Thermo-mechanical design of the ITER Neutral Beam Injector grids for Radio Frequency Ion Source and SINGAP Accelerator
This paper focuses on the thermo-mechanical design of the ITER Neutral Beam Injector plasma, extraction and acceleration grids, considering the Radio Frequency option for the negative ion source and the SINGAP option for the accelerator. The SINGle Aperture -SINgle GAP (SINGAP) accelerator for ITER NBI foresees four grids for the extraction and acceleration of negative ions, instead of the seven grids of the Multi Aperture Multi Grid (MAMuG) reference configuration. The Radio Frequency ion source is a promising alternative to the Arc Driven one, showing very good performances in recent experiments at IPP Garching (D) and having the advantage of reduced maintenance requirements. A specific plasma grid was designed for RF source considering lower heat loads and different operational requirements. In particular the thermo-hydraulic and thermo-mechanical design aims at having all over the plasma grid a precisely controlled temperature to enhance the negative ions yield inside the caesium seeded source. Analytical and numerical (FE) thermo-mechanical analyses were also carried out for the extraction and acceleration grids. Structural verifications were accomplished according to the ITER Structural Design Criteria for In-Vessel Components. Design optimizations were performed in order to limit the misalignment of the grids within the tolerance specified by beam optics requirements (0.4 mm of maximum misalignment between corresponding apertures axes). The optimum cooling parameters under different operational scenarios were identified. The paper describes the design status of the grid system for the RF ion source and discusses in detail the numerical work carried out for thermo-mechanical and fluid dynamic behaviour.
SINGAP: The European concept for negative ion acceleration in the ITER neutral injectors
In contrast to the multiaperture–multigrid concept of the International Thermonuclear Experimental Reactor (ITER) injector reference design in which D− acceleration to 40 A, 1 MeV is achieved through seven grids containing 1280 apertures each, the European SINGAP (single gap–single aperture) concept proposes acceleration of 1280 preaccelerated (20–50 keV) beamlets to 1 MeV in a single step. During acceleration the beamlets are merged into 16 groups of 80 beamlets. These 16 so-called hyperbeamlets then emerge from an exit grid containing only 16 very large apertures. This concept is expected to reduce cost and increase the tolerance to mechanical errors and stray magnetic fields. The SINGAP physics is described here. The SINGAP beam optics is calculated to provide good beam transmission (86%) to the ITER.
Papers presented at the18th IAEA Fusion Energy Conference, Sorrento, Italy, October 4 - 10, 2000
Keywords: LRP 684 Note: IAEA, Participants Reference CRPP-REPORT-2000-010 Record created on 2008-04-18, modified on 2017-05-12