Ballooning Instabilities in the Scrape-Off-Layer of Diverted Tokamaks as Giant ELM Precursors

摘要

1. For ideal ballooning modes near the separatrix the plasma is shielded from the target plates by the X-pointrn2. Critical (marginal) pressure gradient β_(crit) is lower in the SOL, and small (instability may set in for typical SOL pressures).rn3. Perturbations of physical quantities (e.g. δB_ρ, v_ρ) are localised at the separatrix, near the X-pointrn4. For modes strongly localised near the separatrix shear is stabilisingrn5. SOL ballooning instability may be precursor for giant ELM: SOL instability destroys the X-point (precursor) → creates wall contact → impurity influx → instability inside the separatrix (main event) → diffusive refilling of expelled layer.