Application of dynamic mode decomposition to rotating structures in detached linear plasmas

Abstract

Dynamic mode decomposition (DMD) was applied to time-series snapshots of dynamic behavior in detached plasmas with a fast framing camera in the linear plasma device NAGDIS-II. The DMD extracted radial plasma ejection and E r × B rotation structures, which are associated with blob-like plasma structures. Besides, we investigated the influences from neutral gas pressure on the growth rates of the DMD modes. By increasing the neutral gas flow rate in the detached plasma, the growth rate of rotation mode became larger while the frequency decreased. The results indicated that the ejected plasma existed for a longer time in the periphery region. It is likely due to the fact that the ratio of the radial velocity to the rotation velocity of the ejected plasma decreased.