Ion temperature gradient mode in the weak density gradient limit

Abstract

The toroidal ion temperature gradient mode (ITG mode) is analyzed in the fluid limit for flat density profiles, typical of many H-mode plasmas. It is shown that the stability boundary is not Ln/LTi=const ≊O(1 ■2) (Ln and LTi are the density and ion temperature gradient scale lengths, respectively), as typically quoted. Rather, for large Ln/R the stability threshold is characterized by LTi/R =const≊O(0.1) with R the major radius. This result could substantially reduce the impact of ITG-mode turbulence, allowing a reconciliation of present drift wave transport models with improved H-mode energy confinement.