ITER's large and powerful neutral beam injection system is based on a modular concept, where eight cylindrical ’drivers’ are attached to one common expansion and extraction region. In each driver, a plasma is sustained via inductive coupling with powers of up to 100 kW at a driving radio-frequency (RF) of 1 MHz to produce fusion-relevant hydrogen beams. These high powers impose great stress on...
Inductive coupling of radiofrequency power to plasma is a complicate process, since it depends from the density of plasma itself for two major reason: (1) ionization is a chain reaction process; (2) with no Faraday screen (as in many sources and until now NIO1), a capacitative coupling may mix with inductive coupling. Several empirical 2D model can be developed, depending on collisional...
In H$^–$ ion sources for neutral beam heating applications, the creation of negative ions relies on the surface conversion of H atoms and positive ions at the plasma grid surface. The yield of this process is strongly influenced by the energy of the impacting particles. In general, a higher energy or velocity of H or H$^+_x$ results in a higher conversion rate. However, the velocity of the...
Reduction of beamlet divergence angle is one of the most important targets of negative ion sources driven with Radio-Frequency (RF) to decrease the damages on the accelerator grid and improve the beam injection efficiency. Minimum beamlet divergence of RF driven source is ~12 mrad and is much wider than the divergence accelerated from Filament-Arc (FA) drive sources; required beam divergences...
