Operation and upgrade of diagnostic neutral beam injector RUDI at TEXTOR tokamak

Multi-slit triode ion optical system with ballistic beam focusing

Multi-slit triode ion-optical systems with spherical electrodes are of interest for formation of intense focused neutral beams for plasma heating. At present, two versions of focusing multi-slit triode ion optical system are developed. The first ion optical system forms the proton beam with 15 keV energy, 140 A current, and 30 ms duration. The second ion optical system is intended for heating neutral beam injector of Tokamak Configuration Variable (TCV). The injector produces focused deuterium neutral beam with 35 keV energy, 1 MW power, and 2 s duration. In the later case, the angular beam divergence of the neutral beam is 20-22 mrad in the direction across the slits of the ion optical system and 12 mrad in the direction along the slits.

Study of sublevel population mixing effects in hydrogen neutral beams

Intensity of hydrogen Balmer-alpha line is sensitive to distribution of populations of sublevels of excited state due to difference of radiative decay branching ratio for sublevels with different orbital quantum number. Since these sublevels are degenerate transitions between sublevels and mixing of its population may be caused by very weak action of environment. A beam of fast hydrogen atoms is a system in which these fine effects of population mixing can be observed. Experimental data of Hα line radiation intensities in hydrogen neutral beams are compared with calculations assumed different models of sublevel population. The comparison most probably point out that population mixing effects cause transitions from long-lived 3s to 3p sublevel with corresponding changes in Hα radiation intensities. Discussed effects may influence to results of Doppler-shift spectroscopy measurements of the neutral beam parameters such as species and impurities content and neutralizing efficiency.

Use of the focusing multi-slit ion optical system at RUssian Diagnostic Injector (RUDI)

The upgrade of the diagnostic neutral beam injector RUDI in 2010 was performed to increase the beam density at the focal plane in accordance with the requirements of charge-exchange recombination spectroscopy diagnostics. A new focusing ion-optical system (IOS) with slit beamlets and an enlarged aperture was optimized for 50% higher nominal beam current and reduced angular divergence with respect to the previous multi-aperture IOS version. The upgraded injector provides the beam current up to 3 A, the measured beam divergence in the direction along the slits is 0.35°. Additionally, the plasma generator was modified to extend the beam pulse to 8 s.