Helium Ash Exhaust with Single-Null Poloidal Divertor in Doublet III

The helium ash exhaust function of a divertor has been experimentally demonstrated. Helium atoms accumulate in the divertor region as the electron density of the main plasma increases. With a helium concentration of \ensuremath{\sim} 1.6% of electron density in the main plasma, neutral helium pressure at the divertor region is as high as 1.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ Torr. This experiment indicates the possibility of helium ash exhaust in an $\ensuremath{\alpha}$-particle-heated diverted tokamak with use of pumping ducts of a practical size.