Simulation Of Deuterium And Impurity Supersonic Molecular Beam Injection In Tokamak Plasma

For achieving the high confinement steady-state operation in tokamak fusion machine,it is necessary to improve the fueling efficiency and injection depth.At present,a large number of experiments have been performed on the plasma fueling via supersonic molcular beam injection(SMBI),however,there are only very limited investigations on the simulation work.The present simulations are carried out with fixed injection velocity and flux.By varing the injection density and injection width,the feuling depth and efficiency were studied under the real magnetic field configuration of HL-2A tokamak.The simulation results show that:1)the SMB with smaller density and larger width can achieve larger injection depth,on the contrary,the injection depth of the SMB will be reduced;2)the SMB with smaller density and larger width can last longer time in the deeper position of the plasma.Edge localized mode(ELM)can be mitigated by helium SMBI.To explore the mechanism of ELM mitigation by helium SMBI,we urgently need a model and code.Based on the Boltzmann kinetic equation with a source distribution function,the general multi-fluid transport equations are derived.The transport model of impurity SMBI is obtained by simplifying the derived equations.The simplified transport equations for impurity SMBI were numerically solved under the framework of BOUT++.The newly-developed code,trans-imp,was used to study the transport of helium particles,momentum and energy,the response of background plasma to the helium SMB.During the simulation process,the ionization and recombination reactions of helium species are considered,but the charge exchange reaction is ignored.Besides,four kinds of radiation energy-loss schemes are considered:ionizing radiation,recombining radiation,bremsstrahlung radiation,and cyclotron radiation.It is found that:1)during the injecting phase,almost all the injected helium particles can strip off all their electrons;the monovalent helium ions can't accumulate while the divalent helium ions continue to accumulate in the injection channel.There are two transport channels for helium ions:one is the parallel velocity driven by the pressure of helium ions,the other is the radial diffusion coefficient of helium ions,1 m~2/s.The radial diffusion coefficients of helium ions have a great influence on their radial profiles.During He-SMBI,helium particles will interact strongly with the background plasma along the injection path,driving the parallel velocity of deuterium ions.Then deuterium ion density at the helium deposition location is reduced.It also causes slight deuterium ion temperature decrease but significant electron temperature decrease.2)during the relaxing phase,large density gradient of helium ions is formed,causing helium ions to be transported inward and outward.The helium ion profiles end up being flat,while the electron and deuterium ion profiles recover gradually.