D. Fasolo

Negative ion beam characterisation in BATMAN by mini-STRIKE: Improved design and new measurements

The ITER project requires additional heating provided by two injectors of neutral beams resulting from the neutralisation of accelerated negative ions. To study and optimise negative ion production, the SPIDER test facility (particle energy 100keV; beam current 50A) is under construction in Padova, with the aim of testing beam characteristics and to verify the source proper operation. The SPIDER beam will be characterised by the instrumented calorimeter STRIKE, whose main components are one-directional carbon fibre carbon composite tiles. Some prototype tiles have been employed in 2012 as a small-scale version (mini-STRIKE) of the entire system to investigate the features of the beam from BATMAN at IPP-Garching. As the BATMAN beamlets are superposed at the measurement position, about 1m from the grounded grid, an actively cooled copper mask is located in front of the tiles; holes in the mask create an artificial beamlet structure. Recently the mini-STRIKE has been updated, taking into account the results obtained in the first campaign. In particular the spatial resolution of the system has been improved by increasing the number of the copper mask holes. Moreover a custom measurement system has been realized for the thermocouple signals and employed in BATMAN in view of its use in SPIDER. The present contribution gives a description of the new design of the system as well as of the thermocouple measurements system and its field test. A new series of measurements has been carried out in BATMAN. The BATMAN beam characterisation in different experimental conditions is presented.

Design, installation, commissioning and operation of a beamlet monitor in the negative ion beam test stand at NIFS

In the framework of the accompanying activity for the development of the two neutral beam injectors for the ITER fusion experiment, an instrumented beam calorimeter is being designed at Consorzio RFX, to be used in the SPIDER test facility (particle energy 100keV; beam current 50A), with the aim of testing beam characteristics and to verify the source proper operation. The main components of the instrumented calorimeter are one-directional carbon-fibre-carbon composite tiles. Some prototype tiles have been used as a small-scale version of the entire calorimeter in the test stand of the neutral beam injectors of the LHD experiment, with the aim of characterising the beam features in various operating conditions. The extraction system of the NIFS test stand source was modified, by applying a mask to the first gridded electrode, in order to isolate only a subset of the beamlets, arranged in two 3×5 matrices, resembling the beamlet groups of the ITER beam sources. The present contribution gives a description ...

Thermal simulations of STRIKE tiles for the assessment of the CFC prototypes and of the configuration for SPIDER

The ITER project requires additional heating via injection of neutral beams, provided by two injectors accelerating negative ions. To study and optimise negative ion production, the SPIDER prototype is under construction in Padova, whose beam has an energy of 100keV and a current of 50A. The instrumented calorimeter STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) has been developed with the main purpose of characterising the SPIDER negative ion beam in terms of beam uniformity and beam divergence during short pulse operations (several seconds). STRIKE is made of 16 1D Carbon Fibre Composite (CFC) tiles, intercepting the whole beam and observed on the rear side by infrared (IR) cameras. Prototypes of the CFC material were procured and this contribution presents experimental tests and numerical simulations devoted to the characterisation of the CFC properties and to the assessment of the performance of the diagnostic. Tests are described, performed using a CO2 laser to investigate the sp...

Design and specifications of the diagnostics for the instrumented calorimeter of Source for the Production of Ions of Deuterium Extracted from Radio frequency plasmaa)

In the development of the neutral beam injector for ITER experiment, the test facility SPIDER is going to be built. To measure the beam parameters, several diagnostics are used. One of them is the Short-Time Retractable Instrumented Kalorimeter Experiment (STRIKE) which measures beam uniformity, beamlet divergence, and stripping losses. This contribution gives an overview of the diagnostics dedicated to these measurements: thermal cameras, thermocouples, current sensors, and electrostatic sensors. The specifications of these diagnostics have been defined according to the results of electrostatic and thermal simulations. A failure modes and effects analysis has been performed during the design. Consequently the project of the STRIKE diagnostics has been optimized to reduce the possible failure risks.

High energy flux thermo-mechanical test of 1D-carbon-carbon fibre composite prototypes for the SPIDER diagnostic calorimeter.

Operation of the thermonuclear fusion experiment ITER requires additional heating via injection of neutral beams from accelerated negative ions. In the SPIDER test facility, under construction in Padova, the production of negative ions will be studied and optimised. STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) is a diagnostic used to characterise the SPIDER beam during short pulse operation (several seconds) to verify if the beam meets the ITER requirements about the maximum allowed beam non-uniformity (below ±10%). The major components of STRIKE are 16 1D-CFC (Carbon-Carbon Fibre Composite) tiles, observed at the rear side by a thermal camera. This contribution gives an overview of some tests under high energy particle flux, aimed at verifying the thermo-mechanical behaviour of several CFC prototype tiles. The tests were performed in the GLADIS facility at IPP (Max-Plank-Institut für Plasmaphysik), Garching. Dedicated linear and nonlinear simulations were carried out to interpret the experiments and a comparison of the experimental data with the simulation results is presented. The results of some morphological and structural studies on the material after exposure to the GLADIS beam are also given.

Improvements of the versatile multiaperture negative ion source NIO1

The ion source NIO1 (Negative Ion Optimization 1) was developed and installed as a reduced-size model of multi-aperture sources used in neutral beam injectors. NIO1 beam optics is optimized for a 135 mA H− current (subdivided in 9 beamlets) at a Vs = 60 kV extraction voltage, with an electron-to-ion current ratio Rj up to 2. Depending on gas pressure used, NIO1 was up to now operated with Vs < 25 kV for beam extraction and Vs = 60 kV for insulation tests. The distinction between capacitively coupled plasma (E-mode, consistent with a low electron density plasma ne) and inductively coupled plasma (H-mode, requiring larger ne) was clearly related to several experimental signatures, and was confirmed for several gases, when applied radiofrequency power exceeds a given threshold Pt (with hysteresis). For hydrogen Pt was reduced below 1 kW, with a clean rf window and molybdenum liners on other walls; for oxygen Pt ≤ 400 W. Beams of H− and O− were separately extracted; since no caesium is yet introduced into the...

Thermal and electrostatic simulations of the diagnostic calorimeter for the Source for Production of Ion of Deuterium Extracted from RF plasma beam

To study and optimise negative ion production for the ITER neutral beam injectors, a test facility is under construction in Padova with the aim of testing beam characteristics and to verify the source proper operation. The instrumented calorimeter STRIKE (short-time retractable instrumented kalorimeter experiment) is being developed to characterise the SPIDER (Source for Production of Ion of Deuterium Extracted from RF plasma) beam during short operations. The paper presents an investigation of the response of STRIKE measurement systems. It results that biasing is necessary to cope with the influence of secondary electrons on current measurements; moreover, despite the discretisation of the recorded thermal patterns introduced by the pixels of thermal cameras, a sufficient spatial resolution is expected.

Castellated tiles as the beam-facing components for the diagnostic calorimeter of the negative ion source SPIDER

This paper presents the results of numerical simulations and experimental tests carried out to assess the feasibility and suitability of graphite castellated tiles as beam-facing component in the diagnostic calorimeter of the negative ion source SPIDER (Source for Production of Ions of Deuterium Extracted from Radio frequency plasma). The results indicate that this concept could be a reliable, although less performing, alternative for the present design based on carbon fiber composite tiles, as it provides thermal measurements on the required spatial scale.

Prototype of a Diagnostic Calorimeter for BATMAN: Design and Preliminary Measurements

The ITER neutral beam injection system is being designed to provide 33 MW of heating from two injectors, with an upgrade to 50 MW possible with a third injector; such heating power will be provided by accelerating negative ions to high energies, 1 MeV, and neutralizing them. These neutrals are then injected into the tokamak where they impart their energy by collisions. To study and optimize negative ion production, the SPIDER prototype is under construction in Padova, Italy, whose beam has an energy of 100 keV and a current of 48 A. The instrumented calorimeter Short-Time Retractable Instrumented Kalorimeter Experiment (STRIKE) has been designed with the main purpose of characterizing the SPIDER negative ion beam in terms of beam uniformity and beam divergence during short operations (several seconds). STRIKE is made of 16 1-D carbon fiber composite (CFC) tiles, intercepting the whole beam and observed from the rear side by infrared (IR) cameras. With two identical samples of the CFC material and the IR camera under assessment, a reduced version of the entire calorimeter has been built, with the purpose of characterizing its diagnostic properties. This mini-STRIKE was used in the BATMAN experiment at Max Planck Institut für Plasmaphysik (Garching, Germany). As the beamlet divergence in BATMAN is large, the beamlets overlap each other in the measurement position; therefore, the mini-STRIKE for BATMAN includes a copper mask, facing the beam and featuring eight apertures. Thus, eight different portions of the beam can be simultaneously sampled, with minimal overlapping of the power coming from adjacent apertures. The copper mask was actively cooled, and calorimetry was carried out. The temperature in the center of the mask and some positions along the CFC tiles was also measured. In this paper, the design of the system is presented. The calorimetry system is presented in detail as well as the procedure adopted for calorimetrical data analysis. The results of calorimetry are presented together with preliminary correlations with the BATMAN beam features.

Design and preliminary measurements of a diagnostic calorimeter for BATMAN

The ITER project requires neutral beam injection; such additional heating power will be provided by two injectors accelerating negative ions. To study and optimise negative ion production, the SPIDER prototype is under construction in Padova, Italy, whose beam has an energy of 100 keV and a current of 50 A. The instrumented calorimeter STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment) has been designed with the main purpose of characterising the SPIDER negative ion beam in terms of beam uniformity and beam divergence during short operations (several seconds). STRIKE is made of 16 1D Carbon Fibre Composite (CFC) tiles, intercepting the whole beam and observed on the rear side by infrared (IR) cameras. With two identical samples of the CFC material and with the IR camera under assessment, a reduced version of the entire calorimeter has been built, with the purpose of characterising its diagnostic properties. This mini-STRIKE was used in the BATMAN experiment at IPP (Garching, Germany). As the beamlet divergence in BATMAN is large, the beamlets are superposed in the position where the diagnostic is located; consequently the mini-STRIKE for BATMAN includes a copper mask, facing the beam and featuring 8 apertures. Thus, eight different portions of the beam can be simultaneously sampled, with minimal overlapping of the power coming from adjacent apertures. The copper mask was actively cooled and calorimetry was carried out. The temperature in the centre of the mask and in some positions along the CFC tiles was also measured. In this contribution the design of the system is presented, along with the tests performed before the installation of mini-STRIKE in BATMAN. The calorimetry system is presented in detail as well as the procedure adopted for calorimetrical data analysis. Results of calorimetry are presented together with preliminary correlations with the BATMAN beam features.