Ion heat pinch in reversed magnetic shear tokamak plasmas

Abstract

In the well-known reversed shear discharges, it is observed that the ion thermal diffusivity (χi) falls below the standard neoclassical value (χineo), i.e., χi<χineo. In this paper, local turbulent ion thermal pinch (χit<0) is proposed as a candidate for interpreting the experimental results from χi=χineo+χit<χineo. To test the idea, the two-fluid theory, developed by Weiland and the Chalmers group [J. Weiland et al., Nucl. Fusion 29, 1810 (1989); H. Nordman et al., ibid 30, 983 (1990)], is used in the reversed magnetic shear tokamak plasma to study the drift mode and associated ion heat transport. The theory is extended here to include both the radial electrical field shear (dEr/dr) and electron fluid velocity (Ve) in the sheared coordinate system. Remarkably different from B−1dEr/dr, k⋅Ve directly includes the safety factor q as well as the E×B velocity VE itself, where k is the magnetic configuration-dependent wave vector. As a result, the synergetic effects of B−1dEr/dr and k⋅Ve, especially those of k⋅Ve, lead to the local turbulent ion heat pinch in the negative and weak magnetic shear region because of the wave-particle resonance. The impact of B−1dEr/dr and k⋅Ve on the growth rate and ion heat pinch is numerically investigated. Qualitatively, the present results are in good agreement with the experimental trends.

Effects of current density on ion-temperature-gradient modes

“…Then, for the perpendicular dynamics of ion motion (i.e. k ρ i 1), the linearized continuity and energy equations of ions are written as [33]…”