4,427
edits
Pedestal: Difference between revisions
no edit summary
No edit summary |
No edit summary |
||
| Line 1: | Line 1: | ||
[[File:H-mode.png|300px|thumb|right|Sketch of L- and H-mode profiles and pedestal.]] | [[File:H-mode.png|300px|thumb|right|Sketch of L- and H-mode profiles and pedestal.]] | ||
In the context of magnetic confinement fusion, the term ''pedestal'' refers to a relatively narrow edge plasma region with significantly enhanced | In the context of magnetic confinement fusion, the term ''pedestal'' refers to a global increase of a profile (such as the pressure), caused by the formation of a relatively narrow edge plasma region with significantly enhanced profile gradients, associated with an edge transport barrier, characteristic of the [[H-mode]]. | ||
<ref>[http://dx.doi.org/10.1088/0029-5515/29/11/010 ASDEX Team, ''The H-Mode of ASDEX'', Nucl. Fusion '''29''' (1989) 1959]</ref> | <ref>[http://dx.doi.org/10.1088/0029-5515/29/11/010 ASDEX Team, ''The H-Mode of ASDEX'', Nucl. Fusion '''29''' (1989) 1959]</ref> | ||
When transiting from the L-mode to the H-mode, the appearance of the pedestal often leaves the profile gradients in the core region intact (due to [[Profile consistency|profile consistency]]) whereas the edge gradients increase sharply. Thus, it appears as if the core profiles are merely shifted upward (as if put upon a pedestal), hence the terminology. | When transiting from the L-mode to the H-mode, the appearance of the pedestal often leaves the profile gradients in the core region intact (due to [[Profile consistency|profile consistency]]) whereas the edge gradients increase sharply. Thus, it appears as if the core profiles are merely shifted upward (as if put upon a pedestal), hence the terminology. | ||
Physically, the edge region is complex as it contains the transition ([[Separatrix|separatrix]]) from the confined plasma with closed field lines to the scrape-off layer (SOL) with open field lines; transport fluxes are large there; and the interaction with the wall (atomic and molecular physics) is important. | Physically, the edge region is complex as it contains the transition ([[Separatrix|separatrix]]) from the confined plasma with closed field lines to the scrape-off layer (SOL) with open field lines; transport fluxes are large there; and the interaction with the wall (atomic and molecular physics) is important. | ||
The understanding of this region is still imperfect. | The understanding of this region, and therefore of the pedestal, is still imperfect. | ||
Many attempts have been made to derive [[Scaling law|scaling laws]] of phenomenological pedestal parameters (such as its width and height), with limited success. | Many attempts have been made to derive [[Scaling law|scaling laws]] of phenomenological pedestal parameters (such as its width and height), with limited success. | ||
<ref>[http://dx.doi.org/10.1088/0741-3335/42/5A/302 A.E. Hubbard, ''Physics and scaling of the H-mode pedestal'', Plasma Phys. Control. Fusion '''42''' (2000) A15]</ref> | <ref>[http://dx.doi.org/10.1088/0741-3335/42/5A/302 A.E. Hubbard, ''Physics and scaling of the H-mode pedestal'', Plasma Phys. Control. Fusion '''42''' (2000) A15]</ref> | ||