Theoretical Research On The Interplay Between Impurity And Drift Wave-zonal Flow System In The D-T Plasma

The future fusion reactor is demanded to achieve a long time stable control about the high temperature,high density and high confinement plasmas in the core.However,the accumulation of non-hydrogenic impurity ions and helium ash?the slowed down alpha particles?in the core can cause radiation enhancement and fuel dilution,which will cause the drop of plasma temperature and fusion power,even result in the major disruption and then bring great damage to the fusion machine and the safty operation of fusion reactor.Therefore,avoiding and controlling the accumulation of impurities is one of the big challenge for the steady and safety operation of fusion reactor.The experimental observed cross field particle transport level is much larger than the prediction of classical and neoclassical collisional theory.This is called the anomalous transport phenomenon and drift wave?DW?turbulence is recognized to be responsible for it.The DW can drive the zonal flow?ZF?through the nonlinear interaction,in turn,the ZF can suppress the DW turbulence and the associated anomalous transport.Understanding the interplay between impurity and DW-ZF system,studying the impurity impact on plasma confinement and avoiding impurity accumulation are the key and urgent problems for the high confinement and steady and safety operation of fusion reactor.The impact of impurities on DW-ZF system is systematically studied in this thesis,and then the turbulent impurity transport is also theoretically studied.Based on the bounce kinetic theory,the general expression for the arbitrary radial wavelength residual ZF with impurity is derived.Then,the effects of various impurities on the residual ZF is systematically investigated in the deuterium?D?-tritium?T?plasmas.The introduction of impurities has very weak influence on the long wavelength residual ZF level;impurities with gyroradius larger?smaller?than that of main ions can increase?decrease?the level of intermediate wavelength residual ZF;the level of short wavelength residual ZF is increased?decreased?by impurity which increases?decreases?the total polarization shielding.Even for the high Z trace W impurity with concentration being 10^-4,it can still have the significant effects on the level of residual ZF,where Z is the charge number.The effects of helium ash from the D-T reaction on residual ZF depend on the temperature ratio between electron and impurity.Moreover,the trend of stronger intermediate wavelength residual ZF in D-T plasmas with heavier effective isotope mass is weakened by non-trace light impurities,but is not influenced by trace W.These results provide theoretical basis for integrated simulating the impact of impurity on the multi-scale turbulence and ZF,and even supply some possible theoretical references for predicting the effects of impurity on plasma confinement and the transition between low confinement mode to high confinement mode in the future.Furthermore,the impact of impurities on the generation of ZF driven by collisonless trapped electron mode?CTEM?turbulence in deuterium?D?-tritium?T?plasmas is also investigated.Impurity effects on both polarization shielding and CTEM instability are comprehensively considered.The expression for ZF growth rate with impurities is derived by balancing the ZF potential shielded by polarization effects and the ZF modulated radial turbulent current.Then,it is found that the normalized ZF growth rate is positively correlated with impurity effects on CTEM instability,but inversely proportional to the total polarization shielding with impurity.Finally,it is shown that the normalized ZF growth rate can be enhanced by fully ionized non-trace light impurities with relatively steep density profile.In DIII-D,the flow shearing rate is found to be increased due to the injection of neon?Ne?and confinement improvement is also observed.Our findings shown here are qualitatively consistent with this experimental result and could provide a possible theoretical explanation for it.In particular,we also found that high temperature helium from D-T reaction on ZF can enhance the normalized ZF growth rate,thus is possible to improve the confinement of future burning plasmas.Meanwhile,various drift wave turbulence can also drive the anomalous transport of impurities.Thus,we also investigate the impurity transport driven by ion temperature gradient?ITG?turbulence using the gyrokinetic theory.The intervals of parameters which are favorable for expelling impurities are pointed out.It is easier for expelling the impurities by lowering their ionized stage and increasing the magnetic shear.Decreasing the temperature of helium ash from the D-T reaction is also beneficial for the successful expelling.Hydrogenic ion mass effects,namely the isotopic effects on impurity transport driven by ITG turbulence are investigated.The increase of hydrogenic ion mass is favorable for transporting light impurity and high Z W impurity.Moreover,the isotopic effects get stronger with stronger magnetic shear.