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 ∼ 1.6% of electron density in the main plasma, neutral helium pressure at the divertor region is as high as 1.0×${10}^{-4\mathrm{}}$ Torr. This experiment indicates the possibility of helium ash exhaust in an $\alpha$-particle-heated diverted tokamak with use of pumping ducts of a practical size.

• Received 6 April 1981

DOI:https://doi.org/10.1103/PhysRevLett.47.796