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A dedicated Neutral Beam Test Facility (NBTF) has been set up to verify ITER requirements for the neutral beam injectors. The facility, located at Consorzio RFX in Padua (Italy), hosts two experiments: SPIDER and MITICA. SPIDER (Source for the Production of Ions of Deuterium Extracted from Rf plasma) is the full-scale prototype of the ITER source injectors. Its accelerator can be set up to 100 kV and its aim is to investigate and optimize the properties of the ion source. MITICA (Megavolt ITER Injector and Concept Advancement) is the full-scale prototype of the entire injector, devoted to the issues related to the accelerator, including voltage holding at low gas pressure. SPIDER has started operations in 2019 and the plasma without caesium has been characterized. Caesium evaporation, aimed at enhancing the production of negative ions, has recently started during SPIDER experimental campaigns. Understanding the behaviour of caesium during plasma operation is necessary to optimize the generation of negative Hydrogen ions. There are several kinds of contribution to the caesium evaporation in a plasma source. To determine the relative contribution of these fluxes, it is necessary to know the desorption energy of the Cs compounds deposited over the source walls. The Temperature Programmed Desorption (TPD) diagnostic allows to to estimate these energies thanks to a pair of tungsten filaments. The design and development of the device are presented. The diagnostic has been duplicated so it was possible to test its reliability while installing the twin one in SPIDER. First SPIDER experimental results, both using the diagnostic as a TPD and as a Langmuir-Taylor Detector, are shown. Finally, first estimations of the desorption energy are determined in order to finalize plasma-Cs model for SPIDER.

At the beginning of 2020 the SPIDER Cs Oven 03 was tested on the CAesium Test Stand (CATS). This document concerns the description of the functional tests carried out on this oven and the presentation of the obtained experimental results. It is submitted as deliverable AWP21- DMCS/D1.

In SPIDER, the prototype of the ITER HNB Ion Source (IS), where a 100 keV ion beam is accelerated by an electrostatic accelerator, Thermocouples (TCs) are installed on the components of the IS, embedded on the grids, and on the Beam Dump water cooled elements. These measurements are important to monitor the level and the uniformity of heat loads and to protect components under operating conditions that include breakdown events, expected every 10s or even less. In particular for TCs on the grounded grid (GG) and for the calorimetry of the Beam Dump, a custom conditioning and acquisition module with isolated power supply and optical signal transmission has been designed and manufactured. This solution provides electrical insulation during high voltage breakdowns expected up to 20kV. The other sensors are acquired through a commercial Analog Devices solution. The 24 signals from thermal sensors embedded on the GG are acquired by three boards with 8 TC input channels each installed in a box screwed to the frame of the GG together with its isolated power supply based on a 1:1 transformer, able to withstand voltages up to 20kV. Each input signal passes through a low pass filter; any possible voltage transient is stopped by surge protectors before the signal reaches the Cold-Junction Compensated Thermocouple-to-Digital Converter (MAX31856 by Maxim) which digitizes the data from the thermocouples. The data from the MAX31856 devices are collected by a microcontroller which processes and sends them through its internal UART peripheral. The microcontroller TTL UART is connected to a RS-485/RS-422 transceivers which provide 2750 VRMS (for 60s) of galvanic isolation between the serial port and the cable plugged into the output. The most important technical aspect for this custom front-end electronics is its high isolation capability both on the input and on the output sides. This isolation improves communication by breaking ground loops and reduces noise when there are large differences in ground potential between ports. Electro-optical converters are used to send the output to three optical fibers with Peek insulation for the in-vessel path. The signals pass then the vacuum barrier through flange and are fed to an opto-receiver which converts the signal to RS-485 serial format before being acquired by a Moxa port server. The data are here converted to standard Transmission Control Protocol (TCP) simplifying the acquisition and the storage managed by CODAC (Control, Data Access and Communication) and MDSplus. This paper deals with the description of the developed custom electronic front end for the thermocouples embedded on the Grounded Grid, its commissioning during the start of the operations with SPIDER and some experimental results.

This document represents deliverable D1.3.6of the Specific Contract F4E-OFC-531-02-Neutral Beam Test Facility Diagnostics, Task Order No.2: SPIDER Diagnostics #2 and MITICA Diagnostics #1.The final design and specification, layout, list of components, installation and commissioning of STRIKE diagnostic for SPIDER is reported, particularly the embedded sensors and ex-vacuum-part, procured within this contract.

This document reports on the joint experiments carried out at NIFS finalized to further advance the understanding of source plasma physics by measurement of the positive and negative ion energy distributions. NIFS test stand is among the best diagnosed ion sources for negative hydrogen ion beams in the world, and routinely operates low-divergence beamlets at SPIDER-relevant ion energy range. Two newly developed compact diagnostics (gridded retarding field energy analysers) were constructed and installed at the upstream surface of the plasma grid, commissioned, and used to characterize the plasma source with and without caesium. The trends and the ion energy distributions were analysed and a correlation with the source parameters was attempted.

The full-size ITER ion source prototype SPIDER has recently started beam operation; goal parameters: 100keV, 60A negative hydrogen-like ions for one hour. The source is presently operated in volume regime and the beam power is consequently limited. In such configuration, the high resolution calorimeter STRIKE, 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 which are exposed to the beam while their temperature is recorded by 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.

The ITER Heating Neutral Beam (HNB) injector is required to deliver 16.7 MW of 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 ion source needs to be coated with caesium to reduce its work function. Cs must be routinely evaporated in the source by means of dedicated ovens embedded in the source. Controlling and monitoring the evaporation rate of caesium inside the source is fundamental to attain the desired performances on the ITER HNB. In the Neutral Beam Test Facility at Consorzio RFX the prototype RF negative ion source SPIDER has been developed and built. Currently SPIDER is in operation. In SPIDER, liquid Cs based ovens will be used to inject Cs vapours inside the source. The CAesium Test Stand (CATS) has been specifically designed and set up for testing, commissioning, and characterizing Cs ovens in vacuum, in terms of repeatability of the Cs evaporation and deposition onto surfaces. To this aim, a set of diagnostics were installed: fixed Surface Ionization Detectors (SID), embedded in the oven and located in front of the oven nozzle apertures, movable SIDs, to reconstruct the angular distribution of the emission, a quartz microbalance, at a fixed position to provide the cumulated caesium flux, and the laser absorption spectroscopy, to measure the line-integrated caesium density. The poster will present the CATS set- up with a description of the layout and the present configuration of the diagnostic set-up and future upgrades.

In view of the long term operation of neutral beam injectors (NBI) used for stellaratorand tokamak heating and current drive, the negative ion source must be carefully optimized,especially because not only plasma but also surface wall conditions are involved in H- or D-production. The NIO1 (negative ion optimization phase 1) installation was developed and isoperated since 2014 (in close collaboration between Consorzio RFX and INFN), as a convenientbenchmark to study innovative solutions and to address physical questions. The comparativelysmaller size of NIO1 (a relatively compact and modular 9 beamlet H- source) is of evidentadvantage for detailed modeling. The apparent plasma impedance is well in agreement withnegligible rf reflection at plasma on, and reflections with plasma off (about 25 %) are well withinlimits tolerable by rf amplifier; transition between E and H modes of rf coupling can be controlledby increasing rf power or by decreasing gas pressure. The filter field intensity, Bx, has beenextended to span the [-12, 5] mT range, and as a trend, source performances improve with |Bx|.Status and results of a first NIO1 cesium oven are reported. Installation of the Cavity Ring DownSpectrometer (CRDS) and recent years progress of beam diagnostics and of the quality of thevolume-produced H- beam are briefly discussed, together with the status of the NIO1 full power"end calorimeter/beam imaging attenuator", to be placed at the end flange with auxiliary flangesfor infrared observation. Conceptual tests of energy recovery system, perhaps using this fullpower calorimeter are also summarized.

Negative ion sources are a critical component of neutral beam injectors NBI (used for stellarator and tokamak heating and current drive), due to the stringent requirement current density, beam divergence and operational stability. In support to the NBI development, a relatively compact 9 beamlet H- source (named NIO1, for negative ion optimization phase 1) was developed in close collaboration between Consorzio RFX and INFN, and is operated since 2014, for studying the influence of magnetic field configuration and other conditions on extracted beam. A robust rf system (amplifier can tolerate the load mismatch at plasma onset) and strong water cooling of the ion source and accelerator allow CW operation of the beam, well over the one hour pulse length required by ITER. A dedicated Cs oven (including a hot closure valve) was verified in separated test stand, where final calibrations are in progress, for installation in NIO1. Effects of several magnetic field configurations were studied in NIO1 in pure volume production conditions, which in principle should guarantee long term stability of extracted beam; spontaneous and unexpected fluctuations of plasma regime (with time scale in the order of minutes, or tens of minutes) were sometimes observed, and partly related to several changes in operational procedures (history of pressure changes). As a general trend, the typical source perfomances improve with strength of the magnetic field filter (with collected data spanning from 1 to 12 mT), which also helps to reduce the coextracted electron current. Evolution of diagnostic and simulation development is also summarized in this contribution: the beam images taken by two orthogonal cameras and the beam optics simulation are in fair agreement. Some development of energy recovery system and related full power beam calorimeter are also noted. More detailed modelling of source plasma will benefit from data of Cavity Ring Down Spectrometer whose installation, nearly finished, is also described.

At the end of January2019 the procurement of the three SPIDER Cs ovens (series production -Batch B) was completed and the ovens were delivered to PRIMA site.TwoSPIDER Cs ovens (Oven 01 and Oven 02) were tested on CAesium Test Stand (CATS).This document concernsthedescription of the functional test carried out on these twoovens and the experimental resultsand represent the deliverable T5.9 -P1.1 Report of tests on Cs ovensof the Work Programme 2019.Moreover, analyses on Cs residual after functional tests are also reported in this document and represent the deliverable T5.4/P1.2 -ICMATE-CNR Activity report on caesium chemistry investigations.

This document concerns the description of the CAesium Test Stand (CATS) and the testing activities on the SPIDER Cs ovens (prototype and series production). The setup of CATS and the thermal test on Cs oven prototype were carried out under WP2017 T5.9. During WP2018 CATS has been upgraded with implementation of new diagnostics and components, it has been commissioned for Cs operation and Cs flux tests on Cs oven prototype were carried out.

This document represents deliverable D1.3 of the Specific Contract F4E - OFC - 531 - 01 - Neutral Beam Test Facility Diagnostics, Task Order No.1: SPIDER Diagn ostics #1 . The description of the final layout and components , the installation activities and the results of the tests carried out for the thermal sensors on the Beam Source, Beam Dump and Vacuum Vessel are provided, in particular for the following subsys tems : - conditioning electronics in the HVD for sensors in the Beam Source ; - interface, cabling, feedthroughs & conditioning electronics for sensors provided by ITER INDA and installed on the cooling pipes of the HTEs of the Beam Dump ; - sensors, cabling & cond itioning electronics for Temperatu re measurements of the HTEs surface - sensors, cabling & conditioning electronics for Temperatu re measurements of the vacuum vessel.

This document reports on the preparation of next joint experiments at NIFS. NIFS test stand is among the best diagnosed ion sources for hydrogen negative ion beams in the world, and routinely operates lowdivergence beamlets at SPIDER-relevant ion energy range. It is proposed to investigate the extraction region in the ion source, in particular to measure the negative ion distribution function in the extraction region and to correlate it with the beam properties in different configurations. In addition to that, the use of a movable probe for positive ion measurement along the magnetic field lines is also proposed.

This report describes the main activities carried out at the High Voltage Padova Test Facility HVPTF in 2018 and the ones related to the installation of a new high voltage test stand at the Consorzio RFX . The activities of the subtask 5.7 have been carried out according with the Work Programme (WP) 2018 between F4E and the Consorzio RFX, agreement on the Neutral Beam Test Facility. The activities mainly consisted in: ? studying of the X-ray spectra to investigate the nature of the physical phenomena which occurs during the high voltage conditioning ? testing instrumentation for precise current measurements and for determining type and position of discharges (visible imaging, IR imaging, RX spectra and Residual Gas Analyzer) ? maintenance of both positive and negative HV power supplies and the refurbishment of high voltage ceramic feedthroughs ? evaluation of other methods for improving voltage holding capabilities: tests of surface treatments on electrodes (e.g. alumina spray) ? testing the behaviour of "transparent anodes", i.e. anodes in which the surface is screened by a thin metallic mesh, aimed at zeroing the electric field at surface behind ? experimental study of two-electrode configurations subjected to a combination of Common-Mode Voltage (CMV) and differential-mode voltage to understand the different contribution of anode and cathode on the discharge initiation ? ordinary maintenance of the vacuum plant and controlling system ? construction of a small experimental set-up to measure with sufficient accuracy the FN emission insulating the electrodes by short vacuum gaps, the experimental set up has been called High Voltage Short Gap Test Facility (HVSGTF) The activity mentioned at the last point is partially reported in sec. 10. The specific technical note T5.7 - P1.4_RFX-IE-TN-59 has been prepared to indicate the data for the radiological safety assessment of the HVSGTF.

This document is the test plan for the electrical tests to be carried out on the SPIDER Beam Source at the Site. Only electrical tests to be performed outside the vessel are described .

SPIDER BEAM SOURC E ELECTRICAL TEST REPORT PBS element: 53.SI.A1

Understanding the distribution of caesium by plasma within the expansion region of the SPIDER beam source is essential to maximise the efficiency of negative ion surface-production. The caesium is redistributed by plasma diffusion and is greatly affected by the plasma-wall interactions with the molybdenum walls. This work considers the processes, which make up the plasma wall interaction, and the transmission of generated particles across the plasma sheath. An analytic model is set-up for each of the four main processes that occur at the wall: thermal desorption (evaporation), physical desorption (sputtering), backscattering and adsorption, with the latter being the most significant. These processes occur in response not only to the wall temperature but also to the influx of particles to the wall, and generate atoms/ions outwards to the plasma bulk which must first cross the collisional plasma sheath and pre-sheath. The probability of re-entering the bulk is quantified by a transmission factor, which is calculated specifically for each charge state and process, as it considers the energies at which each process occurs. The transmission factor considers the mean free path of ionising collisions, along with comparing the potential and kinetic energy of each ion with the threshold energy to leave the sheath. The combination of the probability of transmission and the fluxes generated at the wall allows for the study of the redistribution from the plasma discharge within the beam source. The attached manuscript was presented at the NIBS conference 2018 [1].

The calorimeter STRIKE has been developed to study and optimise the beam uniformity and extracted ion current density in SPIDER. The thermal image of the beamlet footprints that appea rs on the rear side of the calorimeter panels made of one - dimensional Carbon Fibre Composite (CFC) tiles is observed by thermal cameras, which permit to reconstruct the beam shape. Changing the measurement position of STRIKE allows a double characterisatio n of the beam, which results in the possibility of measuring the beam divergence and the halo. Each tile is electrically insulated to give a measure of the ion current reaching it and it is instrumented with a thermocouple array for absolute calibration of thermal camera measurements. The tiles are also polarized to pull secondary electrons back to the calorimeter surface. In fact t he voltage gradient in the vicinity of the tiles must guarantee that electrons emitted from one tile are attracted back to the same tile, so that the current profile measurement is not affected. 3D simulations of STRIKE inside the SPIDER vessel have been carried out and showed that 150V is enough to maintain the secondary electron trajectories shorter than the distance between the expected beamlet impact position and the edge of STRIKE tiles, the electrons should be re - absorbed on the same tile . The procurement of STRIKE is in the scope of the OFC - 531 contract. This includes the mechanical structure, the CFC tiles, the thermocoupl es and the electrostatic probes. Within this procurement, fou r power supplies was bought for the biasing of the tiles. This document reports the results of the functional tests carried out on these power supplies.

The activities carried out in 2017 under the RF R&D subtask (5.8) of the 2017 Work Programme were focused in particular on the commissioning, first operation and further development of the High Voltage Radio Frequency Test Facility (HVRFTF): a simple, accessible and flexible test bed to characterize the dielectric strength in vacuum of the RF drivers of SPIDER and MITICA ion sources and address the issues related to their voltage hold off when subjected to their operational radiofrequency E - fields and pressure.

The report outlines the procedure for the execution of the insulation test of the SPIDER Transmission Line and the experimental results, including the high voltage conditioning in vacuum.

This document reports the final design and the technical specifications for the procurement of custom thermocouple input modules. The modules can accept as input both grounded and isolated thermocouples. The modules here described will be used for the acquisition of the thermal signals from the grounded grid of SPIDER beam source, from the SPIDER beam dump and from the vessel. Prototypes of these modules have been realized and tested in different experimental devices (e.g. BATMAN, NIFS NBTS, NIO1) and under different environmental conditions either EM noise or strong high voltages.

The NIO1 (Negative Ion Optimization, phase 1) experiment is a versatile test bench operated by Consorzio RFX and INFN in the framework of the activities aimed at the enhancement of negative ion sources for production of large ion beams for plasma heating in nuclear fusion devices and accelerator applications. The nominal beam current of 135mA at -60kV is divided into 9 beamlets, with multi-aperture extraction electrodes. The plasma is continuously sustained by a 2MHz radiofrequency power supply, with a standard matching box. A High Voltage Deck (HVD) is placed inside the lead shielding surrounding NIO1 and is fed by an insulation transformer installed in a nearby box. It contains the radiofrequency generator, the gas control, electronics and power supplies for the ion source. A closed-circuit water cooling system was installed for the whole system, with a branch towards the HVD. The present contribution gives a detailed description of the electrical plants and the fast protection systems for NIO1. High voltage and low voltage circuits are present in NIO1. The description of the former include the extraction and accelerator power supplies and the passive devices devoted to protecting the power supplies themselves against possible breakdowns in the accelerator. Low voltage circuits are dedicated to biasing the plasma grid and the bias plate as well as to producing a static magnetic field (magnetic filter field) and are protected against the effect of accelerator breakdowns. A specific system was developed to coordinate the fast switch-off of the power supplies and to trigger the main control unit in case a breakdown is detected in either high-voltage power supplies. Details on the fast protection circuitry and examples of its operation are presented. This work was performed with partial financial support by EUROfusion.

A Retarding Field Energy Analyzer - RFEA, based on the analysis of the energy spectrum of particles, was developed to study the plasma potential in the drift region of a travelling beam and, specifically, to analyze the energy spectrum of the secondary particles. This diagnostic has four grids biased with variable voltage s to select the particles and to measure the collected currents. To this purpose a polarization and acquisitions ystem was designed and developed suitable to the RFEA.

This document reports the first part of the experimental campaign carried out at NIFS, in collaboration between Consorzio RFX and NIFS. The joint experiments were done in the period September/November 2016. This first report part deals with the preparation of the experiment, and the first preliminary measurements to test and optimize the data acquisition.

The present report, summarizes the work carried out in 2016 on the NIO1 experiment at Consorzio RFX in Padova, Italy. Experimental campaigns will be presented together with the modelling activities and the activities carried out on various plants.

This technical specification concerns the supply of the Caesium (Cs) oven for the SPIDER experiment that will be hosted in PRIMA facility. The main aim of the SPIDER experiment is to test and optimise the Beam Source that is the core component of the ITER Neutral Beam Injectors. The production of hydrogen (or deuterium) negative ions inside the sources relies mainly on the generation on a caesiated surface with a low work function, which enhances the ion yield and reduces the co - extracted electrons. In the SPIDER beam source fresh Cs has to be injected in a controlled way by means of three Cs ovens. Since the Cs ovens are embedded in the source, their design has to assure vacuum and high temperature compatibility. The present document gives a complementary description of the SPIDER Cs ovens design for their procurement. The document takes care in particular all the precautions to guarantee a good functioning in vacuum environment (e.g.: materials, cleaning, outgassing...). Information for the Cs oven procurement, delivery and acceptance tests are also given. The Supply shall be done in two batches: a Cs oven prototype (Batch A) and 3 Cs ovens (Batch B, series production), after testing of the prototype in vacuum by Consorzio RFX. Based on this Technical Specification, the Supplier shall manufacture, as semble and test the Cs ovens at the factory and then shall deliver them at the PRIMA Site, together with the as built drawings.

The NIO1 (Negative Ion Optimization, phase 1) experiment is a versatile test bench operated by Consorzio RFX and INFN in the framework of the activities aimed at the enhancement of negative ion sources for production of large ion beams for plasma heating in nuclear fusion devices and accelerator applications. The nominal beam current of 135mA at -60kV is divided into 9 beamlets, with multi-aperture extraction electrodes. The plasma is continuously sustained by a 2MHz radiofrequency power supply, with a standard matching box. A High Voltage Deck (HVD) is placed inside the lead shielding surrounding NIO1 and is fed by an insulation transformer installed in a nearby box. It contains the radiofrequency generator, the gas control, electronics and power supplies for the ion source. A closed-circuit water cooling system was installed for the whole system, with a branch towards the HVD. The present contribution describes the control, interlock, acquisition and data retrieval systems for NIO1. Control and data acquisition system implementation require versatility and flexibility for an experiment such as NIO1; for example, new hardware components (e.g. Raspberry PI board, Arduino board, homemade hardware acquisition board) and different types of serial communication (RS232, GPIB, Ethernet) should be rapidly integrated in the communication network (Ethernet switches and electro-optical media-converters), while optical fibre uplinks are implemented to interconnect devices operating in the HVD. The software solution was to adopt Labview as the core of the control and of the acquisition systems (with the development of a synoptic panel) and MDSplus (including the most recent features, like support for long pulse discharge and MDSplus-Labview integration) for data archiving, distribution and visualization. A description is also given of the interlocks that are presently implemented to protect NIO1 against failures of the cooling system and to detect high voltage breakdown occurrences and over-temperatures. A Relational Data Base (based on PostgreSQL) is used to store time-averaged (summary) data for subsequent efficient data analysis in any programming language via standard connectors.

The paper reports on the results of the activity aimed at the experimental characterisation of the NIO1 RF driver electrical impedance at different frequencies.