Abstract
The use of beryllium as a wall and limiter material is investigated in the small Tokamak UNITOR. The transport of neutral and ionized beryllium released from poloidal limiter is studied both experimentally and numerically. The numerical simulation is based on an impurity transport algorithm in cylindrical geometry. It comprises anomalous diffusion as well as ionization; recombination via charge exchange processes is included for highly ionized beryllium atoms. The code yields the spatial distribution of the various ionization states with densities up to 4% of the electron density ne and fluxes up to 1019 m-2s-1. The contribution of beryllium to Zeff is evaluated to be well below 1. The spatial and temporal distribution of neutral beryllium is measured by laser induced fluorescence. For this purpose, the Be I resonance line at 234.9 nm is pumped by a frequency doubled dye laser. These measurements yield the densities as well as the fluxes of neutral beryllium released from the limiter. The experimental results reveal that besides sputtering additional erosion mechanisms are of importance.
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