Heat and momentum transport of ion internal transport barrier plasmas on the Large Helical Device

Abstract

The peaked ion-temperature profile with steep gradient so called ion internal transport barrier (ion ITB) was formed in the neutral beam heated plasmas on the Large Helical Device (LHD) and the high-iontemperature regime of helical plasmas has been significantly extended. The ion thermal diffusivity in the ion ITB plasma decreases down to the neoclassical transport level. The heavy ion beam probe (HIBP) observed the smooth potential profile with negative radial electric field (ion root) in the core region where the ion thermal diffusivity decreases significantly. The large toroidal rotation was also observed in the ion ITB core and the transport of toroidal momentum was analyzed qualitatively. The decrease of momentum diffusivity with ion temperature increase was observed in the ion ITB core. The toroidal rotation driven by ion temperature gradient so called intrinsic rotation is also identified.

23rd IAEA Fusion Energy Conference: summary of sessions EX/C and ICC

“…These results are generally consistent with previously reported observations of the Prandtl number and the pinch; however, the JET experimental results for the intrinsic rotation in ICRF heated discharges result in a value much lower than predicted by the empirical scaling [79,80]. For comparison, the value of the measured Prandtl number in the LHD stellarator is 0.5-1.0 [81].…”

“…These results suggest that turbulent residual stress may be key in generating intrinsic rotation [81][82][83][84]. As discussed in [83] in the framework of residual stress, the generation process of flows can be understood as a conversion of thermal energy, which is injected into a system by heating, into macroscopic flow by drift wave turbulence excited by ∇T, ∇n, etc.…”

“…In addition, measurements on DIII-D indicate that ECH can generate counter torque in the core [82]. Also on LHD, the existence of temperature gradient effects on the momentum transport in the core was also observed in ion ITB plasmas [81].…”

3-D effects on viscosity and generation of toroidal and poloidal flows in LHD

“…[11][12][13][14] There is an effect of flow damping in helical plasmas even in the toroidal direction caused by non-axisymmetry in toroidal direction, which is called the "parallel viscosity" and has been experimentally confirmed in the compact helical system (CHS) for the first time. 11,15 Spontaneous flows driven by radial electric field and ion temperature gradient were also observed where the parallel viscosity is relatively large, 16,17 and they are qualitatively consistent with neoclassical prediction.…”

“…Recently, a large offset toroidal flow was observed with ion internal transport barrier (ion ITB) formation in the large helical device (LHD) and correlates with ion temperature gradient. 13 The dynamic behavior of the toroidal flow was investigated with ion ITB formation, and a hysteresis curve was observed in the relation between velocity shear and ion temperature gradient. 18 These observations provide evidence of nonlinear bifurcation of spontaneous flow even in the 3D helical plasmas.…”