Sheaths with Dust Particles in the Oblique Magnetic Field

It is simulated the non-linear one-dimensional sheaths with dust particles of the given size, density and profile in an oblique magnetic field, using the modified PIC method with self-consistent dust particle charge. The Coulomb scattering and the collection of electrons and ions by dust particles are simulated by the Monte-Carlo method with 3D velocity distribution functions for electrons and ions. It is shown that an influence of dust particles on sheaths is depending on the ratio between characteristic times and lengths of the considered problem. Dust particles change boundary conditions and spatial distributions of sheath parameters causing a double structure of sheaths at an effective collection of ions by dust particles in sheaths. Keywgrrds: sheath, dust particle, oblique magnetic field, edge plasma, fusion device 1. lntroduction It is well known [] that electrostatic sheaths separate plasma from electrodes or walls adsorbing charged particles (usually electrons and ions) from the plasma. The sheaths are appeared due to a difference between fluxes of the adsorbed charged particles to electrodes or walls without sheaths. In the simple case of plasma without a magnetic field, the electron flux essentially exceeds the ion flux so that positively charged sheaths are created around negatively charged walls. However a magnetic field can strongly modifies the situation so that the ion flux can exceed the electron flux and sheaths will be negatively charged around positively charged walls [2-5]. Usually the electrodes or walls disturb plasmas far from sheaths creating quasineutral non-uniform plasma regions with slow electric fields and slow gradients of the plasma density which are called preasheaths [6,7]. The presheaths provide boundary conditions for the sheaths and therefore the sheaths have to be considered together with the self-consistent presheaths. In the case *Corresponding author's e-mail: yuch@ boy.rpd.univ.kiev.ua of electron-ion collisionless plasma without a magnetic field, the presheath provides the well known Bohm criterion according to which ions have to be accelerated in a presheath to the velocity more or equal to the ion sound speed. Dust particles can strongly influence on sheaths without a magnetic field [8-11] due to the selective adsorption of background electrons and ions (penetrating through sheaths) by dust particles. In the result, dust particles create the space electric charge influencing on the sheath structure. Note that the selective adsorption of electrons and ions can cause a deviation of electrons and ions from their equilibrium in the non-disturbed plasma including their energy distribution functions [l2]. However.sheaths with dust particles are considered usually [9-11] under the assumption of the electron and ion equilibrium except [8] where a self-consistent treatment is developed of background electrons and ions in the sheaths with dust