Radial convection of finite ion temperature, high amplitude plasma blobs

Abstract

We present results from simulations of seeded blob convection in the scrape-off-layer of magnetically confined fusion plasmas. We consistently incorporate high fluctuation amplitude levels and finite Larmor radius (FLR) effects using a fully nonlinear global gyrofluid model. This is in line with conditions found in tokamak scrape-off-layers (SOL) regions. Varying the ion temperature, the initial blob width, and the initial amplitude, we found an FLR dominated regime where the blob behavior is significantly different from what is predicted by cold-ion models. The transition to this regime is very well described by the ratio of the ion gyroradius to the characteristic gradient scale length of the blob. We compare the global gyrofluid model with a partly linearized local model. For low ion temperatures we find that simulations of the global model show more coherent blobs with an increased cross-field transport compared to blobs simulated with the local model. The maximal blob amplitude is significantly higher in the global simulations than in the local ones. When the ion temperature is comparable to the electron temperature, global blob simulations show a reduced blob coherence and a decreased cross-field transport in comparison with local blob simulations

Auto-correlation function and frequency spectrum due to a super-position of uncorrelated exponential pulses

“…[22][23][24][25][26][27][28][29][30][31][32][33][34][35] During their radial propagation, the blob-like structures develop a steep front and a trailing wake, which can also be observed in numerical simulations of isolated blob structures [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] and simulations of scrape-off layer turbulence. [51][52][53][54][55][56][57][58][59][60][61] Conditional averaging of experimental measurement data have shown that large-amplitude fluctuations are well described by an exponential wave form.…”

Mean flows and blob velocities in scrape-off layer (SOLT) simulations of an L-mode discharge on Alcator C-Mod

“…37 The second point is important as warm ions, which are expected to be present in the edge and SOL region, 38,39 influence the dynamics of turbulence and blob propagation. [40][41][42][43][44][45] The underlying linear normal mode of interest in the present simulations is the interchange mode, importantly modified by the finite ion temperature (cf. Sec.…”

Amplitude and size scaling for interchange motions of plasma filaments

“…This may be used to describe astrophysical plasmas, specifically ionospherical irregularities such as equatorial spread F phenomena, which are thought to be caused by the interchange instability [29 and 44]. The model with α = β = 1 also arises when taking the long wavelength limit of a delta-f gyrofluid model [38] and describes compressible electrostatic motions in a non-uniform magnetic field.…”

“…Within this approximation, which is valid for small particle density perturbations n relative to the background N , | n|/N ≪ 1, one neglects particle density gradients in the inertial terms of the fluid equations while retaining them in the other terms. Recent work avoids this simplification [34][35][36][37][38][39].…”