The Kinetic Theory Of Intrinsic Current Driven By Electromagnetic Turbulence In Tokamak Plasma

Understanding the mechanisms for current drive,predicting and controlling the current density profile precisely are essential for the steady state operation and the magnetohydromagnetic instability control of the tokamak fusion reactor.The bootstrap(BS)current is driven by the pressure gradient and the toroidal effects in tokamak plasmas,which is an economic and efficient way of driving non-inductive toroidal current.However,the BS current density profile measured from experiments is not always consistent with the theoretical prediction.Inspired by the intrinsic rotation driven by micro-turbulence,the intrinsic current driven by micro-turbulence seems a natural idea.Up to now,there has been no experimental works on the intrinsic current driven by micro-turbulence,and some theoretical works focus on electrostatic turbulence driven intrinsic current.While,in the future reactor with high performance,especially for the pedestal with steep pressure gradient,the electromagnetic effects are of great importance.Therefore,considering the intrinsic current driven by electromagnetic micro-turbulence is necessary for the future tokamak fusion reactor.This thesis analytically investigates the intrinsic current driven by electromagnetic micro-turbulence using drift kinetic theory in both core region and pedestal region of tokamak plasmas.The intrinsic current driven by electromagnetic electron temperature gardient(ETG)turbulence in tokamak core region is investigated,and the ratio of intrinsic current density to the local BS current density can reach about 80%.Starting from the conservative form of electromagnetic drift kinetic equation,the mean parallel current density equation with microturbulence is derived.There are two types of mechanisms of intrinsic current drive.The first one is the divergence of residual turbulent flux including a residual stress-like term and a kinetic stress-like term.The second one is the turbulent source,which is driven by the correlation between electron density and parallel electric field fluctuations.Using analytical expression obtained from quasi-linear theory,the intrinsic current density in the core plasmas of International Thermonuclear Experimental Reactor(ITER)standerd scenario is studied.It is found that the ratio of intrinsic current density driven by the turbulent source to the local BS current density is less than 1%,and can be neglected.The ratio of intrinsic current driven by the residual turbulent flux to the local BS current density can reach about 80%,although it cannot drive a net current.Thus,the intrinsic current density can change the current density profile in the core region of ITER,and may further affect neoclassical tearing mode(NTM)instability.The intrinsic current driven by electromagnetic electron drift wave(DW)turbulence in pedestal region is also analytically investigated in this thesis.The scaling law of intrinsic current density is obtained,and the cancelling of electrostatic contribution by the electromagnetic part is found.The electron density,parallel current density and the parallel electron pressure fluctuations are obtained from the perturbed electron distribution function.Using quasi-linear theory,the scaling law of the ratio of intrinsic current density to the local BS current density is derived,which shows that the higher electron temperature and ion temperature,the more important intrinsic current density.The intrinsic current density driven by the electromagnetic electron DW turbulence can reach about 65% of the local BS current density in ITER pedestal region,but can be negligible in DIII-D pedestal region.It is also found that the intrinsic current density driven by the electrostatic part is nearly cancelled by the electromagnetic part,and the final intrinsic current density is mainly driven by the kinetic stress-like term(electromagnetic effects).These theoretical results indicate that electromagnetic effects are important for intrinsic current drive,and could further affect the edge localized mode(ELM)instability in the pedestal of future reactor.In conclusion,the analytical results of intrinsic current driven by electromagnetic microturbulence shows that,in future tokamak reactor with high performance,although the net intrinsic current driven by the electromagnetic micro-turbulence can be neglected,the local current density profile can be modified significantly by the intrinsic current.Thus,the NTM in core region and the ELM in pedestal region could be affected.In the pedestal region with steep gradient of future tokamak reactor,the electromagnetic effects should be considered carefully for intrinsic current drive.This thesis provides valuable theoretical reference for understanding the mechanisms of intrinsic current drive in future tokamak fusion reactor.