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A beam optics study using the ITER-relevant high intense negative ion beams, such as 1 MeV, 200 A/m2, has been performed experimentally and analytically using a multi-aperture and five-stage accelerator. Initially, multi-beamlets generated from this accelerator were deflected in various directions due to the magnetic field and space charge repulsion between beams and showed various divergences. These had limited the pulse length and the beam energy. Compensation methods of the beamlet deflections have worked effectively and contributed to achieving the ITER requirement, the divergence angle of <7 mrad, and the deflection angle of <1 mrad for 1 MeV beam. The beam pulse has been gradually extended from 1 to 100 s and is now going to a longer pulse based on these results. One of the remaining issues is to understand and suppress peripheral components of the beam, namely, the halo, and to reduce the local heat loads observed around the aperture edge. This halo component has been successfully distinguished from the beam core by using a newly developed beam emittance measurement system for high intense beams. By combining this measured beam emittance and the beam simulation, it was clarified for the first time that the halo components are generated in an area of 1 mm width from the aperture edge. [ABSTRACT FROM AUTHOR]

High power and long-pulse negative ion extractor, which is composed of the plasma grid (PG) and the extraction grid (EXG), is newly developed toward the neutral beam injector for heating and current drive of future fusion machines such as ITER, JT-60 Super Advanced and DEMO reactor. The PG is designed to enhance surface production of negative ions efficiently by applying the chamfered aperture. The efficiency of the negative ion production for the discharge power increased by a factor of 1.3 against that of the conventional PG. The EXG is also designed with the thermal analysis to upgrade the cooling capability for the long pulse operation of >1000 s required in ITER. Though the magnetic field for electron suppression is reduced to 0.75 of that in the conventional EXG due to this upgrade, it was experimentally confirmed that the extracted electron current can be suppressed to the allowable level for the long pulse operation. These results show that newly developed extractor has the high potential for the long pulse extraction of the negative ions. [ABSTRACT FROM AUTHOR]

In order to realize neutral beam systems in International Thermonuclear Experimental Reactor whose target is to produce a 1 MeV, 200 A/m² during 3600 s D- ion beam, the electrostatic five-stages negative ion accelerator so-called "MeV accelerator" has been developed at Japan Atomic Energy Agency. To extend pulse length, heat load of the acceleration grids was reduced by controlling the ion beam trajectory. Namely, the beam deflection due to the residual magnetic field of filter magnet was suppressed with the newly developed extractor with a 0.5 mm off-set aperture displacement. The new extractor improved the deflection angle from 6 mrad to 1 mrad, resulting in the reduction of direct interception of negative ions from 23% to 15% of the total acceleration power, respectively. As a result, the pulse length of 130 A/m², 881 keV H- ion beam has been successfully extended from a previous value of 0.4 s to 8.7 s. This is the first long pulse negative ion beam acceleration over 100 MW/m². [ABSTRACT FROM AUTHOR]

Based on previous studies on the spatial uniformity of the negative ion beam, the external magnetic filter was replaced to a novel tent-shaped magnetic filter in the JAEA 10 A negative ion source. The line-cusp field configuration on the source chamber was also changed to form a symmetric magnetic field like many of positive ion sources aiming at high proton yield. This magnetic field configuration allows fast electrons emitted from filament cathodes to rotate azimuthally inside the source chamber. The source configuration thus prevents localization of fast electrons due to their B×grad B drift in the filter field. As a result, the H- ion beam profile extracted from a wide region of 340×170 mm2 showed reduction of standard deviation from 16% in the original to 7.9% with the tent filter. The negative ion source with the tent filter satisfied the requirement of the beam uniformity for a large negative ion source in the ITER neutral beam injection. [ABSTRACT FROM AUTHOR]

Abstract: Neutral beam (NB) injectors for JT-60 Super Advanced (JT-60SA) have been designed and developed. Twelve positive-ion-based and one negative-ion-based NB injectors are allocated to inject 30MW D0 beams in total for 100s. Each of the positive-ion-based NB injector is designed to inject 1.7MW for 100s at 85keV. A part of the power supplies and magnetic shield utilized on JT-60U are upgraded and reused on JT-60SA. To realize the negative-ion-based NB injector for JT-60SA where the injection of 500keV, 10MW D0 beams for 100s is required, R&Ds of the negative ion source have been carried out. High-energy negative ion beams of 490–500keV have been successfully produced at a beam current of 1–2.8A through 20% of the total ion extraction area, by improving voltage holding capability of the ion source. This is the first demonstration of a high-current negative ion acceleration of >1A to 500keV. The design of the power supplies and the beamline is also in progress. The procurement of the acceleration power supply starts in 2010. [Copyright &y& Elsevier]

The influence of magnetic filter configuration on the beam uniformity was examined to improve beam uniformity in a large Cs-seeded negative-ion source. By reducing the filter strength of the transverse magnetic field used in a typical negative-ion source, the beam uniformity was largely improved with the improvement of the plasma uniformity while the beam intensity was kept to be nearly constant. However, the coextracted electron current greatly increased. To suppress the coextracted electron current, a tent-shaped magnetic filter was applied together with modifications in the cusp magnets to form a typical multicusp positive-ion source arrangement. The uniformity in longitudinal beam profile was improved with the deviation of local beam intensity within 16% that was nearly equal to the deviation obtained at 50 G cm of the transverse filter strength. In the meantime, the coextracted electron current was kept to be the same as the H- ion current. The present result suggests that the uniformity of H- ion-beam profile is affected by the uniformity of atoms or protons in the source plasma, which are the primary species of negative ions under Cs-seeded surface production. [ABSTRACT FROM AUTHOR]