Effect of an oblique magnetic field on a plasma sheath consisting two-species positive ions

H. Ghomi, M. M. Hatami, A. R. Niknam, B. Shokri
Laser-Plasma Research Institute of Shahid Beheshti University, Tehran, Iran.
Abstract. A magnetized collisionless plasma sheath which is consists of two-species positive ions will be investigated by hydrodynamics model. These ions have the same ionization ratio (z=1) but different mass. The effects of the magnetic field’s direction on ion velocities and their density distributions will be calculated numerically.
Keywords: Plasma, Plasma sheath, Magnetic field
PACS: 52.40.Kh, 94.30.Cj
Introduction
The plasma sheath problem has many applications in ion implantation. Many authors investigate this problem under various conditions such as passive and active plasma sheath [1-2], positive and negative ions [3-4], etc. But most of them ignore the effect of the magnetic field on the plasma sheath. However, the problem will be complicated in the presence of a magnetic field but ions have some interesting behavior in a magnetized plasma sheath structure. Recently, some papers about a magnetized plasma sheath which is consist of one-species positive ion are published [5]. We consider a magnetized plasma sheath which is consist of two-species positive ions which have different masses but same ionization ratio. It is shown that depending on the direction of the magnetic field the behavior of these ions may be different from each other.
Model and obtained results
The plasma sheath which we consider is one-dimensional with spatial coordinate and three-dimensional with speed coordinate in the presence of an oblique magnetic field. Figure (1) shows the arrangement of the magnetic field and cathode. We assume electrons and ions are isothermal in the sheath and the electrons are in thermal equilibrium with a Maxwellian density. In addition we ignore the effect of collisions and we assume the plasma is passive. By considering the above assumption the basic equations will have the following form:
where, and are the ion densities and ion masses, respectively. By using some dimentionless quantity the above equations can be solved by numerical methods. Obtained numerical results show that under influence of the oblique magnetic field with constant strength the velocity and the density distribution of both ions will experience fluctuations in the x-direction (toward cathode) and with increasing the angle of the magnetic field with respect to x- direction(1n2n21,mm)θ these fluctuations will be more intense and the ions will impact to cathode with greater velocity which in turn has importance in ion implantation methods. Figures (2-5) show the ion velocities and ion where, and are the ion densities and ion masses, respectively. By using some dimentionless quantity the above equations can be solved by numerical methods. Obtained numerical results show that under influence of the oblique magnetic field with constant strength the velocity and the density distribution of both ions will experience fluctuations in the x-direction (toward cathode) and with increasing the angle of the magnetic field with respect to x- direction(1n2n21,mm)θ these fluctuations will be more intense and the ions will impact to cathode with greater velocity which in turn has importance in ion implantation methods. Figures (2-5) show the ion velocities and ion
density distributions in various magnetic field directions. In these figures is the dimensionless ion density and iNeλis electron Debye length.

References
1. A. Kono, J. Phys. D: Appl. Phys. 37, 1945-1953(2004)
2. R. N. Franklin, J. Phys. D: Appl. Phys. 36, 34-38(2003)
3. R. N. Franklin, J. Phys. D: Appl. Phys. 36, 1806-1809(2003)
4. R. N. Franklin, J. Phys. D: Appl. Phys. 25, 453-457(1992)
5. Xiu Zou, Jin-Yuan Liu, Ye Gong, Zheng-Xiong Wang, Yue Liu, Xiao-Gang Wang. Vaccum 73, 681-685(2004)

Опубликовано в рубрике Documents