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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

Power efficiency of neutral beam injectors for DEMO reactor and other fusion applications critically depends on components, including a multiaperture negative ion source. Its optimization promotes the research of a rich variety of physical issues, for which reduced-size model sources are of great help. The ion source NIO1 (Negative Ion Optimization 1) built in Consorzio RFX aims to provide such model, and a versatile test bench for innovations and for simulation code validations. The modular design of source and accelerator column allows for replacement of improved parts and electrodes, and many ports are provided for beam diagnostics and pumping. Electrode design and power supplies are rated for a nominal beam current of 130 mA at -60 kV, divided into 9 beamlets with multiaperture extraction electrodes; a 2 MHz radiofrequency generator can provide up to 2.5 kW power in continuous regime. This poster describes the NIO1 control and data acquisition system, with a special consideration on the indications arisen during its operation. The details of the two main versions of the control software will be presented, together with the operational differences between the two releases. An upgrade of the control and data acquisition system is proposed to increase the reliability and the scalability of the device. Subsystems will be distributed and organized following a concurrent scheme. Programming changes will be shown together with their impact on the system. In this new version the unique server dedicated to the overall control will be split into several separated clients and servers, each one dedicated to a specific subsystem. All data will be stored in a hierarchical database, and summary data will be archived in a relational database. External users will be able to visualize elaborated data and interact in real time. In addition, the websocket communication standard protocol will be adapted to NIO1.

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.

Negative ion sources are the first stage of several types of accelerators, ranging from medical applications to materials testing and to heating systems for nuclear fusion devices. One of the most important aspects of the sources is the amount of extracted ion current, which depends on the extraction voltage and on the availability of ions inside the source plasma; this situation is described by the Child-Langmuir law. The extraction of ions from the source is facilitated by an initial ion velocity. In the case of negative ions, plasma electrons also play a role in the definition of the maximum extractable ion current, which can be significantly decreased for the possibly combined effects of large electron current and magnetic field configuration. The present contribution gives a comprehensive theory of the electrostatic extraction of particles from the meniscus, the plasma boundary which forms at the apertures of a negative ion source in the aforementioned conditions. A normalised treatment is adopted, which is suitable for application to different types of plasmas. Data from the flexible multi-aperture RF-based caesium-free negative ion source NIO1 are studied, which exhibit saturation in the extracted current depending on the plasma parameters both in hydrogen and in oxygen. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

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 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 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).

In order to reduce the beam losses of the negative ion beam in the NIO1 experiment, the vacuum system was improved by installing an additional cryogenic pump. In the upgraded configuration, the negative ion beam can be operated in two regimes of high and low background pressures. The gas flow in the improved configuration was simulated, characterizing the existing pumping system and verifying the best configuration for the improved pumping scheme. The charge state of the negative ion beam moving through the background hydrogen gas is calculated, thus providing the stripping losses inside the accelerator and in the transport region. The expected values are compared with the experimental data obtained with a diagnostic beam dump, a one-dimensional carbon fiber calorimeter, and other beam-plasma diagnostics measuring the parameters of the secondary plasma. The collected electric current and the heat flux reconstructed from thermal measurements are compared with the expected beam particle flux. The measurements indicate as expected an increase of negative ion current at full acceleration and a decrease of the plasma electron contribution.

An ion source called NIO1 (Negative Ion Optimization, phase 1) has been developed by Consorzio RFX and INFN-LNL and is currently in operation in the Consorzio RFX premises in Padova. NIO1 has a radio frequency (RF) inductively coupled (IC) ion source designed to produce a total of 130 mA H- current and to accelerate the ions up to energy of 60 keV; it operates at a frequency of 2 ± 0.2 MHz with maximum RF power of 2.5 kW. In the IC RF ion source, plasma is generated and heated in a component called driver by the RF field induced by a coil. In a preliminary work, a methodology was developed to evaluate the equivalent electrical parameters for IC RF ion sources and power transfer efficiency to the plasma. This methodology takes into account various relevant mechanisms of plasma particle dynamics like ohmic heating, stochastic heating and classical skin depth, which are modelled based on the available literature. These formulations are then integrated with a simplified scheme describing the magnetic coupling between plasma and the RF coil (2- windings transformer model). In order to develop the methodology further, this work provides an improved equivalent electrical model of the driver based on a multiple winding transformer scheme accounting for the mutual coupling between the RF coil, plasma and the surrounding metallic structures. The developed methodology is then applied to NIO1 ion source. The results in terms of equivalent electrical parameters and power transfer efficiency will be presented based on both the simplified and the improved approach.

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.