Effects Of The Ions Motion On Rotating Magenetic Field Drive In Rotamak

A rotamak is one kind of compact magnetic confinement plasma experimental device. The mainly difference between rotamak and the conventional tokamak is that in rotamak the toroidal plasma current is driven in a steady-state, noninductive fashion by means of a rotating magnetic field(RMF). Drive and maintain plasma current by a RMF have been extensively studied both in experiments and theories. Theoretical models usually assume that electrons circulated synchronously with the RMF while ions is regarded as a static background based on the condition ofω_ci<<ω<<ω_ce. However owing to the existence of the collision between ions and electrons, the motion of ions will be produced and the current drive efficiency will be affected. At same time a viscosity will appeared when there is a velocity shear of plasma fluids along the r profile. So it is need to extend the present theoretical model to examine the effect of the ions motion and viscous terms on the RMF current drive.Starting from the electron and ion two fluids equations, the ratio of ion's and electron's velocity along the toroidal direction is calculate under the suppose that RMF penetrated the whole column of plasmas. Then the effects of the ion motion on the rotating magnetic field (RMF) current drive have been studied. The difference of RMF current drive with and without the inclusion of the ion motion have been compared. The effect of viscosity and radial motion on the calculation results is analyzed.It is indicated that owing to the collision between the ions and electrons, the ions will spin up and rotate in the same direction of electron's, and the RMF current drive efficiency will be reduced. The higher the ionization rate, the faster the ion motion. And in high ionization rate the ion speed can reach around 30% of that of electrons.The existence of the viscous force and radial motion of ions, will inhabit the ion toroidal motion and reduce ion rotating speed caused by the electron-ion collision and attenuate the effect of ion motion on the RMF current drive. The influence of viscous on the ion motion is more distinctive than the electron's one. The viscousity will cause a drag force which is opposed to the electron-ion collision friction and prevent the ion move with electron along. The stronger the viscousity, the larger the drag force. When the viscous coefficient is fixed, the ratio of ions motion velocity and the elctrons' is rising with increasing radius. It is to say that the effect of ion motion on reducing plasma current is more seriously on the larger radius. The radial motion of ions will dissipate the ion momentum and so the ion toroidal speed will be reduced. Specially in low ionization, the ion toroidal speed will near to zero. So the ion motion along the toroidal direction resulted from the electron-ion collision will be weak or disappear if the ion radial motion is happened.