Study on particle pinch mechanism for DEMO

The particle transport is an important research topic for burning control in DEMO reactors. For example, the hollow density profile is often seen after pellet injection or gas-puff. In such a case, the inverted density gradient appears in the edge region which produces the particle pinch. To understand particle pinch mechanism, we have performed local gyrokinetic simulation using DEFEFI code with the inverted density gradient (dn/dr > 0). We have observed inward particle flux for such condition. To understand the mechanism of particle pinch, we have revisited the ion-mixing mode theory proposed by B. Coppi. It is found that the electron drift wave contributes to the particle pinch rather than the ion-mixing mode for the inverted density gradient.