ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The theory of collisionless fluid ion temperature-gradient-driven turbulence is extended to the collisional banana-plateau regime. Neoclassical ion fluid evolution equations are developed and utilized to investigate linear and nonlinear dynamics of negative compressibility ηi modes (ηi≡d ln Ti/d ln ni). In the low-frequency limit (ω〈μi, where ω is the mode frequency and μi is the neoclassical viscous damping frequency), neoclassical effects modify the sonic ηi mode by introducing strong viscous damping of parallel flows, which renders the long wavelength response dissipative rather than inertial. Also, the linear and nonlinear polarization drifts are enhanced by a factor of B2t/B2p. As a result of these modifications, growth rates are dissipative, rather than sonic, and radial mode widths are broadened [i.e., γ∼k2(parallel)c2s(ηi −(2)/(3) )/μi, Δx∼ρs(Bt/Bp) (1+ηi)1/2, where k(parallel), cs, and ρs are the parallel wave number, sound velocity, and ion gyroradius, respectively]. In the limit of weak viscous damping, enhanced neoclassical polarization persists and broadens radial mode widths. Linear mixing length estimates and renormalized turbulence theory are used to determine the ion thermal diffusivity in both cases. In both cases, a strong favorable dependence of ion thermal diffusivity on Bp (and hence plasma current) is exhibited. Furthermore, the ion thermal diffusivity for long wavelength modes exhibits favorable density scaling. The possible role of neoclassical ion temperature-gradient-driven modes in edge fluctuations and transport in L-phase discharges and the L to H transition is discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.859748
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