The development of a large-area RF source for negative hydrogen ions, an official EFDA task agreement, is aiming at demonstrating ITER-relevant ion source parameters. This implies a current density of 20 mA/cm 2 accelerated Dions at a source filling pressure of ≤ 0.3 Pa and an electron to ion ratio of ≤ 1 from a PINI-size extraction area for pulse lengths of up to 1 hour. The work is progressing along three lines in parallel: (i) optimisation of current densities at low pressure and electron/ion ratio, utilising small extraction areas (< 100 cm 2) and short pulses (< 10 s); (ii); investigation of extended extraction areas (< 300 cm 2) and pulse lengths of up to 3600 s; (iii) investigation of a size-scaling on a half-size ITER plasma source. Three different testbeds are being used to carry out those investigations in parallel. An extensive diagnostic and modelling programme accompanies the activities. The paper contains the recent achievements and the status of preparations in those four areas of development

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Following the allocation of the procurement of the diagnostic neutral beam (DNB) to the Indian DA, a series of tasks have been undertaken to first assess the DNB configuration and arrive at an optimal beam-line configuration folding in the gas-feed and vacuum-pumping requirements. Specific emphasis is placed on the thermal, structural, and electrical designs of beam-line components, in order to ensure their compatibility with the criteria specified for ITER in vessel components, i.e., Structural Design Criteria for In-Vessel Components. The detailed assessment of manufacturing technologies and their compatibility with the ITER standards forms an integral part of the design. A common approach to manufacturing for DNB and heating-and-current-drive NB components shall be undertaken through a comprehensive prototyping phase which shall lead to built-to-print specifications. In addition to safety and remote-handling issues, the design also addresses the requirements of interfaces related to other systems such as cryo, hydraulic, pneumatic, vacuum pumping, gas feed, civil, power supplies and transmission, CODAC, etc. The successful delivery of DNB is dependent on two critical R&D aspects: 1) the production of a uniform low-divergence beam from the beam source and 2) a well-controlled transmission through lengths of ∼22 m. The first shall primarily be a subject of the Ion Source Test Facility-SPIDER [part of NB test facility (MITICA in Padova)]-where India is involved as a collaborator and the Indian test bed, where issues for DNB beam source which were not resolved in the SPIDER would be taken up. The second shall form one of the primary objectives of the Indian test bed to characterize the DNB. This paper presents the progress in DNB from the concept level to an engineered system along with the plans for system integration and an R&D intensive implementation.Index Terms-Beam transmission, beam-line components (BLCs), concept, diagnostic neutral beam (NB) (DNB), ITER.

The ITER project requires additional heating by two neutral beam injectors, each accelerating to 1 MV a 40 A beam of negative deuterium ions, to deliver to the plasma a power of about 17 MW for one hour. As these requirements have never been experimentally met, it was Nuclear Fusion Progress in the realization of the PRIMA neutral beam test facility

H− ion based neutral beam injector is a critical heating and current drive system in a fusion reactor. However, the present H− ion source configuration has limitations in terms of production, extraction, cesium (Cs) inventory and management. To overcome these limitations, a proof-of-principle experiment based on a novel concept regarding surface assisted volume H− ions production by sprinkling Cs coated tungsten (W) dust grains (low work function surface) into a hydrogen plasma is carried out. Four different diagnostics have been used to validate the concept. The H− ion fraction is estimated from (a) Langmuir probe diagnostic, (b) phase velocity of ion acoustic waves, (c) dust current and confirmed by the measurement of (d) Balmer line ratio. The measured H− ion fraction with respect to the plasma density for different discharge conditions varies from ~0.2 to 0.3 in presence of Cs coated W dust particles. The experimental results show good agreement with the theoretical estimation.

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The effect of external magnetic field on the Langmuir probe measurement and dust charging are studied in low-pressure hydrogen plasma. The experiment is performed in a dusty plasma device where plasma is created by the hot cathode filament discharge technique. A strong Strontium ferrite magnet is used inside the plasma, near the dust zone. The plasma parameters are measured at different distances from the magnet with the help of Langmuir probe system. It is observed that even at “low magnetic field case,” where rLe≥rP, rLi〉〉rP; the electron collection by the probe deviates strongly from the actual value, until rLe≥10rP. The observations of electron energy probability function show that at higher magnetic field, the Langmuir probe collects only the higher energy electrons compared to the low energy electrons. Both Quasi-neutrality condition and capacitance model are used separately to calculate the charge accumulated on the dust grain. Introducing the reduction factor on quasi-neutrality condition, it is observed that the influence of magnetic field on dust charge is almost negligible for “low magnetic field” case. The dust charge calculated from quasi-neutrality condition matches well with the experimentally observed dust current results, within the experimental error range. However, capacitance model deviates from the experimental results at higher magnetic field.

Measurements of ion flow in an ion source made for negative ion extraction are reported in this letter. The ion flow has been measured using the Mach probe as two single probes compared with the results as a double probe. The measured values of the Mach number lie between 0.2 and 0.4. The maximum value of the Mach number is observed near the radio-frequency excitation coil. The flow shows a dominant direction toward the extraction grid; however, the flow pattern, away from the central axis of the source, shows a direction reversal and, therefore, convection. The presence of an ion flow has a strong influence on negative ion motion toward the extraction grid and on the sheath potential. The ion flow will play a dominant role in the ion dynamics and negative ion beam overall efficiency