Abstract
Modern tokamaks can produce transport barriers (TBs)-localized regions with an increased energy confinement. Previous studies have been unable to examine the stability of internal TBs to radially extended short-wavelength magnetohydrodynamic instabilities ("ballooning modes"), for the usual case with a sheared plasma flow and a magnetic shear that passes through zero near the TB. An established technique is adapted to study this situation, finding instability if (1) there is a low-pressure gradient, and if (2) the nearest "resonant surface" at which a Fourier mode is resonant, is sufficiently close. Surprisingly, flow shear is no more stabilizing than for magnetic shears of order one. This is explained. Without a strongly stabilizing mechanism, ballooning modes will fundamentally limit a TB's radial extent, preventing them from extending across the entire plasma radius.
| Original language | English |
|---|---|
| Article number | 092502 |
| Pages (from-to) | 1-5 |
| Number of pages | 5 |
| Journal | Physics of Plasmas |
| Volume | 12 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 2005 |
| Externally published | Yes |
Funding
Thanks to J. W. Connor and F. L. Waelbroeck for helpful comments. This work was jointly funded by the United Kingdom’s Engineering and Physical Sciences Research Council, and Euratom.