Cross-field and parallel dynamics of SOL filaments in TCV

Abstract

Using recently installed scrape-off layer diagnostics on the tokamak à configuration variable, we characterise the poloidal and parallel properties of turbulent filaments. We access both attached and detached divertor conditions across a wide range of core densities (f G ∈ [0.09, 0.66]) in diverted L-mode plasma configurations. With a gas puff imaging (GPI) diagnostic at the outer midplane we observed filaments with a monotonic increase in radial velocity (from 390 m s−1 to 800 m s−1) and cross-field radii (from 8.5 mm to 13.4 mm) with increasing core density. Interpreting the filament behaviour in the context of the two-region model by Myra et al (2006 Phys. Plasmas 13 112502), we find that they populate the ideal-interchange regime (C i) in discharges at very low densities, and the resistive X (RX)-point regime for all other discharges. The scaling of filament velocity versus size shows good agreement with this interpretation. These results are discussed and compared with previous probe-based measurements for similar conditions, which mostly placed filaments in TCV in the resistive ballooning (RB) regime (Tsui et al 2018 Phys. Plasmas 25 072506). In addition, for the first time in TCV, the parallel filament extension is studied by magnetically aligning the GPI measurements at the outboard midplane with a reciprocating probe in the divertor. In agreement with the filaments being in the ideal-interchange and the RX-point regimes, they are found to extend beyond the X-point into the outer divertor leg.

Dependence of scrape-off layer profiles and turbulence on gas fuelling in high density H-mode regimes in TCV

“…In particular, in this analysis the blobs are seen to become bigger in size as α t increases, mainly related to a corresponding increase of their radial propagation velocity by means of equation (11), while neither the FWHM of the filament waveforms nor the poloidal velocity show any clear trend. This observation is well in line with previous H-mode studies on ASDEX-Upgrade [14,19] as well as a recent L-mode analysis on TCV [55] showing that a higher resistive-interchange turbulence activity close to the separatrix, resulting from an increase in gas fuelling and therefore separatrix collisionality, drives bigger and radially faster filaments to be expelled into the far SOL. Finally, in figure 10 it is also shown by means of the color map that the blob properties are substantially independent of their radial position across the SOL.…”

Tracking blobs in the turbulent edge plasma of a tokamak fusion device

“…The additional problem that we are addressing, facilitating closer experimental comparisons with theoretical models of blob transport, is essential for experimental validation tests of these models. These tests of the models (e.g., 14 ) are made more valuable with accurate determinations of the size, shape, and motion of blobs.…”

“…Traditional approaches to blob analysis include a family of conditional averaging methods, custom-made workflows that track high signal regions, and spatio-temporal cross-correlation techniques 5 , 14 , 15 . The conditional averaging methods and the cross-correlation techniques have the limitations of only providing averaged characteristics of blobs.…”

“…The performance comparisons are given in Results, as is a description of the results obtained by human detection, which shows some ambiguity in what constitutes a blob in real experimental data. Finally, the trained models are applied to an active plasma-physics research topic, i.e., finding the regime of the blob dynamics, as described in Myra et al 9 , 10 , and the models’ results are compared with the result from a Conditional Average Sampling (CAS) method that has been used previously for this purpose 14 . The work is summarized in Conclusions.…”

Effect of sheared E × B flow on the blob dynamics in the scrape-off layer of HL-2A tokamak

“…2004; Myra, Russell & D'Ippolito 2006 b ; Russell, Myra & D'Ippolito 2007; Offeddu et al. 2022) have been active research topics. Earlier simulation work demonstrated that the sheared E × B flow plays a crucial role in the turbulence transport (Burrell 1998) and can also stop the blob radial motion within the shear layer (Ghendrih et al.…”