Modelling the ion source for ITER NBI: from the generation of negative hydrogen ions to their extraction

Abstract

Abstract. The neutral beam injection system for ITER is based on a large (A source = 1.9 × 0.9 m 2 ) negative hydrogen or deuterium ion source. In this source negative ions are produced in a low-pressure (p fill ≈ 0.3 Pa) plasma by conversion of atoms and protons on a caesiated molybdenum surface with low work function. Then the negative ions are transported through the plasma to the extraction system where extraction of these ions and also co-extraction of electrons take place. This paper describes the status of the modeling activities connected with the negative ion test facilities of IPP Garching. It is illustrated that these modelling activities constitute a strong support of the experimental activities connected with the development of the negative ion source for ITER NBI. Several numerical codes developed in the past years -in close collaboration with the experiment -and their results are introduced. Focus is laid on the production, transport and extraction of negative hydrogen ions and on the inevitable co-extraction of electrons. Size scaling from the IPP prototype source to the ion source of the ELISE test facility to the full negative ion source for ITER NBI. Modeling the ion source for ITER NBI

Alternative RF coupling configurations for H− ion sources

“…The measurements were performed with a highresolution spectrometer (Δλ FWHM ≈ 50 pm) along an axial line of sight (radially centered). As discharge parameters especially the electron density (as measure for the integrated density of the positive hydrogen ions) and the density ratio of atomic to molecular hydrogen n H /n H 2 (as measure for the atomic hydrogen density) are important with respect to the H − production in ion sources [4]. Therefore these parameters and the electron temperature have been determined from the absolute emission of the Balmer lines and the molecular Fulcher emission via applying the collisional radiative models Yacora H for atomic [12] and Yacora H 2 for molecular hydrogen [13,14].…”

“…These high RF powers pose strong demands on the RF circuit and generators which makes a reduction of the required powers very desirable. However, these plasma parameters which determine the negative hydrogen ion production and therefore the source performance (for the surface production process of H − the density of atomic hydrogen and the density of the positive hydrogen ions [4]) must at least be retained. In order to achieve this goal, alternative coupling concepts such as Helicon coupling or inductive coupling using a planar antenna surrounded by ferrites are investigated.…”

Two-Dimensional Simulations of H-Ions Extraction

“…Both 2D and 3D simulations showed also that the extracted negative ion current increases with the magnetic field in the extraction area [15][16][17] which was also experimentally observed [18]. Detailed studies of H − and D − ion production and extraction are in progress using both the trajectory-tracking and self-consistent models [12,19].…”

Upgrade of the BATMAN test facility for H− source development

“…By combining two circular drivers to one racetrack driver the volume to surface ratio and therefore the efficiency of the source increases as the loss area is reduced for the same plasma volume. Furthermore the dissociation degree is expected to be higher due to the reduced recombination surface enhancing therefore the negative ion production by neutral atoms [19].…”