Scattering of magnetized electrons at the boundary of low temperature plasmas

作者：Krueger Dennis; Trieschmann Jan; Brinkmann Ralf Peter

来源：Plasma Sources Science and Technology, 2018, 27(2): 025011.

DOI：10.1088/1361-6595/aaaa85

• HiPIMS
• magnetron
• electron dynamics
• guiding center drift

Magnetized technological plasmas with magnetic fields of 10-200 mT, plasma densities of 10(17)-10(19) m(-3), gas pressures of less than 1 Pa, and electron energies from a few to (at most) a few hundred electron volts are characterized by electron Larmor radii r(L), that are small compared to all other length scales of the system, including the spatial scale L of the magnetic field and the collisional mean free path lambda. In this regime, the classical drift approximation applies. In the boundary sheath of these discharges, however, that approximation breaks down: The sheath penetration depth of electrons (a few to some ten Debye length lambda(D); depending on the kinetic energy; typically much smaller than the sheath thickness of tens/hundreds of lambda(D)) is even smaller than r(L). For a model description of the electron dynamics, an appropriate boundary condition for the plasma/sheath interface is required. To develop such, the interaction of magnetized electrons with the boundary sheath is investigated using a 3D kinetic single electron model that sets the larger scales L and lambda to infinity, i.e. neglects magnetic field gradients, the electric field in the bulk, and collisions. A detailed comparison of the interaction for a Bohm sheath (which assumes a finite Debye length) and a hard wall model (representing the limit lambda(D) -> 0; also called the specular reflection model) is conducted. Both models are found to be in remarkable agreement with respect to the sheath-induced drift. It is concluded that the assumption of specular reflection can be used as a valid boundary condition for more realistic kinetic models of magnetized technological plasmas.

• 出版日期2018-2