Light impurity exhaust with the Wendelstein 7-X island divertor

Preventing impurity accumulation in improved energy confinement regimes to maintain stationary plasma conditions is of great importance in fusion research. This is important for helium, the ash of the fusion process as well for impurities used for radiative edge cooling. A set of ORNL Filterscopes [1] was used to observe line integrated intensities of the impurity lines while a set of WISP gauges [2] was used to monitor the partial neutral pressure in the divertor pump gap of the island divertor at W7-X. The results from experiments utilizing short injections of moderate flux densities of He, N and Ne will be discussed. The response of these injections in the line-averaged density and in the partial neutral pressure in the pump gaps will be discussed. In particular the effective confinement time τ_p^* will be analysed for hydrogen as well as for He.

References

[1] Colchin, R J et al, Rev. Sci. Instrum. 74 (2003)

[2] Flesch, K et al, Rev. Sci. Instrum. 87 (2016)