Simulation Of Radial Electric Field In Tokamaks

In the experimental studies of tokamak fusion,the drift wave turbulence induced transport has been a difficult problem for a long time.In order to achieve fusion energy generation conditions and reduce the cost of experimental fusion device,it is necessary to reduce plasma radial transport and improve plasma confinement properties.It is found that turbulence can induce zonal flow during the turbulence development process,while zonal flow can be divided into two branches.One is the low frequency zonal flow(LFZF),the other one is geodesic acoustic mode(GAM).The common features of them are toroidal and poloidal symmetric perturbated electric potentials,the difference is that the LFZF density perturbation is also toroidal and poloidal symmetry,and the GAM has m=1 density perturbation.Because the two modes can produce poloidal flow,which can suppresses turbulence and its transport.In recent years,more and more attention has been paid to the interaction between zonal flow and turbulence.In this paper,we first introduce the research history of fusion energy,and the basic properties of the drift wave.Next,we introduce the particle simulation program GTS used in our research and its basic physics.Then we introduced the three part of our study:(1)the radial nature of GAM.GAM has an important effect on the plasma confinement,but people pay little attention to it.Because the plasma density and temperature is non-uniform in Tokamak small radius direction,GAM frequency in small radius forming a continuous spectrum.Our results obtained in simula-tions and existing theories were compared and found them in good agreement at ?/??0.7.At the same time,the continuous spectrum will lead GAM appear larger radial mode number phe-nomenon.We observed this phenomenon in the simulation,and measured the rate of krchanging.Compared with the theory,we found that it was in good agreement.At the same time,we also studied the spread of GAM in the radial direction,we found tthe he phase velocity have a positive proportion relationship to the ion thermal velocity,and rate is about 0.05.(2)we have studied the relation between the size of the radial electric field produced by turbulence and the mass ratio of the electron to ion.It is found that the radial electric field becomes smaller with the increase of the electron to mass ratio,and the turbulence intensity and the resulting transport in the simu-lation become larger.This is qualitatively consistent with the confinement properties of deuterium plasma than hydrogen plasma discharge under the same discharge conditions observed in Tokamak experiments.At the same time,the L-H mode conversion of deuterium plasma has been observed in experiments,and the heating threshold is lower than that of hydrogen plasma.This is also in agreement with our simulation results.(3)we study the evolution of zonal flow and turbulence intensity in the nonlinear phase,and find that they exhibit an anti phase relation,i.e.,when the radial electric field is large,the turbulence is weak and vice versa.The same phase relation was observed in the experiment.We have discussed the cause of such phase relation,and explored the mechanism of turbulence suppression by zonal flow.Finally,we summarize the results of our research and look forward to the future work.