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The negative ion source development has reached performances very close to those required by the ITER project; see for example the test facility ELISE results*. A main residual problem seems to be the great amount of co-extracted electrons in the top part of the source. The introduction of a magnetic filter to remove the electrons from the extraction zone of the source causes ExB particle drifts (or shifts) which move both ions and electrons towards the top (or bottom depending on the B direction); in the top part the electron concentration and extracted current increase and that limits the extracted ion amount. In this contribution, as a possible solution, the application of a Planar Ion Funnel (PIF) extraction electric field configuration** on the source exit is proposed. The electric field line shape of PIF configuration, not only should break the perpendicularity between the magnetic filter B and the extraction electric field E in such a way to prevents the ExB particle drifts, but also should give a more efficient field shape for the H-/D- extraction. Preliminary simulations of D- and e⁻ trajectories are presented to confirm the efficiency of the PIF system., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

High mass resolution spectrometers (HRMS) for separation of exotic ion species in nuclear physics experiment request a low emittance and small energy spread (with D E the peak-to-peak value, and sE the rms value) of the input beam, so that ion cooler devices, as a Radio Frequency Quadrupole Coolers (RFQC), are typically envisioned. The SPES (Selective Production of Exotic Species) project at LNL requests M/(D M) about 20000, rms normalized emittance in the order of 2 nm, and for 160 keV ions, spread sE about 1 eV. Typical limits of RFQC[*] and HRMS[**] performances are discussed, and relevant formulas are implemented in easy reference tools. The necessary collisional data are reviewed, in particular for Cs+ against He gas, whose pressure ranges from 2 to 9 Pa; status of Milan test bench is briefly updated. Practical consideration on gas pumping, voltage stability and magnet design are also included., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Experimental Fusion Reactor ITER will use fast Neutral Beams (NBs) injectors to increase the plasma temperature in order to drive the plasma current necessary for stability. The NBs are produced by D- beams, which are generated by negative ion sources and neutralized by gas cells with an efficiency of 60%. In order to improve the electrical efficiency of the NB production, a beam recovery system of the residual charged particles could be foreseen. In particular, we have already proposed an energy recovery device with an axisymmetric cylindrical ion collector. A scaled ITER type negative ion source, NIO1 (Negative Ion Optimization 1), has been developed at RFX (Padua) for studying and improving the ion extraction efficiency. An experimental test on beam energy recovery by using the NIO1 ion beam has been recently proposed. However, one important issue related to the beam energy recovery are the secondary electrons generated by the interaction of the ions with the collector walls which may escape from the device, reducing energy recovery efficiency and cause damages. In this contribution, the problem of minimizing the secondary electrons production in the energy recovery device has been studied and simulated. Although a fraction of the secondary electrons escapes from the ion collector, they are greatly stopped in the axisymmetric geometry cup. A simple test bench for secondary electron emission to verify the simulation results is in preparation at INFN-BA laboratory.

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

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. 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. Several modifications of the magnetic configuration (both inside the ion source and for the embedded magnets inside the accelerator grids) were 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. Saturation of filter field beneficial effect at large (>100 G) amplitudes is discussed, as well as the advantages of crossed field operation. 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).

The cooling of beams of exotic nuclei (both in energy spread and in transverse oscillations) is critical to downstream mass spectrometry devices and can be provided by collisions with light gases as in the Radio Frequency Quadrupole Cooler (RFQC). As in other traps, several electromagnetic systems can be used for beam deceleration confinement and deceleration, as a radiofrequency (rf) quadrupole, a magnetic solenoid and electrostatic acceleration. Since rf contributes both to beam cooling and heating, operational parameters should be carefully optimized. The LNL RFQC prototype is going to be placed inside the existing Eltrap solenoid, capable of providing a magnetic flux density component B_{z} up to 0.2 T, where z is the solenoid axis. Setup progress and related rf component development are reported; in particular simple matching boxes are discussed; the differential gas pumping system is also described., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The RF negative ion source NIO1, built at Consorzio RFX in Padua (Italy), is aimed to investigate general issues on ion source physics, as well as innovative solutions for electrical efficiency, in view of their use as sources of neutral beam injectors (NBIs) in future fusion experiments, like MITICA, the ITER NBI prototype. NIO1 has been designed to produce 9 H- beamlets (in a 3x3 pattern) of each (when using cesium) and 60 keV, using a three-electrode system (plasma grid, extraction grid and post accelerated grid) downstream the plasma source. Since no cesium has been used yet in NIO1, the negative ion production relies on the volume process only. In order to maximize its efficiency, some solutions have been proposed. Inside the source chamber, in front of the plasma grid, an electrically insulated bias plate has been located, which can be independently biased with respect to the plasma grid or, in turn, with respect to the source walls. The original design solution for the filter field (generated by current flowing through the plasma grid and external return coil), was modified in order to increase its absolute value inside the source chamber, by a different configuration of the cusp field magnets. The aim of this contribution is to show the beneficial effect of these two design solutions in improving negative ion current in NIO1.

The NIO1 (Negative Ion Optimization 1) experiment hosts a flexible RF H- ion source, developed by Consorzio RFX and INFN-LNL 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 installed 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? photons emitted by the fast beam particles and collected along lines of sight. The article will present 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.

The installation of molybdenum liners in the ion source NIO1 (Negative Ion Optimization phase 1) has proven to be successful in order to largely decrease the contamination of rf window by wall sputtering; intense hydrogen plasma are thus achievable even at moderate rf power (1200 W) in a continuous regime operation (much longer than one hour), which enabled prolongated campaign at several plasma conditions; operation down to 0.5 Pa is possible, while best beam conditions were observed among 1 and 2 Pa, which is satisfying considering that NIO1 was never cesiated up to now. This has motivated a delay in the installation of the existing Cs oven, to investigate the following items: best combination of plasma grid (PG) and bias plate (BP) voltages (usually separately controllable in NIO1) in order to reduce the coextracted electrode current Ie; effect of magnetic filter; improved extraction grid EG with ion deflection compensation; correlation of EG magnetic field and discharges in the extraction gap: achieved acceleration voltage for H- is indeed 12 kV up to now, at the relatively high pressure there (>0.2 Pa) due to the limited pumping installed. Database of results with H is compared to previous results with Oxygen (and Oxygen/Argon mixtures), where a much larger coextracted electron current Ie was measured as expected, and ion beam current was thus limited below 3 mA. On the contrary for H, the limited rf power used resulted in a low extracted current (6 mA), consistently with the stated limitation in voltage. Maintenance experience, concerning gasket erosion and ceramic surface alteration is discussed; the thin insulators among BP and PG and other walls show plasma related embrittlement, and are being rebuilt in a more compact BN grade. Performance of some installed beam diagnostic (side view luminosity, Doppler-shifted emission, and carbon plate calorimetry) is critically reviewed, especially for effectiveness of beam imaging, as also compared to other beam diagnostics. As to the former method, in vertical side view projection, three columns of beamlets clearly show, while the horizontal projection is somewhat blurred by ion deflection up to now. Finally steady progress of acquisition software is noted. Related advancement of simulation tools is summarized.

Negative ion sources are a key component of neutral beam Injection systems, which are used in fusion experiments to raise the plasma parameters close to start ignition. A novel concept for a negative ion source based on existing well tested Hall thrusters (HT) is presented. The thruster scheme is modified in order to maximize the hydrogen dissociation so as to produce an atom flux at an energy optimized to maximize the yield of negative ions when impinging on a low work function surface. The novel concept can in principle offer several advantages among which a limited amount of co-extracted electrons, a more uniform generation of negative ions and a lower rate of destruction of negative ions. In this contribution the numerical simulations aimed to identify the optimum geometry, magnetic field map and operational parameters of the source are presented discussing the effect of the HT working point on the dissociation rate. A preliminary design of the experimental equipment is also presented including the ion source and the vacuum chamber, focusing on the aspects related to the gas injection and the operational pressure and describing the main diagnostics.

3PB8 Design and Experimental Characterization of the Prototype of NIO1 High Voltage Power Supply Protection System Mauro Recchia 1 , Bruno Laterza 1 , Gianluigi Serianni 1 , and Marco Cavenago 2 1 Consorzio RFX 2 INFN-LNL The Negative ion sources are a key component of the Neutral Bea m Injector for ITER, the world largest experiment to prove the feasibility of fusion as a source of energy. The requirements for the ITER NBI, to inject into the plasma 40 A of negative ion energized at 1 MV for one hour, are never been met all together, thus it was recognized the need to develop a test facility named PRIMA (Padova Research on ITER Megavolt Accelerator) including two experiments: SPIDER, a full size ITER NBI ion source and MITICA, the full scale prototype of the 1 MV ITER NBI, now under construction in Padova Italy, at Consorzio RFX premises. NIO1 (Negative Ion Optimization phase 1 ) is another experiment being developed in parallel; it is a reduced size so urce of negative ions equipped with a high voltage electrostatic grid system for beam extraction and acceleration. The negative ions are generated via radio frequen cy at 2 MHz with 2.5 kW rated and the high voltage stages are fed respectively by a 10 kV voltage 0.6 A current Extraction Grid Power Supply (EGPS) and a 60 kV voltage 0.170 A current Acceleration Grid Power Supply (AGPS). NIO1 experiment aims at addressing several important issues to be faced in SPIDER, related to beam extraction and di agnostic optimization. Beam sources are prone to arc occurring between grids which need to be treated as normal operating condition; this means that a suitable protecti on system has to be provided. At this purpose, an electrical model based on a conceptual design of the high voltage circuit was developed to study the electrical waveform induced by the arc and identify the preliminary requirements of the protection system. The paper reports on the development of a prototype of the high voltage protection system for NIO1, for operations at reduced rated voltages: 5 kV for EGPS and 20 kV f or AGPS. Details on the design, the realization and the performance verification done w ith dedicated experimental campaigns are given. The validation of the electrical model aga inst the experimental results will be also presented and discussed.

The ITER neutral beam test facility under construction in Padova will host two experimental devices: SPIDER, a 100 kV negative hydrogen/deuterium RF source, and MITICA, a full scale, 1 MeV deuterium beam injector. A number of diagnostics will be deployed in the two facilities to qualify the beams [1]. This paper reports the progresses achieved on the realization of a neutron diagnostic for SPIDER, that represents a first step towards the application of this diagnostic technique to MITICA. The proposed detection system is called CNESM which stands for Close-contact Neutron Emission Surface Mapping. The CNESM diagnostic is placed right behind the SPIDER beam dump, as close to the neutron emitting surface as possible and aims at providing the map of the neutron emission on the beam dump surface. The CNESM uses nGEM as neutron detectors [2]. These are Gas Electron Multiplier equipped with a cathode that also serves as neutron-proton converter foil. The cathode is at about 30 mm from the beam dump front surface. It is designed to ensure that most of the detected neutrons at a point of the nGEM surface are emitted from the corresponding 40x22 mm2 beamlet footprint on the dump front surface. The 256 nGEM readout pads (area 12x22 mm2) will record a useful count rate of ?5 kHz providing a time resolution of better than 1 s. Each nGEM detector maps the neutron emission from a group of 5x16 beamlets: 16 nGEM would be needed to cover the entire beam dump. The CNESM was designed on the basis of simulations of the different steps from the deuteron beam interaction with the beam dump to the neutron detection in the nGEM in order to be capable to detect a 10% change in the neutron emission from individual beamlets. The main information output from the CNESM diagnostic is the map of the deuterium beamlets intensity, derived from the neutron emission map with a suitable unfolding algorithm. This information is unique and can be used to diagnose any malfunction of individual beamlets or groups of beamlets. Several small area nGEM prototypes (100 cm2) equipped with cathodes with different features have been built and tested in recent years at neutron sources (such as ISIS in the UK and FNG in Italy) in order to measure the neutron detection efficiency, directionality and gamma background levels [2-5]. Based on the small area prototype results, a first full size prototype for SPIDER with optimized geometrical parameters have been built in 2013. This detector represents the largest area neutron detector based on the GEM technology ever realized. After a first calibration using laboratory measurements, the full size prototype was successfully tested on the ISIS neutron beam where its neutron efficiency map over all the area was measured. The detector operated in the configuration that will be used in SPIDER for one week continuously without showing any issue. Further measurements will be performed in order to complete the characterization and a second prototype will be built in the next year. This work was set up in collaboration and financial support of F4E and of INFN Group 5 (Technology Research). [1] R. Pasqualotto et Al, Review of Scientific Instruments, 83, 02B103 (2012) [2] G. Croci et Al, JINST 7 C03010

The thermonuclear fusion experiment ITER, requires 33 MW of auxiliary heating power from two Neutral Beam Injectors (NBI), each of them providing 40 A of negative deuterium ions. The EU activities oriented to the realisation of the electrostatic accelerator comprise the construction in Padova of SPIDER, a facility devoted to the optimisation of the beam source. SPIDER parameters are: 100 keV acceleration, 40/60 A (deuterium/hydrogen) current. For the optimised SPIDER accelerator the present contribution provides a characterisation of secondary particles, which include electrons produced by impact of ions on grid surfaces, stripped from negative ions inside the accelerator, and produced by ionisation of the background gas, and the corresponding positive ions. Currents and heat deposited on the various grids and spatial distribution by secondaries will be described. It is found that most of the heat loads on the accelerator grids is due to electrons; moreover the features of secondaries exiting the accelerator and back-streaming towards the source will be presented. The results will be compared with old investigations concerning the NBI 1 MeV accelerator., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In a Malmberg¿Penning trap like ELTRAP an electron beam can be stored or propagated in a space charge dominated condition, due to the low acceleration voltage used; in particular we can test the longitudinal expansion of the electron bunch with several diagnostics, including Thomson scattering. Pulsed electron beams produced by an external photocathode source in the 1¿10 keV energy range and with 4 ns length have been measured also by two electrostatic diagnostic systems. A proper software is needed to compensate for the capacitance of the pickup electrodes. Rf can be applied to the sectored electrode to produce a plasma source or to excite or to detect rotational modes; in particular the use of a new 8 sector electrode will allow up to m=3 modes., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In singly charged positive ion sources, the study of beam extraction is greatly simplified by the existence of a well defined place for plasma to beam transition, given by the well known Bohm criterion, where the ion flow speed equals the speed of sonic perturbation, known as Bohm speed. Most of the ion extraction simulation codes are implicity based on the concept of quasi neutrality in the plasma region, as limited by the Bohm criterion. In negative ion source the existence of an electron coextracted beam and of a magnetic filter makes the relevant speed less clear. Moreover there are several scale lengths to be considered: the Debye length, that is typically 0.01 mm, the electron and ion gyroradius, the H⁻ scattering, absorbtion and production length. In the development of negative ion source for NBI injector for ITER, the production of H⁻ at wall and the negative sheath so generated is also important. A critical evaluation of these regimes is obtained with 1D (one space dimension) models, mostly restricted to magnetic filter parallel to the extraction wall. Some remarks on 2D simulation codes is also given., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The development of neutral beam injectors (NBI) for tokamak like the ITER project and beyond requires high performance and huge negative ion sources (40 A of D- beam required); it was recently accepted that inductive plasma coupled (ICP) radiofrequency sources are the preferred option. It is therefore useful to have a moderate size source of modular design to test and verify both construction technologies and components and simulation codes; here the NIO1 design (60 kV, 9 beamlets of 15 mA H⁻ each) and construction status are described. Source is assembled from disk shaped modules, for rapid replacement; the beamlets are arranged in 3 times 3 square matrix so that 90 degree rotation of modules is possible and allows to cross or to align the magnetic filters used in the source. The 2 MHz rf coil and the rf window are a simply replaceable module. Extensive rf absorption and magnetic coil simulations were performed. Related beam simulation and fast emittance scanner development are described elsewhere., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

Nell’agosto del 1961, a Zagabria per la mostra nove tendencije, si riunì un gruppo di artisti, provenienti da diverse aree culturali: italiana, francese e tedesca. Le neoavanguardie così costituitesi erano maturate nello stesso ambiente culturale, quello della rivista “Čovjek i Prostor” (Uomo e spazio), che era stato un laboratorio anche per l’attività critica di Vera Horvat Pintarić (1926) e principalmente di Matko Meštrović (1933) e Radoslav Putar (1929-1994). Osservando i nuovi fermenti artistici di ambito italiano, francese e tedesco, questi ultimi due studiosi contribuirono, ognuno con un peso diverso, a elaborare l’ideologia originaria della manifestazione internazionale di nove tendencije.