Energetic Helium Ion Injection into Helium Recombining Plasma in Radio-Frequency Plasma Source

This technical note reports the first experimental investigation aiming for divertor plasma dynamics study using helium recombining plasma and energetic helium ion beam. A divertor plasma relevant experiment was performed using a linear plasma device, DT-ALPHA, and a multicusp ion source. The radial profiles of the line emission intensities from helium Rydberg atoms were investigated, and the reaction rate of volumetric recombination was confirmed to increase in the central region of the cylindrical plasma. Then an energetic helium ion beam was superimposed onto the helium recombining plasma. The optical emission intensities from the helium recombining plasma with and without energetic ions were obtained and compared. The temporal evolution of the optical emission indicated that charge-exchange momentum transfer between energetic helium ions and ground state helium atoms can affect population density even in recombining plasma where population density is dominated by recombining processes rather than ionizing processes.