Gyrokinetic simulations of the kinetic electron effects on the electrostatic instabilities on the ITER baseline scenario

The linear and nonlinear simulations are carried out using the gyrokinetic code NLT for the electrostatic instabilities in the core region of a deuterium plasma based on the International Thermonuclear Experimental Reactor(ITER)baseline scenario.The kinetic electron effects on the linear frequency and nonlinear transport are studied by adopting the adiabatic electron model and the fully drift-kinetic electron model in the NLT code,respectively.The linear simulations focus on the dependence of linear frequency on the plasma parameters,such as the ion and electron temperature gradientsκ_(Ti,e)≡R=L_(Ti,e),the density gradientκ_(n)≡R/L_(n)and the ion-electron temperature ratioτ=T_(e)=T_(i).Here,is the major radius,and T_(e)and T_(i)denote the electron and ion temperatures,respectively.L_(A)=-(δ_(r)lnA)^(-1)is the gradient scale length,with denoting the density,the ion and electron temperatures,respectively.In the kinetic electron model,the ion temperature gradient(ITG)instability and the trapped electron mode(TEM)dominate in the small and large k_(θ)region,respectively,wherek_(θ)is the poloidal wavenumber.The TEMdominant region becomes wider by increasing(decreasing)κ_(T_(e))(κ_(T_(i)))or by decreasingκ_(n).For the nominal parameters of the ITER baseline scenario,the maximum growth rate of dominant ITG instability in the kinetic electron model is about three times larger than that in the adiabatic electron model.The normalized linear frequency depends on the value ofτ,rather than the value of T_(e)or T_(i),in both the adiabatic and kinetic electron models.The nonlinear simulation results show that the ion heat diffusivity in the kinetic electron model is quite a lot larger than that in the adiabatic electron model,the radial structure is finer and the time oscillation is more rapid.In addition,the magnitude of the fluctuated potential at the saturated stage peaks in the ITGdominated region,and contributions from the TEM(dominating in the higher k_(θ)region)to the nonlinear transport can be neglected.In the adiabatic electron model,the zonal radial electric field is found to be mainly driven by the turbulent energy flux,and the contribution of turbulent poloidal Reynolds stress is quite small due to the toroidal shielding effect.However,in the kinetic electron model,the turbulent energy flux is not strong enough to drive the zonal radial electric field in the nonlinear saturated stage.The kinetic electron effects on the mechanism of the turbulence-driven zonal radial electric field should be further investigated.

Simulation on the transition of electrostatic instabilities in EAST steady-state scenario

The parameter dependence of transition between electrostatic instabilities is studied using gyrokinetic simulation based on a real discharge of steady-state scenario in the Experimental Advanced Superconducting Tokamak.The scan of radial locations shows that trapped electron mode(TEM)dominates around the core while the ion temperature gradient mode(ITG)simultaneously dominates outside.The maximum growth rate of TEM appears aroundρ=0.24,where the maximum electron temperature gradient R/LTelocates,ρis the normalized poloidal flux.Effects of the parameters on the transition between TEM and ITG instability are studied atρ=0.24.It is found that TEM dominates in the scanning with individually changing R/LTe from 2.50 to 25.02 or the density gradient R/L_(n)from 1.38 to 13.76.Meanwhile,the electron-ion temperature ratio T_(e)/T_(i)is found to destabilize TEM,the effect of Teis more sensitive than that of T_(i).The dominant instability diagrams in the(R/L_(Te),R/L_(Ti))plane at different T_(e)/T_(i)and R/Lnare numerically obtained,which clearly show the parameter range of the dominant TEM or dominant ITG instability region.It is found that the dominant TEM region becomes narrower in the plane by decreasing R/L_(n)when T_(e)/T_(i)>0.5.

Anomalous transport driven by ion temperature gradient instability in an anisotropic deuterium-tritium plasma

In this work,the anomalous transport driven by the ion temperature gradient instability is investigated in an anisotropic deuterium-tritium(D-T)plasma.The anisotropic factorα,defined as the ratio of perpendicular temperature to parallel temperature,is introduced to describe the temperature anisotropy in the equilibrium distribution function.The linear dispersion relation in local kinetic limit is derived,and then numerically evaluated to study the dependence of mode frequency on the anisotropic factorαof D and the fraction of T particleεTby choosing three sets of typical parameters,denoted as the cyclone base case,ITER and CFETR cases.Based on the linear results,the mixing length model approximation is adopted to analyze the quasi-linear particle and energy fluxes for D and T.It is found that choosing smallαand largeεTis beneficial for the confinement of particle and energy for D and T.This work may be helpful for the estimation of turbulent transport level in the ITER and CFETR devices.

Simulations of energetic alpha particle loss in the presence of toroidal field ripple in the CFETR tokamak

Energetic alpha particle losses with the toroidal field ripple and the Coulomb collision in the CFETR tokamak have been simulated by using the orbit-following code GYCAVA for the steady-state and hybrid scenarios.The effects of the outer boundary and the ripple amplitude on alpha particle losses have been investigated.The loss fractions and heat loads of alpha particles in the hybrid scenario are much smaller than those in the steady-state scenario for a significant ripple amplitude.Some alpha particles in the plasma core are lost due to the ripple stochastic transport for a large ripple amplitude parameter.The heat loads with the last closed flux surface boundary are different from those with the wall boundary for the CFETR tokamak,which can be explained by typical alpha particle orbits.Discrete heat load spots have been observed in alpha particle loss simulations,which is due to the ripple well loss.The transition of the lost alpha particle behavior from the ripple stochastic diffusion to the ripple well trapping has been identified in our CFETR simulations.The Coulomb collision effect is responsible for this transition.