Transport Simulation for Helical Plasmas by use of Gyrokinetic Transport Model

Abstract

Transport simulation for the electron and ion temperature profiles is performed in helical plasmas by using the heat diffusivity models and the quasilinear flux models [S. Toda et al., Phys. Plasmas 26, 012510 (2019)] for the electron and ion heat turbulent transport. The turbulent transport for the nonlinear simulation results can be evaluated by these models. The high-T i and low-T i plasmas for the discharge in the Large Helical Device (LHD) are studied, where the ion temperature gradient mode is unstable. The electron and the ion temperature profiles of the dynamical simulation results do not contradict with those of the experimental results in the LHD. For the plasmas of the LHD in this study, the transport simulation results by the diffusivity models and the quasilinear flux models for the heat transport to reproduce the nonlinear simulation results in the allowable errors are found to explain the experimental results for the temperature profiles.

A comparison of turbulent transport in a quasi-helical and a quasi-axisymmetric stellarator

“…It should be noted that results presented by Mynick et al (Mynick et al 2010) have shown the successful optimization of ITG turbulent transport over a range of quasi-axisymmetric stellarator configurations by using a quasilinear proxy for the nonlinear heat flux. It should also be noted that recent results have successfully reproduced ITG turbulent transport in |ŝ| > 0.5 helical plasmas using quasilinear estimates that include the effects of zonal flows (Nunami et al 2013;Toda et al 2019). However, as will be discussed here, quasilinear proxies are sometimes problematic for quasi-helically symmetric stellarators, where nonlinear corrections to quasilinear theory play a more important role relative to quasi-axisymmetric configurations.…”

“…It should also be noted that recent results have successfully reproduced ITG turbulent transport in helical plasmas using quasilinear estimates that include the effects of zonal flows (Nunami, Watanabe & Sugama 2013; Toda et al. 2019). However, as will be discussed here, quasilinear proxies are sometimes problematic for quasi-helically symmetric stellarators, where nonlinear corrections to quasilinear theory play a more important role relative to quasi-axisymmetric configurations.…”

Reduced models of turbulent transport in helical plasmas including effects of zonal flows and trapped electrons

“…In helical plasmas, the reduced models for the heat diffusivities have been installed in transport codes, such as TASK3D, when the term L related to the mixing length estimate is modelled by the ion temperature gradient at the dynamically fixed magnetic field, i.e. using the dynamically fixedτ ZF profile (Toda et al 2014(Toda et al , 2019b. In tokamak plasmas, the one-dimensional transport simulation, which is directly coupled to local gyrokinetic analyses, is performed (Candy et al 2009;Barnes et al 2010).…”

“…Recently, a large number of gyrokinetic simulations of the turbulent transport in toroidal plasmas have been performed (Garbet et al 1994;Jenko & Dorland 2001;Candy & Waltz 2003;Xanthopoulos et al 2007;Nunami et al 2011;Ishizawa et al 2014). The gyrokinetic simulation results for tokamak (Kotschenreuther et al 1995;Holland et al 2011;Rhodes et al 2011;Nakata et al 2016) and helical (Nunami et al 2012;Nunami, Watanabe & Sugama 2013;Ishizawa et al , 2017Toda et al 2019b) plasmas have been compared with the experimental observation results. Since it is known that zonal flows can regulate the turbulent transport, numerous studies have been done to investigate the efficiency of zonal flows to improve plasma confinement in toroidal devices.…”

Calculating the linear critical gradient for the ion-temperature-gradient mode in magnetically confined plasmas

“…This mode, which is driven by gradients in ion temperature, causes heat losses that act to reduce the steep gradient imposed by heating in the core of the device. Several different approaches to modelling the ITG mode in stellarators have emerged over the past decade, such as incorporating the effect of zonal flows into quasilinear turbulence saturation (Nunami, Watanabe & Sugama 2013;Toda et al 2019), which add the contributions of subdominant eigenmodes into quasilinear saturation estimates (Pueschel et al 2016) and calculate mode saturation by energy transfer to damped modes (Terry, Baver & Gupta 2006;Hatch et al 2011). Some optimization strategies based on nonlinear modelling have also been identified, e.g.…”