Meeting Summary |
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The scope of the meeting was to bring together experts on the field to present the latest results and to discuss the issues on physics and technology of neutral particle injection for steady state operation in ITER (namely current density 200 A/m2 and acceleration voltage 1MV for pulses up to 1h). The topics covered during the meeting were: physics of the negative ion sources, beam operation, injector technology, and status reports and programmes. Progress in all fields was reported. In particular, both arc and radio frequency (RF) sources have improved performance and operation reliability. RF sources have been proved to be able to meet the ITER requirements in terms of current density, operating pressure and electron co-extraction, while testing of long pulse operation in deuterium and of current density uniformity in large size sources is in progress or under preparation. Arc driven sources have demonstrated that current density and beam uniformity can be improved by optimization of magnetic filter and filament arc current control. Modeling of sources (in H and D) has confirmed that excited molecules are the precursors of negative ions and that the processes at the surfaces play a key role for operation with caesium. New diagnostics have allowed detailed comparison of plasma properties to be carried out, showing not much difference in terms of atom, molecule and ion populations between the two sources when operating at comparable current densities and pressures. Operation at 836 kV, 146 A/ m2 with H- ion beams has been achieved in multi-grid accelerator systems, while improvement in optics and beam steering have been reported from single gap accelerator systems operating at 727 keV, 120 A/ m2 with D-. Performance of negative ion beam systems has been further improved increasing total injection power and acceleration voltage and extending the pulse length. The outcomes of the engineering revision of the neutral beam injector design for ITER were reported, focussing on the technological aspects of the realization of the bushing and of the beam line components (neutralizer, residual ion dump and calorimeter). The modifications required to adapt the injector design to a Test Facility aimed at demonstrating high voltage acceleration at ITER-relevant currents were presented and discussed. All the programmes presented by the laboratories presently involved in the negative ion neutral beam R&D confirmed the will to continue the research activity with a constructive spirit of scientific collaboration. Dr. V. Antoni, Consorzio RFX, Associazione Euratom-ENEA sulla Fusione, Padova, Italy |