2005/02/01 by C. Bourdelle, C Bourdelle, G. T. Hoang +9 · 3 citations
Physics and Astronomy · Engineering · #Magnetic confinement fusion research #Superconducting Materials and Applications #Ionosphere and magnetosphere dynamics
paper · doi:10.1088/0029-5515/45/2/005
In plasmas exhibiting an internal transport barrier (ITB), locally very high pressure gradient (?P) is obtained. It induces high values of the magnetohydrodynamic ? parameter (? = ?q 2 ?R?P/P, with R the major radius, q the safety factor, P the pressure, ? the radial gradient and ? the ratio between kinetic and magnetic pressure). Similarly to low or negative magnetic shear (s), high ? reduces the curvature and ? B drifts driving curvature-type microinstabilities. Therefore, high values of ? can stabilize part of the microturbulence, which leads to higher pressure gradient and to even higher ?. This possibility for entering a positive feedback loop is very attractive to sustain ITBs in high performance plasmas. Indeed, ? scales favourably with higher pressure and does not require any external momentum input. In this paper, after having discussed the ? stabilization mechanism in detail, we report the experimental microstability analyses of ITBs from an international multi-machine database?the International Tokamak Physics Activity database, accessible on the web. We show that ? is indeed a relevant parameter of ITB physics that should be taken into account in interpretative and predictive one-dimensional transport codes.