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The important task (NBI neutral beam injector for fusion) and the complexity of radiofrequency ion source need large tests (as ELISE and SPIDER) and intermediate scale tests (as NIO1 in this poster) for optimization. Conditioning (with gas) was found necessary in Cs-free operation. Cs-based operation has begun: stability improves at lower oven temperature; in both cases, lateral view cameras show beam quality. Energy recovery plugin almost ready for NIO1 (or at a test station at TRIPS).

The important task (NBI neutral beam injector for fusion) and the complexity of radiofrequency ion source need large tests (as ELISE and SPIDER) and intermediate scale tests (as NIO1 in this poster) for optimization. Conditioning (with gas) was found necessary in Cs-free operation. Cs-based operation has begun: stability improves at lower oven temperature; in both cases, lateral view cameras show beam quality. Energy recovery plugin almost ready for NIO1 (or at a test station at TRIPS).

Observation of a transient, in Cs-free regime and long term NIO1 operation, led to the development of stabilization techniques, including conditioning (with oxygen or other gases, as argon, nitrogen, and xenon), interleaved with days of use of H2 as a process gas. Stabilization of transients gave more H- current and less plasma luminosity. After installation of a cesium oven, some additional increase (up to a factor of 2 reaching an average about 50 A/m2) of current was observed, but effect saturates at a moderate oven reservoir temperature. Obtained beam optics will be compared with theoretical expectation and old results in the Cs-free regime in similar conditions (as source voltage, often set to 11 kV). In both regimes, central beamlet apparent density is larger, possibly because a bias plate BP mask reduces side ones. Further improvements including long term conditioning of oven, modification of BP mask and of Cs pipe nozzle (with supporting simulations) are discussed.

The next fusion project DEMO which will be the evolution of the Experimental Fusion Reactor ITER, would require a high efficient energy production. As in ITER, DEMO will use fast Neutral Beam (NB) injectors to increase the plasma temperature needed for the fusion reaction ignition in the TOKAMAK. A way to recover the electric energy production efficiency in DEMO could be the beam energy recover in the NB production [1]. The NB are produced by a Dbeam generated by e negative ion source which is neutralized by a gas cell with an efficiency of 60%. beam energy recovery system of the residual charged particles would improve that efficiency. A proposal of a very simple energy recovery device with an axisymmetric cylindrical ion collector which uses only decelerating electric fields combined with the beam space charge effect has been recently done [2]. This energy recovery system will be tested on the beam of the NIO1 source. It is a compact ion source (scaled down from ITER size sources) which has been developed at INFN-LNL and Consorzio RFX (Padua), where effect of wall condition and source magnetic field changes on negative ion production can be easily studied [3]. In this contribution the detailed collector design to be used in the test on one of the beamlet of the NIO1 source will be presented and discussed. Furthermore, a preliminary trajectory simulation for a beam with a rectangular geometry similar to the beam used in ITER to verify the beam recovery for a non-axial symmetric geometry will be also argued.

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.

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 nine beamlet extraction, operated since 2014 in close collaboration between Consorzio RFX and INFN-LNL. It aims to partly reproduce the conditions of the much larger ion sources built or in construction for 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. Due to the need of assessing negative ion production limits (especially without cesiation) in continuous operation for the perspective of future fusion reactors and to the large importance of magnetic field for source optimization, several configuration changes were tried (both inside the ion source and for the embedded magnets inside the accelerator grids) and investigated, with material ranging from hard ferrite to SmCo to NdFeB. Evidence of the effect of the accelerator fringe field inside the ion source is discussed here and in companion presentations. The radiofrequency system takes full advantage of the frequency tuning amplifier capability (+/- 150 kHz installed, 0/+20 kHz used), and it is worth noting, that no adjustment of matching box capacitors was necessary in the last 3 years. Major diagnostic systems (including CCD cameras and BES measurement) have been integrated with the acquisition system along with the date measured by several power supplies (including the high voltage supplies, the RF generator and bias supplies, the pressure measurements and the beam currents).

This report summarizes the proposals for additional joint experiments in the framework of the collaboration between Consorzio RFX, Padova (Italy) and QST (formerly JAEA ) , Naka (Japan) regarding the development and testing of new magnetic configurations for accelerators of negative ion based neutral beam injectors. First, the results of the first Joint Experimental campaign of Feb - Mar 2016 are summarized and the open issues are discussed. Then, a series of additional experiments for better investigation of the beamlet for mation and transport are proposed. Three chapters are dedicated to simulations devoted to the investigation of the experimental results which are not completely explained yet, and finally an analysis of the proposed experiments for 2017 is carried out.

This document reports about the activities devoted to the simulation of the early operation of SPIDER. Particularly, the operation without caesium is considered and a 5% current density of negative ions with respect to the nominal value; correspondingly the extraction and acceleration voltage s are reduced so as to comply with the Child.Langmuir conditions. The beam o ptics is studied for all three cases of compensation of the magnetic deflection of the beamlets. The activity resulted in the presentation of poster T5_Tu_54 at the latest International C o nference on Ion Sources , held in Geneva on 15 - 20 October 2017 . The poster and the corresponding paper accepted for publication in AIP Conference Proceedings are annexed.

This report summarizes the design of the optics configuration and Extraction Grid to be installed on the Negative Ion Test Stand (NITS) during the joint experiments, to be carried out during the first part of 2016 in collaborati on between Consorzio RFX, Padova (Italy) and QST (formerly JAEA), Naka (Japan) . The main purpose of the joint experiments on NITS is to test for the first time, under realistic similarity conditions, the optics design of the MITICA accelerator, including the new magnetic configurations for the compensation of the typical ion beamlet deflection caused by the electron - suppression magnetic field. The results will allow to optimize the optics design of the negative ion accelerator for MITICA and for the next generation of Neutral Beam Inje c tors for ITER , JT60 - SA [1] and DEMO [8] . The first part of the report describes the mechanical design of the new grid, while in the second part the design of the related permanent magnets is illustrated.

In multi-beamlet negative ion accelerators for fusion applications, the required transverse magnetic field for the suppression of co-extracted electrons is generated by permanent magnets arranged in parallel arrays, embedded in the Extraction Grid. However, such configuration also produces an undesired "criss-cross" deflection of ion trajectories, which can downgrade the overall beam optics. This deflection is traditionally counterbalanced by electrostatic means, i.e. by introducing a small offset in the axis of the grid apertures. During the final design of MITICA, which is the prototype of the ITER Heating Neutral Beam Injector presently under construction in Padova [1], an innovative magnetic configuration called ADCM (Asymmetric Deflection Compensation Magnets) has been conceived [2] and adopted, offering several advantages in terms of operational flexibility compared to the traditional solution. In the framework of a research collaboration between RFX and QST, the new concept has been experimentally tested for the first time in 2016 by a joint RFX-QST team. A new ITER-like [3] Extraction Grid (designed and built at RFX) was mounted on the existing NITS device at the QST lab in Naka. For direct comparison, half of the Extraction Grid was provided with the new ADCM configuration, whereas the rest of the grid had standard magnets with no compensation. A target made of monoaxial carbon-carbon fibre composite and an infrared camera were used for accurate beam optics measurement. The results obtained have confirmed the effectiveness of the ADCM concept for the compensation of the criss-cross ion deflection. Some discrepancies in the scaling of ion deflection with respect to 3D simulations were also evidenced and investigated. The paper presents the main results obtained during the experimental campaign on NITS at QST, which lasted in total six weeks, together with a discussion of the first data analysis results.

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.

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.

This report contains the presentations given during the WP2016 meetings.

The ion source test facility Extraction from a Large Ion Source Experiment (ELISE) has been built at Max Planck Institute for Plasma Physics (IPP) Garching (Germany) and has been operational since December 2012. ELISE is an important intermediate step in the R&D roadmap that the European domestic agency Fusion for Energy has defined for the International Thermonuclear Experimental Reactor (ITER) neutral beam injectors. This new test facility for a large radio frequency ion source builds up on the experience gained during many years of successful operation of smaller testbeds at IPP. The purpose of ELISE is to extract a negative ion beam, at ITER relevant parameters, using an ion source with the full width (1 m) and half the height of the ITER source. ELISE is designed to generate plasma for up to 1 h and extract a H- or D- beam at up to 60 kV. Available power supplies allow beam pulses of 10 s every 150-180 s. Although ELISE is designed to be as close as possible to the ITER source, technical solutions have been implemented that allow considerable experimental flexibility. This report describes the training activities carried out in November and December 2016 with personnel from Consorzio RFX Padova.

An axisymmetric system to recover beam energy from partially neutralized H- beams was recently proposed, for a given beam acceleration voltage Vs [1]. In the case of ion source NIO1 Vs may range from 20 to 60 kV. A first nominal H- beam for simulation was assumed having 60 keV and 20 mA with a 4 mm radius and 0 mrad divergence. A second more realistic beam with 3 mrad divergence, and a composition of 25 : 50 : 25 of H- , H0 and H+ has also been considered. The collector works by decelerating the H- ions (into a system similar to a Faraday cup provided with an exit hole electrode), so that they are radially deflected by space charge and anode lens effects, and collected to a low kinetic energy Kc (less than 1 keV), while neutral and H+ ions can pass through the exit hole electrode. A following collector can recover H+ energy. Several tools were compared for simulations, from commercial programs to user prepared codes, which are challenging for highly nonlinear problem and for a possible (numerically unstable) virtual cathode phenomena; stabilization techniques are compared. Limits for local perveance are discussed. Also mesh asymmetry effects and the related transverse oscillations of H + beam may be observed. Efficiency over 90 % can be reached in typical conditions. The secondary yield (which is low thanks to low impact energy Kc and Faraday cup concept) is estimated.

n the multi-beamlet, negative-ion based Heating Neutral Beam (HNB) Injectors presently used in fusion research, arrays of permanent magnets are embedded in the Extraction Grid (EG) for the suppression of the unwanted co-extracted electrons. These magnets cause a significant undesired deflection of the negative ion beamlets, with a typical alternate pattern, matching the orientation of the magnet arrays. As a consequence, a delicate adjustment of the profile of the EG apertures has to be introduced in order to compensate for this deflection by the electrostatic means. During the final design of MITICA, which is the full-scale prototype of the ITER Heating Neutral Beam presently under construction in Padova, a new solution has been developed by Consorzio RFX for the compensation of this undesired deflection. This new approach makes use of an additional set of permanent magnets, called Asymmetric Deflection Compensation Magnets (ADCM), also embedded in the EG, with a series of advantages in terms of performances and versatility with respect to the traditional electrostatic compensation. For this reason, this solution has been adopted as the reference for MITICA, ITER and possibly for DEMO NBI. After a thorough validation of the design by different numerical models, this solution will be experimentally tested for the first time on the Negative Ion Test Stand (NITS) at JAEA Naka Fusion Institute within the framework of a scientific cooperation agreement between JAEA and Consorzio RFX. To this purpose, an EG having an ITER-like profile and compatible with NITS accelerator has been designed and constructed at Consorzio RFX. This paper describes the design solutions adopted for this grid, the construction, and the final assembly procedure of the permanent magnets inside the grid.

The present report contains the slides presented in the following intermediate and final meetings of the 2015 F4E Work Programme: - Intermediate meeting held on 21 May 2015 (due to global delays of the meeting, the presentatio n was deferred to 16 June 2015), in which the following topics were discussed: o MITICA off-normal conditions o Flux gate sensor prototype o Electrons generated between NEU & RID - Mo dification of RID fringe fields o Th ermal loads on MITICA cryopumps o SPIDER off-normal conditions - OPERA simulations: analyses with single beamlets and with 40 beamlets o Neutral gas profile in SPIDER o Molecular dynamics computation of accommodation coefficients o Simulations of BATMAN accelerator and mini-STRIKE measurements o Simulations of NIFS test stand accelerator and mini-STRIKE measurements - Intermediate meeting held on 16 September 2015, in which the following topics were discussed: o tolerance on B R of permanent magnets in MITICA o demagnetization of permanent ma gnet in MITICA o breakdown between MITICA grids o PG current failure in MITICA o non uniform extracted current/gas density in MITICA o power load onto vessel and cryogenic pumps in MITICA o SPIDER Compensation System Simulations o Simulation of first SPIDER experiments o Development of SAMANTHA code o Molecular-dynamical computations of accommodation coefficients o Interpretation of mini-STRIKE measurements: i n BATMAN (P. Agostinetti et al, ICIS 2015) and i n NIFS negative ion test stand (P. Veltri et al., ICIS 2015) - Closure meeting held on 26 January 2016, presentation by G. Serianni, in which the following topics were discussed: o SPIDER integrated commissioning o SPIDER preliminary operational plan o Characterisation of BATMAN beam by mini-STRIKE o Characterisation of NIFS-RNIS beam by mini-STRIKE o Networks theory application to NBI o Training in NIO1 - Closure meeting held on 26 January 2016, presentation by G. Chitarin, in which the following topics were discussed: o Flux-gate sensor for MITICA/HNB: numerical studies and prototyping o Collaboration between Consorzio RFX and JAEA: common objectives; proposal of activities; assembly of magnets in extraction grid.

This report summarizes the proposals for additional joint experiments in the framework of the collaboration between Consorzio RFX, Padova (Italy) and QST (formerly JAEA ) , Naka (Japan) reg arding the development and testing of new magnetic configurations for accelerators of negative ion based neutral beam injectors. First, the results of the first Joint Experimental campaign of Feb - Mar 2016 are summarized and the open issues are discussed. Then, a series of additional experiments for better investigation of the beamlet formation and transport are proposed. Three chapters are dedicated to simulations devoted to the investigation of the experimental results which are not completely explained yet, and finally an analysis of the proposed experiments for 2017 is carried out.

The RF negative ion source NIO1[1], built at Consorzio RFX in Padua (Italy), is aimed to investigate general issues on ion source physics in view of the full-size ITER injector MITICA [2-3] as well as DEMO relevant solutions, like energy recovery and alternative neutralization systems, crucial for neutral beam injectors in future fusion experiments. NIO1 has been designed to produce 9 H- beamlets (in a 3x3 pattern) of 15mA each and 60keV, using a three electrodes system downstream the plasma source. At the moment the source is at its early operational stage [4] and only operation at low power and low beam energy is possible. In particular NIO1 presents a too strong set of SmCo co-extraction electron suppression magnets (CESM) in the extraction grid (EG) that will be replaced by a weaker set of Ferrite magnets. A completely new set of magnets will be also designed and mounted on the new EG[5] that will be installed next year, replacing the present one. In this paper, the finite element code OPERA 3D is used to investigate the effects of the three sets of magnets on beamlet optics. A comparison of numerical results with measurements will be provided where possible. Both operations in oxygen and hydrogen gases will be compared in the investigation.

The negative ion accelerators for the ITER neutral beam system has been designed by using the conventional beam codes for the positive ion accelerators because mechanism of meniscus formation of negative ions has not been clarified well. In this way, the operational window of the negative ion accelerators can be simply predicted, but the grid heat loading by peripheral beam (beam halo) could not be simulated. To understand the applicable range of the conventional codes to the negative ion accelerators, and then to understand the negative ion meniscus consequently, the benchmark tests between the conventional codes (BEAMORBT (BO) [1] and SLACCAD (SC)[2]) and the experiments have been performed under a joint experiment by RFX and QST on the Negative Ion Test Stand in Naka. Figure 1 shows one numerical results as an example with the grid configuration. The extraction voltage (Vext) is applied between the plasma grid (PG) and the extraction grid (EXG). The acceleration voltage (Vacc) is applied between EXG and the grounded grid (GG). Figure 2 shows the beam divergence angle as a function of Vext at Vacc of 20 kV. Vext with the minimum divergence angle are shown around 4.0 kV both in the numerical codes and the experimental result. The operational window can be predicted in the numerical codes. However, the absolute values of the divergence angle of the experiment was larger than those of the numerical result. One of reasons will be that the numerical code cannot represent the beam halo. Even in the numerical results, the divergence angle in the BO is slightly lower than that of the SC. To understand the meniscus effect to the beam divergence, the relationship between meniscus depth ?zmenis and beam divergence in the numerical results was compared as shown in Figure 3. The details are reported in the paper.

The report describes the benchmark between the two f.e.m. codes OPERA and COMSOL in modelling the negative ion source and accelerator NITS (Negative Ion Te st Stand) located in QST lab (formerly JAEA) at Naka (Japan) . The experiments have been carried out in the framework of the RFX - QST collaboration regarding the development and testing of new magnetic configurations for accelerators of negative ion based n eutral beam injectors.

The optics design of the multi-beamlet negative ion accelerator for MITICA has been verified by means of specific experiments in the NITS test facility at the QST lab, employing a scaled-down configuration having the same features as the accelerator of MITICA and ITER HNB. The experiments confirmed the validity of the accelerator design. However it was found that, in the presence of transverse magnetic field in the ion extraction stage, the ion beamlet deflection in numerical simulations was somehow underestimated with respect to the beamlet deflection inferred from thermal images of a CFC target exposed to the negative ion beam. A detailed benchmark, using also another (completely independent) numerical model of the accelerator, has allowed the identification of possible origins of the differences.