Thermal transport catastrophe and the tokamak edge density limit
- Lodestar Research Corporation, 2400 Central Avenue, Boulder, Colorado 80301 (United States)
Experiments on the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)] have demonstrated the existence of a density limit that appears to be caused not by radiation but by perpendicular heat convection in the scrape-off layer (SOL). The present paper shows that the collisionality dependence of the blob model provides a plausible explanation for this convective density limit under certain conditions. The thermal equilibrium and stability of the SOL are studied in a two-point (midplane, divertor) model including perpendicular heat convection. A general scaling of the perpendicular heat flux q{sub perpendicular} with temperature is used to derive conditions for the SOL thermal equilibrium to have two roots and a fold catastrophe associated with root merger. For the particular scaling of q{sub perpendicular} given by a 'disconnected' blob model, this equilibrium limit can be interpreted as a SOL density limit associated with X-point cooling in which the blob heat transport plays a role analogous to radiation in other theories.
- OSTI ID:
- 20787363
- Journal Information:
- Physics of Plasmas, Vol. 13, Issue 6; Other Information: DOI: 10.1063/1.2206168; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Plasma fluctuations in the scrape-off layer and at the divertor target in Alcator C-Mod and their relationship to divertor collisionality and density shoulder formation