Origin and turbulence spreading of plasma blobs

Abstract

The formation of plasma blobs is studied by analyzing their trajectories in a gyrofluid simulation in the vicinity of the separatrix. Most blobs arise at the maximum radial electric field outside the separatrix. In general, blob generation is not bound to one particular radial position or instability. A simple model of turbulence spreading for the scrape-off layer is derived. The simulations show that the blob dynamics can be represented by turbulence spreading, which constitutes a substantial energy drive for far scrape-off layer turbulence and is a more suitable quantity to study blob generation compared to the skewness. V C 2015 AIP Publishing LLC.

Turbulent transport across shear layers in magnetically confined plasmas

“…The blob generated in the SOL propagates not only poloidally with the background flow, but also radially outward. How this mechanism contributes to the turbulence level in the near SOL quantitatively will be presented in a subsequent study [48].…”

Estimation of the plasma blob occurrence rate

“…A physical explanation for blobs preferentially generated outside the confined region can be found in Refs. [34,41]. For the following procedure the generation area is defined by the smallest possible region in which 50 % of all trajectories originate from.…”

Isotope effect on blob-statistics in gyrofluid simulations of scrape-off layer turbulence

“…Similarly, we record the waiting times between conditional peaks and fit a truncated complementary cumulative exponential distribution, resulting in figure 5 (right), clearly showing that bursts are less frequent for higher ion mass. In figure 6 (left) we present results from fitting the two-sided exponential pulse shape from equation (9) to the conditionally averaged waveforms. We obtain estimates for the rise time, τ r , fall time, τ f and total pulse duration, τ r + τ f .…”