The structure of an electronegative discharge is investigated in the presence of an oblique, uniform, and constant magnetic field. For different magnetic field strengths, the densities of the positive ion, electron, as well as negative ion have been calculated. Furthermore, the profiles of positive ion's velocity and electric potential are obtained. Under high values of electronegativity and for sufficiently cold negative ions, different magnetic field values constitute three types of discharge structure. For a very small magnetic field strength, a uniform structure is formed; for an intermediate magnetic field, a stratified multiple layer structure emerges, which is followed by electric potential oscillations; while for an intense magnetic field, these oscillations disappear. The flux of the positive ion reaching the cathode as a function of the magnetic field strength is also obtained and the result is compared with the electropositive discharge.
The plasma sheath structure in an electronegative magnetized discharge is investigated. The profiles of the positive ion density and flux velocity as well as those of the plasma potential and sheath thickness are obtained under the influence of various parameters such as collision frequency, negative ion concentration and negative ion temperature. In addition, the influences of these parameters on the profiles of the electron and negative ion density are obtained. The results are compared with the electropositive as well as the collisionless electronegative sheath. There is competition between the effects of collisions and the magnetic field, which determines the plasma sheath properties.
The influence of the elastic collisions on the structure of a magnetized electronegative discharge is investigated. For a constant magnetic field, the profiles of the velocities of positive ions, the density of species, and electric potential are obtained. Furthermore, the positive ion flux is obtained as a function of magnetic field strength for different values of the collision frequency. The results show that in the absence of collision in a constant magnetic field, the discharge structure is uniform while by taking the collision into account, the structure becomes multilayer stratified. By increasing the collision frequency the discharge leaves the multilayer structure, and related oscillations in the plasma potential and space charge vanish. The parameter space region is obtained for collisionless and collisional cases. In this paper it is shown that a combined effect of collision and magnetic field determines the presheath-sheath structure.
The plasma sheath formation in the vicinity of a surrounding wall of magnetized plasma is studied in the presence of the electronegative ions and the positive ion-neutral background collisions. Fluid equations are used to treat the plasma particles species. By using the Sagdeev potential, the influence of the collisions and the magnetic field on the Bohm criterion are investigated. The space-charge profiles are obtained in the presence of a magnetic field in different collision frequencies as well as electronegative ions concentration. It is shown that the collision and the magnetic field raise a space-charge peak, while the presence of the electronegative ions results in damping the peaks. Moreover, it is observed that in the case of high magnetic field, some fluctuations emerge in the space-charge profiles. The influences of the magnetic field and electronegative ion concentration as well as negative ion temperature on the positive ion kinetic energy reaching the plasma surrounding wall and positive ion velocity perpendicular to the sheath axis are investigated. Finally, the net current through the sheath region is obtained for different collisionality and magnetic field values in both electropositive and electronegative plasmas.
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