaction. Carbon fibers are aligned along the tile thickness to transfer the heat flux from the front to the rear surface with limited thermal pattern broadening thanks to the ten times higher thermal conductivity along the fibers. This feature of the tiles allows to detect thermal radiation at the tile rear surface by thermographic cameras, producing curves to be correlated to energy, intensity profile, and duration of the particle beam. Thermal patterns with spatial resolution of a few mm, time resolution up to 40 ms, and maximum temperature of 1300 °C have been measured on CFC tiles exposed to accelerated hydrogen beam pulses with power densities up to 13 MW m−2 in thehigh heat flux test facility GLADIS. Multiphysics transient non-linear parametric finite-element models have been developed to simulate thermal transfer inside tiles, thermal patterns at surfaces, and thermal deformations of tiles by varying spatial distribution and peak value of the power density. Temperature gradients, hoop deformations around the heated region, location of failure region, and failure time have been analysed and discussed to recognise the tile behaviour during the high heat flux tests. Simulation models have been validated by comparing outputs to experimental measurements. Finally, model geometry and parameters have been changed to simulate the behaviour of the complete diagnostic to be used in the Source for the Production of Ions of Deuterium Extracted from a Radio-frequency plasma (SPIDER) test bed of the ITER Neutral Beam Test Facility with expected power density up to 20 MW m−2.

SPIDER is the prototype beam source of the ITER Heating Neutral Beam injector. A movable diagnostic calorimeter will be used as a direct mean to obtain the beam footprint in short-pulses, while a fixed beam-dump is installed for steady-state operation. For the comparison between experiment and numerical simulations of ion beam extraction, measuring the beam emittance is extremely useful, being the most complete characterization for a particle beam. We discuss in this paper two proposals for beam-emittance measurements in SPIDER: at high beam energies, a fixed electric-sweep scanner is proposed for integration in the water-cooled beam-dump; at relatively low beam energies, a movable emittance scanner is proposed for the installation on the movable diagnostic calorimeter. The synthetic signals of the scanner are calculated considering the multibeamlet setup. The constraints given by the integration in high heat load components and the thermal design are discussed. The fixed ESS can be used to reconstruct the beam divergence, even if it detects only a limited section of the beamlet emittance, if identical single-beamlet optics is assumed. The movable emittance scanner is easy to integrate in the present design, and allows a full characterization of the single beamlet optics.

Along the route to the development of a neutral beam injector for ITER, the Padua based Source for Production of Ion of Deuterium Extracted from Rf plasma (SPIDER) and megavolt ITER injector and concept advancement facilities will make use of neutron diagnostics to quantify the homogeneity of the neutral beam profile by measuring the map of the neutron emission from the beam dump with the close-contact neutron emission surface mapping (CNESM) system. Neutrons are here produced from beam-target reactions between the deuterium beam and the deuterons previously adsorbed in the calorimeter. In order to aid the interpretation of the diagnostic data, a dedicated experiment on neutron emission from beam-target reactions with beam parameters approaching those expected at SPIDER has been performed at the Extraction from a Large Ion Source Experiment (ELISE) neutral beam test facility. The time trace of neutron emission has been measured using a calibrated liquid scintillator detector at increasing power densities on the target. Compared to calculations based on the local mixing model, a systematic discrepancy was observed exceeding the statistical accuracy of the measurements and increasing as a linear function of the power density. The data are used to derive an empirical temperature dependent correction for applications to neutron measurements at SPIDER.

International audience; Cavity Ring Down Spectroscopy (CRDS) is used to measure the D− absolute density produced in the helicon plasma reactor RAID (Resonant Antenna Ion Device) at the Swiss Plasma Center. The birdcage geometry of the helicon antenna produces a homogeneous, high-density plasma column (ne ≅ 1.5 × 1018 m−3 in H2 and D2 at 0.3 Pa and 3 kW of input power) 1.4 m long. We present the CRDS experimental setup, its positioning on the RAID reactor, and how the mechanical and thermal effects of the plasma affect the measurement. First results in deuterium plasma confirm the production of negative ions (D−) with a significant density: an average value of 3.0 × 1016 m−3 of D− is obtained at 0.3 Pa and 5 kW of power input in Cs-free plasma. This result is in good agreement with calculations performed with the collisional radiative code YACORA.

After installation of Mo liners in the source NIO1 (Negative Ion Optimization phase 1), hydrogen plasmas in a continuous regime operation (much longer than one hour) are routinely maintained, with more than 1 kW rf power and 0.5 Pa pressure, allowing a systematic investigation of pure H− volume effect, which requests a much lower acceleration voltage Vs ≅ 12 kV than future Cs operations at Vs ≅ 60 kV. A new extraction grid EG was installed (replacing some eroded insulators) and preliminary beam images are compared to old EG ones, discussing effects of different deflection field strength and need of intermediate values. Large improvements in beam diagnostics and the effect of installation of a cryogenic pump are also reported.

The ITER tokamak requires two injectors of neutral beams resulting from the neutralisation of accelerated negative hydrogen/deuterium ions. To optimise the source operation, a specific test facility ("PRIMA") was established in Padova, comprising the experiment SPIDER (full-size negative ion source with 40A beam, 100keV particle energy). The design of SPIDER accelerator was based on the most advanced numerical codes available for the investigation of the expected beam properties. Several diagnostic systems will characterise source and beam during the experiments. In view of the operation, this paper describes the preparation of the experiments by means of numerical simulations of the accelerator. The simulations provide also estimates of the current and power deposited onto the accelerator grids and will be the basis for further work aimed at computing the expected measurements by the various beam diagnostics.

SPIDER, the full-size prototype of the ITER heating neutral beams (HNBs) radio frequency (RF) ion source, has been designed and is under construction at Consorzio RFX in Padua, Italy. Several thermocouples will be installed in both SPIDER and HNB source to characterize and monitor the possibly severe thermal load on mechanical components. The presence of about 1 MW RF power ionizing the gas and frequent electrical breakdowns on the 100 kV beam accelerator represent a very harsh environment for thermal measurements, both in terms of possible sensors damage and of disturbances induced on the signals. A complete measurement chain prototype, composed of two sensors, conditioning electronics and data acquisition system, was realized to test and validate technologies and design solutions. The prototype was installed and tested inside the BATMAN RF ion source at IPP-Garching, where measurement conditions are very similar to those expected in SPIDER, and in particular high RF power and high voltage breakdowns are present. A careful installation was carried out, with extensive optimization of grounding and shielding configuration, to achieve sufficient ElectroMagnetic Interference immunity. Analog and digital filtering were also implemented on signals to eliminate the residual noise. Results produced during a dedicated experimental campaign on BATMAN have been very successful: 0.5 °C measurement global accuracy can be obtained during RF plasma pulses and no damage occurred on sensors or electronic equipments. The paper describes the prototype design detailing the technical solutions implemented, in particular regarding sensors design and installation, signal conditioning, and noise reduction. Hardware and software characteristics of the data acquisition system are presented and discussed. Experimental results obtained are also described and their significance for future work is analyzed.

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.

The realization of the ITER Neutral Beam Test Facility (NBTF) and the start the experimental phase are important tasks of the fusion roadmap, since the target requirements of injecting to the plasma a beam of Deuterium atoms with a power up to 16.5 MW, at 1MeV of energy and with a pulse length up to 3600s have never been reached together before. The ITER NBTF, called PRIMA (Padova Research on ITER Megavolt Accelerator), is hosted in Padova, Italy; it includes two experiments: MITICA, the full-scale prototype of the ITER injector and SPIDER, the full-size negative ion source. The realization promoted by the ITER organization is carried out with the contribution of the European Union, channeled through the Joint Undertaking for ITER (F4E), of the Consorzio RFX which hosts the Test Facility, the Japanese and the Indian ITER Domestic Agencies (JADA and INDA) and several European laboratories, such as IPP-Garching, KIT-Karlsruhe, CCFECulham, CEA-Cadarache. The early start of operation of PRIMA experiments is urgent because sufficient experimental time is necessary to face and solve the issues related to the achievement of the desired performance in time for the ITER operation, requiring NBI since the beginning. Substantial progresses have been recently achieved: the buildings construction, begun in October 2012, has been completed by the end of 2015 and the installation of some components has been started since the end of 2014. The SPIDER realization is well advanced: the installation phase is proceeding in good agreement with the general plan; it is expected to be almost completed by the end of 2016. In parallel, the commissioning of the SPIDER power supply (PS) and auxiliary plant systems is being proceeding. Tests at full power and remote control are planned, including also those addressed to reproduce the grid breakdowns and to test the relevant protections. The design of the MITICA injector components was completed in 2015their procurement is being made through a number of tenders, some of them already launched. The HV Power Supply system of the MITICA 1MV accelerator, provided by JADA, was delivered on site in December 2015. The challenging installation of these components, including the step-up transformers and the SF6 gas insulated transmission line, started soon after and will go on throughout 2016. The present phase, with the PRIMA buildings continuously filled with new components, with the installation activities progressing and with also the commissioning and testing phase starting represents a substantial step forward toward the main target. The paper will describe the main challenges the Project Team has dealt during this phase and the important feedback derived for the ITER HNB systems both from the technical and the organizational standpoints.

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.

SPIDER experiment, the full size prototype of the beam source for the ITER heating neutral beam injector, has to demonstrate extraction and acceleration to 100 kV of a large negative ion hydrogen or deuterium beam with coextracted electron fraction e-/D

Mineral insulated (MI) thermocouples will be connected to the MI extension cables through custom connectors for sensors positioned on the in-vessel components of the ITER neutral beam injectors. A first connector position is located at the vessel wall to allow for junction of the in-vessel components with the in-vessel extension cables, the second one at the signal feedthroughs in order to pass the vacuum barrier and arrive at signal conditioning. This in-vessel mating plug and socket design allows for maintenance and replacement of components with multiple connections and reliable signal transmission. The connectors have been developed from previous experience on connectors manufactured for other fusion diagnostics and can house up to 63 metal-ceramic terminations of MI thermocouples locked in position by insulating plates and bushes; an external shielding shell will be mounted as protection. Coupling between shields and insulating plates have been developed with shadow edges to avoid deposition of conductive coatings of sputtered materials, so preserving the electrical insulation. Electrical design has been developed to shield signals from electromagnetic interference and to isolate the sensor shield from the vessel grounding, so avoiding ground loops. Remote handling design incorporates a long ball-ended dowel that locates in a circular hole and short parallel dowels that locate in a short slot to provide high level of position control within a compact arrangement. The plug has been provided with two grip linkage for the manipulator interface. Mechanical design has been accomplished by selecting materials and solutions compatible with vacuum and radiation resistance in the ITER environment, considering the manufacturing feasibility especially for machinable glass-ceramic used for plates and bushes, verifying the mating alignment of standard contact pins also at the signal feedthrough interface.

The ITER project requires additional heating provided by two neutral beam injectors using 40 A negative deuterium ions accelerated at 1 MV. As the beam requirements have never been experimentally met, a test facility is under construction at Consorzio RFX, which hosts two experiments: SPIDER, full-size 100 kV ion source prototype, and MITICA, 1 MeV full-size ITER injector prototype. Since diagnostics in ITER injectors will be mainly limited to thermocouples, due to neutron and gamma radiation and to limited access, it is crucial to thoroughly investigate and characterize in more accessible experiments the key parameters of source plasma and beam, using several complementary diagnostics assisted by modelling. In SPIDER and MITICA the ion source parameters will be measured by optical emission spectroscopy, electrostatic probes, cavity ring down spectroscopy for H^− density and laser absorption spectroscopy for cesium density. Measurements over multiple lines-of-sight will provide the spatial distribution of the parameters over the source extension. The beam profile uniformity and its divergence are studied with beam emission spectroscopy, complemented by visible tomography and neutron imaging, which are novel techniques, while an instrumented calorimeter based on custom unidirectional carbon fiber composite tiles observed by infrared cameras will measure the beam footprint on short pulses with the highest spatial resolution. All heated components will be monitored with thermocouples: as these will likely be the only measurements available in ITER injectors, their capabilities will be investigated by comparison with other techniques. SPIDER and MITICA diagnostics are described in the present paper with a focus on their rationale, key solutions and most original and effective implementations.

The ion source NIO1 (Negative Ion Optimization 1) was developed and installed as a reduced-size model of multi-aperture sources used in neutral beam injectors. NIO1 beam optics is optimized for a 130 mA H- current (subdivided in 9 beamlets) at a Vs=60 kV extraction voltage, with an electron-to-ion current ratio Rj up to 2. In an initial phase, NIO1 was operated with Vs=0 to verify the coupling of radiofrequency (rf) power Pf to plasma. The distinction between capacitively coupled plasma (E-mode, consistent with a low electron density plasma ne) and inductively coupled plasma (H-mode, requiring larger ne) was clearly related to several experimental signatures, especially for air or nitrogen plasmas, where E to H transition was observed with Pf about 0.5 kW (with hysteresis). In hydrogen, the same transition may require about 1 kW, so that air cooling of the rf window was improved. Beams of H- and O- were separately extracted (using pure gases as input); since no caesium is yet introduced into the source, the expected ion currents are typically lower than 10 mA; this requires a lower acceleration voltage Vs (to keep the same perveance). Operation at lower voltages and current (as appropriate in this phase) is possible, but use of weaker deflection magnets in the extraction grid (EG) or use of heavier gases (oxygen) is then advisable. Preliminary experiments indicate the need of increasing the ampere-turns in magnetic filter and the bias voltage to reduce Rj (still very large, about 150 for oxygen), in qualitative agreement with theoretical and numerical models. In a separate test stand, NIO1 caesium oven was tested, with deposition on a molybdenum substrate, and advanced Cs dispensers are in development.

SPIDER is one of two projects of the ITER Neutral Beam Test Facility under construction in Padova, Italy, at the Consorzio RFX premises. It will have a 100 keV beam source with a full-size prototype of the radiofrequency ion source for the ITER neutral beam injector (NBI) and also, similar to the ITER diagnostic neutral beam, it is designed to operate with a pulse length of up to 3600 s, featuring an ITER-like magnetic filter field configuration (for high extraction of negative ions) and caesium oven (for high production of negative ions) layout as well as a wide set of diagnostics. These features will allow a reproduction of the ion source operation in ITER, which cannot be done in any other existing test facility. SPIDER realization is well advanced and the first operation is expected at the beginning of 2018, with the mission of achieving the ITER heating and diagnostic NBI ion source requirements and of improving its performance in terms of reliability and availability. This paper mainly focuses on the preparation of the first SPIDER operations - integration and testing of SPIDER components, completion and implementation of diagnostics and control and formulation of operation and research plan, based on a staged strategy