There are two important propagation regimes for plasma lobs or filaments. These depend on the parallel connection to the plasma wall. Blobs are driven by the interchange instability. Charge separation is induced by the magnetic field curvature. This is responsible for the radial propagation. However, there is associated a divergence in the current and this must be compensated to ensure quasineutrality In the sheath-limited regime this is done by the divergence in the parallel current. This in turn is determined by the plasma boundary (sheath). In this regime, larger blobs are slower. Now it can happen that the blobs are not connected to the boundary. This happens at high collisionalities (high densities), especially in detached plasmas and probably also near the separatrix. If the electric circuit cannot be closed via the wall, the blob must close the electric circuit internally. This is done by the polarization current. In the so-called inertial regime of blob propagation, the divergence of the polarization current balances the charge separation of the magnetic field curvature. In the inertial regime larger blobs are also faster.

In particular, we have intensively studied the transition from the sheath-limited to the inertial regime of blob propagation at high densities. And we investigated the influence of ion temperature on the different blob propagation regimes. The experiments showed good agreement with the analytical model. Even though the agreement of experiment and theory for propagation velocity of blobs is relatively superior, it gives us particular concern that for individual variables, such as the magnetic field strength, the scaling does not seem to be satisfied.

relevant publications

Relevante Publikationen

D. Carralero, P. Manz  et al. 'Experimental Validation of a Filament Transport Model in Turbulent Magnetized Plasmas' Phys. Rev. Lett. 115, 215002 (2015)

P. Manz et al. 'Filament velocity scaling laws for warm ions' Physics of Plasmas 20, 102307 (2013)

G. Fuchert et al. Blob properties in L- and H-mode from gas-puff imaging in ASDEX upgrade Plasma Phys. Control. Fusion 56 125001 (2014)

G. Birkenmeier et al. 'Magnetic field dependence of the blob dynamics in the edge of ASDEX upgrade L-mode plasmas' Plasma Phys. Control. Fusion 56 075019 (2014)