BIBLIOS

Document type
Journal articles

Document subtype
Full paper

Title
Exact conservative solutions of fluid models for the scrape-off layer as the ancestors of plasma blobs?

Participants in the publication
João P.S. Bizarro (Author)
Luís Venâncio (Author)
R. Vilela Mendes (Author)
CMAFcIO

Summary
New exact, analytical solutions are presented for the conservative part of a standard two-fluid\n(density plus vorticity) model of the scrape-off layer (SOL) which are of the travelling-wave\ntype and describe the transport of large, machine-scale structures across a plasma cross-section\n(radially and/or poloidally). It is conjectured that amongst these conservative solutions (some\nextended throughout space, others much more localised) might be the ancestors of propagating\ncoherent structures, known as blobs, often seen in experiments and numerical simulations\nof SOL turbulence. Several types of solutions can be obtained, capable of mimicking not\nonly high-density blobs propagating outwards, but also inwardly moving plasma holes\n(structures with densities lower than the background’s). Besides their fundamental interest as\nconservative solutions of the equations describing SOL turbulence, these exact solutions have\nthe added value of providing benchmarks for the verification of numerical algorithms, as is\nhere illustrated. Having thus verified one’s numerical implementation, a more realistic SOL\nmodel (including diffusion, parallel losses and a source of core plasma) is solved (by gradually\nadding the extra terms to the conservative part) to check whether these conservative solutions\nsurvive the full dynamics or not. They actually do survive (albeit enduring some degree of\ndistortion, ending up by being eventually lost) for parameters representative of SOL plasmas\nin present-day fusion devices, thus somewhat vindicating one’s original conjecture that they\nmight be the ancestors of blobs. In addition, being actual solutions of the conservative part\nof the fluid SOL equations (and with the possibility of taking essentially Gaussian forms),\nthere is no need to further justify their use as seeds with which to initialise (so-called seeded)\nsimulations. A further characteristic that these Gaussian, blob-like conservative solutions\npossess is that they have intrinsic net vorticity (or spin), which is also believed to be the case\nfor turbulence-created blobs.


Where published
Nuclear Fusion

Publication Identifiers
ISSN - 0029-5515,1741-4326

Publisher
IOP Publishing



Document Identifiers
DOI - https://doi.org/10.1088/1741-4326/ab3ea4
URL - http://dx.doi.org/10.1088/1741-4326/ab3ea4