Impurity transport in tokamak

What is it about?

The numerical simulations conducted to investigate the behavior of impurity ions generated when plasma interacts with medium-Z (N2, Ne, and Ar) impurity gases in the edge and SOL (Scrape-Off Layer) regions. The study reveals that the motion of these impurity ions is strongly influenced by plasma vorticity. An analytical relationship has been derived that connects impurity ion density with plasma vorticity, sources and sinks, and mass-to-charge ratio. Specifically, Ar+ ions exhibit stronger inward motion compared to N+ and Ne+ ions. The most abundant species display both inward and outward motion, but overall, they tend to move outward in the edge and SOL regions. This behavior has been quantified using cross-correlation techniques.

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Photo by Google DeepMind on Unsplash

Photo by Google DeepMind on Unsplash

Why is it important?

The simulations indicate that the inward transport (negative flux) of impurity ions is directly associated with monopolar density holes in the presence of an electron temperature gradient. On the other hand, outward transport is linked to plasma blobs. Understanding and optimizing these transport processes can be beneficial for managing radiative losses in tokamak-related experiments. To quantify the inward impurity transport, hole fraction analysis has been employed. It has been found that approximately 44% of Ar+ ions, 28% of Ne+ ions, and 25% of N+ ions from their total impurity density are transported inside the edge region through intermittent turbulent plasma events. The inward propagation of these impurity ions leads to increased radiation cooling in the hot or core region of a tokamak, which is generally an undesirable effect.

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