Impact of bootstrap current and Landau-fluid closure on ELM crashes and transport

Abstract

Results presented here are from 6-field Landau-Fluid simulations using shifted circular cross-section tokamak equilibria on BOUT++ framework. Linear benchmark results imply that the collisional and collisionless Landau resonance closures make a little difference on linear growth rate spectra which are quite close to the results with the flux limited Spitzer-Härm parallel flux. Both linear and nonlinear simulations show that the plasma current profile plays dual roles on the peeling-ballooning modes that it can drive the low-n peeling modes and stabilize the high-n ballooning modes. For fixed total pressure and current, as the pedestal current decreases due to the bootstrap current which becomes smaller when the density (collisionality) increases, the operational point is shifted downwards vertically in the Jped – α diagram, resulting in threshold changes of different modes. The bootstrap current can slightly increase radial turbulence spreading range and enhance the energy and particle transports by increasing the perturbed amplitude and broadening cross-phase frequency distribution.

Simulation study of particle transport by weakly coherent mode in the Alcator C-Mod tokamak

“…We use the neoclassical resistivity η = η neo from a fitting formula for arbitrary electron trapped fraction f t , ν * e , and effective charge Z eff [31,32], in which the Spitzer resistivity η Sptz is also Z eff -dependent [33]. ν * e has been implemented in BOUT++ and discussed in reference [34]. To avoid the difficulty of numerical double integration [35], f t is estimated simply by the inverse aspect ratio = a/R 0 [36],…”

Edge localized mode characteristics and divertor heat flux during stationary and transient phase for CFETR hybrid scenario

“…This is due to the divergence of parallel collisional thermal diffusivity between ion and electron, which follows Braginskii [26] and has the ratio κ ∥,i /κ ∥,e = √ m e /m i ~1/60 based on current fluid model. It is worthy to take kinetic closure effect into consideration to check whether it would change the parallel transport dynamics in future study [28,29]. It should be mentioned that due to the massive computation time that BOUT++ required, the simulation is stopped on the relaxation side of the first crash in figure 5 at 1.53 ms, which is indicated by the yellow-dash vertical curve in figure 5(a).…”