OPTIMIZATION OF AN ION-OPTICS SYSTEM WITH THICK ELECTRODES FOR THE DIAGNOSTIC NEUTRAL BEAM INJECTOR OF THE TEXTOR TOKAMAK

The optimization results of the ion-optics system in a neutral beam in jector are considered which is developed for application of beam emiss ion spectroscopy in the TEXTOR tokamak. The injector is capable to del iver a neutral beam of at least 1 A in hydrogen and deuterium at 50 ke V for a pulse length of 5 s into the plasma. The simulation results wi th the AXCEL code for grids of 4 mm thickness are discussed. The ion c urrent of 2 A extracted by a multihole grid system at a current densit y of 120 mA/cm(2) is generated by a rf driven ion source. The beamlet half angular divergence is below 0.6 degrees for the optimized four-el ectrode ion optics system. The estimated temperature rise of the inert ially cooled molybdenum grids with 150 holes and 58% transparency is m ax. 270 K and the related degradation in beam quality by thermal grid expansion is acceptable. (C) 1997 American Institute of Physics.