The global dynamic of plasma blobs in a shear flow is investigated in a simple magnetized torus using the spatial Fourier harmonics ($\mathbf{k}$-space) framework. Direct experimental evidence of a linear drift in $\mathbf{k}$ space of the density fluctuation energy synchronized with blob events is presented. During this drift, an increase of the fluctuation energy and a production of the kinetic energy associated with blobs are observed. The energy source of the blob is analyzed using an advection-dissipation-type equation that includes blob-flow exchange energy, linear drift in $\mathbf{k}$ space, nonlinear processes, and viscous dissipations. We show that blobs tap their energy from the dominant $\mathbf{E}\times \mathbf{B}$ vertical background flow during the linear drift stage. The exchange of energy is unidirectional as there is no evidence that blobs return energy to the flow.

• Received 5 March 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.115005